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    Ackermann, F. Airborne laser scanning - present status and future expectations 1999 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 54(2-3), pp. 64-67 
    article  
    BibTeX:
    @article{ackermann,
      author = {Friedrich Ackermann},
      title = {Airborne laser scanning - present status and future expectations},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {1999},
      volume = {54},
      number = {2-3},
      pages = {64-67}
    }
    
    Ahokas, E., Yu, X., Oksanen, J., Hyyppä, J., Kaartinen, H. & Hyyppä, H. Optimization of the scanning angle for countrywide laser scanning 2005
    Vol. XXXVI, PART 3/W19(ISSN 1682-1777)International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences 
    inproceedings  
    BibTeX:
    @inproceedings{ahokas05,
      author = {Eero Ahokas and Xiaowei Yu and Juha Oksanen and Juha Hyyppä and Harri Kaartinen and Hannu Hyyppä},
      title = {Optimization of the scanning angle for countrywide laser scanning},
      booktitle = {International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences},
      year = {2005},
      volume = {XXXVI, PART 3/W19},
      number = {ISSN 1682-1777}
    }
    
    Allgöwer, B., Bur, M., Stähli, M., Koutsias, N., Tinner, W., Conedera, M., Stadler, M. & Kaltenbrunner, A. Can Long-term Wildland Fire History Help to Design Future Fire and Landscape Management? An Approach from the Swiss Alps. 2003 3rd International Wildland Fire Conference and Exhibition, Sydney, Australia, pp. 11  article  
    BibTeX:
    @article{allgoewer03,
      author = {B. Allgöwer and M. Bur and M. Stähli and N. Koutsias and W. Tinner and M. Conedera and M. Stadler and A. Kaltenbrunner},
      title = {Can Long-term Wildland Fire History Help to Design Future Fire and Landscape Management? An Approach from the Swiss Alps.},
      journal = {3rd International Wildland Fire Conference and Exhibition, Sydney, Australia},
      year = {2003},
      pages = {11}
    }
    
    Allgöwer, B., Harvey, S. & Rüegsegger, M. Fuel Models for Switzerland: Description, Spatial Pattern, Index for Crowning and Torching. 1998 3rd International Conference on Forest Fire Research / 14th Conference on Fire and Forest Meteorology, Luso, Portugal, pp. 2605-2620  article  
    BibTeX:
    @article{allgoewer98,
      author = {B. Allgöwer and S. Harvey and M. Rüegsegger},
      title = {Fuel Models for Switzerland: Description, Spatial Pattern, Index for Crowning and Torching.},
      journal = {3rd International Conference on Forest Fire Research / 14th Conference on Fire and Forest Meteorology, Luso, Portugal},
      year = {1998},
      pages = {2605-2620}
    }
    
    Allgöwer, B., Kötz, B., Koutsias, N. & Morsdorf, F. Brandforschung: Auch die Schweiz brennt! 2003 arcaktuell
    Vol. 4, pp. 12-15 
    article  
    BibTeX:
    @article{allgoewer03_arc,
      author = {Allgöwer, B. and Kötz, B. and Koutsias, N. and Morsdorf, F.},
      title = {Brandforschung: Auch die Schweiz brennt!},
      journal = {arcaktuell},
      year = {2003},
      volume = {4},
      pages = {12-15}
    }
    
    Allgöwer, B., Stähli, M., Bur, M., Koutsias, N., Koetz, B., Morsdorf, F., Finsinger, W., Tinner, W. & Haller, R. Long-term fire history and high-resolution remote sensing based fuel assessment: Key elements for fire and landscape management in nature conservation areas 2006 Forest Ecology and Management
    Vol. 234(Supplement 1), pp. S212-S212 
    article  
    BibTeX:
    @article{Allgoewer2006,
      author = {Allgöwer, Britta and Stähli, Markus and Bur, Michael and Koutsias, Nikos and Koetz, Benjamin and Morsdorf, Felix and Finsinger, Walter and Tinner, Willy and Haller, Ruedi},
      title = {Long-term fire history and high-resolution remote sensing based fuel assessment: Key elements for fire and landscape management in nature conservation areas},
      journal = {Forest Ecology and Management},
      year = {2006},
      volume = {234},
      number = {Supplement 1},
      pages = {S212--S212}
    }
    
    Allombert, S., Gaston, A.J. & Martin, J.L. A natural experiment on the impact of overabundant deer on songbird populations. 2005 Biological Conservation
    Vol. 126, pp. 1-13 
    article  
    BibTeX:
    @article{Allombert2005b,
      author = {Allombert, S. and Gaston, A. J. and Martin, J. L.},
      title = {A natural experiment on the impact of overabundant deer on songbird populations.},
      journal = {Biological Conservation},
      year = {2005},
      volume = {126},
      pages = {1-13}
    }
    
    Allombert, S., Stockton, S. & Martin, J.L. A natural experiment on the impact of overabundant deer on forest invertebrates 2005 Conservation Biology
    Vol. 19, pp. 1917-1929 
    article  
    BibTeX:
    @article{Allombert2005,
      author = {Allombert, S. and Stockton, S. and Martin, J. L.},
      title = {A natural experiment on the impact of overabundant deer on forest invertebrates},
      journal = {Conservation Biology},
      year = {2005},
      volume = {19},
      pages = {1917-1929}
    }
    
    Andersen, H.E., Mcgaughey, R.J. & Reutebuch, S.E. Assessing the influence of flight parameters, interferometric processing, slope and canopy density on the accuracy of X-band IFSAR-derived forest canopy height models 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1495-1510 
    article  
    Abstract: High resolution, active remote sensing technologies, such as interferometric synthetic aperture radar (IFSAR) and airborne laser scanning (lidar) have the capability to provide forest managers with direct measurements of 3-dimensional forest canopy surface structure. While lidar systems can provide highly accurate measurements of canopy and terrain surfaces, high resolution (X-band) IFSAR systems provide slightly less accurate measurements of canopy surface elevation over very large areas with a much higher data collection rate, leading to a lower cost per unit area. In addition, canopy height can be measured by taking the difference between the IFSAR-derived canopy surface elevation and a lidar-derived terrain surface elevation. Therefore, in areas where high-accuracy terrain models are available, IFSAR may be used to economically monitor changes in forest structure and height over large areas on a relatively frequent basis. However, IFSAR flight parameters and processing techniques are not currently optimized for the forest canopy mapping application. In order to determine optimal flight parameters for IFSAR forest canopy measurement, we evaluated the accuracy of high resolution, X-band canopy surface models obtained over a mountainous forested area in central Washington state (USA) from two different flying heights (6000??m and 4500??m), from different look directions, and with different interferometric processing. In addition, we assessed the influence of terrain slope and canopy density on the accuracy of IFSAR canopy height models. High-accuracy lidar-derived canopy height models were used as a basis for comparison. Results indicate that sensing geometry is the single most important factor influencing the accuracy of IFSAR canopy height measurements, therefore acquiring IFSAR from multiple look directions can be critically important when using IFSAR for forest canopy measurement applications, especially in mountainous areas.
    BibTeX:
    @article{Andersen2008,
      author = {Andersen, H. E. and Mcgaughey, R. J. and Reutebuch, S. E.},
      title = {Assessing the influence of flight parameters, interferometric processing, slope and canopy density on the accuracy of X-band IFSAR-derived forest canopy height models},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1495--1510}
    }
    
    Andersen, H.-E., McGaughey, R.J. & Reutebuch, S.E. Estimating forest canopy fuel parameters using LIDAR data 2005 Remote Sensing of Environment
    Vol. 94(4), pp. 441-449 
    article  
    Abstract: Fire researchers and resource managers are dependent upon accurate, spatially-explicit forest structure information to support the application of forest fire behavior models. In particular, reliable estimates of several critical forest canopy structure metrics, including canopy bulk density, canopy height, canopy fuel weight, and canopy base height, are required to accurately map the spatial distribution of canopy fuels and model fire behavior over the landscape. The use of airborne laser scanning (LIDAR), a high-resolution active remote sensing technology, provides for accurate and efficient measurement of three-dimensional forest structure over extensive areas. In this study, regression analysis was used to develop predictive models relating a variety of LIDAR-based metrics to the canopy fuel parameters estimated from inventory data collected at plots established within stands of varying condition within Capitol State Forest, in western Washington State. Strong relationships between LIDAR-derived metrics and field-based fuel estimates were found for all parameters [sqrt(crown fuel weight): R2=0.86; ln(crown bulk density): R2=0.84; canopy base height: R2=0.77; canopy height: R2=0.98]. A cross-validation procedure was used to assess the reliability of these models. LIDAR-based fuel prediction models can be used to develop maps of critical canopy fuel parameters over forest areas in the Pacific Northwest.
    BibTeX:
    @article{andersen05,
      author = {Hans-Erik Andersen and Robert J. McGaughey and Stephen E. Reutebuch},
      title = {Estimating forest canopy fuel parameters using LIDAR data},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {94},
      number = {4},
      pages = {441-449}
    }
    
    Andersen, H.-E., Reutebuch, S.E. & Schreuder, G.F. Bayesian Object Recognition for the Analysis of Complex Forest Scenes in Airborne Laser Scanner Data 2002 ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria, pp. A-035 ff (7 pages)  inproceedings  
    Abstract: Bayesian object recognition is applied to the analysis of complex forest object configurations measured in high-density airborne laser scanning (LIDAR) data. With the emergence of high-resolution active remote sensing technologies, highly detailed, spatially explicit forest measurement information can be extracted through the application of statistical object recognition algorithms. A Bayesian approach to object recognition incorporates a probabilistic model of the active sensing process and places a prior probability model on object configurations. LIDAR sensing geometry is explicitly modelled in the domain of scan space, a three- dimensional analogue to two-dimensional image space. Prior models for object configurations take the form of Markov marked point processes, where pair-wise object interactions depend upon object attributes. Inferences are based upon the posterior distribution of the object configuration given the observed LIDAR. Given the complexity of the posterior distribution, inferences are based upon dependent samples generated via Markov chain Monte Carlo simulation. This algorithm was applied to a 0.21 ha area within Capitol State Forest, WA, USA. Algorithm-based estimates are compared to photogrammetric crown measurements and field inventory data.
    BibTeX:
    @inproceedings{andersen02,
      author = {Hans-Erik Andersen and Stephen E. Reutebuch and Gerard F. Schreuder},
      title = {Bayesian Object Recognition for the Analysis of Complex Forest Scenes in Airborne Laser Scanner Data},
      booktitle = {ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria},
      year = {2002},
      pages = {A-035 ff (7 pages)}
    }
    
    Andersen, H.-E., Reutebuch, S.E. & Schreuder, G.F. Automated Individual Tree Measurement through Morphological Analysis of a LIDAR-based Canopy Surface Model 2001   inproceedings  
    Abstract: An algorithm for automated individual tree measurement was developed that is driven by a morphological analysis of a high-resolution LIDAR-based canopy surface model. Binary and grayscale mathematical morphology was used to relate structure within a three-dimensional forest canopy model to the location of individual tree crown apexes. This information was used to extract LIDAR measurements of individual tree position and height. Algorithm measurements were compared to photogrammetric measurements from large (1:3000) scale aerial photography. Given a range of optimal input parameters, the algorithm was successful in locating and measuring individual tree crowns. The algorithm identified individual tree crown apexes in a mature forest with closed canopy within 2 meters of photogrammetrically-measured crown apexes with a User s accuracy of 89 $%$ and a Producer s accuracy of 83 $%$ . With another set of input parameters, the algorithm identified tree crown apexes in a younger stand with dense, closed canopy within 2 meters of photogrammetrically-measured crown apexes with a User s accuracy of 84 $%$ and a Producer s accuracy of 82 $%$ . The difference between algorithm and photogrammetric tree crown apex height measurements was approximately 1 meter in both study areas.
    BibTeX:
    @inproceedings{andersen01,
      author = {Hans-Erik Andersen and Stephen E. Reutebuch and Gerard F. Schreuder},
      title = {Automated Individual Tree Measurement through Morphological Analysis of a LIDAR-based Canopy Surface Model},
      year = {2001}
    }
    
    Anderson, J., Martin, M., Smith, M.-L., Dubayah, R., Hofton, M., Hyde, P., Peterson, B., Blair, J. & Knox, R. The use of waveform lidar to measure northern temperate mixed conifer and deciduous forest structure in New Hampshire 2006 Remote Sensing of Environment
    Vol. 105(3), pp. 248-261 
    article  
    Abstract: The direct retrieval of canopy height and the estimation of aboveground biomass are two important measures of forest structure that can be quantified by airborne laser scanning at landscape scales. These and other metrics are central to studies attempting to quantify global carbon cycles and to improve understanding of the spatial variation in forest structure evident within differing biomes. Data acquired using NASA's Laser Vegetation Imaging Sensor (LVIS) over the Bartlett Experimental Forest (BEF) in central New Hampshire (USA) was used to assess the performance of waveform lidar in a northern temperate mixed conifer and deciduous forest. Using coincident plots established for this study, we found strong agreement between field and lidar measurements of height (r2 = 0.80, p < 0.000) at the footprint level. Allometric calculations of aboveground biomass (AGBM) and LVIS metrics (AGBM: r2 = 0.61, PRESS RMSE = 58.0 Mg ha- 1, p < 0.000) and quadratic mean stem diameter (QMSD) and LVIS metrics (r2 = 0.54, p = 0.002) also showed good agreement at the footprint level. Application of a generalized equation for determining AGBM proposed by to footprint-level field data from Bartlett resulted in a coefficient of determination of 0.55; RMSE = 64.4 Mg ha- 1; p = 0.002. This is slightly weaker than the strongest relationship found with the best-fit single term regression model. Relationships between a permanent grid of USDA Forest Service inventory plots and the mean values of aggregated LVIS metrics, however, were not as strong. This discrepancy suggests that validation efforts must be cautious in using pre-existing field data networks as a sole means of calibrating and verifying such remote sensing data. Stratification based on land-use or species composition, however, did provide the means to improve regression relationships at this scale. Regression models established at the footprint level for AGBM and QMSD were applied to LVIS data to generate predicted values for the whole of Bartlett. The accuracy of these models was assessed using varying subsets of the USFS NERS plot data. Coefficient of determinations ranged from fair to strong with aspects of land-use history and species composition influencing both the fit and the level of error seen in the predicted relationships.
    BibTeX:
    @article{Anderson2006,
      author = {Anderson, Jeanne and Martin, M.E. and Smith, M-L. and Dubayah, R.O. and Hofton, M.A. and Hyde, P. and Peterson, B.E. and Blair, J.B. and Knox, R.G.},
      title = {The use of waveform lidar to measure northern temperate mixed conifer and deciduous forest structure in New Hampshire},
      journal = {Remote Sensing of Environment},
      year = {2006},
      volume = {105},
      number = {3},
      pages = {248--261}
    }
    
    Andrews, P. BEHAVE: Fire behaviour prediction and fuel modelling system - BURN subsystem, part 1 1986   techreport  
    BibTeX:
    @techreport{andrews86,
      author = {Andrews, P.L.},
      title = {BEHAVE: Fire behaviour prediction and fuel modelling system - BURN subsystem, part 1},
      year = {1986}
    }
    
    Asner, G.P. Biophysical and Biochemical Sources of Variability in Canopy Reflectance 1998 Remote Sensing of Environment
    Vol. 64(3), pp. 234-253 
    article  
    Abstract: Analyses of various biophysical and biochemical factors affecting plant canopy reflectance have been carried out over the past few decades, yet the relative importance of these factors has not been adequately addressed. A combination of field and modeling techniques were used to quantify the relative contribution of leaf, stem, and litter optical properties (incorporating known variation in foliar biochemical properties) and canopy structural attributes to nadir-viewed vegetation reflectance data. Variability in tissue optical properties was wavelength-dependent. For green foliage, the lowest variation was in the visible (VIS) spectral region and the highest in the near-infrared (NIR). For standing litter material, minimum variation occurred in the VIS/NIR, while the largest differences were observed in the shortwave-IR (SWIR). Woody stem material showed opposite trends, with lowest variation in the SWIR and highest in the NIR. Leaf area index (LAI) and leaf angle distribution (LAD) were the dominant controls on canopy reflectance data with the exception of soil reflectance and vegetation cover in sparse canopies. Leaf optical properties (and thus foliar chemistry) were expressed most directly at the canopy level in the NIR, but LAI and LAD strongly controlled the relationship between leaf and canopy spectral characteristics. Stem material played a small but significant role in determining canopy reflectance in woody plant canopies, especially those with LAI<5.0. Standing litter significantly affected the reflectance characteristics of grassland canopies; small increases in the percentage of standing litter had a disproportionately large affect on canopy reflectance. The structural attributes of ecosystems determine the relative contribution of tissue, canopy, and landscape factors that drive variation in a reflectance signal. Deconvolution of these factors requires an understanding of the sources of variance at each scale (which is ecosystem dependent) as well as an adequate sampling (spectral, angular, and temporal) of the shortwave (400-2500 nm) spectrum.
    BibTeX:
    @article{Asner1998,
      author = {Asner, Gregory P.},
      title = {Biophysical and Biochemical Sources of Variability in Canopy Reflectance},
      journal = {Remote Sensing of Environment},
      year = {1998},
      volume = {64},
      number = {3},
      pages = {234--253}
    }
    
    Asner, G.P., Braswell, B.H., Schimel, D.S. & Wessman, C.A. Ecological Research Needs from Multiangle Remote Sensing Data 1998 Remote Sensing of Environment
    Vol. 63(2), pp. 155-165 
    article  
    Abstract: Remotely sensed land surface reflectance depends upon changing sun and sensor viewing geometry, and this dependence is governed by the bidirectional reflectance distribution function (BRDF). Because the reflectance distribution of vegetation is strongly anisotropic, multi-view angle (MVA) observations of terrestrial ecosystems contain additional and unique information beyond that acquired with nadir or single-angle spectral measurements alone. With the NASA EOS instruments MODIS and MISR and France's POLDER, new capabilities in MVA remote sensing will become widely available for ecological, biogeochemical, and land-surface biophysical research. However, a communication gap exists between the remote sensing and ecological communities in terms of the capabilities of the former and the needs of the latter. In this article, we present a summary of ecological research needs for remotely sensed data. Based on these needs, we present a review of some of the most promising MVA remote sensing methods for fulfilling these requirements. With this article, we hope to facilitate increased communication between the remote sensing, ecological, and biogeochemical research communities.
    BibTeX:
    @article{Asner1998a,
      author = {Asner, Gregory P. and Braswell, B. H. and Schimel, David S. and Wessman, Carol A.},
      title = {Ecological Research Needs from Multiangle Remote Sensing Data},
      journal = {Remote Sensing of Environment},
      year = {1998},
      volume = {63},
      number = {2},
      pages = {155--165}
    }
    
    Asner, G.P., Bustamante, M.M.C. & Townsend, A.R. Scale dependence of biophysical structure in deforested areas bordering the Tapaj?s National Forest, Central Amazon 2003 Remote Sensing of Environment
    Vol. 87(4)Large Scale Biosphere Atmosphere Experiment in Amazonia, pp. 507-520 
    article  
    Abstract: Spatial variation of land-surface properties is a major challenge to ecological and biogeochemical studies in the Amazon basin. The scale dependence of biophysical variation (e.g., mixtures of vegetation cover types), as depicted in Landsat observations, was assessed for the common land-cover types bordering the Tapaj?s National Forest, Central Brazilian Amazon. We first collected hyperspectral signatures of vegetation and soils contributing to the optical reflectance of landscapes in a 600-km2 region. We then employed a spectral mixture model AutoMCU that utilizes bundles of the field spectra with Monte Carlo analysis to estimate sub-pixel cover of green plants, senescent vegetation and soils in Landsat Thematic Mapper (TM) pixels. The method proved useful for quantifying biophysical variability within and between individual land parcels (e.g., across different pasture conditions). Image textural analysis was then performed to assess surface variability at the inter-pixel scale. We compared the results from the textural analysis (inter-pixel scale) to spectral mixture analysis (sub-pixel scale). We tested the hypothesis that very high resolution, sub-pixel estimates of surface constituents are needed to detect important differences in the biophysical structure of deforested lands. Across a range of deforestation categories common to the region, there was strong correlation between the fractional green and senescent vegetation cover values derived from spectral unmixing and texture analysis variance results (r2>0.85, p<0.05). These results support the argument that, in deforested areas, biophysical heterogeneity at the scale of individual field plots (sub-pixel) is similar to that of whole clearings when viewed from the Landsat vantage point.
    BibTeX:
    @article{Asner2003a,
      author = {Asner, Gregory P. and Bustamante, Mercedes M. C. and Townsend, Alan R.},
      title = {Scale dependence of biophysical structure in deforested areas bordering the Tapaj?s National Forest, Central Amazon},
      booktitle = {Large Scale Biosphere Atmosphere Experiment in Amazonia},
      journal = {Remote Sensing of Environment},
      year = {2003},
      volume = {87},
      number = {4},
      pages = {507--520}
    }
    
    Asner, G.P., Carlson, K.M. & Martin, R.E. Substrate age and precipitation effects on Hawaiian forest canopies from spaceborne imaging spectroscopy 2005 Remote Sensing of Environment
    Vol. 98(4), pp. 457-467 
    article  
    Abstract: We used spaceborne imaging spectroscopy provided by the Earth Observing-1 Hyperion sensor to quantify the relative importance of precipitation and substrate age that control ecosystem development and functioning in Metrosideros polymorpha rainforests of Hawaii. Four hyperspectral vegetation indices provided metrics of forest canopy structure, biochemistry and physiology to compare along gradients of annual rainfall (750 to >?6000 mm year-?1) and substrate age (0 to 250,000 years). The canopy greenness index NDVI increased with annual precipitation and substrate age, but saturated in forests with rainfall of 3000 mm year-?1. Precipitation and substrate age were roughly equal contributors to the observed greenness of the forests. A canopy water content index (NDWI) also increased with precipitation and substrate age, but did not reach a maximum until very wet (>?5000 mm year-?1) forest conditions were encountered on the oldest substrates. The water index appears superior to the NDVI in capturing spatial and climate-substrate driven variations in canopy structure. The photochemical reflectance index (PRI) indicated highest light-use efficiency levels in canopies on the most developed substrates and at annual precipitation levels of 3-4500 mm year-?1. A leaf carotenoid index (CRI) suggested a maximum canopy photosynthetic capacity at ~?4000 mm rainfall year-?1 on the oldest substrates. These results quantify the sensitivity of rainforest canopies to changing precipitation and soil conditions, and they corroborate plot-scale analyses in native Hawaiian forests ecosystems. Structural and functional studies of remote rainforest regions are possible with spaceborne imaging spectroscopy, and could be used to understand the dynamics of rainforests with climate change.
    BibTeX:
    @article{Asner2005a,
      author = {Asner, Gregory P. and Carlson, Kimberly M. and Martin, Roberta E.},
      title = {Substrate age and precipitation effects on Hawaiian forest canopies from spaceborne imaging spectroscopy},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {98},
      number = {4},
      pages = {457--467}
    }
    
    Asner, G.P., Elmore, A.J., Flint Hughes, R., Warner, A.S. & Vitousek, P.M. Ecosystem structure along bioclimatic gradients in Hawai'i from imaging spectroscopy 2005 Remote Sensing of Environment
    Vol. 96(3-4), pp. 497-508 
    article  
    Abstract: The Hawaiian Islands contain more than two-thirds of the life zones delineated by Holdridge, L.R., 1947. Determination of world plant formations from simple climate data. Science, 105, 367-368, and is thus an ideal testing ground for remote sensing studies of ecosystem function and structure. We tested the generality of imaging spectroscopy with "tied" red-edge and shortwave-infrared (RE-SWIR2) spectral mixture modeling for automated analysis of the lateral distribution of plant tissues and bare substrate across diverse bioclimatic gradients in Hawai'i. Unique quantities of the fractional cover of photosynthetic and non-photosynthetic vegetation (PV, NPV) and bare substrate identified fundamental differences in ecosystem structure across life zones. There was a ~20-fold increase in fractional PV cover with a 10-fold increase in mean annual precipitation (<=?250-2000 mm year-?1). This rate of increase diminished from 2000 to 3000 mm year-?1 of rainfall, suggesting that photosynthetic canopy cover may be limited by water saturation at 3000 mm year-?1. The amount of exposed surface senescent material (NPV) remained nearly constant at ~50% in ecosystems with a mean annual precipitation
    BibTeX:
    @article{Asner2005,
      author = {Asner, Gregory P. and Elmore, Andrew J. and Flint Hughes, R. and Warner, Amanda S. and Vitousek, Peter M.},
      title = {Ecosystem structure along bioclimatic gradients in Hawai'i from imaging spectroscopy},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {96},
      number = {3-4},
      pages = {497--508}
    }
    
    Asner, G.P., Jones, M.O., Martin, R.E., Knapp, D.E. & Hughes, R.F. Remote sensing of native and invasive species in Hawaiian forests 2008 Remote Sensing of Environment
    Vol. 112(5)Earth Observations for Terrestrial Biodiversity and Ecosystems Special Issue, pp. 1912-1926 
    article  
    Abstract: Detection and mapping of invasive species is an important component of conservation and management efforts in Hawai'i, but the spectral separability of native, introduced, and invasive species has not been established. We used high spatial resolution airborne imaging spectroscopy to analyze the canopy hyperspectral reflectance properties of 37 distinct species or phenotypes, 7 common native and 24 introduced tree species, the latter group containing 12 highly invasive species. Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) reflectance and derivative-reflectance signatures of Hawaiian native trees were generically unique from those of introduced trees. Nitrogen-fixing trees were also spectrally unique from other groups of non-fixing trees. There were subtle but significant differences in the spectral properties of highly invasive tree species in comparison to introduced species that do not proliferate across Hawaiian ecosystems. The observed differences in canopy spectral signatures were linked to relative differences in measured leaf pigment (chlorophyll, carotenoids), nutrient (N, P), and structural (specific leaf area; SLA) properties, as well as to canopy leaf area index. These leaf and canopy properties contributed variably to the spectral separability of the trees, with wavelength-specific reflectance and absorption features that overlapped, but which were unique from one another. A combination of canopy reflectance from 1125-2500?nm associated with leaf and canopy water content, along with pigment-related absorption features (reflectance derivatives) in the 400-700?nm range, was best for delineating native, introduced, and invasive species. There was no single spectral region that always defined the separability of the species groups, and thus the full-range (400-2500?nm) spectrum was highly advantageous in differentiating these groups. These results provide a basis for more detailed studies of invasive species in Hawai'i, along with more explicit treatment of the biochemical properties of the canopies and their prediction using imaging spectroscopy.
    BibTeX:
    @article{Asner2008a,
      author = {Asner, Gregory P. and Jones, Matthew O. and Martin, Roberta E. and Knapp, David E. and Hughes, R. Flint},
      title = {Remote sensing of native and invasive species in Hawaiian forests},
      booktitle = {Earth Observations for Terrestrial Biodiversity and Ecosystems Special Issue},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {5},
      pages = {1912--1926}
    }
    
    Asner, G.P., Keller, M., Pereira, R. & Zweede, J.C. Remote sensing of selective logging in Amazonia: Assessing limitations based on detailed field observations, Landsat ETM+, and textural analysis 2002 Remote Sensing of Environment
    Vol. 80(3), pp. 483-496 
    article  
    Abstract: We combined a detailed field study of forest canopy damage with calibrated Landsat 7 Enhanced Thematic Mapper Plus (ETM+) reflectance data and texture analysis to assess the sensitivity of basic broadband optical remote sensing to selective logging in Amazonia. Our field study encompassed measurements of ground damage and canopy gap fractions along a chronosequence of postharvest regrowth of 0.5-3.5 years. We found that canopy damage and regrowth rates varied according to the logging method used, either conventional logging or reduced impact logging. Areas used to stage felled trees prior to transport, log decks, had the largest gap fractions immediately following cutting. Log decks were quickly colonized by early successional plant species, resulting in significant gap fraction decreases within 1.5 years after site abandonment. Although log decks were the most obvious damage areas on the ground and in satellite imagery, they accounted for only 1-2% of the total harvested area of the blocks studied. Other forest damage features such as tree-fall gaps, skid trails, and roads were difficult to recognize in Landsat reflectance data or through textural analysis. These landscape features could be only crudely resolved in the most intensively logged forests and within about 0.5 years following harvest. We found that forest damage within any of the landscape strata (decks, roads, skids, tree falls) could not be resolved with Landsat reflectance or texture data when the canopy gap fraction was <50%. The basic Landsat ETM+ imagery lacks the resolution of forest structural features required for quantitative studies of logging damage. Landsat textural analyses may be useful for broad delineation of logged forests, but detailed ecological and biogeochemical studies will probably need to rely on other remote sensing approaches. Until spatial gradients of canopy damage and regrowth resulting from selective logging operations in tropical forests in the Amazon region are resolved, the impacts of this land use on a continental scale will remain poorly understood.
    BibTeX:
    @article{Asner2002,
      author = {Asner, Gregory P. and Keller, Michael and Pereira, Rodrigo and Zweede, Johan C.},
      title = {Remote sensing of selective logging in Amazonia: Assessing limitations based on detailed field observations, Landsat ETM+, and textural analysis},
      journal = {Remote Sensing of Environment},
      year = {2002},
      volume = {80},
      number = {3},
      pages = {483--496}
    }
    
    Asner, G.P., Knapp, D.E., Kennedy-Bowdoin, T., Jones, M.O., Martin, R.E., Boardman, J. & Hughes, R.F. Invasive species detection in Hawaiian rainforests using airborne imaging spectroscopy and LiDAR 2008 Remote Sensing of Environment
    Vol. 112(5)Earth Observations for Terrestrial Biodiversity and Ecosystems Special Issue, pp. 1942-1955 
    article  
    Abstract: Remote sensing of invasive species is a critical component of conservation and management efforts, but reliable methods for the detection of invaders have not been widely established. In Hawaiian forests, we recently found that invasive trees often have hyperspectral signatures unique from that of native trees, but mapping based on spectral reflectance properties alone is confounded by issues of canopy senescence and mortality, intra- and inter-canopy gaps and shadowing, and terrain variability. We deployed a new hybrid airborne system combining the Carnegie Airborne Observatory (CAO) small-footprint light detection and ranging (LiDAR) system with the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) to map the three-dimensional spectral and structural properties of Hawaiian forests. The CAO-AVIRIS systems and data were fully integrated using in-flight and post-flight fusion techniques, facilitating an analysis of forest canopy properties to determine the presence and abundance of three highly invasive tree species in Hawaiian rainforests. The LiDAR sub-system was used to model forest canopy height and top-of-canopy surfaces; these structural data allowed for automated masking of forest gaps, intra- and inter-canopy shadows, and minimum vegetation height in the AVIRIS images. The remaining sunlit canopy spectra were analyzed using spatially-constrained spectral mixture analysis. The results of the combined LiDAR-spectroscopic analysis highlighted the location and fractional abundance of each invasive tree species throughout the rainforest sites. Field validation studies demonstrated
    BibTeX:
    @article{Asner2008,
      author = {Asner, Gregory P. and Knapp, David E. and Kennedy-Bowdoin, Ty and Jones, Matthew O. and Martin, Roberta E. and Boardman, Joseph and Hughes, R. Flint},
      title = {Invasive species detection in Hawaiian rainforests using airborne imaging spectroscopy and LiDAR},
      booktitle = {Earth Observations for Terrestrial Biodiversity and Ecosystems Special Issue},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {5},
      pages = {1942--1955}
    }
    
    Asner, G.P. & Lobell, D.B. A Biogeophysical Approach for Automated SWIR Unmixing of Soils and Vegetation 2000 Remote Sensing of Environment
    Vol. 74(1), pp. 99-112 
    article  
    Abstract: Arid and semiarid ecosystems endure strong spatial and temporal variation of climate and land use that results in uniquely dynamic vegetation phenology, cover, and leaf area characteristics. Previous remote sensing efforts have not fully captured the spatial heterogeneity of vegetation properties required for functional analyses of these ecosystems, or have done so only with manually intensive algorithms of spectral mixture analysis that have limited operational use. These limitations motivated the development of an automated spectral unmixing approach based on a comprehensive analysis of vegetation and soil spectral variability resulting from biogeophysical variation in arid and semiarid regions. A field spectroscopic database of bare soils, green canopies, and litter canopies was compiled for 17 arid and semiarid sites in North and South America, representing a wide array of plant growth forms and species, vegetation conditions, and soil mineralogical-hydrological properties. Spectral reflectance of dominant cover types (green vegetation, litter, and bare soil) varied widely within and between sites, but the reflectance derivatives in the shortwave-infrared (SWIR2: 2,100-2,400 nm) were similar within and separable between each cover type. Using this result, an automated SWIR2 spectral unmixing algorithm was developed that includes a Monte Carlo approach for estimating errors in derived subpixel cover fractions resulting from endmember variability. The algorithm was applied to SWIR2 spectral data collected by the Airborne Visible and Infrared Imaging Spectrometer instrument over the Sevilleta and Jornada Long-Term Ecological Research sites. Subsequent comparisons to field data and geographical information system (GIS) maps were deemed successful. The SWIR2 region of the reflected solar spectrum provides a robust means to estimate the extent of bare soil and vegetation covers in arid and semiarid regions. The computationally efficient method developed here could be extended globally using SWIR2 spectrometer data to be collected from platforms such as the NASA Earth Observing-1 satellite.
    BibTeX:
    @article{Asner2000,
      author = {Asner, Gregory P. and Lobell, David B.},
      title = {A Biogeophysical Approach for Automated SWIR Unmixing of Soils and Vegetation},
      journal = {Remote Sensing of Environment},
      year = {2000},
      volume = {74},
      number = {1},
      pages = {99--112}
    }
    
    Asner, G.P. & Martin, R.E. Spectral and chemical analysis of tropical forests: Scaling from leaf to canopy levels 2008 Remote Sensing of Environment
    Vol. 112(10), pp. 3958-3970 
    article  
    Abstract: Variation in the foliar chemistry of humid tropical forests is poorly understood, and airborne imaging spectroscopy could provide useful information at leaf and canopy scales. However, variation in canopy structure affects our ability to estimate foliar properties from airborne spectrometer data, yet these structural affects remain poorly quantified. Using leaf spectral (400-2500?nm) and chemical data collected from 162 Australian tropical forest species, along with partial least squares (PLS) analysis and canopy radiative transfer modeling, we determined the strength of the relationship between canopy reflectance and foliar properties under conditions of varying canopy structure. At the leaf level, chlorophylls, carotenoids and specific leaf area (SLA) were highly correlated with leaf spectral reflectance (r?=?0.90-0.91). Foliar nutrients and water were also well represented by the leaf spectra (r?=?0.79-0.85). When the leaf spectra were incorporated into the canopy radiative transfer simulations with an idealistic leaf area index (LAI)?=?5.0, correlations between canopy reflectance spectra and leaf properties increased in strength by 4-18%. The effects of random LAI (=?3.0-6.5) variation on the retrieval of leaf properties remained minimal, particularly for pigments and SLA (r?=?0.92-0.93). In contrast, correlations between leaf nitrogen (N) and canopy reflectance estimates decreased from r?=?0.87 at constant LAI?=?5 to r?=?0.65 with randomly varying LAI?=?3.0-6.5. Progressive increases in the structural variability among simulated tree crowns had relatively little effect on pigment, SLA and water predictions. However, N and phosphorus (P) were more sensitive to canopy structural variability. Our modeling results suggest that multiple leaf chemicals and SLA can be estimated from leaf and canopy reflectance spectroscopy, and that the high-LAI canopies found in tropical forests enhance the signal via multiple scattering. Finally, the two factors we found to most negatively impact leaf chemical predictions from canopy reflectance were variation in LAI and viewing geometry, which can be managed with new airborne technologies and analytical methods.
    BibTeX:
    @article{Asner2008b,
      author = {Asner, Gregory P. and Martin, Roberta E.},
      title = {Spectral and chemical analysis of tropical forests: Scaling from leaf to canopy levels},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {10},
      pages = {3958--3970}
    }
    
    Asner, G.P. & Warner, A.S. Canopy shadow in IKONOS satellite observations of tropical forests and savannas 2003 Remote Sensing of Environment
    Vol. 87(4)Large Scale Biosphere Atmosphere Experiment in Amazonia, pp. 521-533 
    article  
    Abstract: The biological and structural complexity of tropical forests and savannas results in marked spatial variation in shadows inherent to remotely sensed measurements. While the biophysical and observational factors driving variations in apparent shadow are known, little quantitative information exists on the magnitude and variability of shadow in remotely sensed data acquired over tropical regions. Even less is known about shadow effects in multispectral observations from satellites (e.g., Landsat). The IKONOS satellite, with 1-m panchromatic and 4-m multispectral capabilities, provides an opportunity to observe tropical canopies and their shadows at spatial scales approaching the size of individual crowns and vegetation clusters. We used 44 IKONOS images from the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) data archive to quantify the spatial variation of canopy shadow fraction across a broad range of forests in the Brazilian Amazon and savannas in the Brazilian Cerrado. Forests had substantial apparent shadow fractions as viewed from the satellite vantage point. The global mean (?S.D.) shadow fraction was 0.25?0.12, and within-scene (e.g., forest stand) variability was similar to interscene (e.g., regional) variation. The distribution of shadow fractions for forest stands was skewed, with 30% of pixels having fractional shadow values above 0.30. Shadow fractions in savannas increased from 0.0?0.01 to 0.12?0.04 to 0.16?0.05 for areas with woody vegetation at low (<25% cover), medium (25-75%), and high (>75%) density, respectively. Landsat-like observations using both red (0.63-0.70 [mu]m) and near-infrared (NIR) (0.76-0.85 [mu]m) wavelength regions were highly sensitive to sub-pixel shadow fractions in tropical forests, accounting for ~30-50% of the variance in red and NIR responses. A 10% increase in shadow fraction resulted in a 3% and 10% decrease in red and NIR channel response, respectively. The normalized difference vegetation index (NDVI) of tropical forests was weakly sensitive to changes in shadow fraction. For low-, medium-, and high-density savannas, a 10% increase in shadow fraction resulted in a 5-7% decrease in red-channel response. Shadows accounted for ~15-50% of the overall variance in red-wavelength responses in the savanna image archive. Weak to no relationship occurred between shadow fraction and either NIR reflectance or the NDVI of savannas. Quantitative information on shadowing is needed to validate or constrain radiative transfer, spectral mixture, and land-surface models used to estimate material and energy exchanges between the tropical biosphere and atmosphere.
    BibTeX:
    @article{Asner2003,
      author = {Asner, Gregory P. and Warner, Amanda S.},
      title = {Canopy shadow in IKONOS satellite observations of tropical forests and savannas},
      booktitle = {Large Scale Biosphere Atmosphere Experiment in Amazonia},
      journal = {Remote Sensing of Environment},
      year = {2003},
      volume = {87},
      number = {4},
      pages = {521--533}
    }
    
    Asner, G.P., Wessman, C.A., Bateson, C.A. & Privette, J.L. Impact of Tissue, Canopy, and Landscape Factors on the Hyperspectral Reflectance Variability of Arid Ecosystems 2000 Remote Sensing of Environment
    Vol. 74(1), pp. 69-84 
    article  
    Abstract: Changes in vegetation distribution and condition commonly occur in arid ecosystems due to land use and climate variability. Most arid land remote sensing efforts have focused on detecting vegetation change using spectral indices, such as the normalized vegetation index, with limited success. Less attention has focused on using the continuous shortwave spectrum (0.4 [mu]m to 2.5 [mu]m) for studying vegetation in arid environments. Using field measurements and a photon transport model, we quantified the absolute and relative importance of tissue, canopy, and landscape factors that drive pixel-level shortwave reflectance variation along a land-cover gradient in the Chihuahuan Desert, New Mexico. Green foliage, wood, standing litter, and bare soil had distinctive spectral properties, often via specific, narrow absorption features and through overall differences in the shape of their shortwave spectra. While the amount of each plant material varied significantly along the land-cover gradient, foliar optical properties remained relatively stable, supporting the hypothesis that resource variation (e.g., water and nutrients) is more strongly resolved at the scale of whole plant canopies (e.g., via allocation and production) than at the leaf level. Significant variation in vegetation type and condition along the gradient resulted in only subtle changes in pixel-level reflectance variability, which could be determined in high spectral resolution Airborne Visible and Infrared Imaging Spectrometer data. Most important, the relative impact of tissue, canopy, and landscape factors on pixel-level reflectance shifted with plant composition and phenology. We compared the ability to resolve these vegetation and soil factors using Airborne Visible and Infrared Imaging Spectrometer, Moderate Resolution Imaging Spectrometer, and Landsat Thematic Mapper optical channels and found that few factors could be accounted for unless most of the spectral range was adequately sampled.
    BibTeX:
    @article{Asner2000a,
      author = {Asner, Gregory P. and Wessman, Carol A. and Bateson, C. Ann and Privette, Jeffrey L.},
      title = {Impact of Tissue, Canopy, and Landscape Factors on the Hyperspectral Reflectance Variability of Arid Ecosystems},
      journal = {Remote Sensing of Environment},
      year = {2000},
      volume = {74},
      number = {1},
      pages = {69--84}
    }
    
    Asner, G.P., Wessman, C.A., Schimel, D.S. & Archer, S. Variability in Leaf and Litter Optical Properties: Implications for BRDF Model Inversions Using AVHRR, MODIS, and MISR 1998 Remote Sensing of Environment
    Vol. 63(3), pp. 243-257 
    article  
    Abstract: Canopy radiative transfer models simulate the bidirectional reflectance distribution function (BRDF) of vegetation covers with differing leaf and soil spectral and canopy structural characteristics. Numerical inversion of these models has provided estimates of vegetation structural and biophysical characteristics from multiangle, remotely sensed optical data. The number of angularly unique observations compared to BRDF model parameters largely determines the accuracy of retrievals. To increase this ratio, additional observations of a target must be acquired and the BRDF models and inversions must be simplified. The former will occur when the EOS instruments become available. Previous studies suggest that simplification of BRDF model inversions may best be accomplished by constraining the leaf optical parameters. This study focused on full-range (400-2500 nm) leaf and litter spectral properties convolved to AVHRR, MODIS, and MISR optical channels. Using a diverse array of woody plant and grass species, we found robust and readily usable interrelationships among spectra through correlation, regression, and principal components analyses. Significant differences between green leaf and litter optical properties and their sensor-specific interrelationships indicate that green leaf optical constraints may be useful with BRDF retrievals to detect the onset of canopy senescence. These findings will provide increased efficiency in canopy BRDF model inversions by decreasing the number of observations required to retrieve canopy structural and biophysical information from multiangle remotely sensed data.
    BibTeX:
    @article{Asner1998b,
      author = {Asner, Gregory P. and Wessman, Carol A. and Schimel, David S. and Archer, Steve},
      title = {Variability in Leaf and Litter Optical Properties: Implications for BRDF Model Inversions Using AVHRR, MODIS, and MISR},
      journal = {Remote Sensing of Environment},
      year = {1998},
      volume = {63},
      number = {3},
      pages = {243--257}
    }
    
    Atzberger, C. Object-based retrieval of biophysical canopy variables using artificial neural nets and radiative transfer models 2004 Remote Sensing of Environment
    Vol. 93(1-2), pp. 53-67 
    article  
    Abstract: The retrieval of biophysical variables using canopy reflectance models is hampered by the fact that the inverse problem is ill-posed. This leads to unstable and often inaccurate inversion results. In order to regularize the model inversion, a novel approach has been developed and tested on synthetic Landsat TM reflectance data. The method takes into account the neighbouring radiometric information of the pixel of interest, named object signature. The neighbourhood data can either be extracted from gliding windows, already segmented images, or using digitized field boundaries. The extracted radiometric data of the neighbourhood pixels are used to calculate 42 descriptive statistical properties that comprehensively characterize the spectral (co)variance of the image object (e.g. mean and standard deviation of the distributions, intercorrelations between spectral bands, etc.). Together with the habitual spectral signature of the pixel being inverted (6 variables), this object signature (42 variables) is used as input in an artificial neural net to estimate simultaneously three important biophysical variables (i.e. leaf area index, leaf chlorophyll, and leaf water content). The use of neural nets for the model inversion avoids time-consuming iterative optimizations and provides a computational effective way to consider simultaneously pixel and object signatures.In order to "learn" the relation between spectral signatures and biophysical variables, the neural nets were previously trained on large synthetic data sets. The data sets consist of pixel signatures and the corresponding signatures of image objects representing various agricultural fields. The signatures were simulated with the SAILH+PROSPECT canopy reflectance model, assuming largely varying intra- and interfield distributions of the model input parameters.To demonstrate the benefits of the object-based inversion, neural nets were also trained on the pixel signatures alone. For this purpose, the object signatures were simply replaced by randomly generated white noise--all other conditions being the same. The intercomparison based on 30,000 independent validation patterns showed that the proposed method significantly enhances the estimation accuracies: for example, the leaf area index (LAI) is estimated with a percental root mean square error (PRMSE) of 18.3% (object-based) compared to 25.1% (pixel based); the corresponding numbers for the leaf chlorophyll content are 12.6% compared to 15.9%; for the equivalent leaf water thickness, 10.6% and 13.9%, respectively.The benefit of the object signature was strongest for the LAI. Concerning this important biophysical variable, the novel concept accounted for almost one-half of the remaining unexplained variance of the traditional pixel-based approach. Increased accuracies were attributed to the fact that intrafield variations of biophysical canopy variables lead to object signatures that are modulated by the actual average leaf angle (ALA) of the canopy. Since ALA can be considered constant insight given an agricultural field, the concurrent use of pixel and object signatures significantly reduces confounding effects between LAI and ALA typical for traditional inversion approaches. Compared to competing approaches, the algorithm can also be applied to monotemporal imagery and does not require a priori information or the identification of crop type.
    BibTeX:
    @article{atzberger04,
      author = {Atzberger, Clement},
      title = {Object-based retrieval of biophysical canopy variables using artificial neural nets and radiative transfer models},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {93},
      number = {1-2},
      pages = {53--67}
    }
    
    Axelsson, P. Processing of laser scanner data -algorithms and applications 1999 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 54(2-3), pp. 138-147 
    article  
    Abstract: airborne laser scanner systems are opening new possibilities for surveys and documentation of difficult areas and objects, such as dense city areas, forest areas and electrical power lines. Laser scanner systems available on the market are presently in a fairly mature state of art while the processing of airborne laser scanner data still is in an early phase of development. To come from irregular 3D point clouds to useful representations and formats for an end-user requires continued research and development of methods and algorithms for interpretation and modelling. This paper presents some methods and algorithms concerning filtering for determining the ground surface, DEM, classification of buildings for 3D City Models and the detection of electrical power lines. The classification algorithms are based on the Minimum Description Length criterion. The use of reflectance data and multiple echoes from the laser scanner is examined and found to be useful in many applications.
    BibTeX:
    @article{axelsson99,
      author = {Peter Axelsson},
      title = {Processing of laser scanner data -algorithms and applications},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {1999},
      volume = {54},
      number = {2-3},
      pages = {138-147}
    }
    
    Baltsavias, E., Gruen, A., Eisenbeiss, H., Zhang, L. & Waser, L.T. High-quality image matching and automated generation of 3D tree models 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1243-1259 
    article  
    Abstract: Image matching is a key procedure in the process of generation of Digital Surface Models (DSM). We have developed a new approach for image matching and the related software package. This technique has proved its good performance in many applications. Here, we demonstrate its use in 3D tree modelling. After a brief description of our image matching technique, we show results from analogue and digital aerial images and high-resolution satellite images (IKONOS). In some cases, comparisons with manual measurements and/or airborne laser data have been performed. The evaluation of the results, qualitative and quantitative, indicate the very good performance of our matcher. Depending on the data acquisition parameters, the photogrammetric DSM can be denser than a DSM generated by laser, and its accuracy may be better than that from laser, as in these investigations. The tree canopy is well modelled, without smoothing of small details and avoiding the canopy penetration occurring with laser. Depending on the image scale, not only dense forest areas but also individual trees can be modelled.
    BibTeX:
    @article{Baltsavias2008,
      author = {Baltsavias, E. and Gruen, A. and Eisenbeiss, H. and Zhang, L. and Waser, L. T.},
      title = {High-quality image matching and automated generation of 3D tree models},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1243--1259}
    }
    
    Baltsavias, E.P. Airborne laser scanning: basic relations and formulas 1999 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 54(2-3), pp. 199-214 
    article  
    Abstract: An overview of basic relations and formulas concerning airborne laser scanning is given. They are divided into two main parts, the first treating lasers and laser ranging, and the second one referring to airborne laser scanning. A separate discussion is devoted to the accuracy of 3D positioning and the factors influencing it. Examples are given for most relations, using typical values for ALS and assuming an airplane platform. The relations refer mostly to pulse lasers, but CW lasers are also treated. Different scan patterns, especially parallel lines, are treated. Due to the complexity of the relations, some formulas represent approximations or are based on assumptions like constant flying speed, vertical scan, etc.
    BibTeX:
    @article{baltsavias99c,
      author = {E. P. Baltsavias},
      title = {Airborne laser scanning: basic relations and formulas},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {1999},
      volume = {54},
      number = {2-3},
      pages = {199-214}
    }
    
    Baltsavias, E.P. Airborne laser scanning: existing systems and firms and other resources 1999 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 54, pp. 164-198 
    article  
    Abstract: .This article gives an overview of resources on airborne laser scanning ALS . The main emphasis is on existing systems and firms, especially commercial ones. Through a very time-consuming search and with the help of numerous persons from firms, organisations and other colleagues, a quite complete survey of existing commercial systems, including detailed system parameters, has been compiled. This survey is by far the most complete and up-to-date information available today on commercial ALS. Additional data on contact information, links and, in some cases, a short background is given for firms involved in ALS manufacturers, service providers, owners . A summary of other non-commercial and research systems, mainly of NASA, and respective links is presented. Finally, some other useful WEB links are given. The developments in ALS have been very rapid the last 1 ? 2 years. This overview reflects these developments and describes rather completely the current situation, thus, being useful for all persons involved in ALS one way or another. q 1999 Elsevier Science B.V. All rights reserved.
    BibTeX:
    @article{baltsavias_sys99,
      author = {E. P. Baltsavias},
      title = {Airborne laser scanning: existing systems and firms and other resources},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {1999},
      volume = {54},
      pages = {164-198}
    }
    
    Begue, A. Leaf area index, intercepted photosynthetically active radiation, and spectral vegetation indices: A sensitivity analysis for regular-clumped canopies 1993 Remote Sensing of Environment
    Vol. 46(1), pp. 45-59 
    article  
    Abstract: In this article, the variability of the relationship between the normalized difference vegetation index (NDVI) and the daily interception efficiency ([epsi]i) of a discontinuous canopy is investigated using a simple radiative transfer model developed for regular-clumped crops. Sensitivity to the canopy and irradiance parameters is first studied for 1)the relationship between [epsi]i and LAI and 2) the relationship between NDVI and LAI. The analysis is conducted varying one parameter at a time to provide an understanding of the influence of that variable on the behavior of the relationships. Next, with the same procedure, the relationship between [epsi]i and NDVI is investigated. This investigation focuses on the sensitivity of the relationship to the structural parameters and its linearity. It shows that for most of the semiarid vegetation types, characterized by low LAI and bright background, the [epsi]i--NDVI relationship could be simplified to a linear relation with an abscissa offset equal to the normalized difference vegetation index of the background (NDVIs): [epsi]i = a(NDVI - NDVIs). Further studies show that 1) the more the canopy is discontinuous, themore the slope a is sensitive to the solar zenith angle, 2) the slope a tends to a unique value 1.3 as the canopy tends to a homogeneous medium, and 3) the relative standard error of [epsi]i is time-dependent (minimum at [theta]s = 30[deg]) and all the higher as the structure of the canopy is unknown. The relevance of these investigations to satellite data is then discussed, resulting in long-term recommendations as satellite orbital characteristics providing the optimal geometric irradiance for [epsi]i estimation, or additional new sensors providing complementary information about the canopy. At short term, further [epsi]i--NDVI sensitivity analyses are encouraged, especially for other types of discontinuous canopies and off-nadir viewing.
    BibTeX:
    @article{begue93,
      author = {Begue, Agnes},
      title = {Leaf area index, intercepted photosynthetically active radiation, and spectral vegetation indices: A sensitivity analysis for regular-clumped canopies},
      journal = {Remote Sensing of Environment},
      year = {1993},
      volume = {46},
      number = {1},
      pages = {45--59}
    }
    
    Behan, A. ON THE MATCHING ACCURACY OF RASTERISED SCANNING LASER ALTIMETER DATA 2000 IAPRS
    Vol. Vol. XXXIII, Amsterdam 
    article  
    Abstract: For certain applications irregularly distributed scanning laser altimeter data need to be rasterised - such as for use in GIS systems and for creating DEMs. Also, least squares matching on a raster grid can enable the measurement of planimetric and height shifts between overlapping strips of laser data. The shifts are a manifestation of errors in the laser altimeter, most of which are caused by the positioning elements of the system (GPS and/or INS). These translations form the input into a block adjustment to correct for relative and absolute errors. Here a discussion of the issues related to deriving a regular grid of 2.5D points from the original data is presented, with particular reference to the interpolation method, grid size, and quantisation level. An interpolation method based on a TIN of the original points with a grid size that relates as closely as possible to the point density at acquisition is found to give the best results. 8-bit quantisation is found to be sufficient for height differences of up to 100m.
    BibTeX:
    @article{behan,
      author = {Avril Behan},
      title = {ON THE MATCHING ACCURACY OF RASTERISED SCANNING LASER ALTIMETER DATA},
      journal = {IAPRS},
      year = {2000},
      volume = {Vol. XXXIII, Amsterdam}
    }
    
    Berg?s, L. R?le des coupes, de la stratification verticale et du mode de traitement dans la conservation de la biodiversit?. 2004 In Gosselin, M. & Laroussinie, O. (eds.) Biodiversit? et gestion foresti?re. Conna?tre pour pr?server. GIP-ECOFOR, Paris.  article  
    BibTeX:
    @article{Berges2004,
      author = {Berg?s, L.},
      title = {R?le des coupes, de la stratification verticale et du mode de traitement dans la conservation de la biodiversit?.},
      journal = {In Gosselin, M. & Laroussinie, O. (eds.) Biodiversit? et gestion foresti?re. Conna?tre pour pr?server. GIP-ECOFOR, Paris.},
      year = {2004}
    }
    
    Bergen, K.M., Goetz, S.J., Dubayah, R.O., Henebry, G.M., Hunsaker, C.T., Imhoff, M.L., Nelson, R.F., Parker, G.G. & Radeloff, V.C. Remote sensing of vegetation 3-D structure for biodiversity and habitat: Review and implications for lidar and radar spaceborne missions 2009 Journal of Geophysical Research
    Vol. 114, pp. G00E06 
    article DOI  
    Abstract: Biodiversity and habitat face increasing pressures due to human and natural influences that alter vegetation structure. Because of the inherent difficulty of measuring forested vegetation three-dimensional (3-D) structure on the ground, this important component of biodiversity and habitat has been, until recently, largely restricted to local measurements, or at larger scales to generalizations. New lidar and radar remote sensing instruments such as those proposed for spaceborne missions will provide the capability to fill this gap. This paper reviews the state of the art for incorporatinginformation on vegetation 3-D structure into biodiversity and habitat science and management approaches, with emphasis on use of lidar and radar data. First we review relationships between vegetation 3-D structure, biodiversity and habitat, and metrics commonly used to describe those relationships. Next, we review the technical capabilities of new lidar and radar sensors and their application to biodiversity and habitat studies to date. We then define variables that have been identified as both useful and feasible to retrieve from spaceborne lidar and radar observations and provide their accuracy and precision requirements. We conclude with a brief discussion of implications for spaceborne missions and research programs. The possibility to derive vegetation 3-D measurements from spaceborne active sensors and to integrate them into science and management comes at a critical juncture for global biodiversity conservation and opens new possibilities for advanced scientific analysis of habitat and biodiversity.
    BibTeX:
    @article{Bergen2009,
      author = {K. M. Bergen and S. J. Goetz and R. O. Dubayah and G. M. Henebry and C. T. Hunsaker and M. L. Imhoff and R. F. Nelson and G. G. Parker and V. C. Radeloff},
      title = {Remote sensing of vegetation 3-D structure for biodiversity and habitat: Review and implications for lidar and radar spaceborne missions},
      journal = {Journal of Geophysical Research},
      year = {2009},
      volume = {114},
      pages = {G00E06},
      doi = {http://dx.doi.org/10.1029/2008JG000883}
    }
    
    Berger, A.L. & Puettmann, K.J. Overstory composition and stand structure influence herbaceous plant diversity in the mixed aspen forest of northern Minnesota. 2000 American Midland Naturalist
    Vol. 143, pp. 111-125 
    article  
    BibTeX:
    @article{Berger2000,
      author = {Berger, A. L. and Puettmann, K. J.},
      title = {Overstory composition and stand structure influence herbaceous plant diversity in the mixed aspen forest of northern Minnesota.},
      journal = {American Midland Naturalist},
      year = {2000},
      volume = {143},
      pages = {111-125}
    }
    
    Bergeron, C., Ruel, J., Elie, J. & Mitchell, S. 82:29.-41.. Root anchorage and stem strength of black spruce (Picea mariana) trees in regular and irregular stands. 2009 Forestry
    Vol. 82, pp. 29-41 
    article  
    BibTeX:
    @article{bergeron09,
      author = {Bergeron, C. and Ruel, J.C. and Elie, J.G. and Mitchell, S.J. 82:29-41.},
      title = {Root anchorage and stem strength of black spruce (Picea mariana) trees in regular and irregular stands.},
      journal = {Forestry},
      year = {2009},
      volume = {82},
      pages = {29-41}
    }
    
    Bernard, M.L., Carbonel, M. & Nimour, N. Are large wildland fires - as anomalous ecologic processes - natural hazards 2000 Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy
    Vol. 25(12), pp. 763-768 
    article  
    Abstract: To account for the annual intensity of wildland fires, a theory has been formerly proposed : it is based on the effect of UV-B radiation on the sensitiveness of plants to fire ignition and propagation. It accounts very satisfactorily for the statistics of annual burned area in the French Mediterranean region. The paper is more particularly devoted to daily variation of the total ozone content of the atmosphere and its possible large daily drop : in the French Mediterranean region, large fires occur in general at the end of such drops, simultaneously in different parts of this region. The UV-B sensitiveness theory based on annual data may predict such large fire occurrence. So, taking into account the daily variation of ozone and solar flux helps to make short-term forecasts of the possibility of large fires in a determined region.
    BibTeX:
    @article{Bernard2000,
      author = {Bernard, M. L. and Carbonel, M. and Nimour, N.},
      title = {Are large wildland fires - as anomalous ecologic processes - natural hazards},
      journal = {Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy},
      year = {2000},
      volume = {25},
      number = {12},
      pages = {763--768}
    }
    
    Bicheron, P. & Leroy, M. A Method of Biophysical Parameter Retrieval at Global Scale by Inversion of a Vegetation Reflectance Model 1999 Remote Sensing of Environment
    Vol. 67(3), pp. 251-266 
    article  
    Abstract: The objective of the paper is to study a physically based method of retrieval of leaf area index (LAI) and fraction of absorbed photosynthetically active radiation (fAPAR) parameters from global data sets of new generation wide field of view optical satellite sensors, such as POLDER/ADEOS, VGT/SPOT4, MODIS/EOS, MISR/EOS, MERIS/ENVISAT, and so forth. The method uses the bidirectional reflectance distribution function (BRDF) model of , which simultaneously predicts the spectral and directional behavior of reflectances, as a function of LAI, chlorophyll concentration, ratio of leaf size to canopy height, and other optical or structural parameters of the soil and vegetation. The same model is used irrespective of surface type, and no ancillary data is needed. This approach is evaluated with field and airborne data acquired over three different types of surfaces: Sahelian vegetation in the HAPEX-Sahel (1992) experiment, boreal forest in the BOREAS (1994) experiment, and cultivated areas in the Alpilles (1996) experiment. The results show that the LAI is restituted with a fair accuracy [root-mean-square (rms) difference between model results and observations of 0.70], better than that obtained with a semiempirical relation LAI-vegetation index. The daily fAPAR is restituted accurately, with a rms difference between measured and modeled fAPAR of 0.097. In the example of HAPEX, the model reproduces to some extent the temporal evolution of measured LAI and fAPAR. Reflectances reconstructed with the model are in acceptable agreement with observed reflectances, with a rms difference between observed and measured values of 0.017 on average. It is concluded that the retrieval of biophysical parameters from inversion of a BRDF model is promising from the perspective of a quantitative characterization of the terrestrial biosphere from space.
    BibTeX:
    @article{bicheron99,
      author = {Bicheron, Patrice and Leroy, Marc},
      title = {A Method of Biophysical Parameter Retrieval at Global Scale by Inversion of a Vegetation Reflectance Model},
      journal = {Remote Sensing of Environment},
      year = {1999},
      volume = {67},
      number = {3},
      pages = {251--266}
    }
    
    Bienert, A., Queck, R., Schmidt, A., Bernhofer, C. & Maas, H.-G. VOXEL SPACE ANALYSIS OF TERRESTRIAL LASER SCANS IN FORESTS FOR WIND FIELD MODELING 2010 International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. XXXVIII, Part 5 Commission V Symposium, Newcastle upon Tyne, UK.  inproceedings  
    Abstract: Meteorological simulation tools to model gas exchange phenomena within forests require well defined information of forest structure (e.g., 3D forest models) as a basis for the computation of the turbulent flow shaped by the drag of the vegetation. The paper describes techniques to obtain 3D data describing forest stands from dense terrestrial laser scanner point clouds. In a first step, stems are automatically detected from the laser scanner data, forming a basis for the determination of tree density, distance patterns and average stem distance. In a second step, the 3D point cloud is translated into a voxel structure representing the forest. A method to segment voxel clusters with the goal of a tree wise interpretation, is presented. From this voxel structure, drag coefficients can be derived via the local density and distribution of stems, branches and leaves. Therefore different voxel attributes are calculated.
    BibTeX:
    @inproceedings{bienert2010,
      author = {A. Bienert and R. Queck and A. Schmidt and Ch. Bernhofer and H.-G. Maas},
      title = {VOXEL SPACE ANALYSIS OF TERRESTRIAL LASER SCANS IN FORESTS FOR WIND FIELD MODELING},
      booktitle = {International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. XXXVIII, Part 5 Commission V Symposium, Newcastle upon Tyne, UK.},
      year = {2010}
    }
    
    Bigler, C. & Bugmann, H. Assessing the performance of theoretical and empirical tree mortality models using tree-ring series of Norway spruce 2004 Ecological Modelling
    Vol. 174(3), pp. 225-239 
    article  
    Abstract: Successional dynamics of forests under current and changed climate are often investigated using gap models, a subset of forest succession models that simulate establishment, growth, and mortality of trees. However, the mortality submodels of gap models are largely based on theoretical assumptions, and have not been tested in detail. In the present study, we compared the performance of a range of theoretical mortality functions (TMFs) that are commonly used in gap models with several empirical mortality functions (EMFs) that were derived using logistic regression from growth patterns of tree-ring series as predictor variables. Data from dead and living Norway spruce (Picea abies (L.) Karst.) trees from subalpine forests at three study sites in Switzerland were used to this end. Three of the four EMFs consistently performed better at all three sites, while three of the four TMFs performed worse than the remaining mortality functions. At one site, these three EMFs correctly classified 71-78% of the dead trees (48-72% for the three TMFs) and 73% (49-64%) of the living trees. 44-54% (21-25%) of the dead trees were predicted to die within 15 years prior to death. 0-2% (7-10%) of the dead trees and 5% (19-31%) of the living trees were predicted to die more than 60 years prior to the last measured year. We conclude that, unless the parameters of the TMFs are optimized for individual species, the TMFs are not appropriate to predict the time of tree death, in spite of their widespread use. A substantial change in simulated forest succession is to be expected if the currently implemented TMFs in gap models are replaced by species-specific EMFs.
    BibTeX:
    @article{Bigler2004,
      author = {Bigler, Christof and Bugmann, Harald},
      title = {Assessing the performance of theoretical and empirical tree mortality models using tree-ring series of Norway spruce},
      journal = {Ecological Modelling},
      year = {2004},
      volume = {174},
      number = {3},
      pages = {225--239}
    }
    
    Bindschadler, R., Choi, H., Shuman, C. & Markus, T. Detecting and measuring new snow accumulation on ice sheets by satellite remote sensing 2005 Remote Sensing of Environment
    Vol. 98(4), pp. 388 - 402 
    article DOI URL 
    Abstract: A new technique is described that detects when and where new snow falls on ice sheets and then determines the thickness of new accumulation. Measurements of vertically polarized passive emission at 85 GHz are filtered with the Hilbert-Huang Transform to identify periods where the surface snow has changed significantly. These are shown to be commonly the result of new snow by comparison with both field observations and in situ instrumentation. Temperature, atmospheric emission and clouds all affect the passive microwave signal but each is examined and shown not to prevent the identification of new snow events. The magnitude of the brightness temperature change is not strongly correlated with snowfall amount. To quantify the amount of new snow, the spatial extent and timing of new snowfalls are examined with ICESat/GLAS laser altimetry data. Crossover differences between altimetric profiles taken before, during, and after the snowfall event provide a measure of the thickness of new snow. Specific cases are presented where 11 and 13 cm of new snow were detected over large regions.
    BibTeX:
    @article{Bindschadler2005388,
      author = {Robert Bindschadler and Hyeungu Choi and Christopher Shuman and Thorsten Markus},
      title = {Detecting and measuring new snow accumulation on ice sheets by satellite remote sensing},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {98},
      number = {4},
      pages = {388 - 402},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4H6GPRG-2/2/3c2b4908cca86e73cd40fb56d35d253a},
      doi = {DOI: 10.1016/j.rse.2005.07.014}
    }
    
    Blackburn, G.A. Remote sensing of forest pigments using airborne imaging spectrometer and LIDAR imagery 2002 Remote Sens. Environ.
    Vol. 82(2-3), pp. 311-321 
    article  
    Abstract: This study created and tested predictive models developed using airborne imaging spectrometer and light detection and ranging (LIDAR) instruments for estimating the concentrations of photosynthetic pigments in broad-leaved and coniferous forest plantations. Data were acquired using a Compact Airborne Spectrographic Imager (CASI) and an Airborne Laser Terrain Mapping (ALTM) 1020 instrument in midsummer for study sites in the New Forest, England, along with concomitant in situ measurements of canopy properties. The stands used displayed a wide variation in the biophysical and biochemical properties of interest. When employing the imaging spectrometer data alone, there were no relationships between any spectral variables (band reflectance, band ratios, or first derivatives of reflectance) and canopy biophysical and biochemical properties when both broad-leaved and coniferous stands were analysed as a combined data set. However, for the broad-leaved stands alone, curvilinear relationships were found between the wavelength position of the red edge (small lambda, GreekRE) and pigment concentrations per unit ground area (e.g., R2=0.88** for chlorophyll a [Chl a]) and per unit leaf mass (e.g., R2=0.76** for Chl a). The predictive value of these models was somewhat limited; for example, the root mean squared error (RMSE) was 300 mg m-2 (27% of the mean) for Chl a concentration per unit ground area and 1.17 mg g-1 (24% of the mean) for Chl a concentration per unit leaf mass. A ratio of a near-infrared and a green band (865 nm/553 nm) was linearly related to leaf area index (LAI) of the broad-leaved stands (R2=0.71**) and the regression model was a reasonable predictor of the LAI for the independent test sites (RMSE=0.88; 18.6% of the mean). Canopy height information derived from the ALTM data was used to mask out canopy gap areas from the CASI imagery of each stand. This process had limited impact on the relationships between spectral and canopy variables for the broad-leaved stands, and small lambda, GreekRE remained unrelated to pigment concentrations per unit ground area for the coniferous stands. However, the masking process substantially improved the strength of the relationship between small lambda, GreekRE and pigment concentrations per unit leaf mass for the coniferous stands (e.g., for Chl a R2=0.85**; RMSE of PREDICTION=0.84 mg g-1 [22% of the mean]). Therefore, the study demonstrates that for broad-leaved stands, spectral models can be applied to imaging spectrometer data to quantify forest pigments and LAI with moderate accuracy. For coniferous stands, the use of LIDAR data to remove canopy gap areas from the CASI imagery considerably increases the accuracy of spectral predictive models for quantifying pigment concentrations per unit leaf mass.
    BibTeX:
    @article{blackburn02,
      author = {George Alan Blackburn},
      title = {Remote sensing of forest pigments using airborne imaging spectrometer and LIDAR imagery},
      journal = {Remote Sens. Environ.},
      year = {2002},
      volume = {82},
      number = {2-3},
      pages = {311-321}
    }
    
    Blair, J.B., Hofton, M.A. & Luthcke, S.B. WIDE-SWATH IMAGING LIDAR DEVELOPMENT FOR AIRBORNE AND SPACEBORNE APPLICATIONS 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 17-20 
    article  
    Abstract: With laser altimetry becoming increasingly accepted by the global Earth science community as a source for accurate topographic data, there is now a desire to apply this technology to large area mapping. Commonly, airborne laser systems provide data at several meter resolution and across swaths up to 1-2 km in width. Economic factors drive commercial systems to widen swaths further, but off-nadir incident angles degrade accuracy and significantly diminish the ability to penetrate dense vegetation canopies effectively limiting swath width. Higher operational altitudes (e.g., 10 km vs. 1 km) can provide up to a factor of ten increase in swath width within a selected angular range. However, higher altitude operations require significantly more laser output power, smaller divergence angles and higher beam quality to achieve smaller footprints. At NASA Goddard Space Flight Center, we have been prototyping spaceborne instrumentation and science applications of wide-swath lidar in aircraft for the last several years. This experience has led to the development of several satellite laser altimeters such as the Shuttle Laser Altimeter (SLA) and Vegetation Canopy Lidar (VCL). Technologies and methods utilized in the spaceborne environment are prototyped in the wide-swath, full-waveform airborne Laser Vegetation Imaging Sensor (LVIS). This sensor will undertake a large-area mapping mission in Brazil in June-August 2002. The sensor will use a 3 km-wide data swath and plans are underway to increase the swath width further. Spaceborne imaging applications require significantly higher effective rep-rates than airborne systems and are much less tolerant of unreliable mechanical scanning and equipment maintenance requirements. Unique scanning and ranging techniques for medium-large footprint, full-waveform mapping laser altimeters are currently under development to enable a spaceborne, wide-swath operational mapping laser altimeter capable of full-Earth mapping and dense vegetation penetration. A sample of some of the techniques being developed at NASA Goddard Space Flight Center for future airborne and spaceborne imaging lidar will be presented, including methods for achieving MHz scanning rates.
    BibTeX:
    @article{blair01,
      author = {J. Bryan Blair and Michelle A. Hofton and Scott B. Luthcke},
      title = {WIDE-SWATH IMAGING LIDAR DEVELOPMENT FOR AIRBORNE AND SPACEBORNE APPLICATIONS},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {17-20}
    }
    
    Blair, J.B., Rabine, D.L. & Hofton, M.A. The Laser Vegetation Imaging Sensor: a medium-altitude, digitisation-only, airborne laser altimeter for mapping vegetation and topography 1999 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 54(2-3), pp. 115-122 
    article  
    Abstract: The Laser Vegetation Imaging Sensor (LVIS) is an airborne, scanning laser altimeter, designed and developed at NASA's Goddard Space Flight Center (GSFC). LVIS operates at altitudes up to 10 km above ground, and is capable of producing a data swath up to 1000 m wide nominally with 25-m wide footprints. The entire time history of the outgoing and return pulses is digitised, allowing unambiguous determination of range and return pulse structure. Combined with aircraft position and attitude knowledge, this instrument produces topographic maps with dm accuracy and vertical height and structure measurements of vegetation. The laser transmitter is a diode-pumped Nd:YAG oscillator producing 1064 nm, 10 ns, 5 mJ pulses at repetition rates up to 500 Hz. LVIS has recently demonstrated its ability to determine topography (including sub-canopy) and vegetation height and structure on flight missions to various forested regions in the US and Central America. The LVIS system is the airborne simulator for the Vegetation Canopy Lidar (VCL) mission (a NASA Earth remote sensing satellite due for launch in year 2000), providing simulated data sets and a platform for instrument proof-of-concept studies. The topography maps and return waveforms produced by LVIS provide Earth scientists with a unique data set allowing studies of topography, hydrology, and vegetation with unmatched accuracy and coverage.
    BibTeX:
    @article{blair99,
      author = {J. Bryan Blair and David L. Rabine and Michelle A. Hofton},
      title = {The Laser Vegetation Imaging Sensor: a medium-altitude, digitisation-only, airborne laser altimeter for mapping vegetation and topography},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {1999},
      volume = {54},
      number = {2-3},
      pages = {115-122}
    }
    
    Bolliger, J., Kienast, F. & Bugmann, H. Comparing models for tree distributions: concept, structures, and behavior 2000 Ecological Modelling
    Vol. 134(1), pp. 89-102 
    article  
    Abstract: Vegetation models are increasingly used for assessing impacts of a changing environment on landscapes. Model evaluation is an important task since it allows us to determine of model accuracy and applicability. Rarely, model evaluation includes comparisons with model outputs from approaches that are based on completely different ecosystem-theoretical concepts. However, such comparisons are important for improving the understanding of model behavior. In this paper, two model concepts the static equilibrium and the dynamic-transient are compared using simulations of tree distributions. The simulations were compared against empirical data of the Swiss National Forest Inventory (NFI). Static equilibrium models (e.g., regression model) simulate tree distributions primarily as a function of the abiotic biophysical environment. The approach can be considered as [`]top-down' since the data used to calculate the abiotic environment integrate over large spatial scales up to km2, and hence mirror major features of the tree habitat, but does not describe individual physiological properties of the tree species. Such models are calibrated with empirical data sets, and thus the resulting simulations can be considered to mirror realized niches that account for management. The dynamic-transient approach (e.g. ForClim gap model) simulates trees in a [`]bottom-up' approach since detailed species-specific local-scale life-history attributes and environmental variables are considered to describe the trees. As management schemes are not intrinsic to ForClim, resulting simulations may be viewed as realized niches in the absence of management. Results of the model comparison show that at large spatial scales both models discriminate well between major tree distribution characteristics and can be considered as valid estimators for assessing regional vegetation patterns. Specifically, the model comparison generated valuable insights into human-induced alterations of species-specific distribution patterns. For example, simulations of the regression model and observations of the NFI agreed to a large extent regarding the distribution of Fagus sylvatica. ForClim, however, clearly overestimated this species in most ecoregions. Thus, these results suggest that F. sylvatica would be more frequent if management effects had not reduced its range; similar conclusions can be drawn in other respects, as discussed in the paper.
    BibTeX:
    @article{Bolliger2000,
      author = {Bolliger, Janine and Kienast, Felix and Bugmann, Harald},
      title = {Comparing models for tree distributions: concept, structures, and behavior},
      journal = {Ecological Modelling},
      year = {2000},
      volume = {134},
      number = {1},
      pages = {89--102}
    }
    
    Bonan, G.B. Importance of leaf area index and forest type when estimating photosynthesis in boreal forests 1993 Remote Sensing of Environment
    Vol. 43(3), pp. 303-314 
    article  
    Abstract: Leaf area index (LAI) and vegetation type are two ecological variables that influence atmosphere-biosphere exchange of CO2 and that can be estimated from remote sensing techniques. A forest ecosystem process model was used to examine the importance of LAI and species-dependent physiology when estimating photosynthesis in 21 black spruce, white spruce, quaking aspen, paper birch, and balsam poplar forests near Fairbanks, Alaska. Model sensitivity analyses for these 21 stands showed that uncertainty in LAI and species composition caused errors in net canopy assimilation of as much as 42-70% and 14-36%, respectively, depending on forest type. The sensitivity of net canopy assimilation to species-dependent physiology was greater between needleleaf coniferous and broadleaf deciduous life forms than among species within life forms. A simple regression model that recognized stand differences in LAI and life-form type (needleleaf coniferous, broadleaf deciduous) accounted for 94% of the variation in simulated net canopy assimilation for the 21 stands. Expanding the model to include species composition rather than life-form type only accounted for an additional 1% of the variation in simulated net canopy assimilation. The statistical model was applied to a synthetic aperture radar scene that discriminatted black spruce, white spruce, balsam poplar, and alder forests in a 76.8 km2 region near Fairbanks. This analysis showed that regional net canopy assimilation was as sensitive to the area of each forest type as it was to the LAI of each forest type. The analyses reported in this article highlight the importance of recognizing physiological differences among needleleaf coniferous and broadleaf deciduous forest types when estimating regional net canopy assimilation in boreal forests.
    BibTeX:
    @article{bonan93,
      author = {Bonan, Gordon B.},
      title = {Importance of leaf area index and forest type when estimating photosynthesis in boreal forests},
      journal = {Remote Sensing of Environment},
      year = {1993},
      volume = {43},
      number = {3},
      pages = {303--314}
    }
    
    Boudreau, J., Nelson, R.F., Margolis, H.A., Beaudoin, A., Guindon, L. & Kimes, D.S. Regional aboveground forest biomass using airborne and spaceborne LiDAR in Qu?bec 2008 Remote Sensing of Environment
    Vol. 112(10), pp. 3876-3890 
    article  
    Abstract: Aboveground dry biomass was estimated for the 1.3?M km2 forested area south of the treeline in the eastern Canadian province of Qu?bec by combining data from an airborne and spaceborne LiDAR, a Landsat ETM+ land cover map, a Shuttle Radar Topographic Mission (SRTM) digital elevation model, ground inventory plots, and vegetation zone maps. Plot-level biomass was calculated using allometric relationships between tree attributes and biomass. A small footprint portable laser profiler then flew over these inventory plots to develop a generic airborne LiDAR-based biomass equation (R2?=?0.65, n?=?207). The same airborne LiDAR system flew along four portions of orbits of the ICESat Geoscience Laser Altimeter System (GLAS). A square-root transformed equation was developed to predict airborne profiling LiDAR estimates of aboveground dry biomass from GLAS waveform parameters combined with an SRTM slope index (R2?=?0.59, n?=?1325). Using the 104,044 quality-filtered GLAS pulses obtained during autumn 2003 from 97 orbits over the study area, we then predicted aboveground dry biomass for the main vegetation areas of Qu?bec as well as for the entire Province south of the treeline. Including cover type covariances both within and between GLAS orbits increased standard errors of the estimates by two to five times at the vegetation zone level and as much as threefold at the provincial level. Aboveground biomass for the whole study area averaged 39.0???2.2 (standard error) Mg ha-?1 and totalled 4.9???0.3 Pg. Biomass distributions were 12.6% northern hardwoods, 12.6% northern mixedwood, 38.4% commercial boreal, 13% non-commercial boreal, 14.2% taiga, and 9.2% treed tundra. Non-commercial forests represented 36% of the estimated aboveground biomass, thus highlighting the importance of remote northern forests to C sequestration. This study has shown that space-based forest inventories of northern forests could be an efficient way of estimating the amount, distribution, and uncertainty of aboveground biomass and carbon stocks at large spatial scales.
    BibTeX:
    @article{Boudreau2008,
      author = {Boudreau, Jonathan and Nelson, Ross F. and Margolis, Hank A. and Beaudoin, Andr? and Guindon, Luc and Kimes, Daniel S.},
      title = {Regional aboveground forest biomass using airborne and spaceborne LiDAR in Qu?bec},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {10},
      pages = {3876--3890}
    }
    
    Boyd, D. & Danson, F. Satellite remote sensing of

    forest resources: three decades of research develop-

    ment.

    2005 Progress in Physical Geography
    Vol. 29, pp. 1-26 
    article  
    BibTeX:
    @article{boyd05,
      author = {Boyd, D.S. and Danson, F.M.},
      title = {Satellite remote sensing of 

    forest resources: three decades of research develop-

    ment.}, journal = {Progress in Physical Geography}, year = {2005}, volume = {29}, pages = {1-26} }

    Brandtberg, T., Warner, T.A., Landenberger, R.E. & McGraw, J.B. Detection and analysis of individual leaf-off tree crowns in small footprint, high sampling density lidar data from the eastern deciduous forest in North America 2003 Remote Sens. Environ.
    Vol. 85(3), pp. 290-303 
    article  
    Abstract: Leaf-off individual trees in a deciduous forest in the eastern USA are detected and analysed in small footprint, high sampling density lidar data. The data were acquired February 1, 2001, using a SAAB TopEye laser profiling system, with a sampling density of approximately 12 returns per square meter. The sparse and complex configuration of the branches of the leaf-off forest provides sufficient returns to allow the detection of the trees as individual objects and to analyse their vertical structures. Initially, for the detection of the individual trees only, the lidar data are first inserted in a 2D digital image, with the height as the pixel value or brightness level. The empty pixels are interpolated, and height outliers are removed. Gaussian smoothing at different scales is performed to create a three-dimensional scale-space structure. Blob signatures based on second-order image derivatives are calculated, and then normalised so they can be compared at different scale-levels. The grey-level blobs with the strongest normalised signatures are selected within the scale-space structure. The support regions of the blobs are marked one-at-a-time in the segmentation result image with higher priority for stronger blobs. The segmentation results of six individual hectare plots are assessed by a computerised, objective method that makes use of a ground reference data set of the individual tree crowns. For analysis of individual trees, a subset of the original laser returns is selected within each tree crown region of the canopy reference map. Indices based on moments of the first four orders, maximum value and number of canopy and ground returns, are estimated. The indices are derived separately for height and laser reflectance of branches for the two echoes. Significant differences (p<0.05) are detected for numerous indices for three major native species groups: oaks (Quercus spp.), red maple (Acer rubrum) and yellow poplar (Liriodendron tuliperifera). Tree species classification results of different indices suggest a moderate to high degree of accuracy using single or multiple variables. Furthermore, the maximum tree height is compared to ground reference tree height for 48 sample trees and a 1.1-m standard error (R2=68% (adj.)) within the test-site is observed.
    BibTeX:
    @article{brandtberg03,
      author = {Tomas Brandtberg and Timothy A. Warner and Rick E. Landenberger and James B. McGraw},
      title = {Detection and analysis of individual leaf-off tree crowns in small footprint, high sampling density lidar data from the eastern deciduous forest in North America},
      journal = {Remote Sens. Environ.},
      year = {2003},
      volume = {85},
      number = {3},
      pages = {290-303}
    }
    
    Breidenbach, J., Koch, B., Kändler, G. & Kleusberg, A. Quantifying the influence of slope, aspect, crown shape and stem density on the estimation of tree height at plot level using lidar and InSAR data 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1511-1536 
    article  
    Abstract: This study compared the use of light detection and ranging (lidar) data and X-band interferometric synthetic aperture radar (InSAR) data for estimating Lorey's height (H L) within inventory plots. At plot level, H L can be estimated with a root mean squared error (RMSE) of 1.8??m or 6.0% using lidar data and 2.7??m or 9.0% using InSAR data. The most effective predictor variables were found to be the 75th percentile of the vegetation heights for lidar (p75 lidar) and the 90th percentile for InSAR (p90 InSAR). Estimation results can be improved considerably by incorporating ground slope into the models. An increase in slope, given the same field-measured H L, was associated with an upward shift in height percentiles. We assume that this is a cause of the asymmetrical crown shape on slopes. An interaction between slope and aspect was noted for InSAR data, with a tendency for the influence of slope to be stronger on upward (i.e. for slopes facing the InSAR sensor) than downward slopes. Comparison of the lidar- and InSAR-derived vegetation heights revealed that the p90 InSAR is more commonly below the p75 lidar. This difference was greater on upward than downward slopes. Estimations of H L can be further improved if additional information, such as the conifer proportion (CP) (as a surrogate for crown shape) or stem density (SD), is included in the models. It was possible to substitute the predictor variable CP by means of density metrics in the statistical models that depend on InSAR data. However, this was not possible for the statistical models depending on lidar data. Density metrics were also not able to explain the variability that was explained by the predictor variable SD (this was the case for models that depend on lidar and on InSAR data).
    BibTeX:
    @article{Breidenbach2008,
      author = {Breidenbach, J. and Koch, B. and Kändler, G. and Kleusberg, A.},
      title = {Quantifying the influence of slope, aspect, crown shape and stem density on the estimation of tree height at plot level using lidar and InSAR data},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1511--1536}
    }
    
    Brenner, C. Building reconstruction from images and laser scanning 2005 International Journal of Applied Earth Observation and Geoinformation
    Vol. 6(3-4), pp. 187-198 
    article  
    Abstract: The automatic extraction of objects from laser scans and images has been a topic of research for decades. Nowadays, with new services expected, especially in the area of navigation systems, location based services, and augmented reality, the need for automated, efficient extraction systems becomes more urgent than ever. This paper reviews a number of automatic and semi-automatic reconstruction methods in more detail in order to reveal their underlying principles. It then discusses some general properties of reconstruction approaches which have evolved. This shows that, although research is still far from the goal of the initially envisioned fully automatic reconstruction systems, there is now a much better understanding of the problem and the ways it can be tackled.
    BibTeX:
    @article{brenner05,
      author = {Brenner, Claus},
      title = {Building reconstruction from images and laser scanning},
      journal = {International Journal of Applied Earth Observation and Geoinformation},
      year = {2005},
      volume = {6},
      number = {3-4},
      pages = {187-198}
    }
    
    Brock, J.C., Wright, C.W., Kuffner, I.B., Hernandez, R. & Thompson, P. Airborne lidar sensing of massive stony coral colonies on patch reefs in the northern Florida reef tract 2006 Remote Sensing of Environment
    Vol. 104(1), pp. 31-42 
    article  
    Abstract: In this study we examined the ability of the NASA Experimental Advanced Airborne Research Lidar (EAARL) to discriminate cluster zones of massive stony coral colonies on northern Florida reef tract (NFRT) patch reefs based on their topographic complexity (rugosity). Spatially dense EAARL laser submarine topographic soundings acquired in August 2002 were used to create a 1-m resolution digital rugosity map for adjacent NFRT study areas characterized by patch reefs (Region A) and diverse substratums (Region B). In both regions, sites with lidar-sensed rugosities above 1.2 were imaged by an along-track underwater videography system that incorporated the acquisition of instantaneous GPS positions. Subsequent manual interpretation of videotape segments was performed to identify substratum types that caused elevated lidar-sensed rugosity. Our study determined that massive coral colony formation, modified by subsequent physical and biological processes that breakdown patch reef framework, was the primary source of topographic complexity sensed by the EAARL in the NFRT. Sites recognized by lidar scanning to be topographically complex preferentially occurred around the margins of patch reefs, constituted a minor fraction of the reef system, and usually reflected the presence of massive coral colonies in cluster zones, or their derivatives created by mortality, bioerosion, and physical breakdown.
    BibTeX:
    @article{Brock2006,
      author = {Brock, John C. and Wright, C. Wayne and Kuffner, Ilsa B. and Hernandez, Raquel and Thompson, Philip},
      title = {Airborne lidar sensing of massive stony coral colonies on patch reefs in the northern Florida reef tract},
      journal = {Remote Sensing of Environment},
      year = {2006},
      volume = {104},
      number = {1},
      pages = {31--42}
    }
    
    Brown, J.K. Estimating shrub biomass from basal stem diameters 1976 Canadian Journal of Forest Research
    Vol. 6, pp. 153-158 
    article  
    BibTeX:
    @article{brown76,
      author = {Brown, J. K.},
      title = {Estimating shrub biomass from basal stem diameters},
      journal = {Canadian Journal of Forest Research},
      year = {1976},
      volume = {6},
      pages = {153-158}
    }
    
    Bugmann, H., Fischlin, A. & Kienast, F. Model convergence and state variable update in forest gap models 1996 Ecological Modelling
    Vol. 89(1-3), pp. 197-208 
    article  
    Abstract: During the last 25 years, models of the type ([`]gap models') were increasingly applied to study forest succession. By adding more and more details, they have grown to rather complex systems, but little is known about the importance of the numerous ecological processes included in the models and about their exact mathematical properties from a systems theoretical point of view. Based on the stochastic gap model developed for European forests we analysed two generally relevant aspects of gap models: (1) the sample size needed to reliably compute the statistical properties of the model behaviour; (2) inconsistencies in the mechanism used to update the state variables. It was found that 150-200 simulation runs are required to warrant the convergence of the average species-specific biomass values. This sample size is considerably larger than that used in most previous studies. The analysis of the mechanism used for updating the state variables revealed that it does not conform to the requirements of systems theory. A new consistent update mechanism is presented, which even leads to more efficient calculations. While the model produces only minor differences of the simulated species-specific biomass values when using the old vs. the new update mechanism, the frequency distribution of stem numbers may be affected significantly. It is concluded that rigorous systems theoretical and statistical investigations of the properties of forest gap models are required to render the application of those models more robust. It is proposed to revise the update mechanism for the state variables in the existing forest gap models as outlined in the present study. The design of future simulation studies with these models should be improved so as to sample sufficiently large numbers of about 200 simulation runs.
    BibTeX:
    @article{Bugmann1996,
      author = {Bugmann, Harald and Fischlin, Andreas and Kienast, Felix},
      title = {Model convergence and state variable update in forest gap models},
      journal = {Ecological Modelling},
      year = {1996},
      volume = {89},
      number = {1-3},
      pages = {197--208}
    }
    
    Burman, H. Laser Strip Adjustment for Data Calibration and Verification 2002 ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria, pp. A-067 ff (6 pages)  inproceedings  
    Abstract: Laser scanning is dependent on georeferencing by satellite positioning and inertial navigation to give orientation of each laser shot. Orientation errors are at the same time one of the main contributors to the laser data error budget. Satellite positioning error like atmospheric delay, cycle slips and loss-of-lock together with drifts in accelerometers and gyros in the inertial system results in orientation errors which often are of a systematic nature. Some errors can be corrected for by making overlapping laser strips coincide and by making laser strips coincide with ground truth. In this purpose a laser strip adjustment program, TerraMatch, was developed. This paper presents the mathematical model used, the main features of the program and results from practical tests.
    BibTeX:
    @inproceedings{burman02,
      author = {Helen Burman},
      title = {Laser Strip Adjustment for Data Calibration and Verification},
      booktitle = {ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria},
      year = {2002},
      pages = {A-067 ff (6 pages)}
    }
    
    C?t?, J.-F., Widlowski, J.-L., Fournier, R.A. & Verstraete, M.M. The structural and radiative consistency of three-dimensional tree reconstructions from terrestrial lidar 2009 Remote Sensing of Environment
    Vol. 113(5), pp. 1067 - 1081 
    article DOI  
    Abstract: A novel methodology is proposed to reconstruct 3D tree architectures from terrestrial LiDAR (TLiDAR) scans. The methodology is robust and relatively insensitive to wind- and occlusion-induced artefacts in the 3D TLiDAR point clouds. A quantitative evaluation of structural attributes, like the vertical foliage and wood area profiles, as well as the shoot orientation distribution, was performed. Due to the difficulties of acquiring reliable and accurate estimates of these parameters in the field, an original evaluation approach was chosen that reproduces the TLiDAR scanning and subsequent tree reconstruction process in a virtual environment. In a second step the reconstructed tree models were ingested in a validated 3D radiative transfer model to simulate both their reflectance signatures (observable by space borne instruments) and directional transmission properties (measurable during field campaigns) under various spectral, illumination and tree density scenarios. The results of these evaluations confirm the appropriateness of the proposed tree reconstruction model for the generation of structurally and radiatively faithful copies of existing plant and canopy architectures.
    BibTeX:
    @article{Cote2009,
      author = {Jean-Fran?ois C?t? and Jean-Luc Widlowski and Richard A. Fournier and Michel M. Verstraete},
      title = {The structural and radiative consistency of three-dimensional tree reconstructions from terrestrial lidar},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {5},
      pages = {1067 - 1081},
      doi = {DOI: 10.1016/j.rse.2009.01.017}
    }
    
    Camprodon, J. & Brotons, L. Effects of undergrowth clearing on the bird communities of the Northwestern Mediterranean coppice holm oak forests. 2006 Forest Ecology and Management
    Vol. 221, pp. 72-82 
    article  
    BibTeX:
    @article{camprodon06,
      author = {Camprodon, J. and Brotons, L.},
      title = {Effects of undergrowth clearing on the bird communities of the Northwestern Mediterranean coppice holm oak forests.},
      journal = {Forest Ecology and Management},
      year = {2006},
      volume = {221},
      pages = {72-82}
    }
    
    Camprodon, J. & Brotons, L. Effects of undergrowth clearing on the bird communities of the Northwestern Mediterranean Coppice Holm oak forests. 2006 Forest Ecology and Management
    Vol. 221, pp. 72-82 
    article  
    BibTeX:
    @article{Camprodon2006,
      author = {Camprodon, J. and Brotons, L.},
      title = {Effects of undergrowth clearing on the bird communities of the Northwestern Mediterranean Coppice Holm oak forests.},
      journal = {Forest Ecology and Management},
      year = {2006},
      volume = {221},
      pages = {72-82}
    }
    
    Carabajal, C.C. & Harding, D.J. EVALUATION OF GEOSCIENCE LASER ALTIMETER SYSTEM (GLAS) WAVEFORMS FOR VEGETATED LANDSCAPES USING AIRBORNE LASER ALTIMETER SCANNING DATA 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 125-128 
    article  
    Abstract: The Geoscience Laser Altimeter System aboard NASA s Ice, Cloud and land Elevation Satellite will record the height distribution of laser energy reflected from surfaces within 70 m diameter footprints. For land surfaces, post-processing of this waveform data will be used to estimate the within-footprint mean elevation and surface relief due to ground slope and roughness, vegetation cover, buildings and other structures. A methodology is described for validating the derived surface properties for vegetated and urbanized landscapes using a GLAS waveform simulator applied to high-resolution, airborne, scanning laser altimeter data being acquired by the Puget Sound Lidar Consortium (PSLC) in northwestern Washington state. The GLAS waveform simulator is being modified to operate on 3- dimensional representations of topography and vegetation cover with the incorporation of digital elevation models derived from the airborne laser data and representations of the spatial distribution of surface reflectance, the transmitted laser energy measured on a perpulse basis by the GLAS instrument, and detector's field-of-view responsivity. The attributes of the PSLC airborne laser mapping data are also described.
    BibTeX:
    @article{carabajal01,
      author = {Claudia C. Carabajal and David J. Harding},
      title = {EVALUATION OF GEOSCIENCE LASER ALTIMETER SYSTEM (GLAS) WAVEFORMS FOR VEGETATED LANDSCAPES USING AIRBORNE LASER ALTIMETER SCANNING DATA},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {125-128}
    }
    
    Carlson, T.N. & Ripley, D.A. On the relation between NDVI, fractional vegetation cover, and leaf area index 1997 Remote Sensing of Environment
    Vol. 62(3), pp. 241-252 
    article  
    Abstract: We use a simple radiative transfer model with vegetation, soil, and atmospheric components to illustrate how the normalized difference vegetation index (NDVI), leaf area index (LAI), and fractional vegetation cover are dependent. In particular, we suggest that LAI and fractional vegetation cover may not be independent quantitites, at least when the former is defined without regard to the presence of bare patches between plants, and that the customary variation of LAI with NDVI can be explained as resulting from a variation in fractional vegetation cover. The following points are made: i) Fractional vegetation cover and LAI are not entirely independent quantities, depending on how LAI is defined. Care must be taken in using LAI and fractional vegetation cover independently in a model because the former may partially take account of the latter; ii) A scaled NDVI taken between the limits of minimum (bare soil) and miximum fractional vegetation cover is insenstive to atmospheric correction for both clear and hazy conditions, at least for viewing angles less than about 20 degrees from nadir; iii) A simple relation between scaled NDVI and fractional vegetation cover, previously described in the literature, is further confirmed by the .simulations; iv) The sensitive dependence of LAI on NDVI when the former is below a value of about 2-4 may be viewed as being due to the variation in the bare soil component.
    BibTeX:
    @article{carlson97,
      author = {Carlson, Toby N. and Ripley, David A.},
      title = {On the relation between NDVI, fractional vegetation cover, and leaf area index},
      journal = {Remote Sensing of Environment},
      year = {1997},
      volume = {62},
      number = {3},
      pages = {241--252}
    }
    
    Castel, T., Beaudoin, A., Floury, N., Toan, T.L., Caraglio, Y. & Barczi, J. Deriving forest canopy parameters for backscatter models using the AMAP architectural plant model 2001 IEEE Transactions on Geoscience and Remote Sensing
    Vol. 39(3), pp. 571-583 
    article  
    Abstract: A new approach using an architectural plant model to feed various theoretical scattering models is presented as a better interpretation of future remote sensing data acquired over natural media. The method is based on the architectural plant model (AMAP), which integrates knowledge of botanical growth processes and real plant measurements. AMAP is encapsulated in a flexible interface software called AMAP2SAR that allows one to (1) simulate a three-dimensional (3-D) plant such as a tree, (2) transform the tree into a collection of cylinders, and (3) feed theoretical models such as radiative transfer (RT) models. The method is illustrated by an example of Austrian black pine plantations in southern France. Simulated characteristics of black pines are validated for stands up to 50 years old and for a given environment. The results show the ability to derive classical forest parameters as well as those needed for electromagnetic models (such as geometry) as a function of age. Vertical profiles of canopy elements are derived and point out the vertical heterogeneity of the stands after they are 20 years old for parameters having an impact on the backscatter such as diameter and number of branches. Consequently, the crown layer variability with age and canopy depth should be considered in RT models. An RT model is modified in order to take account of accurate canopy descriptions and deal with encouraging modeling results at Cand L-band over the same test site.
    BibTeX:
    @article{castel01,
      author = {T. Castel and A. Beaudoin and N. Floury and T. Le Toan and Y. Caraglio and J.F. Barczi},
      title = {Deriving forest canopy parameters for backscatter models using the AMAP architectural plant model},
      journal = {IEEE Transactions on Geoscience and Remote Sensing},
      year = {2001},
      volume = {39},
      number = {3},
      pages = {571-583}
    }
    
    Castel, T., Caraglio, Y., Beaudoin, A. & Borne, F. Using SIR-C SAR Data and the AMAP Model for Forest Attributes Retrieval and 3-D Stand Simulation 2001 Remote Sensing of Environment
    Vol. 75(2), pp. 279-290 
    article  
    Abstract: Space-borne Synthetic Aperture Radar (SAR) data and the plant architectural model AMAP are new tools, currently under development and validation, for the retrieval and mapping of forest parameters through a Geographical Information System (GIS). On one hand, L-band SAR data are useful for the retrieval of some forest attributes such as age and woody volume. On the other hand, validated growth model of tree architecture allows retrieval of many forest parameters at tree level and simulation of virtual 3-D views both at the tree and stand levels. To this aim, a methodology is proposed using L-HV SIR-C SAR data or AMAP alone or their coupling through a GIS for forest attributes retrieval and 3-D stand simulation. This approach is illustrated on a simple forest ecosystem, an Austrian pine forest over hilly terrain in southern of France. Results show the potentialities and interests in using such tools when retrieval bole volume is limited to 300 m3/ha; AMAP allowed estimation according to tree (compartment) partitioning as a function of growth stage. The coupling approach gives realistic 3-D stand visualization when it is exercised with GIS data sets and error sources are pointed out toward future improvement and generalization.
    BibTeX:
    @article{castel01a,
      author = {Thierry Castel and Yves Caraglio and Andre Beaudoin and Frederic Borne},
      title = {Using SIR-C SAR Data and the AMAP Model for Forest Attributes Retrieval and 3-D Stand Simulation},
      journal = {Remote Sensing of Environment},
      year = {2001},
      volume = {75},
      number = {2},
      pages = {279-290}
    }
    
    Chang, S.-H., M.J.W. e. a. 79-Channel Airborne Imaging Spectrometer 1993 Im. Spec. of the Terr. Env., SPIE
    Vol. 1937, pp. 164-172 
    article  
    BibTeX:
    @article{chang93,
      author = {Chang, S.-H., M. J. Westfield, et al.},
      title = {79-Channel Airborne Imaging Spectrometer},
      journal = {Im. Spec. of the Terr. Env., SPIE},
      year = {1993},
      volume = {1937},
      pages = {164-172}
    }
    
    Chasmer, L., Barr, A., Hopkinson, C., McCaughey, H., Treitz, P., Black, A. & Shashkov, A. Scaling and assessment of GPP from MODIS using a combination of airborne lidar and eddy covariance measurements over jack pine forests 2009 Remote Sensing of Environment
    Vol. 113(1), pp. 82 - 93 
    article DOI  
    Abstract: Understanding the influence of within-pixel land cover heterogeneity is essential for the extrapolation of measured and modeled CO2 fluxes from the canopy to regional scales using remote sensing. Airborne light detection and ranging (lidar) was used to estimate spatial and temporal variations of gross primary production (GPP) across a jack pine chronosequence of four sites in Saskatchewan, Canada for comparison with the Moderate Resolution Imaging Spectroradiometer (MODIS) GPP product. This study utilizes high resolution canopy structural information obtained from airborne lidar to bridge gaps in spatial representation between plot, eddy covariance (EC), and MODIS estimates of vegetation GPP. First we investigate linkages between canopy structure obtained from measurements and light response curves at a jack pine chronosequence during the growing season of 2004. Second, we use the measured canopy height and foliage cover inputs to create a structure-based GPP model (GPPLandsberg) which was tested in 2005. The GPP model is then run using lidar data (GPPLidar) and compared with eight-day cumulative MODIS GPP (GPPMODIS) and EC observations (GPPEC). Finally, we apply the lidar GPP model at spatial resolutions of 1 m to 1000 m to examine the influence of within-pixel heterogeneity and scaling (or pixel aggregation) on GPPLidar. When compared over eight-day cumulative periods throughout the 2005 growing season, the standard deviation of differences between GPPlidar and GPPMODIS were less than differences between either of them and GPPEC at all sites. As might be expected, the differences between pixel aggregated GPP estimates are most pronounced at sites with the highest levels of spatial canopy heterogeneity. The results of this study demonstrate one method for using lidar to scale between eddy covariance flux towers and coarse resolution remote sensing pixels using a structure-based Landsberg light curve model.
    BibTeX:
    @article{Chasmer200982,
      author = {L. Chasmer and A. Barr and C. Hopkinson and H. McCaughey and P. Treitz and A. Black and A. Shashkov},
      title = {Scaling and assessment of GPP from MODIS using a combination of airborne lidar and eddy covariance measurements over jack pine forests},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {1},
      pages = {82 - 93},
      doi = {DOI: 10.1016/j.rse.2008.08.009}
    }
    
    Chasmer, L., Hopkinson, C., Smith, B. & Treitz, B. Examining the influence of changing laser pulse repetition frequencies on conifer forest canopy returns. 2006 Photogrammetric Engineering & Remote Sensing
    Vol. 72(12), pp. 1359-1367 
    article  
    BibTeX:
    @article{chasmer06b,
      author = {Chasmer, L.E. and Hopkinson, C. and Smith, B. and Treitz, B.},
      title = {Examining the influence of changing laser pulse repetition frequencies on conifer forest canopy returns.},
      journal = {Photogrammetric Engineering & Remote Sensing},
      year = {2006},
      volume = {72},
      number = {12},
      pages = {1359-1367}
    }
    
    Chasmer, L., Hopkinson, C. & Treitz, P. Investigating laser pulse penetration through a conifer canopy by integrating airborne and terrestrial lidar 2006 Canadian Journal of Remote Sensing
    Vol. 32(2), pp. 116-125 
    article  
    Abstract: This study examines the distribution of laser pulse returns obtained from coincident airborne and terrestrial lidar

    surveys of a closed-canopy red pine (Pinus resinosa) plantation. The purpose of this study is to improve our understanding

    of laser pulse sampling within closed canopies so that estimates of forest structural variables (e.g., biomass, needle-leaf

    area, and base-of-live-crown) can be improved at the individual tree and stand levels using lidar. The results of this study

    indicate the following: (1) There is a statistically significant difference between field measurements of tree height and

    estimates derived from the maximum laser pulse return from airborne and terrestrial lidar. In both cases, maximum laser

    pulse returns underestimate tree height by 1 m, on average. (2) Both terrestrial and airborne lidar are unable to discern the

    base of the measured live crown. Laser pulse returns from airborne lidar are biased towards the top of the tree crown, i.e.,

    lowest laser pulse returns occur 1.4 m on average higher in the canopy than the measured base-of-live-crown. On the other

    hand, terrestrial lidar captures dieback at the base of the live crown, thereby lowering the base-of-live-crown estimate by

    6.6 m, on average. (3) Median airborne laser pulse returns within the canopy (20.4 m), believed to be associated with needle

    leaf area, occur below the maximum frequency of laser pulse returns (20.8 m) but higher in the canopy than the height of

    maximum crown diameter obtained from terrestrial lidar (18.0 m). The bias of airborne laser pulse reflections towards the

    t op of t he canopy wi t h l ess penet rat i on t o a dept h where t he maxi mum crown di amet er occurs may resul t i n an

    underestimation of the needle leaf area. The results of this research suggest that future research should focus on improving

    our understanding of how laser pulse returns are ?triggered? within vegetated environments and how canopy properties or

    data acquisition parameters may influence the location of this ?trigger? event.

    BibTeX:
    @article{chasmer06,
      author = {Laura Chasmer and Chris Hopkinson and Paul Treitz},
      title = {Investigating laser pulse penetration through a conifer canopy by integrating airborne and terrestrial lidar},
      journal = {Canadian Journal of Remote Sensing},
      year = {2006},
      volume = {32},
      number = {2},
      pages = {116-125}
    }
    
    Chasmer, L., Hopkinson, C., Treitz, P., McCaughey, H., Barr, A. & Black, A. A lidar-based hierarchical approach for assessing MODIS fPAR 2008 Remote Sensing of Environment
    Vol. 112(12), pp. 4344 - 4357 
    article DOI  
    Abstract: The purpose of this study was to estimate the fraction of photosynthetically active radiation absorbed by the canopy (fPAR) from point measurements to airborne lidar for hierarchical scaling up and assessment of the Moderate Resolution Imaging Spectroradiometer (MODIS) fPAR product within a #medium-sized# (7 km ? 18 km) watershed. Nine sites across Canada, containing one or more (of 11) distinct species types and age classes at varying stages of regeneration and seasonal phenology were examined using a combination of discrete pulse airborne scanning Light Detection And Ranging (lidar) and coincident analog and digital hemispherical photography (HP). Estimates of fPAR were first compared using three methods: PAR radiation sensors, HP, and airborne lidar. HP provided reasonable estimates of fPAR when compared with radiation sensors. A simplified fractional canopy cover ratio from lidar based on the number of within canopy returns to the total number of returns was then compared with fPAR estimated from HP at 486 geographically registered measurement locations. The return ratio fractional cover method from lidar compared well with HP-derived fPAR (coefficient of determination = 0.72, RMSE = 0.11), despite varying the lidar survey configurations, canopy structural characteristics, seasonal phenologies, and possible slight inaccuracies in location using handheld GPS at some sites. Lidar-derived fractional cover estimates of fPAR were ~ 10% larger than those obtained using HP (after removing wood components), indicating that lidar likely provides a more realistic estimate of fPAR than HP when compared with radiation sensors. Finally, fPAR derived from lidar fractional cover was modelled at 1 m resolution and averaged over 99 1 km areas for comparison with MODIS fPAR. The following study is one of the first to scale between plot measurements and MODIS pixels using airborne lidar.
    BibTeX:
    @article{Chasmer2008,
      author = {L. Chasmer and C. Hopkinson and P. Treitz and H. McCaughey and A. Barr and A. Black},
      title = {A lidar-based hierarchical approach for assessing MODIS fPAR},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {12},
      pages = {4344 - 4357},
      doi = {DOI: 10.1016/j.rse.2008.08.003}
    }
    
    Chatterjee, S. & Hadi, A. Influential Observations, High Leverage Points, and Outliers in Linear Regression 1986 Statistical Science
    Vol. 1(3), pp. 379-416 
    article  
    BibTeX:
    @article{chatterjee86,
      author = {Chatterjee, S. and A.S. Hadi},
      title = {Influential Observations, High Leverage Points, and Outliers in Linear Regression},
      journal = {Statistical Science},
      year = {1986},
      volume = {1},
      number = {3},
      pages = {379-416}
    }
    
    Chen, B., Black, T., Coops, N., Hilker, T., (Tony) Trofymow, J. & Morgenstern, K. Assessing Tower Flux Footprint Climatology and Scaling Between Remotely Sensed and Eddy Covariance Measurements 2009 Boundary-Layer Meteorology
    Vol. 130, pp. 137-167 
    article URL 
    Abstract: We describe pragmatic and reliable methods to examine the influence of patch-scale heterogeneities on the uncertainty in long-term eddy-covariance (EC) carbon flux data and to scale between the carbon flux estimates derived from land surface optical remote sensing and directly derived from EC flux measurements on the basis of the assessment of footprint climatology. Three different aged Douglas-fir stands with EC flux towers located on Vancouver Island and part of the Fluxnet Canada Research Network were selected. Monthly, annual and interannual footprint climatologies, unweighted or weighted by carbon fluxes, were produced by a simple model based on an analytical solution of the Eulerian advection-diffusion equation. The dimensions and orientation of the flux footprint depended on the height of the measurement, surface roughness length, wind speed and direction, and atmospheric stability. The weighted footprint climatology varied with the different carbon flux components and was asymmetrically distributed around the tower, and its size and spatial structure significantly varied monthly, seasonally and inter-annually. Gross primary productivity (GPP) maps at 10-m resolution were produced using a tower-mounted multi-angular spectroradiometer, combined with the canopy structural information derived from airborne laser scanning (Lidar) data. The horizontal arrays of footprint climatology were superimposed on the 10-m-resolution GPP maps. Monthly and annual uncertainties in EC flux caused by variations in footprint climatology of the 59-year-old Douglas-fir stand were estimated to be approximately 15?20% based on a comparison of GPP estimates derived from EC and remote sensing measurements, and on sensor location bias analysis. The footprint-variation-induced uncertainty in long-term EC flux measurements was mainly dependent on the site spatial heterogeneity. The bias in carbon flux estimates using spatially-explicit ecological models or tower-based remote sensing at finer scales can be estimated by comparing the footprint-weighted and EC-derived flux estimates. This bias is useful for model parameter optimizing. The optimization of parameters in remote-sensing algorithms or ecosystem models using satellite data will, in turn, increase the accuracy in the upscaled regional carbon flux estimation.
    BibTeX:
    @article{springerlink:10.1007/s10546-008-9339-1,
      author = {Chen, Baozhang and Black, T. and Coops, Nicholas and Hilker, Thomas and (Tony) Trofymow, J. and Morgenstern, Kai},
      title = {Assessing Tower Flux Footprint Climatology and Scaling Between Remotely Sensed and Eddy Covariance Measurements},
      journal = {Boundary-Layer Meteorology},
      publisher = {Springer Netherlands},
      year = {2009},
      volume = {130},
      pages = {137-167},
      note = {10.1007/s10546-008-9339-1},
      url = {http://dx.doi.org/10.1007/s10546-008-9339-1}
    }
    
    Chen, J.M. & Cihlar, J. Retrieving leaf area index of boreal conifer forests using Landsat TM images 1996 Remote Sensing of Environment
    Vol. 55(2), pp. 153-162 
    article  
    Abstract: Vegetation indices, including the simple ratio (SR) and the normalized difference vegetation index (NDVI), from Landsat TM data were correlated to ground-based measurements of LAI, effective LAI, and the crown closure in boreal conifer forests located near Candle Lake and Prince Albert, Saskatchewan and near Thompson, Manitoba, as part of the Boreal Ecosystem-Atmosphere Study (BOREAS). The measurements were made using two optical instruments: the Plant Canopy Analyzer (LAI-2000, LI-COR) and the TRAC (Tracing Radiation and Architecture of Canopies). The TRAC was recently developed to quantify the effect of canopy architecture on optical measurements of leaf area index. The stands were located on georeferenced Landsat TM images using global positioning system (GPS) measurements. It is found that late spring Landsat images are superior to summer images for determining overstory LAI in boreal conifer stands because the effect of the understory is minimized in the spring before the full growth of the understory and moss cover. The effective LAI, obtained from gap fraction measurements assuming a random distribution of foliage spatial positions, was found to be better correlated to SR and NDVI than LAI. The effective LAI is less variable and easier to measure than LAI, and is also an intrinsic attribute of plant canopies. It is therefore suggested to use effective LAI as the most important parameter for radiation interception considerations.
    BibTeX:
    @article{chen96,
      author = {Chen, Jing M. and Cihlar, Josef},
      title = {Retrieving leaf area index of boreal conifer forests using Landsat TM images},
      journal = {Remote Sensing of Environment},
      year = {1996},
      volume = {55},
      number = {2},
      pages = {153--162}
    }
    
    Chen, J.M., Pavlic, G., Brown, L., Cihlar, J., Leblanc, S.G., White, H.P., Hall, R.J., Peddle, D.R., King, D.J. & Trofymow, J.A. Derivation and validation of Canada-wide coarse-resolution leaf area index maps using high-resolution satellite imagery and ground measurements 2002 Remote Sensing of Environment
    Vol. 80(1), pp. 165-184 
    article  
    Abstract: Leaf area index (LAI) is one of the surface parameters that has importance in climate, weather, and ecological studies, and has been routinely estimated from remote sensing measurements. Canada-wide LAI maps are now being produced using cloud-free Advanced Very High-Resolution Radiometer (AVHRR) imagery every 10 days at 1-km resolution. The archive of these products began in 1993. LAI maps at the same resolution are also being produced with images from the SPOT VEGETATION sensor. To improve the LAI algorithms and validate these products, a group of Canadian scientists acquired LAI measurements during the summer of 1998 in deciduous, conifer, and mixed forests, and in cropland. Common measurement standards using the commercial Tracing Radiation and Architecture of Canopies (TRAC) and LAI-2000 instruments were followed. Eight Landsat Thematic Mapper (TM) scenes at 30-m resolution were used to locate ground sites and to facilitate spatial scaling to 1-km pixels. In this paper, examples of Canada-wide LAI maps are presented after an assessment of their accuracy using ground measurements and the eight Landsat scenes. Methodologies for scaling from high- to coarse-resolution images that consider surface heterogeneity in terms of mixed cover types are evaluated and discussed. Using Landsat LAI images as the standard, it is shown that the accuracy of LAI values of individual AVHRR and VEGETATION pixels was in the range of 50-75%. Random and bias errors were both considerable. Bias was mostly caused by uncertainties in atmospheric correction of the Landsat images, but surface heterogeneity in terms of mixed cover types were also found to cause bias in AVHRR and SPOT VEGETATION LAI calculations. Random errors come from many sources, but pixels with mixed cover types are the main cause of random errors. As radiative signals from different vegetation types were quite different at the same LAI, accurate information about subpixel mixture of the various cover types is identified as the key to improving the accuracy of LAI estimates.
    BibTeX:
    @article{chen02,
      author = {Chen, J. M. and Pavlic, G. and Brown, L. and Cihlar, J. and Leblanc, S. G. and White, H. P. and Hall, R. J. and Peddle, D. R. and King, D. J. and Trofymow, J. A.},
      title = {Derivation and validation of Canada-wide coarse-resolution leaf area index maps using high-resolution satellite imagery and ground measurements},
      journal = {Remote Sensing of Environment},
      year = {2002},
      volume = {80},
      number = {1},
      pages = {165--184}
    }
    
    Chen, J.M., P.M.R. e. a. Leaf area index of boreal forests: Theory, techniques, and measurements. 1997 Journal of Geophysical Research-Atmospheres
    Vol. 102 (D24), pp. 29429-29443 
    article  
    BibTeX:
    @article{chen97,
      author = {Chen, J. M., P. M. Rich, et al.},
      title = {Leaf area index of boreal forests: Theory, techniques, and measurements.},
      journal = {Journal of Geophysical Research-Atmospheres},
      year = {1997},
      volume = {102 (D24)},
      pages = {29429-29443}
    }
    
    Chen, X., Vierlinga, L., Rowell, E. & DeFelice, T. Using lidar and effective LAI data to evaluate IKONOS and Landsat 7 ETM+ vegetation cover estimates in a ponderosa pine forest 2004 Remote Sensing of Environment
    Vol. 91, pp. 14-26 
    article  
    Abstract: Structural and functional analyses of ecosystems benefit when high accuracy vegetation coverages can be derived over large areas. In this study, we utilize IKONOS, Landsat 7 ETM+, and airborne scanning light detection and ranging (lidar) to quantify coniferous forest and understory grass coverages in a ponderosa pine (Pinus ponderosa) dominated ecosystem in the Black Hills of South Dakota. Linear spectral mixture analyses of IKONOS and ETM+ data were used to isolate spectral endmembers (bare soil, understory grass, and tree/shade) and calculate their subpixel fractional coverages. We then compared these endmember cover estimates to similar cover estimates derived from lidar data and field measures. The IKONOS-derived tree/shade fraction was significantly correlated with the field-measured canopy effective leaf area index (LAIe)(r 2 = 0.55, p < 0.001) and with the lidar-derived estimate of tree occurrence (r 2 = 0.79, p < 0.001). The enhanced vegetation index (EVI) calculated from IKONOS imagery showed a negative correlation with the field measured tree canopy effective LAI and lidar tree cover response (r 2 = 0.30, r = 0.55 and r 2 = 0.41, r = 0.64, respectively; p < 0.001) and further analyses indicate a strong linear relationship between EVI and the IKONOS-derived grass fraction (r 2 = 0.99, p < 0.001). We also found that using EVI resulted in better agreement with the subpixel vegetation fractions in this ecosystem than using normalized difference of vegetation index (NDVI). Coarsening the IKONOS data to 30 m resolution imagery revealed a stronger relationship with lidar tree measures (r 2 = 0.77, p < 0.001) than at 4 m resolution (r 2 = 0.58, p < 0.001). Unmixed tree/shade fractions derived from 30 m resolution ETM+ imagery also showed a significant correlation with the lidar data (r 2 = 0.66, p < 0.001). These results demonstrate the power of using high resolution lidar data to validate spectral unmixing results of satellite imagery, and indicate that IKONOS data and Landsat 7 ETM+ data both can serve to make the important distinction between tree/shade coverage and exposed understory grass coverage during peak summertime greenness in a ponderosa pine forest ecosystem.
    BibTeX:
    @article{chen04,
      author = {Xuexia Chen and Lee Vierlinga and Eric Rowell and Thomas DeFelice},
      title = {Using lidar and effective LAI data to evaluate IKONOS and Landsat 7 ETM+ vegetation cover estimates in a ponderosa pine forest},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {91},
      pages = {14-26}
    }
    
    Chuvieco, E., Riano, D., Aguado, I. & Cocero, D. Estimation of fuel moisture content from multitemporal analysis of Landsat Thematic Mapper reflectance data: applications in fire danger assessment 2002
    Vol. 23(11), pp. 2145-2162 
    article  
    Abstract: The objective of this paper was to define indices based on reflectance measurements performed by the Landsat Thematic Mapper (TM) sensor for estimating water content of live Mediterranean fuels for fire danger estimation. Seven Landsat TM images were processed and correlated with fuel moisture content (FMC) of several live species of Mediterranean grassland and shrubland. Raw bands were converted to reflectances, and several indices potentially related to water content were calculated from them. Pearson r correlation coefficients and linear regression analysis were computed in order to estimate FMC. Those indices based on the short wave infrared bands (SWIR: 1.4-2.5 m) and on the contrast between this band and the near-infrared band offered the best estimations. For grassland, the integral of visible and SWIR bands provided the highest correlation, but also raw reflectances and Normalized Difference Vegetation Indices (NDVIs) provide significant r values (r2 above 0.8). For shrub species, indices that include SWIR reflectances performed much better than NDVI, because the SWIR band is more sensitive to water absorption, whereas NDVI estimates FMC indirectly, only from the effects of chlorophyll changes due to water variation content and leaf area index. The most significant relations were found with the derivatives of bands 4-5 and 2-3, and again the integral of visible and SWIR bands. Multiple regression analysis provided adjusted r2 values of 0.84 for grasslands and 0.74 for shrublands. Average errors of 23.45-40 $%$ in the estimation of FMC for grasslands were found, depending on which variables were included in the multiple regression. For the FMC estimation of shrub species, errors were lower (from 7.94 to 19.40 $%$ ), since the range of FMC values was also lower.
    BibTeX:
    @article{chuvieco02,
      author = {E. Chuvieco and D. Riano and I. Aguado and D. Cocero},
      title = {Estimation of fuel moisture content from multitemporal analysis of Landsat Thematic Mapper reflectance data: applications in fire danger assessment},
      year = {2002},
      volume = {23},
      number = {11},
      pages = {2145-2162}
    }
    
    Chuvieco, E., Riano, D. & Morsdorf, F. Wildland Fire Danger Estimation and Mapping - The Role of Remote Sensing Data 2003   book  
    BibTeX:
    @book{chuvieco03,
      author = {Emilio Chuvieco and David Riano and Felix Morsdorf},
      title = {Wildland Fire Danger Estimation and Mapping - The Role of Remote Sensing Data},
      publisher = {World Scientific},
      year = {2003}
    }
    
    Clark, M.L., Clark, D.B. & Roberts, D.A. Small-footprint lidar estimation of sub-canopy elevation and tree height in a tropical rain forest landscape 2003 Remote Sensing of Environment
    Vol. 91, pp. 68-91 
    article  
    Abstract: Meso-scale digital terrain models (DTMs) and canopy-height estimates, or digital canopy models (DCMs), are two lidar products that have immense potential for research in tropical rain forest (TRF) ecology and management. In this study, we used a small-footprint lidar sensor (airborne laser scanner, ALS) to estimate sub-canopy elevation and canopy height in an evergreen tropical rain forest. A fully automated, local-minima algorithm was developed to separate lidar ground returns from overlying vegetation returns. We then assessed inverse distance weighted (IDW) and ordinary kriging (OK) geostatistical techniques for the interpolation of a sub-canopy DTM. OK was determined to be a superior interpolation scheme because it smoothed fine-scale variance created by spurious understory heights in the ground-point dataset. The final DTM had a linear correlation of 1.00 and a root-mean-square error (RMSE) of 2.29 m when compared against 3859 well-distributed ground-survey points. In old-growth forests, RMS error on steep slopes was 0.67 m greater than on flat slopes. On flatter slopes, variation in vegetation complexity associated with land use caused highly significant differences in DTM error distribution across the landscape. The highest DTM accuracy observed in this study was 0.58-m RMSE, under flat, open-canopy areas with relatively smooth surfaces. Lidar ground retrieval was complicated by dense, multi-layered evergreen canopy in old-growth forests, causing DTM overestimation that increased RMS error to 1.95 m. A DCM was calculated from the original lidar surface and the interpolated DTM. Individual and plot-scale heights were estimated from DCM metrics and compared to field data measured using similar spatial supports and metrics. For old-growth forest emergent trees and isolated pasture trees greater than 20 m tall, individual tree heights were underestimated and had 3.67- and 2.33-m mean absolute error (MAE), respectively. Linear-regression models explained 51% (4.15-m RMSE) and 95% (2.41-m RMSE) of the variance, respectively. It was determined that improved elevation and field-height estimation in pastures explained why individual pasture trees could be estimated more accurately than old-growth trees. Mean height of tree stems in 32 young agroforestry plantation plots (0.38 to 18.53 m tall) was estimated with a mean absolute error of 0.90 m (r 2 = 0.97; 1.08-m model RMSE) using the mean of lidar returns in the plot. As in other small-footprint lidar studies, plot mean height was underestimated; however, our plot-scale results have stronger linear models for tropical, leaf-on hardwood trees than has been previously reported for temperate-zone conifer and deciduous hardwoods.
    BibTeX:
    @article{clark03,
      author = {Matthew L. Clark and David B. Clark and Dar A. Roberts},
      title = {Small-footprint lidar estimation of sub-canopy elevation and tree height in a tropical rain forest landscape},
      journal = {Remote Sensing of Environment},
      year = {2003},
      volume = {91},
      pages = {68-91}
    }
    
    Cohen, M., Rigolot, E. & Etienne, M. Modelling fuel distribution with cellular-automata for fuel-break assessment. 18-23 November 2002. Forest fire research and wildland fire safety. Proceedings of IV International Conference on Forest Fire Research 2002, Wildland Fire Safety Summit, Luso, Coimbra, Portugal,  conference  
    BibTeX:
    @conference{cohen02,
      author = {Cohen, M. and Rigolot, E. and Etienne, M.},
      title = {Modelling fuel distribution with cellular-automata for fuel-break assessment.},
      booktitle = {Forest fire research and wildland fire safety. Proceedings of IV International Conference on Forest Fire Research 2002, Wildland Fire Safety Summit, Luso, Coimbra, Portugal,},
      publisher = {Millpress Science Publishers, Rotterdam, Netherlands.},
      year = {18-23 November 2002.}
    }
    
    Cohen, M., R.E. & Etienne, M. 2002. In: . Proceedings of IV International Conference on Forest Fire Research 2002, W.F.S.S.L.C.P. 18.-23.N. 2002..M.S.P.R.N. Modelling fuel distribution with cellular-automata for fuel-break assessment.   article  
    BibTeX:
    @article{,
      author = {Cohen, M., Rigolot, E. and Etienne, M. 2002. In: . Proceedings of IV International Conference on Forest Fire Research 2002, Wildland Fire Safety Summit, Luso, Coimbra, Portugal, 18-23 November 2002. Millpress Science Publishers, Rotterdam, Netherlands.},
      title = {Modelling fuel distribution with cellular-automata for fuel-break assessment.}
    }
    
    Cohen, W.B., Maiersperger, T.K., Gower, S.T. & Turner, D.P. An improved strategy for regression of biophysical variables and Landsat ETM+ data 2003 Remote Sensing of Environment
    Vol. 84(4), pp. 561-571 
    article  
    Abstract: Empirical models are important tools for relating field-measured biophysical variables to remote sensing data. Regression analysis has been a popular empirical method of linking these two types of data to provide continuous estimates for variables such as biomass, percent woody canopy cover, and leaf area index (LAI). Traditional methods of regression are not sufficient when resulting biophysical surfaces derived from remote sensing are subsequently used to drive ecosystem process models. Most regression analyses in remote sensing rely on a single spectral vegetation index (SVI) based on red and near-infrared reflectance from a single date of imagery. There are compelling reasons for utilizing greater spectral dimensionality, and for including SVIs from multiple dates in a regression analysis. Moreover, when including multiple SVIs and/or dates, it is useful to integrate these into a single index for regression modeling. Selection of an appropriate regression model, use of multiple SVIs from multiple dates of imagery as predictor variables, and employment of canonical correlation analysis (CCA) to integrate these multiple indices into a single index represent a significant strategic improvement over existing uses of regression analysis in remote sensing.To demonstrate this improved strategy, we compared three different types of regression models to predict LAI for an agro-ecosystem and live tree canopy cover for a needleleaf evergreen boreal forest: traditional (Y on X) ordinary least squares (OLS) regression, inverse (X on Y) OLS regression, and an orthogonal regression method called reduced major axis (RMA). Each model incorporated multiple SVIs from multiple dates and CCA was used to integrate these. For a given dataset, the three regression-modeling approaches produced identical coefficients of determination and intercepts, but different slopes, giving rise to divergent predictive characteristics. The traditional approach yielded the lowest root mean square error (RMSE), but the variance in the predictions was lower than the variance in the observed dataset. The inverse method had the highest RMSE and the variance was inflated relative to the variance of the observed dataset. RMA provided an intermediate set of predictions in terms of the RMSE, and the variance in the observations was preserved in the predictions. These results are predictable from regression theory, but that theory has been essentially ignored within the discipline of remote sensing.
    BibTeX:
    @article{cohen03a,
      author = {Cohen, Warren B. and Maiersperger, Thomas K. and Gower, Stith T. and Turner, David P.},
      title = {An improved strategy for regression of biophysical variables and Landsat ETM+ data},
      journal = {Remote Sensing of Environment},
      year = {2003},
      volume = {84},
      number = {4},
      pages = {561--571}
    }
    
    Cohen, W.B., Maiersperger, T.K., Yang, Z., Gower, S.T., Turner, D.P., Ritts, W.D., Berterretche, M. & Running, S.W. Comparisons of land cover and LAI estimates derived from ETM+ and MODIS for four sites in North America: a quality assessment of 2000/2001 provisional MODIS products 2003 Remote Sensing of Environment
    Vol. 88(3), pp. 233-255 
    article  
    Abstract: The MODIS land science team produces a number of standard products, including land cover and leaf area index (LAI). Critical to the success of MODIS and other sensor products is an independent evaluation of product quality. In that context, we describe a study using field data and Landsat ETM+ to map land cover and LAI at four 49-km2 sites in North America containing agricultural cropland (AGRO), prairie grassland (KONZ), boreal needleleaf forest, and temperate mixed forest. The purpose was to: (1) develop accurate maps of land cover, based on the MODIS IGBP (International Geosphere-Biosphere Programme) land cover classification scheme; (2) derive continuous surfaces of LAI that capture the mean and variability of the LAI field measurements; and (3) conduct initial MODIS validation exercises to assess the quality of early (i.e., provisional) MODIS products. ETM+ land cover maps varied in overall accuracy from 81% to 95%. The boreal forest was the most spatially complex, had the greatest number of classes, and the lowest accuracy. The intensive agricultural cropland had the simplest spatial structure, the least number of classes, and the highest overall accuracy. At each site, mapped LAI patterns generally followed patterns of land cover across the site. Predicted versus observed LAI indicated a high degree of correspondence between field-based measures and ETM+ predictions of LAI. Direct comparisons of ETM+ land cover maps with Collection 3 MODIS cover maps revealed several important distinctions and similarities. One obvious difference was associated with image/map resolution. ETM+ captured much of the spatial complexity of land cover at the sites. In contrast, the relatively coarse resolution of MODIS did not allow for that level of spatial detail. Over the extent of all sites, the greatest difference was an overprediction by MODIS of evergreen needleleaf forest cover at the boreal forest site, which consisted largely of open shrubland, woody savanna, and savanna. At the agricultural, temperate mixed forest, and prairie grassland sites, ETM+ and MODIS cover estimates were similar. Collection 3 MODIS-based LAI estimates were considerably higher (up to 4 m2 m-2) than those based on ETM+ LAI at each site. There are numerous probable reasons for this, the most important being the algorithms' sensitivity to MODIS reflectance calibration, its use of a prelaunch AVHRR-based land cover map, and its apparent reliance on mainly red and near-IR reflectance. Samples of Collection 4 LAI products were examined and found to consist of significantly improved LAI predictions for KONZ, and to some extent for AGRO, but not for the other two sites. In this study, we demonstrate that MODIS reflectance data are highly correlated with LAI across three study sites, with relationships increasing in strength from 500 to 1000 m spatial resolution, when shortwave-infrared bands are included.
    BibTeX:
    @article{cohen03,
      author = {Cohen, Warren B. and Maiersperger, Thomas K. and Yang, Zhiqiang and Gower, Stith T. and Turner, David P. and Ritts, William D. and Berterretche, Mercedes and Running, Steven W.},
      title = {Comparisons of land cover and LAI estimates derived from ETM+ and MODIS for four sites in North America: a quality assessment of 2000/2001 provisional MODIS products},
      journal = {Remote Sensing of Environment},
      year = {2003},
      volume = {88},
      number = {3},
      pages = {233--255}
    }
    
    Colombo, R., Bellingeri, D., Fasolini, D. & Marino, C.M. Retrieval of leaf area index in different vegetation types using high resolution satellite data 2003 Remote Sensing of Environment
    Vol. 86(1), pp. 120-131 
    article  
    Abstract: With the successful launch of the IKONOS satellite, very high geometric resolution imagery is within reach of civilian users. In the 1-m spatial resolution images acquired by the IKONOS satellite, details of buildings, individual trees, and vegetation structural variations are detectable. The visibility of such details opens up many new applications, which require the use of geometrical information contained in the images. This paper presents an application in which spectral and textural information is used for mapping the leaf area index (LAI) of different vegetation types. This study includes the estimation of LAI by different spectral vegetation indices (SVIs) combined with image textural information and geostatistical parameters derived from high resolution satellite data. It is shown that the relationships between spectral vegetation indices and biophysical parameters should be developed separately for each vegetation type, and that the combination of the texture indices and vegetation indices results in an improved fit of the regression equation for most vegetation types when compared with one derived from SVIs alone. High within-field spatial variability was found in LAI, suggesting that high resolution mapping of LAI may be relevant to the introduction of precision farming techniques in the agricultural management strategies of the investigated area.
    BibTeX:
    @article{colombo03,
      author = {Colombo, Roberto and Bellingeri, Dario and Fasolini, Dante and Marino, Carlo M.},
      title = {Retrieval of leaf area index in different vegetation types using high resolution satellite data},
      journal = {Remote Sensing of Environment},
      year = {2003},
      volume = {86},
      number = {1},
      pages = {120--131}
    }
    
    Cook, B.D., Bolstad, P.V., Næsset, E., Anderson, R.S., Garrigues, S., Morisette, J.T., Nickeson, J. & Davis, K.J. Using LiDAR and quickbird data to model plant production and quantify uncertainties associated with wetland detection and land cover generalizations 2009 Remote Sensing of Environment
    Vol. In Press, Corrected Proof, pp. -  
    article DOI  
    Abstract: Spatiotemporal data from satellite remote sensing and surface meteorology networks have made it possible to continuously monitor global plant production, and to identify global trends associated with land cover/use and climate change. Gross primary production (GPP) and net primary production (NPP) are routinely derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard satellites Terra and Aqua, and estimates generally agree with independent measurements at validation sites across the globe. However, the accuracy of GPP and NPP estimates in some regions may be limited by the quality of model input variables and heterogeneity at fine spatial scales. We developed new methods for deriving model inputs (i.e., land cover, leaf area, and photosynthetically active radiation absorbed by plant canopies) from airborne laser altimetry (LiDAR) and Quickbird multispectral data at resolutions ranging from about 30 m to 1 km. In addition, LiDAR-derived biomass was used as a means for computing carbon-use efficiency. Spatial variables were used with temporal data from ground-based monitoring stations to compute a six-year GPP and NPP time series for a 3600 ha study site in the Great Lakes region of North America. Model results compared favorably with independent observations from a 400 m flux tower and a process-based ecosystem model (BIOME-BGC), but only after removing vapor pressure deficit as a constraint on photosynthesis from the MODIS global algorithm. Fine-resolution inputs captured more of the spatial variability, but estimates were similar to coarse-resolution data when integrated across the entire landscape. Failure to account for wetlands had little impact on landscape-scale estimates, because vegetation structure, composition, and conversion efficiencies were similar to upland plant communities. Plant productivity estimates were noticeably improved using LiDAR-derived variables, while uncertainties associated with land cover generalizations and wetlands in this largely forested landscape were considered less important.
    BibTeX:
    @article{Cook2009,
      author = {Bruce D. Cook and Paul V. Bolstad and Erik Næsset and Ryan S. Anderson and Sebastian Garrigues and Jeffrey T. Morisette and Jaime Nickeson and Kenneth J. Davis},
      title = {Using LiDAR and quickbird data to model plant production and quantify uncertainties associated with wetland detection and land cover generalizations},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {In Press, Corrected Proof},
      pages = { - },
      doi = {DOI: 10.1016/j.rse.2009.06.017}
    }
    
    Coops, N.C., Wulder, M.A., Culvenor, D.S. & St-Onge, B. Comparison of forest attributes extracted from fine spatial resolution multispectral and lidar data 2004 Can. J. Remote Sensing
    Vol. 30(6), pp. 855-866 
    article  
    Abstract: Fine spatial resolution multispectral imagery and light detection and ranging (lidar) data capture differing, yet complementary characteristics of forest structure. Using a dataset consisting of fine spatial resolution multispectral imagery, discrete-return lidar data, and detailed ground-based measurements of individual tree attributes, we applied an automatic tree delineation routine (tree identification and delineation algorithm) to compare and contrast remotely sensed predictions with field observations. The results indicate the automatically extracted crowns derived from lidar data matched tree crown area (coefficient of determination r2 = 0.46, n = 36) and height (r2 = 0.88, n = 36) better than spatial clusters defined in the multispectral imagery (crown area r2 = 0.26, n = 36) for individual trees that were identifiable in both the lidar and multispectral imagery. Differences between crown delineation characteristics were related to the information content of the lidar and multispectral fine spatial resolution data. Investigation of the spectral characteristics of objects defined in the multispectral imagery revealed strong relationships between the vertical positions derived from the lidar data and the apparent multispectral reflectance, with low-reflectance spatial clusters occurring lower in the forest canopy. The application of lidar and multispectral datasets together, in the context of tree crown delineation, provides information not available from either data source independently.
    BibTeX:
    @article{coops04,
      author = {Nicholas C. Coops and Michael A. Wulder and Darius S. Culvenor and Benoi?t St-Onge},
      title = {Comparison of forest attributes extracted from fine spatial resolution multispectral and lidar data},
      journal = {Can. J. Remote Sensing},
      year = {2004},
      volume = {30},
      number = {6},
      pages = {855-866}
    }
    
    Countryman, C.M. The Fire environment concept 1972 Berkley, CA, Pacific Southwest Forest and Range Experiment Station, pp. 12pp  article  
    BibTeX:
    @article{country72,
      author = {C. M. Countryman},
      title = {The Fire environment concept},
      journal = {Berkley, CA, Pacific Southwest Forest and Range Experiment Station},
      year = {1972},
      pages = {12pp}
    }
    
    Cowen, D.J., Jensen, J.R., Hendrix, C., Hodgson, M., Schill, S.R. & Macchiaverna, F. A GIS-Assisted Rail Construction Econometric Model that Incorporates LIDAR Data 2000 Photogrammetric Engineering & Remote Sensing
    Vol. 66(11), pp. 1323-1328 
    article  
    Abstract: Identifying the optimum route for new railroad lead-tracks using traditional field methods is often time-consuming, is costly, and does not allow for easy investigation of alternative routes. The NASA sponsored Affiliated Research Center (ARC) at the University of South Carolina worked with Norfolk Southern Corporation to develop a remote sensing and GIS-assisted lead-track route selection model. The objective was to compare the traditionally surveyed routes to those derived using the output from the remote sensing and GIS-assisted modeling. The critical element in the design of the model was the calculation of a cost surface. The cost variables for the model were developed based on expert advice from Norfolk Southern employees. The solution employed a raster GIS econometric routing model for the exploration of potential routes using construction cost factors such as grade (cut and fill cost), road crossings, stream crossings, and track cost. The use of remotely sensed data was a key element of the research. The digital elevation model used in the grid-based econometric model was obtained from Light Detection and Ranging (LIDAR) data with accurate 0.3- by 0.3-m (1- by 1-ft) elevation postings. The route selected using the remote sensing and GIS-assisted modeling was similar to the traditionally surveyed route. The GIS-based optimal path lead-track model can be used to identify rapidly a variety of potential routes based on the most important cost factors.
    BibTeX:
    @article{cowen00,
      author = {David J. Cowen and John R. Jensen and Chad Hendrix and Mike Hodgson and Steven R. Schill and Frank Macchiaverna},
      title = {A GIS-Assisted Rail Construction Econometric Model that Incorporates LIDAR Data},
      journal = {Photogrammetric Engineering & Remote Sensing},
      year = {2000},
      volume = {66},
      number = {11},
      pages = {1323-1328}
    }
    
    Cox, P., Betts, R., Jones, C., Spall, S. & Totterdell, I. Acceleration of global warming due to carbon-

    cycle feedbacks in a coupled climate.

    2000 Nature
    Vol. 408, pp. 184-187 
    article  
    BibTeX:
    @article{cox00,
      author = {Cox, P.M. and Betts, R.A. and Jones, C.D. and Spall, S.A. and Totterdell, I.J.},
      title = {Acceleration of global warming due to carbon- 

    cycle feedbacks in a coupled climate.}, journal = {Nature}, year = {2000}, volume = {408}, pages = {184-187} }

    Cramer, M. GPS/INS Integration 1997 Photogrammetric Week
    Vol. Wichmann Verlag, Heidelberg 
    article  
    BibTeX:
    @article{cramer97,
      author = {Cramer, M.},
      title = {GPS/INS Integration},
      journal = {Photogrammetric Week},
      year = {1997},
      volume = {Wichmann Verlag, Heidelberg}
    }
    
    Damm, A., Erler, A., Gioli, B., Hamdi, K., Hutjes, R., Kosvancova, M., Meroni, M., Miglietta, F., Moersch, A., Moreno, J., Schickling, A., Sonnenschein, R., Udelhoven, T., van der Linden, S., Hostert, P. & Rascher, U. Remote sensing of sun induced fluorescence yield to improve modelling of diurnal courses of Gross Primary Production (GPP) 2009 Global Change Biology  article DOI  
    BibTeX:
    @article{damm09,
      author = {Damm, A. and Erler, A. and Gioli, B. and Hamdi, K. and Hutjes, R. and Kosvancova, M. and Meroni, M. and Miglietta, F. and Moersch, A. and Moreno, J. and Schickling, A. and Sonnenschein, R. and Udelhoven, T. and van der Linden, S. and Hostert, P. and Rascher, U.},
      title = {Remote sensing of sun induced fluorescence yield to improve modelling of diurnal courses of Gross Primary Production (GPP)},
      journal = {Global Change Biology},
      year = {2009},
      doi = {http://dx.doi.org/10.1111/j.1365-2486.2009.01908.x}
    }
    
    Dan, L., Ji, J. & Li, Y. Climatic and biological simulations in a two-way coupled atmosphere-biosphere model (CABM) Global and Planetary Change
    Vol. In Press, Corrected Proof, pp. - 
    article  
    Abstract: Today, most land surface process models have prescribed seasonal change of vegetation with regard to the exchange processes between land and the atmosphere. However, in order to consider the real interaction between vegetation and atmosphere and represent it best in a climate model, the vegetation growth process should be included. In other words, "life" should be brought into climate models. In this study, we have coupled the physical and biological components of AVIM (Atmosphere-Vegetation Interaction Model), a land surface model including plant ecophysiological processes, into the IAP/LASG L9 R15 GOALS GCM. To exhibit terrestrial vegetation information, the vegetation is given a high resolution of 1.5[deg] by 1.5[deg] to nest and couple the fine grid cells of land with the coarse grid cells of atmosphere, which is 7.5[deg] longitude and 4.5[deg] latitude. The simulated monthly mean surface air temperature and precipitation is close to the observations. The monthly mean Leaf Area Index (LAI) is consistent with the observed data. The global annual mean net primary production (NPP) simulation is also reasonable. The coupled model is stable, providing a good platform for research on two-way interaction between land and atmosphere, and the global terrestrial ecosystem carbon cycle.
    BibTeX:
    @article{dan05,
      author = {Dan, Li and Ji, Jinjun and Li, Yinpeng},
      title = {Climatic and biological simulations in a two-way coupled atmosphere-biosphere model (CABM)},
      journal = {Global and Planetary Change},
      volume = {In Press, Corrected Proof},
      pages = {--}
    }
    
    Danson, F., Morsdorf, F. & Koetz, B. Laser Scanning for the Environmental Sciences 2009   book DOI  
    BibTeX:
    @book{danson09,
      author = {Danson, F.M. and Morsdorf, F. and Koetz, B.},
      title = {Laser Scanning for the Environmental Sciences},
      publisher = {Blackwell Publishing},
      year = {2009},
      doi = {ISBN-10: 1405157178}
    }
    
    Danson, F.M., Hetherington, D., Morsdorf, F., Koetz, B. & Allgöwer, B. Forest Canopy Gap Fraction From Terrestrial Laser Scanning 2007 IEEE Geoscience and Remote Sensing Letters
    Vol. 4(1), pp. 157-160 
    article  
    BibTeX:
    @article{danson07,
      author = {F. Mark Danson and David Hetherington and Felix Morsdorf and Benjamin Koetz and Britta Allgöwer},
      title = {Forest Canopy Gap Fraction From Terrestrial Laser Scanning},
      journal = {IEEE Geoscience and Remote Sensing Letters},
      year = {2007},
      volume = {4},
      number = {1},
      pages = {157-160}
    }
    
    Danson, F.M., Hetherington, D., Morsdorf, F., Koetz, B. & Allgöwer, B. Three-dimensional forest canopy structure from terrestrial laser scanning 2006 3d Remote Sensing in Forestry, 14-15. Feb. 2006, Vienna, Austria  conference  
    BibTeX:
    @conference{danson06,
      author = {F. M. Danson and D. Hetherington and F. Morsdorf and B. Koetz and B. Allgöwer},
      title = {Three-dimensional forest canopy structure from terrestrial laser scanning},
      booktitle = {3d Remote Sensing in Forestry, 14-15. Feb. 2006, Vienna, Austria},
      year = {2006}
    }
    
    Davenport, I.J., Holden, N. & Gurney, R.J. Characterizing Errors in Airborne Laser Altimetry Data to Extract Soil Roughness 2004 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING
    Vol. 42(10), pp. 2130-2141 
    article  
    Abstract: Airborne laser altimetry has the potential to make frequent detailed observations that are important for many aspects of studying land surface processes. However, the uncertainties inherent in airborne laser altimetry data have rarely been well measured. Uncertainty is often specified as generally as 20 cm in elevation and 40 cm planimetric. To better constrain these uncertainties, we present an analysis of several datasets acquired specifi- cally to study the temporal consistency of laser altimetry data and, thus, assess its operational value. The error budget has three main components, each with a time regime. For measurements acquired less than 50 ms apart, elevations have a local standard deviation in height of 3.5 cm, enabling the local measurement of surface roughness of the order of 5 cm. Points acquired seconds apart acquire an additional random error due to differential geographic positioning system fluctuation. Measurements made up to an hour apart show an elevation drift of 7 cm over a half hour. Over months, this drift gives rise to a random elevation offset between swathes, with an average of 6.4 cm. The root mean square planimetric error in point location was derived as 37.4 cm. We conclude by considering the consequences of these uncertainties on the principle application of laser altimetry in the U.K. intertidal zone monitoring.
    BibTeX:
    @article{davenport04,
      author = {Ian J. Davenport and Nick Holden and Robert J. Gurney},
      title = {Characterizing Errors in Airborne Laser Altimetry Data to Extract Soil Roughness},
      journal = {IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING},
      year = {2004},
      volume = {42},
      number = {10},
      pages = {2130-2141}
    }
    
    Davi, H., Baret, F., Huc, R. & Dufresne, E. Effect of thinning on LAI variance in heterogeneous forests 2008 Forest Ecology and Management
    Vol. 256, pp. 890-899 
    article  
    BibTeX:
    @article{davi08,
      author = {Davi, H and Baret, F. and Huc, R. and Dufresne, E.},
      title = {Effect of thinning on LAI variance in heterogeneous forests},
      journal = {Forest Ecology and Management},
      year = {2008},
      volume = {256},
      pages = {890-899}
    }
    
    Dawson, T.P., Curran, P.J., North, P.R.J. & Plummer, S.E. The Propagation of Foliar Biochemical Absorption Features in Forest Canopy Reflectance: A Theoretical Analysis 1999 Remote Sensing of Environment
    Vol. 67(2), pp. 147-159 
    article  
    Abstract: Remotely sensed estimates of the foliar biochemical content of vegetation canopies could be used to derive indicators of ecosystem functioning at regional to global scales. In the past decade, a number of studies have reported strong correlations between the reflectance spectra of vegetation canopies and their foliar biochemical content. However, these studies have commonly employed multiple regression techniques or spectral indices to determine biochemical content, which have been found to be highly sensitive to variation in canopy architecture [such as leaf area index (LAI) and canopy closure] and understory. To date, these effects combined with the low signal-to-noise ratios of airborne spectrometers have inhibited the development of robust and portable spectral techniques for the estimation of canopy biochemical content. This paper reports on a theoretical study in which a leaf model, LIBERTY (leaf incorporating biochemicals exhibiting reflectance and transmittance yields), characterized specifically for conifer needles, was coupled with a hybrid geometric/radiative transfer bidirectional reflectance distribution function FLIGHT (forest light) model. By varying leaf biochemical content, LAI, canopy closure and understory, we analyzed the simulated canopy reflectance spectra to determine if the biochemical absorption features in leaf spectra were preserved at the canopy scale. Absorption features or wavelength regions that were both related to a specific biochemical of interest (water, lignin-cellulose) and persistent at the scale of both the leaf and the canopy were identified at a number of wavelengths or wavelength regions.
    BibTeX:
    @article{Dawson1999,
      author = {Dawson, T. P. and Curran, P. J. and North, P. R. J. and Plummer, S. E.},
      title = {The Propagation of Foliar Biochemical Absorption Features in Forest Canopy Reflectance: A Theoretical Analysis},
      journal = {Remote Sensing of Environment},
      year = {1999},
      volume = {67},
      number = {2},
      pages = {147--159}
    }
    
    Dawson, T.P., Curran, P.J. & Plummer, S.E. LIBERTY--Modeling the Effects of Leaf Biochemical Concentration on Reflectance Spectra 1998 Remote Sensing of Environment
    Vol. 65(1), pp. 50-60 
    article  
    Abstract: The conifer leaf model LIBERTY (Leaf Incorporating Biochemistry Exhibiting Reflectance and Transmittance Yields) is an adaptation of radiative transfer theory for determining the optical properties of powders. LIBERTY provides a simulation, at a fine spectral resolution, of quasiinfinite leaf reflectance (as represented by stacked leaves) and single leaf reflectance. Single leaf reflectance and transmittance are important input variables to vegetation canopy reflectance models. A prototype parameterization of LIBERTY was based upon measurements of pine needles and known absorption coefficients of pure component leaf biochemicals. The estimated infinite-reflectance output was compared with the spectra of both dried and fresh pine needles with root mean square errors (RMSE) of 2.87% and 1.73%, respectively. The comparisons between measured and estimated reflectance and transmittance values for single needles were also very accurate with RSME of 1.84% and 1.12%, respectively. Initial inversion studies have demonstrated that significant improvements can be made to LIBERTY by utilizing in vivo absorption coefficients which have been determined by the inversion process. These results demonstrate the capability of LIBERTY to model accurately the spectral response of pine needles.
    BibTeX:
    @article{Dawson1998,
      author = {Dawson, Terence P. and Curran, Paul J. and Plummer, Stephen E.},
      title = {LIBERTY--Modeling the Effects of Leaf Biochemical Concentration on Reflectance Spectra},
      journal = {Remote Sensing of Environment},
      year = {1998},
      volume = {65},
      number = {1},
      pages = {50--60}
    }
    
    Degnan, J. A conceptual design for a spaceborne 3D imaging lidar 2002 e & i Elektrotechnik und Informationstechnik
    Vol. 119(4), pp. 99-106 
    article URL 
    Abstract: Abstract&nbsp;&nbsp;First generation spaceborne altimetric approaches are not well-suited to generating the few meter level horizontal resolution and decimeter accuracy vertical (range) resolution on the global scale desired by many in the Earth and planetary science communities. The present paper discusses the major technological impediments to achieving few meter transverse resolutions globally using conventional approaches and offers a feasible conceptual design which utilizes modest power kHz rate lasers, array detectors, photoncounting multi-channel timing receivers, and dual wedge optical scanners with transmitter point-ahead correction.
    BibTeX:
    @article{Degnan2002,
      author = {Degnan, J.},
      title = {A conceptual design for a spaceborne 3D imaging lidar},
      journal = {e & i Elektrotechnik und Informationstechnik},
      year = {2002},
      volume = {119},
      number = {4},
      pages = {99--106},
      url = {http://dx.doi.org/10.1007/BF03161616}
    }
    
    Degnan, J., McGarry, J., Zagwodzki, T., Dabney, P. & Geiger, J. DESIGN AND PERFORMANCE OF AN AIRBORNE MULTIKILOHERTZ PHOTON-COUNTING, MICROLASER ALTIMETER 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 9-16 
    article  
    Abstract: The present paper reports on the design and performance of a scanning, photon-counting laser altimeter, capable of daylight operations from aircraft cruise altitudes. In test flights, the system has successfully recorded high repetition rate, single photon returns from clouds, soils, man-made objects, vegetation, and water surfaces under full solar illumination. Following the flights, the signal was reliably extracted from the solar noise background using a Post-Detection Poisson Filtering technique. The passively Q-switched microchip Nd:YAG laser measures only 2.25 mm in length and is pumped by a single 1.2 Watt GaAs laser diode. The output is frequency-doubled to take advantage of higher detector counting efficiencies and narrower spectral filters available at 532 nm. The transmitter produces a few microjoules of green energy in a subnanosecond pulse at few kilohertz rates. The illuminated ground area is imaged by a 14 cm diameter, diffraction-limited, off-axis telescope onto a segmented anode photomultiplier. Each anode segment is input to one channel of "fine" range receiver (5 cm resolution), which records the times-of-flight of individual photons. A parallel "coarse" receiver provides a lower resolution (>75 cm) histogram of all scatterers between the aircraft and ground and centers the "fine" receiver gate on the last set of returns.
    BibTeX:
    @article{degnan01,
      author = {John Degnan and Jan McGarry and Thomas Zagwodzki and Phillip Dabney and Jennifer Geiger},
      title = {DESIGN AND PERFORMANCE OF AN AIRBORNE MULTIKILOHERTZ PHOTON-COUNTING, MICROLASER ALTIMETER},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {9-16}
    }
    
    Didion, M., Kupferschmid, A., Lexer, M., Rammer, W., Seidl, R. & Bugmann, H. Potentials and limitations of using large-scale forest inventory data for evaluating forest succession models 2009 Ecological Modelling
    Vol. 220(2), pp. 133-147 
    article  
    Abstract: Forest gap models have been applied widely to examine forest development under natural conditions and to investigate the effect of climate change on forest succession. Due to the complexity and parameter requirements of such models a rigorous evaluation is required to build confidence in the simulation results. However, appropriate data for model assessment are scarce at the large spatial and temporal scales of successional dynamics. In this study, we explore a data source for the evaluation of forest gap models that has been used only little in the past, i.e., large-scale National Forest Inventory data. The key objectives of this study were (a) to examine the potentials and limitations of using large-scale forest inventory data for evaluating the performance of forest gap models and (b) to test two particular models as case studies to derive recommendations for their future improvement. We used data from the first Swiss National Forest Inventory to examine the species basal area and tree numbers in different diameter classes simulated by the gap models ForClim (version 2.9.3) and PICUS (version 1.4) for forest types that are typical of mountain forests in Switzerland. The results showed the potential of data from large-scale forest inventories for evaluating model performance. Since this type of data is typically based on a large number of samples across environmental gradients, they are particularly suited for investigations at the general level of the dominant species based on stand basal area. However, the surprisingly small variability of juvenile trees (trees <12?cm diameter at breast height; dbh) indicated limitations of the data used. Insufficient representativeness due to small sample plot size and uncertainty regarding past management limit an evaluation of structural forest aspects such as species diversity, and number of small trees (dbh?
    BibTeX:
    @article{Didion2009,
      author = {Didion, M. and Kupferschmid, A.D. and Lexer, M.J. and Rammer, W. and Seidl, R. and Bugmann, H.},
      title = {Potentials and limitations of using large-scale forest inventory data for evaluating forest succession models},
      journal = {Ecological Modelling},
      year = {2009},
      volume = {220},
      number = {2},
      pages = {133--147}
    }
    
    DiMarzio, J., Brenner, A., Schutz, R., Shuman, C.A. & Zwally., H.J. GLAS/ICESat 500 m laser altimetry digital elevation model of Antarctica. 2007.   techreport  
    BibTeX:
    @techreport{DiMarzio2007,
      author = {DiMarzio, J. and A. Brenner and R. Schutz and C. A. Shuman and H. J. Zwally.},
      title = {GLAS/ICESat 500 m laser altimetry digital elevation model of Antarctica.},
      year = {2007.}
    }
    
    Disney, M., Kalogirou, V., Lewis, P., Prieto-Blanco, A., Hancock, S. & Pfeifer, M. Simulating the impact of discrete-return lidar system and survey characteristics over young conifer and broadleaf forests 2010 Remote Sensing of Environment
    Vol. 114(7), pp. 1546 - 1560 
    article DOI  
    Abstract: We present a model-based investigation of the effect of discrete-return lidar system and survey characteristics on the signal recorded over young forest environments. A Monte Carlo ray tracing (MCRT) model of canopy scattering was used to examine the sensitivity of model estimates of lidar-derived canopy height, hlidar to signal triggering method, canopy structure, footprint size, sampling density and scanning angle, for broadleaf and conifer canopies of varying density. Detailed 3D models of Scots pine (Pinus sylvestris) and Downy birch (Betula pubescens) were used to simulate lidar response, with minimal assumptions about canopy structure. Use of such models allowed the impact of lidar parameters on canopy height retrieval to be tested under a range of conditions typically not possible in practice. Retrieved hlidar was generally found to be an underestimate of [`]true' canopy height, hcanopy, but with exceptions. Choice of signal triggering method caused hlidar to underestimate hcanopy by ~ 4% for birch and ~ 7% for pine (up to 66% in extreme cases). Variations in canopy structure resulted on average in underestimation of hcanopy by 13% for birch and between 29 and 48% for pine depending on age, but with over-estimates in some cases of up to 10%. Increasing footprint diameter from 0.1 to 1 m increased retrieved hlidar from significant underestimates of hcanopy to values indistinguishable from hcanopy. Increased sampling density led to slightly increased values of hlidar to close to hcanopy, but not significantly. Increasing scan angle increased hlidar by up to 8% for birch, and 19% for pine at a scan angle of 30?. The impact of scan angle was greater for conifers as a result of large variation in crown height. Results showed that interactions between physically modelled (hypothetical) within canopy returns are similar to findings made in other studies using actual lidar systems, and that these modelled returns can depend strongly on the type of canopy and the lidar acquisition characteristics, as well as interactions between these properties. Physical models of laser pulse/canopy interactions may provide additional information on pulse interactions within the canopy, but require validation and testing before they are applied to actual survey planning and logistics.
    BibTeX:
    @article{Disney2010,
      author = {M.I. Disney and V. Kalogirou and P. Lewis and A. Prieto-Blanco and S. Hancock and M. Pfeifer},
      title = {Simulating the impact of discrete-return lidar system and survey characteristics over young conifer and broadleaf forests},
      journal = {Remote Sensing of Environment},
      year = {2010},
      volume = {114},
      number = {7},
      pages = {1546 - 1560},
      doi = {DOI: 10.1016/j.rse.2010.02.009}
    }
    
    Disney, M., Lewis, P. & Saich, P. 3D modelling of forest canopy structure for remote sensing simulations in the optical and microwave domains 2006 Remote Sensing of Environment
    Vol. 100(1), pp. 114-132 
    article  
    Abstract: A detailed 3D structural model of a conifer forest canopy was developed in order to simulate the reflectance (optical) and backscatter (microwave) signals measured remotely. We show it is feasible to model forest canopy scattering using detailed 3D models of tree structure including the location and orientation of individual needles. An existing structural growth model of Scots pine (Pinus sylvestris L.), Treegrow, was modified to simulate observed growth stages of a Scots pine canopy from age 5 to 50 years. The 3D tree models showed close structural agreement with in situ measurements. Needles were added to the structural models according to observed phyllotaxy (distribution). Individual trees were used to generate model canopies, which in turn were used to drive optical and microwave models of canopy scattering. Simulated canopy radiometric response was compared with airborne hyperspectral reflectance data (HyMAP) and airborne synthetic aperture RADAR (ASAR) backscatter data. Model simulations agreed well in general with observations, particularly at optical wavelengths where model simulations of low and high density canopy stands were shown to bracket observations. Relatively small sensitivity of observed reflectance to canopy age was captured reasonably well by the simulations. The choice of needle shape and phyllotaxy was shown to have a significant impact on multiple scattering behaviour at the branch scale. In the microwave domain, simulated backscatter values agreed reasonably well with observations at L-band, less so at X-band. L-band simulated backscatter significantly underestimated observed backscatter at younger canopy ages, probably as a result of inappropriate modelling of soil/understory. It is demonstrated that a combined structural and radiometric modelling approach provides a flexible and powerful method for simulating the remotely sensed signal of a forest canopy in the optical and microwave domains. This is particularly useful for exploring the impact of canopy structure on the resulting signal and also for combined retrievals of forest structural parameters from optical and microwave data.
    BibTeX:
    @article{Disney2006,
      author = {Disney, M. and Lewis, P. and Saich, P.},
      title = {3D modelling of forest canopy structure for remote sensing simulations in the optical and microwave domains},
      journal = {Remote Sensing of Environment},
      year = {2006},
      volume = {100},
      number = {1},
      pages = {114--132}
    }
    
    Dobbertin, M., Baltensweiler, A. & Rigling, D. Tree mortality in an unmanaged mountain pine (Pinus mugo var. uncinata) stand in the Swiss National Park impacted by root rot fungi. 2001 Forest Ecology and Management
    Vol. 145, pp. 79-89 
    article  
    BibTeX:
    @article{dobbertin01,
      author = {M. Dobbertin and A. Baltensweiler and D. Rigling},
      title = {Tree mortality in an unmanaged mountain pine (Pinus mugo var. uncinata) stand in the Swiss National Park impacted by root rot fungi.},
      journal = {Forest Ecology and Management},
      year = {2001},
      volume = {145},
      pages = {79-89}
    }
    
    Dobson, M., Ulaby, F., LeToan, T., Beaudoin, A., Kasischke, E. & Christensen, N. Dependence of radar backscatter on coniferous forest biomass 1992 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 30(2)Geoscience and Remote Sensing, IEEE Transactions on, pp. 412-415 
    article  
    Abstract: Two independent experimental efforts have examined the dependence of radar backscatter on above-ground biomass of monospecie conifer forests using polarimetric airborne SAR data at P-, L- and C-bands. Plantations of maritime pines near Landes, France, range in age from 8 to 46 years with above-ground biomass between 5 and 105 tons/ha. Loblolly pine stands established on abandoned agricultural fields near Duke, NC, range in age from 4 to 90 years and extend the range of above-ground biomass to 560 tons/ha for the older stands. These two experimental forests are largely complementary with respect to biomass. Radar backscatter is found to increase approximately linearly with increasing biomass until it saturates at a biomass level that depends on the radar frequency. The biomass saturation level is about 200 tons/ha at P-band and 100 tons/ha at L-band, and the C-band backscattering coefficient shows much less sensitivity to total above-ground biomass
    BibTeX:
    @article{Dobson1992,
      author = {Dobson, M.C. and Ulaby, F.T. and LeToan, T. and Beaudoin, A. and Kasischke, E.S. and Christensen, N.},
      title = {Dependence of radar backscatter on coniferous forest biomass},
      booktitle = {Geoscience and Remote Sensing, IEEE Transactions on},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {1992},
      volume = {30},
      number = {2},
      pages = {412--415}
    }
    
    Donoghue, D.N., Watt, P.J., Cox, N.J. & Wilson, J. Remote sensing of species mixtures in conifer plantations using LiDAR height and intensity data 2007 Remote Sensing of Environment
    Vol. 110(4), pp. 509 - 522 
    article DOI  
    Abstract: In even-aged, single species conifer plantations LiDAR height data can be modelled to provide accurate estimates of tree height and volume. However, it is apparent that growth models developed for single species stands are not directly transferable to a more general situation of mixed species plantations. This paper evaluates the ability of small footprint, dual-return, pulsed airborne LiDAR data to estimate the proportion of the productive species when mixed with a nurse crop in closed canopy plantations. A study area located in Galloway Forest District in Scotland is used as an example of Lodgepole pine and Sitka spruce mixed plantation; this area contains good examples of a wide range of pure and mixed species plantation types. Three species groups are studied: areas of pure Sitka spruce, areas of pure Lodgepole pine and areas where the two species have been planted together. Two approaches are assessed for detection of plantation mixtures: the first uses LiDAR intensity data to separate spruce and pine species and the second uses LiDAR-derived canopy density measures, coefficient of variation, skewness, percent of ground returns (which provides a measure of canopy openness) and the mean canopy height, which enables areas with height variations to be identified. From analysis of LiDAR data extracted from 54 study plots using logistic regression, the coefficient of variation and LiDAR intensity data provide the most useful predictors of the proportion of spruce in a pine/spruce mixture with coefficients of determination (R2) of 0.914 and 0.930 respectively. The method could be developed as a mapping tool, which in combination with existing inventory data should help to improve timber volume forecasting for mixed species even-aged plantations.
    BibTeX:
    @article{Donoghue2007,
      author = {Daniel N.M. Donoghue and Peter J. Watt and Nicholas J. Cox and Jimmy Wilson},
      title = {Remote sensing of species mixtures in conifer plantations using LiDAR height and intensity data},
      journal = {Remote Sensing of Environment},
      year = {2007},
      volume = {110},
      number = {4},
      pages = {509 - 522},
      note = {ForestSAT Special Issue, ForestSAT 2005 Conference #Operational##tools##in##forestry##using##remote##sensing##techniques#},
      doi = {DOI: 10.1016/j.rse.2007.02.032}
    }
    
    Drake, J.B., Dubayah, R., Knox, R.G., Clark, D.B. & Condit, R. RELATIONSHIP BETWEEN LIDAR METRICS AND ABOVEGROUND BIOMASS IN CLOSED-CANOPY NEOTROPICAL FORESTS 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 147-154 
    article  
    Abstract: Previous studies have shown that canopy metrics from lidar data are highly correlated with aboveground biomass in a variety of closedcanopy forests, however the generality of these site-specific relationships has remained untested. In this study, we compare relationships between lidar canopy metrics and forest structural summaries from a tropical wet forest site in Costa Rica and across a series of tropical moist forest field sites in Panama. We found that in both regions lidar metrics were strongly correlated with forest structural summaries including mean stem diameter, basal area and aboveground biomass. We also showed that the relationships differed between these regions unless deciduousness of canopy trees in Panama was considered. Adjusting for leaf-drop removed statistically significant differences between the two regions in the relationships between a lidar metric and both mean stem diameter and basal area. The relationships between lidar metrics and aboveground biomass, however, remained significantly different between the two study areas because of different general allometric relationships used to estimate aboveground biomass in tropical wet forests and tropical moist forests. Future efforts should continue to examine climatic factors that may influence the generality of the relationships between lidar metrics and forest structural characteristics, and address the dearth of allometric data on the very large trees that can dominate the biomass of primary tropical forests.
    BibTeX:
    @article{drake01,
      author = {Jason B. Drake and Ralph Dubayah and Robert G. Knox and David B. Clark and Richard Condit},
      title = {RELATIONSHIP BETWEEN LIDAR METRICS AND ABOVEGROUND BIOMASS IN CLOSED-CANOPY NEOTROPICAL FORESTS},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {147-154}
    }
    
    Drake, J.B., Dubayah, R.O., Clark, D.B., Knox, R.G., Blair, J.B., Hofton, M.A., Chazdon, R.L., Weishampel, J.F. & Prince, S.D. Estimation of tropical forest structural characteristics using large-footprint lidar 2002 Remote Sensing of Environment
    Vol. 79, pp. 305-319 
    article  
    Abstract: Quantification of forest structure is important for developing a better understanding of how forest ecosystems function. Additionally, estimation of forest structural attributes, such as aboveground biomass (AGBM), is an important step in identifying the amount of carbon in terrestrial vegetation pools and is central to global carbon cycle studies. Although current remote sensing techniques recover such tropical forest structure poorly, new large-footprint lidar instruments show great promise. As part of a prelaunch validation plan for the Vegetation Canopy Lidar (VCL) mission, the Laser Vegetation Imaging Sensor (LVIS), a large-footprint airborne scanning lidar, was flown over the La Selva Biological Station, a tropical wet forest site in Costa Rica. The primary objective of this study was to test the ability of large-footprint lidar instruments to recover forest structural characteristics across a spectrum of land cover types from pasture to secondary and primary tropical forests. LVIS metrics were able to predict field-derived quadratic mean stem diameter (QMSD), basal area, and AGBM with R2 values of up to .93, .72, and .93, respectively. These relationships were significant and nonasymptotic through the entire range of conditions sampled at the La Selva. Our results confirm the ability of large-footprint lidar instruments to estimate important structural attributes, including biomass in dense tropical forests, and when taken along with similar results from studies in temperate forests, strongly validate the VCL mission framework.
    BibTeX:
    @article{drake02,
      author = {Jason B. Drake and Ralph O. Dubayah and David B. Clark and Robert G. Knox and J. Bryan Blair and Michelle A. Hofton and Robin L. Chazdon and John F. Weishampel and Stephen D. Prince},
      title = {Estimation of tropical forest structural characteristics using large-footprint lidar},
      journal = {Remote Sensing of Environment},
      year = {2002},
      volume = {79},
      pages = {305-319}
    }
    
    Drake, J.B., Dubayah, R.O., Knox, R.G., Clark, D.B. & Blair, J.B. Sensitivity of large-footprint lidar to canopy structure and biomass in a neotropical rainforest 2002 Remote Sensing of Environment
    Vol. 81(2-3), pp. 378-392 
    article  
    Abstract: Accurate estimates of the total biomass in terrestrial vegetation are important for carbon dynamics studies at a variety of scales. Although aboveground biomass is difficult to quantify over large areas using traditional techniques, lidar remote sensing holds great promise for biomass estimation because it directly measures components of canopy structure such as canopy height and the vertical distribution of intercepted canopy surfaces. In this study, our primary goal was to explore the sensitivity of lidar to differences in canopy structure and aboveground biomass in a dense, neotropical rainforest. We first examined the relationship between simple vertical canopy profiles derived from field measurements and the estimated aboveground biomass (EAGB) across a range of field plots located in primary and secondary tropical rainforest and in agroforesty areas. We found that metrics from field-derived vertical canopy profiles are highly correlated (R2 up to .94) with EAGB across the entire range of conditions sampled. Next, we found that vertical canopy profiles from a large-footprint lidar instrument were closely related with coincident field profiles, and that metrics from both field and lidar profiles are highly correlated. As a result, metrics from lidar profiles are also highly correlated (R2 up to .94) with EAGB across this neotropical landscape. These results help to explain the nature of the relationship between lidar data and EAGB, and also lay the foundation to explore the generality of the relationship between vertical canopy profiles and biomass in other tropical regions.
    BibTeX:
    @article{drakedub02,
      author = {Jason B. Drake and Ralph O. Dubayah and Robert G. Knox and David B. Clark and J. B. Blair},
      title = {Sensitivity of large-footprint lidar to canopy structure and biomass in a neotropical rainforest},
      journal = {Remote Sensing of Environment},
      year = {2002},
      volume = {81},
      number = {2-3},
      pages = {378-392}
    }
    
    Drake, J.B. & Weishampel, J.F. Multifractal analysis of canopy height measures in a longleaf pine savanna 2000 Forest Ecology and Management
    Vol. 128(1-2), pp. 121-127 
    article  
    Abstract: Spatial patterns of forest canopies are fractal as they exhibit variation over a continuum of scales. A measure of fractal dimension of a forested landscape represents the spatial summation of physiologic (leaf-level), demographic (population-level), and abiotic (e.g., edaphic) processes, as well as exogenous disturbances (e.g., fire and hurricane) and thus provides a basis to classify or monitor such systems. However, forests typically exhibit a spectrum of fractal parameters which yields further insight to the geometric structure of the system and potentially the underlying processes. We calculated multifractal properties of longleaf pine flatwoods, the predominant ecosystem of central Florida, from canopy profile data derived from an airborne laser altimeter and ground-based measurements in The Nature Conservancy's Disney Wilderness Preserve located near Kissimmee, Florida. These metrics were compared for six [ap]500 m transects to determine the level of consistency between remotely sensed and field measures and within a forest community. Multifractal techniques uncovered subtle differences between transects that could correspond to unique, underlying abiotic and biotic processes. These techniques should be considered a valuable tool for ecological analysis.
    BibTeX:
    @article{drake00,
      author = {Drake, Jason B. and Weishampel, John F.},
      title = {Multifractal analysis of canopy height measures in a longleaf pine savanna},
      journal = {Forest Ecology and Management},
      year = {2000},
      volume = {128},
      number = {1-2},
      pages = {121--127}
    }
    
    Dubayah, R. & Drake, J. Lidar remote sensing for forestry 2000 Journal of Forestry
    Vol. 98, pp. 44-46 
    article  
    BibTeX:
    @article{Dubayah2000,
      author = {Dubayah, R.O. and Drake, J.B.},
      title = {Lidar remote sensing for forestry},
      journal = {Journal of Forestry},
      year = {2000},
      volume = {98},
      pages = {44-46}
    }
    
    Duch?, Y. Aspect l?gaux et r?glementaires : un corpus assez complet existe, encore faut-il l?appliquer ! 2009 For?t Entreprise
    Vol. 185, pp. 41-42 
    article  
    BibTeX:
    @article{duche09,
      author = {Duch?, Y.},
      title = {Aspect l?gaux et r?glementaires : un corpus assez complet existe, encore faut-il l?appliquer !},
      journal = {For?t Entreprise},
      year = {2009},
      volume = {185},
      pages = {41-42}
    }
    
    Ducic, V., Hollaus, M., Ullrich, A., Wagner, W. & Melze, T. 3D vegetation mapping and classification using full-waveform laser scanning 2006 International Workshop 3D Remote Sensing in Forestry
    Vol. Vienna, Feb., 14-15, 2006, pp. 211-217 
    article  
    Abstract: Classifying vegetation points from 3D airborne laser scanner (ALS) point clouds is a challenge and

    focus of current research. In particular, low vegetation points are very difficult to identify. The basic

    problem is that so far the majority of ALS systems have provided only the 3D coordinates of scattering

    objects and most of the criteria used in classifying points had to rely on simple geometric

    characteristics of a point relative to its neighbourhood. Methods for ALS data processing could be

    much improved if ALS systems measure, in addition to the range, further physical observables which

    can be used for vegetation classification. New ALS systems, which record the full echo-waveform,

    may provide crucial information for the classification of vegetation points. In this paper we show that

    the additional features derived from the full-waveform data ? the amplitude, the pulse width and the

    number of pulses - can be used to discriminate between vegetation and non-vegetation points without

    using geometry information. Thus, a truly three dimensional representations of the classified ALS

    points can be obtained. The classification algorithm is based on a decision tree technique. The

    applicability of this method is demonstrated on data collected by the RIEGL LMS-Q560 sensor over

    the Schönbrunn area of Vienna. The performance of the classification algorithm was checked

    manually on 500 points randomly distributed and on several test zones selected over the study area.

    We found an overall accuracy of 88.6% with a kappa coefficient of 0.8.

    BibTeX:
    @article{ducic06,
      author = {V. Ducic and M. Hollaus and A. Ullrich and W. Wagner and Th. Melze},
      title = {3D vegetation mapping and classification using full-waveform laser scanning},
      journal = {International Workshop 3D Remote Sensing in Forestry},
      year = {2006},
      volume = {Vienna, Feb., 14-15, 2006},
      pages = {211-217}
    }
    
    Duncanson, L., Niemann, K. & Wulder, M. Estimating forest canopy height and terrain relief from GLAS waveform metrics 2010 Remote Sensing of Environment
    Vol. 114(1), pp. 138 - 154 
    article DOI URL 
    Abstract: Quantifying aboveground biomass in forest ecosystems is required for carbon stock estimation, aspects of forest management, and further developing a capacity for monitoring carbon stocks over time. Airborne Light Detection And Ranging (LiDAR) systems, of all remote sensing technologies, have been demonstrated to yield the most accurate estimates of aboveground biomass for forested areas over a wide range of biomass values. However, these systems are limited by considerations including large data volumes and high costs. Within the constraints imposed by the nature of the satellite mission, the GeoScience Laser Altimeter System (GLAS) aboard ICESat has provided data conferring information regarding forest vertical structure for large areas at a low end user cost. GLAS data have been demonstrated to accurately estimate forest height and aboveground biomass especially well in topographically smooth areas with homogeneous forested conditions. However in areas with dense forests, high relief, or heterogeneous vegetation cover, GLAS waveforms are more complex and difficult to consistently characterize. We use airborne discrete return LiDAR data to simulate GLAS waveforms and to subsequently deconstruct coregistered GLAS waveforms into vegetation and ground returns. A series of waveform metrics was calculated and compared to topography and vegetation information gleaned from the airborne data. A model to estimate maximum relief directly from waveform metrics was developed with an R2 of 0.76 (n = 110), and used for the classification of the maximum relief of the areas sensed by GLAS. Discriminant analysis was also conducted as an alternative classification technique. A model was also developed estimating forest canopy height from waveform metrics for all of the data (R2 = 0.81, n = 110) and for the three separate relief classes; maximum relief 0-7 m (R2 = 0.83, n = 44), maximum relief 7-15 m (R2 = 0.88, n = 41) and maximum relief > 15 m (R2 = 0.75, n = 25). The moderate relief class model yielded better predictions of forest height than the low relief class model which is attributed to the increasing variability of waveform metrics with terrain relief. The moderate relief class model also yielded better predictions than the high relief class model because of the mixing of vegetation and terrain signals in waveforms from high relief footprints. This research demonstrates that terrain can be accurately modeled directly from GLAS waveforms enabling the inclusion of terrain relief, on a waveform specific basis, as supplemental model input to improve estimates of canopy height.
    BibTeX:
    @article{Duncanson2010138,
      author = {L.I. Duncanson and K.O. Niemann and M.A. Wulder},
      title = {Estimating forest canopy height and terrain relief from GLAS waveform metrics},
      journal = {Remote Sensing of Environment},
      year = {2010},
      volume = {114},
      number = {1},
      pages = {138 - 154},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4XBF8TC-2/2/6b161c50f319b3003892560478903dfb},
      doi = {DOI: 10.1016/j.rse.2009.08.018}
    }
    
    Duong, V.H., Lindenbergh, R., Pfeifer, N. & Vosselman, G. Single and two epoch analysis of ICESat full waveform data over forested areas 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1453-1473 
    article  
    Abstract: Analysis of full-waveform pulses from space-based laser altimeter systems are expected to improve our ability of measuring forests globally. Moreover, with the increase in the number of waveform data sets, it is now possible to study temporal changes in waveform returns over the same spatial domain. ICESat full waveform data from two epochs, i.e. winter and summer (2003) along near-coincident ground tracks, are studied. Data analysis methods are discussed, including normalization and matching of near-coincident waveforms, Gaussian decomposition, and derivation of forest measurement and forest change parameters. We quantify differences between winter and summer waveforms, acquired over broad-leaved, mixed-wood, and needle-leaved forests in Europe. The results indicate that, although maximum tree height barely changes over six months, i.e. &lt;2.2% for all three cover types, the Height of Median Energy (HOME) changed most in broad-leaved (a 148% change) and least for conifers (a 36% change, winter to summer). Ratios of ground energy to canopy energy of normalized waveforms also changed noticeably over time: 67% in broad-leaved, 62% in mixed-wood, and 47% in conifers. Attempts are made to differentiate and classify these three cover types on the basis of these and other canopy metrics. The initial results, with a coefficient ?? of agreement between reference and classified data of 0.57, provide a baseline against which improvements in data and methodology can be gauged.
    BibTeX:
    @article{Duong2008,
      author = {Duong, V. H. and Lindenbergh, R. and Pfeifer, N. and Vosselman, G.},
      title = {Single and two epoch analysis of ICESat full waveform data over forested areas},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1453--1473}
    }
    
    Durden, S., Klein, J. & Zebker, H. Polarimetric radar measurements of a forested area near Mt. Shasta 1991 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 29(3)Geoscience and Remote Sensing, IEEE Transactions on, pp. 444-450 
    article  
    Abstract: The authors present the results of an experiment using the NASA/JPL DC-8 AIRSAR (aircraft synthetic-aperture radar) over a coniferous forest near Mt. Shasta (California) in 1989. Calibration devices were deployed in clearings and under the forest canopy and passes at 20&deg;, 40&deg;, and 55&deg; incidence angles were made with the AIRSAR. A total of eight images at differing incidence angles have been processed and calibrated. The multipolarization multifrequency data were examined, and it was found that the C-band cross section averaged over like and cross polarizations is the best parameter for distinguishing between two stands with differing forest biomass. The average cross section at P- and L-bands is useful only for smaller incidence angles. Parameters describing the polarization behavior of the scattering were primarily useful in identifying the dominant scattering mechanisms for forest backscatter
    BibTeX:
    @article{Durden1991,
      author = {Durden, S.L. and Klein, J.D. and Zebker, H.A.},
      title = {Polarimetric radar measurements of a forested area near Mt. Shasta},
      booktitle = {Geoscience and Remote Sensing, IEEE Transactions on},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {1991},
      volume = {29},
      number = {3},
      pages = {444--450}
    }
    
    Eitel, J.U., Vierling, L.A. & Long, D.S. Simultaneous measurements of plant structure and chlorophyll content in broadleaf saplings with a terrestrial laser scanner 2010 Remote Sensing of Environment
    Vol. 114(10), pp. 2229 - 2237 
    article DOI URL 
    Abstract: Plant structure and chlorophyll content strongly affect rates of photosynthesis. Rapid, objective, and repeatable methods are needed to measure these vegetative parameters to advance our understanding and modeling of plant ecophysiological processes. Terrestrial laser scanners (TLS) can be used to measure structural and potentially chemical properties of objects by quantifying the x,y,z coordinates and intensity of laser light, respectively, returned from an object's surface. The objective of this study was to determine the potential usefulness of TLS with a green (532 nm) laser to simultaneously measure the spatial distribution of chlorophyll a and b content (Chlab), leaf area (LA), and leaf angle (LAN). The TLS measurements were obtained from saplings of two tree species (Quercus macrocarpa and Acer saccharum) and from an angle-adjustable cardboard surface. The green laser return intensity value was strongly correlated with wet-chemically determined Chlab (r2 = 0.77). Strong agreement was shown between measured and TLS-derived LA (r2 = 0.95, intercept = - 1.43, slope = 0.97). The TLS derived LANs of both species followed a plagiophile LAN distribution, and the measured angles of the cardboard surface allowed us to quantify that these LAN values were strongly correlated with TLS derived angles (r2 = 1.0, intercept and slope = 0.98). Our results show that terrestrial laser scanners are feasible for simultaneous measurement of LA, LAN, and Chlab in simple canopies of small broadleaved plants. Further research is needed in more complex and larger canopies.
    BibTeX:
    @article{Eitel20102229,
      author = {Jan U.H. Eitel and Lee A. Vierling and Dan S. Long},
      title = {Simultaneous measurements of plant structure and chlorophyll content in broadleaf saplings with a terrestrial laser scanner},
      journal = {Remote Sensing of Environment},
      year = {2010},
      volume = {114},
      number = {10},
      pages = {2229 - 2237},
      url = {http://www.sciencedirect.com/science/article/B6V6V-507DJX1-1/2/4408ad4fcf6fbd0c7f7a7b784638b2ba},
      doi = {DOI: 10.1016/j.rse.2010.04.025}
    }
    
    Eklundh, L., Harrie, L. & Kuusk, A. Investigating relationships between Landsat ETM+ sensor data and leaf area index in a boreal conifer forest 2001 Remote Sensing of Environment
    Vol. 78(3), pp. 239-251 
    article  
    Abstract: The aim of this paper is to investigate the feasibility of using Landsat ETM+ data for the determination of leaf area index (LAI). The investigation is prompted by the need for obtaining spatially distributed data on LAI to be used as input for carbon modelling of northern boreal forests. Detailed field data have been collected in a coniferous forest area in Uppland, central Sweden, dominated by Norway spruce and Scots pine. A forest canopy reflectance model (Kuusk and Nilson, 2000) has been used to simulate stand reflectances in the Landsat ETM+ wavelength bands as a means of investigating the theoretical reflectance response to LAI changes. The analysis shows that the response to changes in LAI is strongest in the visible wavelength bands, particularly Channel 3, whereas only weak response is noted in the NIR band and for some vegetation indices [simple ratio (SR) and NDVI]. Modelled reflectances are influenced by various other factors, particularly ground reflectance and leaf biochemical properties. Observed reflectances from the Landsat ETM+ sensor have been compared with reflectance modelling results and with field-based LAI estimates. The results indicate that LAI estimation using inverse canopy reflectance modelling may be difficult, given the large number of input parameters required and the current level of uncertainty in these parameters. Statistical relationships between LAI and observed ETM+ reflectances are strongest in ETM+ Channel 7.
    BibTeX:
    @article{eklundh01,
      author = {Eklundh, Lars and Harrie, Lars and Kuusk, Andres},
      title = {Investigating relationships between Landsat ETM+ sensor data and leaf area index in a boreal conifer forest},
      journal = {Remote Sensing of Environment},
      year = {2001},
      volume = {78},
      number = {3},
      pages = {239--251}
    }
    
    Elmqvist, M., Jungert, E., Lantz, F., Persson, A. & Söderman, U. TERRAIN MODELLING AND ANALYSIS USING LASER SCANNER DATA 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 219-226 
    article  
    Abstract: Very detailed high-resolution (3D) digital terrain models can be obtained using airborne laser scanner data. However, laser scanning usually entails huge data sets even for moderate areas, making data management and analysis both complex and time consuming. For this reason, automatic terrain modelling and efficient storage structures supporting data access are needed. In this paper a number of methods supporting automatic construction of 3D digital terrain models, especially ground surface modelling and detection and measurement of individual trees will be discussed. Furthermore automatic and/or interactive terrain feature analysis will be discussed. A special data representation structure for the terrain model allowing efficient data storage and data access will be presented. Beside this, it is possible to create a symbolic information structure from the terrain model that can be used in queries for determination of different terrain features, such as ditches or ridges etc., but also for detection of changes in the terrain.
    BibTeX:
    @article{elmqvist01,
      author = {M. Elmqvist and E. Jungert and F. Lantz and A. Persson and U. Söderman},
      title = {TERRAIN MODELLING AND ANALYSIS USING LASER SCANNER DATA},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {219-226}
    }
    
    Etienne, M., Mas, I. & Rigolot, E. Combining techniques of fuel reduction for fuel-break maintenance in the French Mediterranean Region. 1994
    Vol. 22nd International Conference on Forest Fire research, Coimbra, Portugal, pp. 713-721 
    conference  
    BibTeX:
    @conference{etienne94,
      author = {Etienne, M. and Mas, I. and Rigolot, E.},
      title = {Combining techniques of fuel reduction for fuel-break maintenance in the French Mediterranean Region.},
      booktitle = {2nd International Conference on Forest Fire research, Coimbra, Portugal},
      year = {1994},
      volume = {2},
      pages = {713-721}
    }
    
    Fang, H., Liang, S. & Kuusk, A. Retrieving leaf area index using a genetic algorithm with a canopy radiative transfer model 2003 Remote Sensing of Environment
    Vol. 85(3), pp. 257-270 
    article  
    Abstract: Leaf area index (LAI) is an important structural property of vegetation canopy and is also one of the basic quantities driving the algorithms used in regional and global biogeochemical, ecological and meteorological applications. LAI can be estimated from remotely sensed data through the vegetation indices (VI) and the inversion of a canopy radiative transfer (RT) model. In recent years, applications of the genetic algorithms (GA) to a variety of optimization problems in remote sensing have been successfully demonstrated. In this study, we estimated LAI by integrating a canopy RT model and the GA optimization technique. This method was used to retrieve LAI from field measured reflectance as well as from atmospherically corrected Landsat ETM+ data. Four different ETM+ band combinations were tested to evaluate their effectiveness. The impacts of using the number of the genes were also examined. The results were very promising compared with field measured LAI data, and the best results were obtained with three genes in which the R2 is 0.776 and the root-mean-square error (RMSE) 1.064.
    BibTeX:
    @article{fang03,
      author = {Fang, Hongliang and Liang, Shunlin and Kuusk, Andres},
      title = {Retrieving leaf area index using a genetic algorithm with a canopy radiative transfer model},
      journal = {Remote Sensing of Environment},
      year = {2003},
      volume = {85},
      number = {3},
      pages = {257--270}
    }
    
    Farmer, C.J., Person, D.K. & Bowyer, R.T. Risk factors and mortality of black-tailed deer in a managed forest landscape. 2006 Journal of Wildlife Management
    Vol. 70, pp. 1403-1415 
    article  
    BibTeX:
    @article{Farmer2006,
      author = {Farmer, C. J. and Person, D. K. and Bowyer, R. T.},
      title = {Risk factors and mortality of black-tailed deer in a managed forest landscape.},
      journal = {Journal of Wildlife Management},
      year = {2006},
      volume = {70},
      pages = {1403-1415}
    }
    
    Feret, J.-B., Fran?ois, C., Asner, G.P., Gitelson, A.A., Martin, R.E., Bidel, L.P., Ustin, S.L., le Maire, G. & Jacquemoud, S. PROSPECT-4 and 5: Advances in the leaf optical properties model separating photosynthetic pigments 2008 Remote Sensing of Environment
    Vol. 112(6), pp. 3030-3043 
    article  
    Abstract: The PROSPECT leaf optical model has, to date, combined the effects of photosynthetic pigments, but a finer discrimination among the key pigments is important for physiological and ecological applications of remote sensing. Here we present a new calibration and validation of PROSPECT that separates plant pigment contributions to the visible spectrum using several comprehensive datasets containing hundreds of leaves collected in a wide range of ecosystem types. These data include leaf biochemical (chlorophyll a, chlorophyll b, carotenoids, water, and dry matter) and optical properties (directional-hemispherical reflectance and transmittance measured from 400?nm to 2450?nm). We first provide distinct in vivo specific absorption coefficients for each biochemical constituent and determine an average refractive index of the leaf interior. Then we invert the model on independent datasets to check the prediction of the biochemical content of intact leaves. The main result of this study is that the new chlorophyll and carotenoid specific absorption coefficients agree well with available in vitro absorption spectra, and that the new refractive index displays interesting spectral features in the visible, in accordance with physical principles. Moreover, we improve the chlorophyll estimation (RMSE?=?9??g/cm2) and obtain very encouraging results with carotenoids (RMSE?=?3??g/cm2). Reconstruction of reflectance and transmittance in the 400-2450?nm wavelength domain using PROSPECT is also excellent, with small errors and low to negligible biases. Improvements are particularly noticeable for leaves with low pigment content.
    BibTeX:
    @article{Feret2008,
      author = {Feret, Jean-Baptiste and Fran?ois, Christophe and Asner, Gregory P. and Gitelson, Anatoly A. and Martin, Roberta E. and Bidel, Luc P.R. and Ustin, Susan L. and le Maire, Guerric and Jacquemoud, St?phane},
      title = {PROSPECT-4 and 5: Advances in the leaf optical properties model separating photosynthetic pigments},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {6},
      pages = {3030--3043}
    }
    
    Ferrazzoli, P., Paloscia, S., Pampaloni, P., Schiavon, G., Sigismondi, S. & Solimini, D. The potential of multifrequency polarimetric SAR in assessing agricultural and arboreous biomass 1997 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 35(1)Geoscience and Remote Sensing, IEEE Transactions on, pp. 5-17 
    article  
    Abstract: Polarimetric radar data collected by AIRSAR and SIR-C over agricultural fields, forests, and olive groves of the Italian Montespertoli site are analyzed. The objective is to investigate the radar capability in discriminating among various vegetation species and its sensitivity to agricultural and arboreous biomass. Results indicate that a combined use of P(0.45 GHz) and L- (1.2 GHz) bands allows one to discriminate between agricultural fields and other targets, while a combined use of L- and C- (5.3 GHz) bands allows the authors to discriminate within agricultural areas. To monitor biomass, P-band gives the best results for forests and olive groves, L-band appears to be good for crops with low plant density (m-2), while for crops with high plant density, both L- and C-bands are useful. The availability of crosspolarized data is important for both classification and biomass retrieval
    BibTeX:
    @article{Ferrazzoli1997,
      author = {Ferrazzoli, P. and Paloscia, S. and Pampaloni, P. and Schiavon, G. and Sigismondi, S. and Solimini, D.},
      title = {The potential of multifrequency polarimetric SAR in assessing agricultural and arboreous biomass},
      booktitle = {Geoscience and Remote Sensing, IEEE Transactions on},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {1997},
      volume = {35},
      number = {1},
      pages = {5--17}
    }
    
    Ferris, R. & Humphrey, J. A review of potential biodiversity indicators for application in British forests. 1999 Forestry
    Vol. 72, pp. 313-328 
    article  
    BibTeX:
    @article{Ferris1999,
      author = {Ferris, R. and Humphrey, J.W.},
      title = {A review of potential biodiversity indicators for application in British forests.},
      journal = {Forestry},
      year = {1999},
      volume = {72},
      pages = {313-328}
    }
    
    Ferris, R., Peace, A., Humphrey, J. & Broome, A. Relationships between vegetation, site type and stand structure in coniferous plantations in Britain. 2000 Forest Ecology and Management
    Vol. 136, pp. 35-51 
    article  
    BibTeX:
    @article{ferris00,
      author = {Ferris, R. and Peace, A.J. and Humphrey, J.W. and Broome, A.C.},
      title = {Relationships between vegetation, site type and stand structure in coniferous plantations in Britain.},
      journal = {Forest Ecology and Management},
      year = {2000},
      volume = {136},
      pages = {35-51}
    }
    
    Filin, S. Surface Clustering from Airborne Laser Scanning Data 2002 ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria, pp. A-119 ff (6 pages)  inproceedings  
    Abstract: This paper presents an algorithm for the extraction of surface clusters from airborne laser data. Surface structure analysis is fundamental to almost any application involving LIDAR data, yet most algorithms focus only on identifying planar segments. The proposed algorithm is more general insofar as it aims at extracting surface segments that exhibit an homogeneous behavior, without restriction to one specific pattern. The algorithm adopts a data clustering methodology for this purpose, which offers a very general and flexible way to identify homogeneous patterns in the data.
    BibTeX:
    @inproceedings{filin02,
      author = {Sagi Filin},
      title = {Surface Clustering from Airborne Laser Scanning Data},
      booktitle = {ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria},
      year = {2002},
      pages = {A-119 ff (6 pages)}
    }
    
    Filin, S. Recovery of Systematic Biases in Laser Altimeters Using Natural Surfaces 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 85-91 
    article  
    Abstract: Elements of accuracy of LIDAR systems and the corrections of systematic errors have received growing attention in recent years. The expected level of accuracy and the additional processing that is needed for making the raw data ready to use are aÆected directly by the systematic errors in the laser data. It is evident that calibration of the LIDAR system, both laboratory and in-???àûight, are mandatory to alleviate these deØciencies. This paper presents an error recovery model that is based on modeling the system errors and on deØning adequate control information. The association of the observations and control information, and conØgurations that enhance the reliability of the recovered parameters, are also studied here in detail.
    BibTeX:
    @article{filin01,
      author = {Sagi Filin},
      title = {Recovery of Systematic Biases in Laser Altimeters Using Natural Surfaces},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {85-91}
    }
    
    Filin, S. & Pfeifer, N. Segmentation of airborne laser scanning data using a slope adaptive neighborhood 2006 ISPRS Journal of Photogrammetry and Remote Sensing
    Vol. 60(2), pp. 71-80 
    article  
    Abstract: This paper presents an algorithm for the segmentation of airborne laser scanning data. The segmentation is based on cluster analysis in a feature space. To improve the quality of the computed attributes, a recently proposed neighborhood system, called slope adaptive, is utilized. Key parameters of the laser data, e.g., point density, measurement accuracy, and horizontal and vertical point distribution, are used for defining the neighborhood among the measured points. Accounting for these parameters facilitates the computation of accurate and reliable attributes for the segmentation irrespective of point density and the 3D content of the data (step edges, layered surfaces, etc.) The segmentation with these attributes reveals more of the information that exists in the airborne laser scanning data.
    BibTeX:
    @article{filin06,
      author = {Filin, Sagi and Pfeifer, Norbert},
      title = {Segmentation of airborne laser scanning data using a slope adaptive neighborhood},
      journal = {ISPRS Journal of Photogrammetry and Remote Sensing},
      year = {2006},
      volume = {60},
      number = {2},
      pages = {71--80}
    }
    
    Finney, M. FARSITE: Fire Area Simulator-Model. Development and Evaluation 1998 USDA Forest Service Research Paper, RMRS-RP-4  article  
    BibTeX:
    @article{finney98,
      author = {M.A. Finney},
      title = {FARSITE: Fire Area Simulator-Model. Development and Evaluation},
      journal = {USDA Forest Service Research Paper, RMRS-RP-4},
      year = {1998}
    }
    
    Finney, M.A. The challenge of quantitative risk analysis for wildland fire 2005 Forest Ecology and Management
    Vol. 211(1-2)Relative Risk Assessments for Decision -Making Related To Uncharacteristic Wildfire, pp. 97-108 
    article  
    Abstract: Quantitative fire risk analysis depends on characterizing and combining fire behavior probabilities and effects. Fire behavior probabilities are different from fire occurrence statistics (historic numbers or probabilities of discovered ignitions) because they depend on spatial and temporal factors controlling fire growth. That is, the likelihood of fire burning a specific area is dependent on ignitions occurring off-site and the fuels, topography, weather, and relative fire direction allowing each fire to reach that location. Research is required to compare computational short-cuts that have been proposed for approximating these fire behavior distributions. Fire effects in a risk analysis must also be evaluated on a common scale for the variety of values susceptible to wildland fire. This means that appraisals of fire impacts to human infrastructure and ecological values must be measured by the same currency so that the risk assessment yields a single expectation of fire effects. Ultimately, this will help guide planning and investment into management activities that can alter either the probabilities of damaging fire or the susceptibility to those fire behaviors.
    BibTeX:
    @article{Finney2005,
      author = {Finney, Mark A.},
      title = {The challenge of quantitative risk analysis for wildland fire},
      booktitle = {Relative Risk Assessments for Decision -Making Related To Uncharacteristic Wildfire},
      journal = {Forest Ecology and Management},
      year = {2005},
      volume = {211},
      number = {1-2},
      pages = {97--108}
    }
    
    Flooding in Google Maps http://flood.firetree.net/?ll=54.0000,-2.4000 2006   unpublished  
    BibTeX:
    @unpublished{googlemaps,
      author = {Flooding in Google Maps},
      title = {http://flood.firetree.net/?ll=54.0000,-2.4000},
      year = {2006}
    }
    
    Forestry Department & FAO of the United Nations GLOBAL FOREST FIRE ASSESSMENT 1990-2000 2001   techreport  
    BibTeX:
    @techreport{faorep01,
      author = {Forestry Department and FAO of the United Nations},
      title = {GLOBAL FOREST FIRE ASSESSMENT 1990-2000},
      year = {2001}
    }
    
    Forsberg, R., Keller, K. & Jacobsen, S.M. LASER MONITORING OF ICE ELEVATIONS AND SEA-ICE THICKNESS IN GREENLAND 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 163-168 
    article  
    Abstract: A low-cost Twin-Otter based laser altimetry and scanning system have been set up by KMS in several different commercial aircraft, and flown extensively in connection with airborne gravity activities in the Arctic Ocean north of Greenland, as well as on various research projects on the ice sheet and coastal glaciers in Greenland. The hardware system is based on a Riegl laser swath scanner or Optech laser altimeter combined with numerous GPS receivers. Roll and pitch are provided by either a medium-grade commercial INS or a low-cost custom-made IMU with fiber-optics gyros. The whole system is designed for use on non-dedicated aircraft, with a minimum of set-up time. In the paper we outline the hardware setup, processing schemes and give some examples of field campaigns and estimated accuracies. Measurements over sea-ice in the Polar Sea north of Greenland have shown that sea-ice freeboard can readily be measured combining laser altimetry and a local geoid model, yielding an indirect measurement of sea-ice thickness. Over land ice laser results have, a.o., been used to study radar penetration effects of airborne SAR interferometry, showing large height-dependent variations, corresponding to changes in snow facies.
    BibTeX:
    @article{forsberg01,
      author = {R. Forsberg and K. Keller and S. M. Jacobsen},
      title = {LASER MONITORING OF ICE ELEVATIONS AND SEA-ICE THICKNESS IN GREENLAND},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {163-168}
    }
    
    Fraile, R. & Maybank, S. Comparing Probabilistic and Geometric Models On Lidar Data 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 67-70 
    article  
    Abstract: A bottleneck in the use of Geographic Information Systems (GIS) is the cost of data acquisition. In our case, we are interested in producing GIS layers containing useful information for river ood impact assessment. Geometric models can be used to describe regions of the data which correspond to man-made constructions. Probabilistic models can be used to describe vegetation and other features. Our purpose is to compare geometric and probabilistic models on small regions of interest in lidar data, in order to choose which type of models renders a better description in each region. To do so, we use the Minimum Description Length principle of statistical inference, which states that best descriptions are those which better compress the data. By comparing computer programs that generate the data under different assumptions we can decide which type of models conveys more useful information about each region of interest
    BibTeX:
    @article{fraile01,
      author = {Roberto Fraile and Steve Maybank},
      title = {Comparing Probabilistic and Geometric Models On Lidar Data},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {67-70}
    }
    
    Frazer, G., Trofymow, J. & Lertzman, K. A method for estimating canopy openess, effective leaf area index and photosynthetically active photon flux density using hemispherical photography and computerized image analysis techniques. 1997   techreport  
    BibTeX:
    @techreport{frazer97,
      author = {Frazer, G.W. and Trofymow, J.A. and Lertzman, K.P.},
      title = {A method for estimating canopy openess, effective leaf area index and photosynthetically active photon flux density using hemispherical photography and computerized image analysis techniques.},
      year = {1997}
    }
    
    Frazer, G.W., Wulder, M.A. & Niemann, K.O. Simulation and quantification of the fine-scale spatial pattern and heterogeneity of forest canopy structure: A lacunarity-based method designed for analysis of continuous canopy heights Forest Ecology and Management
    Vol. In Press, Corrected Proof, pp. - 
    article  
    Abstract: Forests canopies are dynamic, continuously varying, three-dimensional structures that display substantial heterogeneity in their spatial arrangement at many scales. At the stand-level, fine-scale spatial heterogeneity influences key canopy processes and contributes to the diversity of niche space and maintenance of forest biodiversity. We present a quantitative method that we developed based on a novel application of two well-established statistical techniques - lacunarity analysis and principal component analysis (PCA) - to determine the fine-scale (0.5-33 m) spatial heterogeneity found in the outer surface of a forest canopy. This method was specifically designed for the analysis of continuous canopy height data generated by airborne LiDAR systems or digital photogrammetry; however, in this study we demonstrate our method using a large, well-documented dataset composed of simulated canopy surfaces only. We found that the magnitude of the lacunarity statistic was strongly associated with canopy cover (R2 = 0.85) and gap volume (R2 = 0.84), while the pattern of decline in lacunarity across discrete measurement scales was related to many size- and density-related attributes of stand and canopy structure (0.27 [less-than or equal to] R2 [less-than or equal to] 0.58) and their diverse vertical and horizontal spatial distributions. PCA uncovered two major gradients of spatial heterogeneity from the 10 dimensions of our original lacunarity dataset. The stronger of these two gradients reflected the continuous variation in canopy cover and gap volume, while a second, more subtle gradient was associated with the array of possible vertical and horizontal spatial configurations that might define any one measure of canopy cover. We expect that this quantitative method can be used to support a broad range of practical applications in sustainable forest management, long-term ecological monitoring, and forest science. Further research is required to understand how these statistical estimates and gradients of measured spatial heterogeneity relate to other ecologically relevant patterns of forest composition, structure, and function.
    BibTeX:
    @article{frazer06,
      author = {Frazer, Gordon W. and Wulder, Michael A. and Niemann, K. Olaf},
      title = {Simulation and quantification of the fine-scale spatial pattern and heterogeneity of forest canopy structure: A lacunarity-based method designed for analysis of continuous canopy heights},
      journal = {Forest Ecology and Management},
      volume = {In Press, Corrected Proof},
      pages = {--}
    }
    
    Frey, O., Morsdorf, F. & Meier, E. Tomographic processing of multi-baseline P-band SAR data for imaging of a forested area {2007} IGARSS: 2007 IEEE INTERNATIONAL GEOSCIENCE AND REMOTE SENSING SYMPOSIUM, VOLS 1-12 - SENSING AND UNDERSTANDING OUR PLANET , pp. {156-159}  article  
    Abstract: Recently, various attempts have been undertaken to obtain information about the structure of forested areas from multi-baseline synthetic aperture radar data. Tomographic processing of such data has been demonstrated but the quality of the focused tomographic image is limited by several factors. In particular Fourier-based focusing methods are susceptible to irregular and sparse sampling, two problems, that are unavoidable in case of multi-pass, multi-baseline SAR data acquired by an airborne system. We propose a tomographic focusing method based on the time-domain back-projection algorithm, which maintains the geometric relationship between the original sensor positions and the imaged target and is therefore able to cope with irregular sampling without introducing any approximations with respect to the geometry. We assess the tomographic focusing quality with the help of the impulse response of simulated point targets and an in-scene corner reflector. And, in particular, preliminary results obtained with the newly acquired P-band tomographic data set consisting of eleven flight tracks are presented.
    BibTeX:
    @article{ISI:000256657300039,
      author = {Frey, Othmar and Morsdorf, Felix and Meier, Erich},
      title = {Tomographic processing of multi-baseline P-band SAR data for imaging of a forested area},
      booktitle = {IGARSS: 2007 IEEE INTERNATIONAL GEOSCIENCE AND REMOTE SENSING SYMPOSIUM, VOLS 1-12 - SENSING AND UNDERSTANDING OUR PLANET },
      year = {2007},
      pages = {156-159},
      note = {IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Barcelona, SPAIN, JUL 23-27, 2007}
    }
    
    Frey, O., Morsdorf, F. & Meier, E. Tomographic Imaging of a Forsted Area by Airborne Multi-Baseline P-Band SAR 2008 Sensors
    Vol. 8(9), pp. 5884-5896 
    article  
    BibTeX:
    @article{frey08,
      author = {Frey, O. and Morsdorf, F. and Meier, E.},
      title = {Tomographic Imaging of a Forsted Area by Airborne Multi-Baseline P-Band SAR},
      journal = {Sensors},
      year = {2008},
      volume = {8},
      number = {9},
      pages = {5884-5896}
    }
    
    Friedlingstein, P., Cox, P., Betts, R., Bopp, L., von Bloh, W., Brovkin, V., Cadule, P., Doney, S., Eby, M., Fung, I., Bala, G., John, J., Jones, C., Joos, F., Kato, T., Kawamiya, M., Knorr, W., Lindsay, K., Matthews, H., Raddatz, T., Rayner, P., Reick, C., Roeckner, E., Schnitzler, K., Schnur, R., Strassmann, K., Waver, A.J., Yoshikawa, C. & Zeng, N. Climate-carbon cycle feedback analysis: Results from the (CMIP)-M-4 model intercomparison 2006 Journal of Climate
    Vol. 19(14), pp. 3337-3353 
    article  
    BibTeX:
    @article{friedlingstein06,
      author = {Friedlingstein, P. and Cox, P. and Betts, R. and Bopp, L. and von Bloh, W. and Brovkin, V. and Cadule, P. and Doney, S. and Eby, M. and Fung, I. and Bala, G. and John, J. and Jones, C. and Joos, F. and Kato, T. and Kawamiya, M. and Knorr, W. and Lindsay, K. and Matthews, H.D. and Raddatz, T. and Rayner, P. and Reick, C. and Roeckner, E. and Schnitzler, K.G. and Schnur, R. and Strassmann, K. and Waver, A. J. and Yoshikawa, C. and Zeng, N.},
      title = {Climate-carbon cycle feedback analysis: Results from the (CMIP)-M-4 model intercomparison},
      journal = {Journal of Climate},
      year = {2006},
      volume = {19},
      number = {14},
      pages = {3337-3353}
    }
    
    Frischknecht, C., Kneubühler, M. & Morsdorf, F. Brandgutdifferenzierung in einem Wildland-Urban-Interface mit Hilfe von Laser Scanning und Bildspektrometrie 2010 Dreiländertagung DGPF, SGPF und ÖVG, Wien, 1-3.7.2010  inproceedings  
    BibTeX:
    @inproceedings{frischknecht2010,
      author = {Christoph Frischknecht and Mathias Kneubühler and Felix Morsdorf},
      title = {Brandgutdifferenzierung in einem Wildland-Urban-Interface mit Hilfe von Laser Scanning und Bildspektrometrie},
      booktitle = {Dreiländertagung DGPF, SGPF und ÖVG, Wien, 1-3.7.2010},
      year = {2010}
    }
    
    FUNAHASHI, M., SETOJIMA, M., AKAMATSU, Y. & IMAI, Y. Investigation of Measuring Accuracy of Forest Area by Means of Airborne Laser Scanner 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 139-146 
    article  
    Abstract: It is an important subject to accurately measure forests that serve as sinks since the global warming is taken up as a serious problem in recent years. Tree height and so on have so far been measured by the conventional direct or indirect measuring method. Presently, however, the measuring accuracy by airborne laser scanner has been improved and it is now reaching the stage of practical use for measuring forests as well. For this study, we selected the forest of Tama Forest Science Garden (Hachioji, Tokyo) of Forestry and Forest Products Research Institute as an investigation field where various types of trees grow and a database is constructed. Then we compared the data obtained with the laser scanner with the results of topographic survey and tree height measurement conducted at the investigation field of a specific range and investigated the accuracy of measuring the forest area. According to the verification result relating to the DEM accuracy, the error of the DEM made from the laser scanner to the actually measured value was about 50cm(min.). As a result of accuracy investigation of tree height, a large difference was found in measuring error depending on the growth condition of trees (tree shape). At a place where trees grow almost vertically, the difference between the DSM and tree height value actually measured was small. However, at places where trees grow obliquely or trees are intertwined in a complicated way, the measuring error was large.
    BibTeX:
    @article{funahashi01,
      author = {Manabu FUNAHASHI and Masahiro SETOJIMA and Yukio AKAMATSU and Yasuteru IMAI},
      title = {Investigation of Measuring Accuracy of Forest Area by Means of Airborne Laser Scanner},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {139-146}
    }
    
    Gamon, J., Serrano, L. & Surfus, J. The photochemical reflectance index: an optical indicator of photosynthetic radiation use efficiency across species, functional types, and nutrient levels. 1997 Oecologia
    Vol. 112, pp. 492-501 
    article  
    BibTeX:
    @article{gamon97,
      author = {Gamon, J.A. and Serrano, L. and Surfus, J.S.},
      title = {The photochemical reflectance index: an optical indicator of photosynthetic radiation use efficiency across species, functional types, and nutrient levels.},
      journal = {Oecologia},
      year = {1997},
      volume = {112},
      pages = {492-501}
    }
    
    Garc?a, M., Ria?o, D., Chuvieco, E. & Danson, F.M. Estimating biomass carbon stocks for a Mediterranean forest in central Spain using LiDAR height and intensity data 2010 Remote Sensing of Environment
    Vol. 114(4), pp. 816 - 830 
    article DOI URL 
    Abstract: Biomass fractions (total aboveground, branches and foliage) were estimated from a small footprint discrete-return LiDAR system in an unmanaged Mediterranean forest in central Spain. Several biomass estimation models based on LiDAR height, intensity or height combined with intensity data were explored. Raw intensity data were normalized to a standard range in order to remove the range dependence of the intensity signal. In general terms, intensity-based models provided more accurate predictions of the biomass fractions. Height models selected were mainly based on a percentile of the height distribution. Intensity models selected included variables that consider the percentage of the intensity accumulated at different height percentiles, which implicitly take into account the height distribution. The general models derived considering all species together were based on height combined with intensity data. These models yielded R2 values greater than 0.58 for the different biomass fractions considered and RMSE values of 28.89, 18.28 and 1.51 Mg ha-1 for aboveground, branch and foliage biomass, respectively. Results greatly improved for species-specific models using the main species present in each plot, with R2 values greater than 0.85, 0.70 and 0.90 for black pine, Spanish juniper and Holm oak, respectively, and with lower RMSE for the biomass fractions. Reductions in LiDAR point density had only a small effect on the results obtained, except for those models based on a variation of the Canopy Reflection Sum, which was weighted by the mean point density. Based on the species-specific equations derived, Holm oak dominated plots showed the highest average carbon contained by aboveground biomass and branch biomass 44.66 and 31.42 Mg ha- 1 respectively, while for foliage biomass carbon, Spanish juniper showed the highest average value (3.04 Mg ha- 1).
    BibTeX:
    @article{Garc?a2010816,
      author = {Mariano Garc?a and David Ria?o and Emilio Chuvieco and F. Mark Danson},
      title = {Estimating biomass carbon stocks for a Mediterranean forest in central Spain using LiDAR height and intensity data},
      journal = {Remote Sensing of Environment},
      year = {2010},
      volume = {114},
      number = {4},
      pages = {816 - 830},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4Y3KV6F-2/2/795ed6f074710387ccea00a774bbde45},
      doi = {DOI: 10.1016/j.rse.2009.11.021}
    }
    
    Garcia-Haro, F.J. & Sommer, S. A fast canopy reflectance model to simulate realistic remote sensing scenarios 2002 Remote Sens. Environ.
    Vol. 81(2-3), pp. 205-227 
    article  
    Abstract: A model for light interaction has been developed to compute spectral and bidirectional reflectance from discontinuous canopies approximated by an arbitrary configuration of plants. The model assumes certain principles of geometric models, e.g., that sensor integrates the radiance reflected from tree plants, shaded soil, and illuminated soil. However, the model attempts to compensate for errors due to multiple scattering in vegetation canopies that lead to nonlinear mixing. In contrast to geometric models, tree crowns are treated as porous (partially transmitting), geometric bodies. Reflectance of canopy and shadowed ground are nonlinear mixtures of leaves and background signatures, which are moreover influenced by parameters of canopy, such as leaf area index (LAI), coefficient of attenuation, and leaves transmittance. Optical parameters are not constant but stochastic variables are controlled by a certain texture in canopy envelopes, and roughness and relief in surface background. The model may also be run using backgrounds presenting variable topography and comprising different landscape features on imported real images. The model predicts the basic features of the Bidirectional Reflectance Factor (BRF), i.e., bowl shape and the hotspot, but unlike common models, it is well suited to address the spectral and spatial domains. For example, the model provides a fast and efficient strategy to derive hyperspectral images at appropriate spatial resolutions (e.g., regional scale) over a wide range of ecosystems.
    BibTeX:
    @article{garcia02,
      author = {F. J. Garcia-Haro and S. Sommer},
      title = {A fast canopy reflectance model to simulate realistic remote sensing scenarios},
      journal = {Remote Sens. Environ.},
      year = {2002},
      volume = {81},
      number = {2-3},
      pages = {205-227}
    }
    
    Gaveau, D. & Hill, R. Quantifying canopy height underestimation by laser pulse penetration in small-footprint airborne laser scanning data. 2003 Canadian Journal of Remote Sensing
    Vol. 29, pp. 650-657 
    article  
    Abstract: There is a well-reported tendency for canopy height to be underestimated in small-footprint ALS data of coniferous woodland. This is commonly explained by a failure to record tree-tops because of insufficient ALS sampling density. This study examines the accuracy of canopy height estimates retrieved from small-footprint dual-return ALS data of broad-leaf woodland. A novel field sampling method was adopted to collect reference canopy upper surface measurements of known horizontal (x-, y-) and vertical (z-) position that had sub-metre accuracy. By investigating the z- differences between ALS and reference canopy measurements with matching x- and y- locations the effects of ALS sampling density were removed from the analysis. For raw point-sample ALS data, a negative bias was observed of 0.91 m for sample shrub canopies and 1.27 m for sample tree canopies. These results suggest that for broad-leaf woodland, a small-footprint laser pulse hitting the upper surface of a canopy often advances into the canopy before reflecting a signal strong enough to be detected by the scanner as a first-return. The depth of laser pulse penetration will vary with canopy structural characteristics and ALS device configuration. Interpolating the point-sample ALS canopy measurements into a grid-based Digital Canopy Height Model propagated the observed errors, resulting in a negative bias of 1.02 m for shrub canopies and 2.12 m for tree canopies. Here the sampling density in relation to canopy surface roughness was important.
    BibTeX:
    @article{gaveau03,
      author = {D.L.A Gaveau and R.A. Hill},
      title = {Quantifying canopy height underestimation by laser pulse penetration in small-footprint airborne laser scanning data.},
      journal = {Canadian Journal of Remote Sensing},
      year = {2003},
      volume = {29},
      pages = {650-657}
    }
    
    Ginzler, C., Boehl, J., Boesch, R. & Waser, L. Accuracy of forest parameters derived from medium footprint LIDAR under operational constraints. 2007 International Archives of Photogrammetry and Remote Sensing

    Volume XXXVI, Part 3 / W52 

    inproceedings  
    BibTeX:
    @inproceedings{ginzler07,
      author = {Ginzler, C. and Boehl, J. and Boesch, R. and Waser, L.},
      title = {Accuracy of forest parameters derived from medium footprint LIDAR under operational constraints.},
      booktitle = {International Archives of Photogrammetry and Remote Sensing 

    Volume XXXVI, Part 3 / W52}, year = {2007} }

    Ginzler, C., Boehl, J., Boesch, R. & Waser, L. Accuracy of forest parameters derived from medium footprint LIDAR under operational constraints. 2007 ISPRS Workshop on Laser Scanning 2007 and SilviLaser 2007, Espoo, September 12-14, 2007, Finland  inproceedings  
    BibTeX:
    @inproceedings{ginzler07_old,
      author = {C. Ginzler and J. Boehl and R. Boesch and L.T. Waser},
      title = {Accuracy of forest parameters derived from medium footprint LIDAR under operational constraints.},
      booktitle = {ISPRS Workshop on Laser Scanning 2007 and SilviLaser 2007, Espoo, September 12-14, 2007, Finland},
      year = {2007}
    }
    
    Gobron, N., Pinty, B., Verstraete, M. & Widlowski, J.-L. Advanced vegetation indices optimized for up-coming sensors: Design, performance, and applications 2000 tgars
    Vol. 38(6), pp. 2489-2505 
    article  
    Abstract: This paper describes the implementation of a physical and mathematical approach to designing advanced vegetation indices optimized for future sensors operating in the solar domain such as the medium resolution imaging spectrometer (MERIS), the global imager (GLI), and the VEGETATION instrument, and proposes an initial evaluation of such indices. These optimized indices address sensor-specific issues such as dependencies with respect to the actual spectral response of the sensor as well as the natural sensitivity of remote sensing measurements to illumination and observing geometry, to atmospheric absorption and scattering effects, and to soil color or brightness changes. The derivation of vegetation index formulae optimized to estimate the same vegetation property fraction of absorbed photosynthetically active radiation (FAPAR) from data generated by different sensors allows the comparison of their relative performances compared with existing vegetation indices, both from a theoretical and experimental point of view and permits the creation of global products, as well as the constitution of long time series from multiple sensors.
    BibTeX:
    @article{gobron00,
      author = {N. Gobron and B. Pinty and M.M. Verstraete and J.-L. Widlowski},
      title = {Advanced vegetation indices optimized for up-coming sensors: Design, performance, and applications},
      journal = {tgars},
      year = {2000},
      volume = {38},
      number = {6},
      pages = {2489-2505}
    }
    
    Goetz, S., Steinberg, D., Dubayah, R. & Blair, B. Laser remote sensing of canopy habitat heterogeneity as a predictor of bird species richness in an eastern temperate forest, USA. 2007 Remote Sensing of Environment
    Vol. 108, pp. 254-263 
    article  
    BibTeX:
    @article{Goetz2007,
      author = {Goetz, S. and Steinberg, D. and Dubayah, R. and Blair, B.},
      title = {Laser remote sensing of canopy habitat heterogeneity as a predictor of bird species richness in an eastern temperate forest, USA.},
      journal = {Remote Sensing of Environment},
      year = {2007},
      volume = {108},
      pages = {254-263}
    }
    
    Gomes Pereira, L.M. & Janssen, L.L.F. Suitability of laser data for DTM generation: a case study in the context of road planning and design 1999 ISPRS Journal of Photogrammetry and Remote Sensing
    Vol. 54(4), pp. 244-253 
    article  
    Abstract: Laser range data acquired from a helicopter are evaluated in terms of the information that can be derived from them and the accuracy. The objective is to study the suitability of laser data to generate a DSM for road planning and design in The Netherlands. The conclusion is that high-density laser measurements allow the reconstruction of the terrain relief with the required accuracy. Nonetheless, they do not allow the extraction of all the information required, particularly semantic information. Thus, the combination of laser data with existing information is a prerequisite. This process of combining laser data with existing geographic information is not trivial. The rate of success depends much on the quality of the individual datasets and the method used to combine them. This problem appears in a much broader context, that of spatial data fusion, and should be the object of future research.
    BibTeX:
    @article{Gomes1999,
      author = {Gomes Pereira, L. M. and Janssen, L. L. F.},
      title = {Suitability of laser data for DTM generation: a case study in the context of road planning and design},
      journal = {ISPRS Journal of Photogrammetry and Remote Sensing},
      year = {1999},
      volume = {54},
      number = {4},
      pages = {244--253}
    }
    
    Gomes Pereira, L.M. & Wicherson, R.J. Suitability of laser data for deriving geographical information: A case study in the context of management of fluvial zones 1999 ISPRS Journal of Photogrammetry and Remote Sensing
    Vol. 54(2-3), pp. 105-114 
    article  
    Abstract: In the Netherlands, around 40% of the territory is below sea level. Rivers that flow through this land have to be constantly monitored to avoid flooding. To this end, terrain information is needed. At present, the relief information is acquired by means of photogrammetry, which makes the information expensive. Furthermore, it is estimated that at least 4 years are needed to collect the relief information of all river zones. A cheaper and faster alternative appears to be the use of laser measurements acquired from an aircraft. Thus, it is of great importance to determine if the user requirements, concerning information needed and related quality, can be fulfilled by high-density laser measurements. In this article, we assess the feasibility of using laser data to help generate a hydrodynamic model. This is needed to determine the effect of high water levels and of earthworks, such as removal of sand in river areas. The conclusion of this study is that as far as the test area is concerned, which appears to be a good representative of the fluvial regions in the Netherlands, the laser data allow one to recover the relief information needed for river management with the desired quality.
    BibTeX:
    @article{Gomes1999a,
      author = {Gomes Pereira, L. M. and Wicherson, R. J.},
      title = {Suitability of laser data for deriving geographical information: A case study in the context of management of fluvial zones},
      journal = {ISPRS Journal of Photogrammetry and Remote Sensing},
      year = {1999},
      volume = {54},
      number = {2-3},
      pages = {105--114}
    }
    
    Gougeon, F.A., St-Onge, B.A., Wulder, M. & Leckie, D.G. Synergy of Airborne Laser Altimetry and Digital Videography for Individual Tree Crown Delineation 2001 Proc. 23rd Canadian Symposium on Remote Sensing / 10e Congrés de l'Association québécoise de télédétection
    Vol. Sainte-Foy, Qu?bec, Canada, pp. (CD-ROM) 
    article  
    Abstract: The obvious advantage of LIDAR data for forestry is as replacement for conventional stereoscopic methods or field measurements of dominant trees to obtain forest stand heights, an important factor in the inference of numerous other forest stand parameters (e.g., volume, biomass). However, when the density of LIDAR data becomes high enough, one can think in terms of individual tree crown heights. An earlier paper (St- Onge, 2000) reported good R2 (0.90) between laser-predicted heights and heights from field measurements of 36 trees. Part of the same dataset over the Lake Duparquet Research Forest, Qu?????bec (79.3 W, 48.5 N) is being used in this study. It consists in a multispectral video image and a LIDAR canopy model coregistered at 50 cm/pixel. However, the laser altimeter mean distance between two hits in about 1.5m. An ideal forest inventory system could incorporate individual tree crown (ITC) delineation and species recognition from multispectral imagery (Gougeon, 1999) with ITC-based height measurements from LIDAR data to produce more precise, accurate and timely ITC-based forest inventories. This could also permit the inference of volume and biomass to be calculated on an ITC-basis and would help in studying the height and crown diameter distributions for ecological or forest productivity studies. This study examines the possible synergy between airborne laser altimeter data and digital video imagery at two processing levels within an automatic image analysis system: (a) the elimination of non-forested or poorly forested areas from analysis, and (b), the possible improvement of individual tree crown delineation. The obvious synergistic effects of knowing height and species on an individual tree basis have been assumed and left to be more fully demonstrated in later works. Used at an appropriate spatial resolution, the individual tree crown delineation algorithm based on following valley of shade between the crowns works generally well on dense to medium dense coniferous forests. When the forest is more open, as is the case here, pre-processing can often be used to eliminate non-forested areas. A combination of masks generated from multispectral rules and by selecting a minimum height from the LIDAR data led to a very good separation of the forested areas and even of individual trees in open fields. The ITC delineation process was then applied to the unmasked areas, first on a smoothed version of the near infrared image and then, on a smoothed version of the LIDAR height image. Both cases produced numerous tree clusters rather than individual tree crowns, but for different reasons. With the video data, crown delineation is hampered by the lack of shade between tree crowns in a direction normal to the illumination angle. With the LIDAR data, crown delineation is hampered by the lack of effective spatial resolution. A post-processing combination of both results led to superior crown delineation, with very few tree clusters.
    BibTeX:
    @article{gougeon01,
      author = {Francois A. Gougeon and Benoit A. St-Onge and Mike Wulder and Donald G. Leckie},
      title = {Synergy of Airborne Laser Altimetry and Digital Videography for Individual Tree Crown Delineation},
      journal = {Proc. 23rd Canadian Symposium on Remote Sensing / 10e Congrés de l'Association québécoise de télédétection},
      year = {2001},
      volume = {Sainte-Foy, Qu?bec, Canada},
      pages = {(CD-ROM)}
    }
    
    Gower, S.T., Kucharik, C.J. & Norman, J.M. Direct and Indirect Estimation of Leaf Area Index, fAPAR, and Net Primary Production of Terrestrial Ecosystems 1999 Remote Sensing of Environment
    Vol. 70, pp. 29-51 
    article  
    Abstract: A primary objective of the Earth Observing System (EOS) is to develop and validate algorithms to estimate leaf area index (L), fraction of absorbed photosyntheti- cally active radiation (fAPAR), and net primary production (NPP) from remotely sensed products. These three prod- ucts are important because they relate to or are compo- nents of the metabolism of the biosphere and can be de- termined for terrestrial ecosystems from satellite-borne sensors. The importance of these products in the EOS program necessitates the need to use standard methods to obtain accurate ground truth estimates of L, fAPAR, and NPP that are correlated to satellite-derived estimates. The objective of this article is to review direct and indirect methods used to estimate L, fAPAR, and NPP in terrestrial ecosystems. Direct estimates of L, biomass, and NPP can be obtained by harvesting individual plants, developing allometric equations, and applying these equations to all individuals in the stand. Using non-site-specific allomet- ric equations to estimate L and foliage production can cause large errors because carbon allocation to foliage is influenced by numerous environmental and ecological factors. All of the optical instruments that indirectly esti- mate L actually estimate ?effective? leaf area index (LE) and underestimate L when foliage in the canopy is non- randomly distributed (i.e., clumped). We discuss several methods, ranging from simple to complex in terms of data needs, that can be used to correct estimates of L when foliage is clumped. Direct estimates of above- ground and below-ground net primary production (NPPA and NPPB, respectively) are laborious, expensive and can only be carried out for small plots, yet there is a great need to obtain global estimates of NPP. Process models, driven by remotely sensed input parameters, are useful tools to examine the influence of global change on the metabolism of terrestrial ecosystems, but an incomplete understanding of carbon allocation continues to hamper development of more accurate NPP models. We summa- rize carbon allocation patterns for major terrestrial biomes and discuss emerging allocation patterns that can be incorporated into global NPP models. One common process model, light use efficiency or epsilon model, uses remotely sensed fAPAR, light use efficiency (LUE) and car- bon allocation coefficients, and other meteorological data to estimates NPP. Such models require reliable estimates of LUE. We summarize the literature and provide LUE coefficients for the major biomes, being careful to correct for inconsistencies in radiation, dry matter and carbon al- location units.
    BibTeX:
    @article{gower_lai,
      author = {Stith T. Gower and Chris J. Kucharik and John M. Norman},
      title = {Direct and Indirect Estimation of Leaf Area Index, fAPAR, and Net Primary Production of Terrestrial Ecosystems},
      journal = {Remote Sensing of Environment},
      year = {1999},
      volume = {70},
      pages = {29-51}
    }
    
    Grace, J., Nichol, C., Disney, M., Lewis, P., Quaife, T. & Bowyer, P. Can we measure terrestrial photosynthesis from space directly, using spectral reflectance and fluorescence? 2007 Global Change Biology
    Vol. 13, pp. 1484-1497 
    article DOI  
    BibTeX:
    @article{grace07,
      author = {J. Grace and C. Nichol and M. Disney and P. Lewis and T. Quaife and P. Bowyer},
      title = {Can we measure terrestrial photosynthesis from space directly, using spectral reflectance and fluorescence?},
      journal = {Global Change Biology},
      year = {2007},
      volume = {13},
      pages = {1484-1497},
      doi = {http://dx.doi.org/10.1111/j.1365-2486.2007.01352.x}
    }
    
    Graf, R., Mathys, L. & Bollmann, K. Habitat assessment for forest dwelling species using LiDAR remote sensing: Capercaillie in the Alps. 2009 Forest Ecology and Management
    Vol. 257, pp. 160-167 
    article  
    BibTeX:
    @article{graf09,
      author = {Graf, R.F. and Mathys, L. and Bollmann, K.},
      title = {Habitat assessment for forest dwelling species using LiDAR remote sensing: Capercaillie in the Alps.},
      journal = {Forest Ecology and Management},
      year = {2009},
      volume = {257},
      pages = {160-167}
    }
    
    Graf, R.F., Mathys, L. & Bollmann, K. Habitat assessment for forest dwelling species using LiDAR remote sensing: Capercaillie in the Alps. 2009 Forest Ecology and Management
    Vol. 257, pp. 160-167 
    article  
    BibTeX:
    @article{Graf2009,
      author = {Graf, R. F. and Mathys, L. and Bollmann, K.},
      title = {Habitat assessment for forest dwelling species using LiDAR remote sensing: Capercaillie in the Alps.},
      journal = {Forest Ecology and Management},
      year = {2009},
      volume = {257},
      pages = {160-167}
    }
    
    Gruen, A. & Zhang, L. Automated Generation of the 3D Structure of Forest Canopy 2006 International Workshop 3D Remote Sensing in Forestry
    Vol. Vienna, Feb., 14-15,, pp. 32-39 
    article  
    Abstract: Classifying vegetation points from 3D airborne laser scanner (ALS) point clouds is a challenge and

    focus of current research. In particular, low vegetation points are very difficult to identify. The basic

    problem is that so far the majority of ALS systems have provided only the 3D coordinates of scattering

    objects and most of the criteria used in classifying points had to rely on simple geometric

    characteristics of a point relative to its neighbourhood. Methods for ALS data processing could be

    much improved if ALS systems measure, in addition to the range, further physical observables which

    can be used for vegetation classification. New ALS systems, which record the full echo-waveform,

    may provide crucial information for the classification of vegetation points. In this paper we show that

    the additional features derived from the full-waveform data ? the amplitude, the pulse width and the

    number of pulses - can be used to discriminate between vegetation and non-vegetation points without

    using geometry information. Thus, a truly three dimensional representations of the classified ALS

    points can be obtained. The classification algorithm is based on a decision tree technique. The

    applicability of this method is demonstrated on data collected by the RIEGL LMS-Q560 sensor over

    the Schönbrunn area of Vienna. The performance of the classification algorithm was checked

    manually on 500 points randomly distributed and on several test zones selected over the study area.

    We found an overall accuracy of 88.6% with a kappa coefficient of 0.8.

    BibTeX:
    @article{gruen06,
      author = {Gruen, Armin and Zhang, Li},
      title = {Automated Generation of the 3D Structure of Forest Canopy},
      journal = {International Workshop 3D Remote Sensing in Forestry},
      year = {2006},
      volume = {Vienna, Feb., 14-15,},
      pages = {32-39}
    }
    
    Guenther, G.C., Brooks, M.W. & LaRocque, P.E. New Capabilities of the ?SHOALS? Airborne Lidar Bathymeter 2000 Remote Sensing of Environment
    Vol. 73(2), pp. 247-255 
    article  
    BibTeX:
    @article{guenther00,
      author = {Gary C. Guenther and Mark W. Brooks and Paul E. LaRocque},
      title = {New Capabilities of the ?SHOALS? Airborne Lidar Bathymeter},
      journal = {Remote Sensing of Environment},
      year = {2000},
      volume = {73},
      number = {2},
      pages = {247-255}
    }
    
    Gundersen, V. & Frivold, L. Public preferences for forest structures: A review of quantitative surveys from Finland, Norway and Sweden. 2008 Urban Forestry and Urban Greening
    Vol. 7, pp. 241-258 
    article  
    BibTeX:
    @article{gundersen08,
      author = {Gundersen, V.S. and Frivold, L.H.},
      title = {Public preferences for forest structures: A review of quantitative surveys from Finland, Norway and Sweden.},
      journal = {Urban Forestry and Urban Greening},
      year = {2008},
      volume = {7},
      pages = {241-258}
    }
    
    Guyette, R.P. & Spetich, M.A. Fire history of oak-pine forests in the Lower Boston Mountains, Arkansas, USA 2003 Forest Ecology and Management
    Vol. 180(1-3), pp. 463-474 
    article  
    Abstract: Perspective on present day issues associated with wildland fire can be gained by studying the long-term interactions among humans, landscape, and fire. Fire frequency and extent over the last 320 years document these interactions north of the Arkansas River on the southern edge of the Lower Boston Mountains. Dendrochronological methods were used to construct three fire chronologies from 309 dated fire scars that were identified on 45 shortleaf pine (Pinus echinata) remnants. Fire frequency increased with human population density from a depopulated period (the late 1600s and early 1700s) to a peak in fire frequency circa 1880. Fire frequency then decreased as human population continued to increase. Fire frequency and human population density were positively correlated during an early period (1680-1880) with low levels of population, but negatively correlated during a later period (1881-1910) with high levels of population. We hypothesized that this difference is due to limits on fire propagation and ignition caused by land use and culture, as well as human population density. Relatively high human population densities (>5 humans/km2) were associated with a peak in the maximum number of fires per decade in this highly dissected, &lsquo;bluff and bench&rsquo; landscape compared to less dissected regions of the Ozarks.
    BibTeX:
    @article{Guyette2003,
      author = {Guyette, R. P. and Spetich, M. A.},
      title = {Fire history of oak-pine forests in the Lower Boston Mountains, Arkansas, USA},
      journal = {Forest Ecology and Management},
      year = {2003},
      volume = {180},
      number = {1-3},
      pages = {463--474}
    }
    
    Haala, N. & Brenner, C. Extraction of buildings and trees in urban environments 1999 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 54(2-3), pp. 130-137 
    article  
    Abstract: In this article, two methods for data collection in urban environments are presented. The first method combines multispectral imagery and laser altimeter data in an integrated classification for the extraction of buildings, trees and grass-covered areas. The second approach uses laser data and 2D ground plan information to obtain 3D reconstructions of buildings.
    BibTeX:
    @article{haala99,
      author = {Norbert Haala and Claus Brenner},
      title = {Extraction of buildings and trees in urban environments},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {1999},
      volume = {54},
      number = {2-3},
      pages = {130-137}
    }
    
    Haala, N. & Brenner, C. Interpretation of Urban Surface Models Using 2D Building Information 1998 Computer Vision and Image Understanding
    Vol. 72(2), pp. 204-214 
    article  
    Abstract: In 3D building reconstruction the interpretation process can be simplified if digital surface models (DSM), which can either be derived from stereo matching of aerial images or be directly measured by scanning laser systems, are used in addition to or instead of image data. Images contain much information, but the resulting complexity causes enormous problems for an automatic interpretation of this data type. Since the information of a DSM is restricted to surface geometry its interpretation is simplified by the absence of unnecessary details. Nevertheless, due to insufficient spatial resolution and quality of the DSM, especially for these applications, optimal results can only be achieved by the use of additional data sources. Within the approach presented in this paper the segmentation of planar surfaces from the DSM is supported by existing ground plans. This 2D building information is also used to derive hypotheses on the possible roof shapes in order to obtain a 3D boundary representation based on the segmented planes.
    BibTeX:
    @article{haala98,
      author = {Haala, Norbert and Brenner, Claus},
      title = {Interpretation of Urban Surface Models Using 2D Building Information},
      journal = {Computer Vision and Image Understanding},
      year = {1998},
      volume = {72},
      number = {2},
      pages = {204--214}
    }
    
    Habeck, J.R. & Mutch, R.W. Fire-dependent forests in the Northern Rocky Mountains 1973 Quaternary Research
    Vol. 3(3)The Ecological Role of Fire in Natural Conifer Forests of Western and Northern America, pp. 408-424 
    article  
    Abstract: One objective of wilderness and parkland fire-ecology research is to describe the relationships between fire and unmanaged ecosystems, so that strategies can be determined that will provide a more nearly natural incidence of fire. More than 50 yr of efforts directed toward exclusion of wildland fires in the Northern Rocky Mountains (western Montana and northern Idaho) have resulted in a definite and observable impact on the forest ecosystems in this region. Fire-ecology investigations in Glacier National Park and the Selway-Bitterroot Wilderness have helped to reveal the nature of this impact and to provide a better understanding of the natural role of fire within these coniferous ecosystems. Such areas provide a unique opportunity to study and test approaches designed to perpetuate unmodified ecosystems. However, we still don't understand all of the long-term consequences of fire control in those forest communities that have evolved fire-dependent characteristics.
    BibTeX:
    @article{Habeck1973,
      author = {Habeck, James R. and Mutch, Robert W.},
      title = {Fire-dependent forests in the Northern Rocky Mountains},
      booktitle = {The Ecological Role of Fire in Natural Conifer Forests of Western and Northern America},
      journal = {Quaternary Research},
      year = {1973},
      volume = {3},
      number = {3},
      pages = {408--424}
    }
    
    Haboudane, D., Miller, J.R., Pattey, E., Zarco-Tejada, P.J. & Strachan, I.B. Hyperspectral vegetation indices and novel algorithms for predicting green LAI of crop canopies: Modeling and validation in the context of precision agriculture 2004 Remote Sensing of Environment
    Vol. 90(3), pp. 337-352 
    article  
    Abstract: A growing number of studies have focused on evaluating spectral indices in terms of their sensitivity to vegetation biophysical parameters, as well as to external factors affecting canopy reflectance. In this context, leaf and canopy radiative transfer models are valuable for modeling and understanding the behavior of such indices. In the present work, PROSPECT and SAILH models have been used to simulate a wide range of crop canopy reflectances in an attempt to study the sensitivity of a set of vegetation indices to green leaf area index (LAI), and to modify some of them in order to enhance their responsivity to LAI variations. The aim of the paper was to present a method for minimizing the effect of leaf chlorophyll content on the prediction of green LAI, and to develop new algorithms that adequately predict the LAI of crop canopies. Analyses based on both simulated and real hyperspectral data were carried out to compare performances of existing vegetation indices (Normalized Difference Vegetation Index [NDVI], Renormalized Difference Vegetation Index [RDVI], Modified Simple Ratio [MSR], Soil-Adjusted Vegetation Index [SAVI], Soil and Atmospherically Resistant Vegetation Index [SARVI], MSAVI, Triangular Vegetation Index [TVI], and Modified Chlorophyll Absorption Ratio Index [MCARI]) and to design new ones (MTVI1, MCARI1, MTVI2, and MCARI2) that are both less sensitive to chlorophyll content variations and linearly related to green LAI. Thorough analyses showed that the above existing vegetation indices were either sensitive to chlorophyll concentration changes or affected by saturation at high LAI levels. Conversely, two of the spectral indices developed as a part of this study, a modified triangular vegetation index (MTVI2) and a modified chlorophyll absorption ratio index (MCARI2), proved to be the best predictors of green LAI. Related predictive algorithms were tested on CASI (Compact Airborne Spectrographic Imager) hyperspectral images and, then, validated using ground truth measurements. The latter were collected simultaneously with image acquisition for different crop types (soybean, corn, and wheat), at different growth stages, and under various fertilization treatments. Prediction power analysis of proposed algorithms based on MCARI2 and MTVI2 resulted in agreements between modeled and ground measurement of non-destructive LAI, with coefficients of determination (r2) being 0.98 for soybean, 0.89 for corn, and 0.74 for wheat. The corresponding RMSE for LAI were estimated at 0.28, 0.46, and 0.85, respectively.
    BibTeX:
    @article{haboudane04,
      author = {Haboudane, Driss and Miller, John R. and Pattey, Elizabeth and Zarco-Tejada, Pablo J. and Strachan, Ian B.},
      title = {Hyperspectral vegetation indices and novel algorithms for predicting green LAI of crop canopies: Modeling and validation in the context of precision agriculture},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {90},
      number = {3},
      pages = {337--352}
    }
    
    Hagiwara, A., Imanishi, J., Hashimoto, H. & Morimoto, Y. ESTIMATING LEAF AREA INDEX IN MIXED FOREST USING AN AIRBORNE LASER SCANNER 2004 International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences

    ISSN 1682-1750 VOLUME XXXVI, PART 8/W2 

    inproceedings  
    Abstract: Leaf area index (LAI) is one of the most important parameter of forest structure. The study site was an isolated forest in Kyoto City in Japan and it vegetation type was mixed forest. We took fisheye photos at 102 points in the study area, and calculated the LAI and Canopy-open. We classified the laser data into 4 classes, that is, First pulse, Last pulse, Only pulse and Ground pulse. We counted the number of the each pulse in the 102 circles those centers were the ground truth points and each diameter was 40m. Here we introduce new indices: the ratio of the Last pulse (LFO) or Ground pulse (GFO) to (First pulse + Only pulse) and vegetation flux (VF). The ratio of the Ground pulse (GFO) and VF had very strong liner correlation to LAI (r = -0.840) and Canopy-open (r = 0.885). We made a multiple regression model for predicting LAI from LFO and GFO, and its adjusted R square was 0.704. Each analysis had a very strong correlation to the LAI estimated from fisheye photos, therefore the estimation of LAI from the laser scanner turned out to be so effective. It remains some problems. The difficulty in estimation of LAI from the laser scanner is getting the Ground pulses. We are only able to estimate the LAI which is lower than 2.360 from the regression model obtained because the constant of the equation is 2.369. Hereafter it will be the subject how to estimate the LAI over 2.360.
    BibTeX:
    @inproceedings{hagiwara04,
      author = {A. Hagiwara and J. Imanishi and H. Hashimoto and Y. Morimoto},
      title = {ESTIMATING LEAF AREA INDEX IN MIXED FOREST USING AN AIRBORNE LASER SCANNER},
      booktitle = {International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences

    ISSN 1682-1750 VOLUME XXXVI, PART 8/W2}, year = {2004} }

    Hall, F.G., Townshend, J.R. & Engman, E.T. Status of remote sensing algorithms for estimation of land surface state parameters 1995 Remote Sensing of Environment
    Vol. 51(1), pp. 138-156 
    article  
    Abstract: Ecosystem process, biosphere-atmosphere transfer, and carbon exchange models all require parameterization of the land surface, including land vegetation cover and soil moisture. Although not yet a demonstrated global capability, the most feasible method for obtaining these parameters and updating them periodically, is satellite remote sensing. In this paper we will summarize our understanding of the desired land surface parameters, including soil moisture, and provide an assessment of the state of the art of surface state remote sensing algorithms to infer those parameters on a global basis.First, we will consider a) modeling requirements for land cover parameters, including vegetation community composition and biophysical parameters, for example, leaf area index (LAI), biomass density, fraction of photosynthetically active radiation (Fear) absorbed by the vegetated land surface, and b) modeling requirements for soil moisture.We will then review the status of remote sensing algorithms for obtaining these parameters and examine a number of issues involved in the global implementation and testing of these algorithms. Finally, we will look at future needs to make global mapping of land cover parameters a reality.
    BibTeX:
    @article{hall95,
      author = {Hall, Forrest G. and Townshend, John R. and Engman, Edwin T.},
      title = {Status of remote sensing algorithms for estimation of land surface state parameters},
      journal = {Remote Sensing of Environment},
      year = {1995},
      volume = {51},
      number = {1},
      pages = {138--156}
    }
    
    Halpern, C.B., Miller, E.A. & A., G.M. Equations for predicting above-ground biomass of plant species in early successional forests of the western Cascade Range, Oregon. 1996 Northwest Science
    Vol. 70, pp. 306-320 
    article  
    BibTeX:
    @article{halpern96,
      author = {Halpern, C. B. and Miller, E. A. and Geyer M. A.},
      title = {Equations for predicting above-ground biomass of plant species in early successional forests of the western Cascade Range, Oregon.},
      journal = {Northwest Science},
      year = {1996},
      volume = {70},
      pages = {306-320}
    }
    
    Hansen, J. & Jonas, D. AIRBORNE LASER SCANNING OR AERIAL PHOTOGRAMMETRY FOR THE MINE SURVEYOR 1999 AAM Surveys Inc.  article  
    Abstract: Airborne Laser Scanning (ALS) was first introduced into Australia in 1998 and has since proved its worth as a broad-acre terrain-modelling tool. But is this technology relevant to the spatial data needs required in the Australian mining industry? This paper discusses the pros and cons of the ALS system in comparison with photogrammetry, the current broad-acre data acquisition technique utilised by most mining operations. The findings are that ALS is not going to revolutionise data acquisition in Australian mines, but that it does provide a useful contribution to the mine surveyor's toolkit. To complete the comparison, recent advances in photogrammetry are also discussed.
    BibTeX:
    @article{hansen99,
      author = {Jamie Hansen and David Jonas},
      title = {AIRBORNE LASER SCANNING OR AERIAL PHOTOGRAMMETRY FOR THE MINE SURVEYOR},
      journal = {AAM Surveys Inc.},
      year = {1999}
    }
    
    Harding, D., Lefsky, M., Parker, G. & Blair, J. Laser altimeter canopy height profiles: Methods and validation for closed-canopy, broadleaf forests 2001 Remote Sensing of Environment
    Vol. 76, pp. 283-297 
    article  
    Abstract: Waveform-recording laser altimeter observations of vegetated landscapes provide a time-resolved measure of laser pulse backscatter energy from canopy surfaces and the underlying ground. Airborne laser altimeter waveform data was acquired using the Scanning Lidar Imager of Canopies by Echo Recovery (SLICER) for a successional sequence of four, closed-canopy, deciduous forest stands in eastern Maryland. The four stands were selected so as to include a range of canopy structures of importance to forest ecosystem function, including variation in the height and roughness of the outermost canopy surface and the vertical organization of canopy stories and gaps. The character of the SLICER backscatter signal is described and a method is developed that accounts for occlusion of the laser energy by canopy surfaces, transforming the backscatter signal to a canopy height profile (CHP) that quantitatively represents the relative vertical distribution of canopy surface area. The transformation applies increased weighting to the backscatter amplitude as a function of closure through the canopy and assumes a horizontally random distribution of the canopy components. SLICER CHPs, averaged over areas of overlap where altimeter ground tracks intersect, are shown to be highly reproducible. CHP transects across the four stands reveal spatial variations in vegetation, at the scale of the individual 10-m-diameter laser footprints, within and between stands. Averaged SLICER CHPs are compared to analogous height profile results derived from ground-based sightings to plant intercepts measured on plots within the four stands. The plots were located on the segments of the altimeter ground tracks from which averaged SLICER CHPs were derived, and the ground observations were acquired within 2 weeks of the SLICER data acquisition to minimize temporal change. The differences in canopy structure between the four stands is similarly described by the SLICER and ground-based CHP results. However, a chi-square test of similarity documents differences that are statistically significant. The differences are discussed in terms of measurement properties that define the smoothness of the resulting CHPs and canopy properties that may vertically bias the CHP representations of canopy structure. The statistical differences are most likely due to the more noisy character of the ground-based CHPs, especially high in the canopy where ground-based sightings are rare resulting in an underestimate of canopy surface area and height, and to departures from assumptions of canopy uniformity, particularly regarding lack of clumping and vertically constant canopy reflectance, which bias the CHPs. The results demonstrate that the SLICER observations reliably provide a measure of canopy structure that reveals ecologically interesting structural variations such as those characterizing a successional sequence of closed-canopy, broadleaf forest stands.
    BibTeX:
    @article{harding01,
      author = {D.J. Harding and M.A. Lefsky and G.G. Parker and J.B. Blair},
      title = {Laser altimeter canopy height profiles: Methods and validation for closed-canopy, broadleaf forests},
      journal = {Remote Sensing of Environment},
      year = {2001},
      volume = {76},
      pages = {283-297}
    }
    
    Harding, D.J. & Carabajal, C.C. ICESat waveform measurements of within-footprint topographic relief and vegetation vertical structure 2005 Geophysical Research Letters
    Vol. 32, pp. L21S10, doi:10.1029/2005GL023471 
    article  
    BibTeX:
    @article{harding05,
      author = {David J. Harding and Claudia C. Carabajal},
      title = {ICESat waveform measurements of within-footprint topographic relief and vegetation vertical structure},
      journal = {Geophysical Research Letters},
      year = {2005},
      volume = {32},
      pages = {L21S10, doi:10.1029/2005GL023471}
    }
    
    Hardy, C.C. Wildland fire hazard and risk: Problems, definitions, and context 2005 Forest Ecology and Management
    Vol. 211(1-2)Relative Risk Assessments for Decision -Making Related To Uncharacteristic Wildfire, pp. 73-82 
    article  
    Abstract: The risks, hazards, and relative severity of wildland fires are presented here within the ecological context of historical natural fire regimes, time, space, and process. As the public dialogue on the role and impacts of wildland fire increases, it is imperative for all partners to converge on clear and concise terminology that defines risk, hazard, and the characteristic (or uncharacteristic) nature of wildland fire. These terms must be defined in the context of scale--both spatial and temporal. The concept of historical natural fire regimes involves a classification of the characteristic, or "natural" processes and effects associated with wildland fire occurring in sustainable ecosystems. When a wildland fire occurs within the time, space, and severity parameters of the historical natural fire regime, the fire can be called natural, or "characteristic". The milieu of disturbance effects we call catastrophic, such as economic losses, damages to communities and structures, or impacts on short-term aesthetic values involve social, cultural, and economic values and risks--none is directly associated with ecological values, damages, or risks. In the context of technical risk assessments, the term "risk" considers not only the probability of an event, but also includes values and expected losses. However, within the fire community it refers only to the probability of ignition (both man- and lightning-caused). 'Hazard' refers to the state of the fuel, exclusive of weather or the environs in which the fuel is found. Unlike many common uses of the term 'severity', fire severity refers specifically to the effect a fire has on wildland systems. It is inappropriate to use the term severity to describe the behavior of the fire phenomenon itself. Instead, we should confine its use to that relating only to a fire's effect. Finally, I discuss the limitations and conflicts to integrating all social, cultural, economic, health, and safety values in our public and policy-forming dialogue relating to fire risk, hazard, and severity. Typical risk assessments consider all relevant endpoints, including socio-economic, management, as well as ecological elements. Herein, I use the Black Mountain 2 Fire from August 2003 in the northern Rockies to illustrate the spatiotemporal extent of fire's impacts on the endpoints. When expressed over all affected spatiotemporal scales, the overlay of all endpoints from this synthetic scenario results in a "decision space" ranging in time from an hour to a century, and in space ranging from a few square meters to the continent.
    BibTeX:
    @article{Hardy2005,
      author = {Hardy, Colin C.},
      title = {Wildland fire hazard and risk: Problems, definitions, and context},
      booktitle = {Relative Risk Assessments for Decision -Making Related To Uncharacteristic Wildfire},
      journal = {Forest Ecology and Management},
      year = {2005},
      volume = {211},
      number = {1-2},
      pages = {73--82}
    }
    
    Haugerud, R.A. & Harding, D.J. SOME ALGORITHMS FOR VIRTUAL DEFORESTATION (VDF) OF LIDAR TOPOGRAPHIC SURVEY DATA 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 211-217 
    article  
    Abstract: Lidar topographic surveys of forested terrain generate XYZ positions for laser returns from numerous points, some on the ground and some from vegetation. Extracting a ground surface model from such data requires virtual deforestation (VDF), preferably by automatic means. A simple error budget for lidar topography of forested terrain suggests that the dominant source of error and the greatest room for improvement lies in VDF procedures. We discuss a despike VDF algorithm that classifies returns as ground or not-ground on the basis of the geometry of the surface in the neighborhood of each return. The despike algorithm is fully automatic, effective, and can recover breaklines. It fails to identify some negative blunders, rounds some sharp corners off the landscape, and as implemented is slow. There are clear paths to improve its speed. If multiple-return data are available, a no-multiple-returns VDF algorithm robustly defines areas where all returns are ground returns. Many groups are using variations on block-minimum VDF algorithms, but these do not work well on slopes and typically require substantial human involvement to adjust block size as the fraction of ground returns changes. Fully automatic VDF algorithms are desirable not only to minimize survey costs but also to produce topography for which all necessary interpretive biases and assumptions are explicit. The development of effective VDF algorithms has been hindered by the tendency of some commercial and academic practitioners to keep their work proprietary. Open dialogue is needed.
    BibTeX:
    @article{haugerud01,
      author = {R. A. Haugerud and D. J. Harding},
      title = {SOME ALGORITHMS FOR VIRTUAL DEFORESTATION (VDF) OF LIDAR TOPOGRAPHIC SURVEY DATA},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {211-217}
    }
    
    Hese, S., Lucht, W., Schmullius, C., Barnsley, M., Dubayah, R., Knorr, D., Neumann, K., Riedel, T. & Schröter, K. Global biomass mapping for an improved understanding of the CO2 balance?the Earth observation mission Carbon-3D 2005 Remote Sensing of Environment
    Vol. 94, pp. 94-104 
    article  
    Abstract: Understanding global climate change and developing strategies for sustainable use of our environmental resources are major scientific and political challenges. In response to an announcement of the German Aerospace Center (DLR) for a national Earth observation (EO) mission, the Friedrich-Schiller University Jena and the JenaOptronik GmbH proposed the EO mission Carbon-3D. The data products of this mission will for the first time accurately estimate aboveground biomass globally, one of the most important parameters of the carbon cycle. Simultaneous acquisition of multiangle optical with Light Detection and Ranging (LIDAR) observations is unprecedented. The optical imager extrapolates the laser-retrieved height profiles to biophysical vegetation maps. This innovative mission will reduce uncertainties about net effects of deforestation and forest regrowth on atmospheric CO2 concentrations and will also provide key biophysical information for biosphere models.
    BibTeX:
    @article{hese05,
      author = {S. Hese and W. Lucht and C. Schmullius and M. Barnsley and R. Dubayah and D. Knorr and K. Neumann and T. Riedel and K. Schröter},
      title = {Global biomass mapping for an improved understanding of the CO2 balance?the Earth observation mission Carbon-3D},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {94},
      pages = {94-104}
    }
    
    Hilker, T., van Leeuwen, M., Coops, N., Wulder, M., Newnham, G., Jupp, D. & Culvenor, D. Comparing canopy metrics derived from terrestrial and airborne laser scanning in a Douglas-fir dominated forest stand 2010 Trees - Structure and Function
    Vol. 24, pp. 819-832 
    article URL 
    Abstract: Accurate estimates of vegetation structure are important for a large number of applications including ecological modeling and carbon budgets. Light detection and ranging (LiDAR) measures the three-dimensional structure of vegetation using laser beams. Most LiDAR applications today rely on airborne platforms for data acquisitions, which typically record between 1 and 5 discrete returns for each outgoing laser pulse. Although airborne LiDAR allows sampling of canopy characteristics at stand and landscape level scales, this method is largely insensitive to below canopy biomass, such as understorey and trunk volumes, as these elements are often occluded by the upper parts of the crown, especially in denser canopies. As a supplement to airborne laser scanning (ALS), a number of recent studies used terrestrial laser scanning (TLS) for the biomass estimation in spatially confined areas. One such instrument is the Echidna Validation Instrument (EVI), which is configured to fully digitize the returned energy of an emitted laser pulse to establish a complete profile of the observed vegetation elements. In this study we assess and compare a number of canopy metrics derived from airborne and TLS. Three different experiments were conducted using discrete return ALS data and discrete and full waveform observations derived from the EVI. Although considerable differences were found in the return distribution of both systems, ALS and TLS were both able to accurately determine canopy height (delta height >?2.5?m) and the vertical distribution of foliage and leaf area (0.86?>?r 2?>?0.90, p
    BibTeX:
    @article{springerlink:10.1007/s00468-010-0452-7,
      author = {Hilker, Thomas and van Leeuwen, Martin and Coops, Nicholas and Wulder, Michael and Newnham, Glenn and Jupp, David and Culvenor, Darius},
      title = {Comparing canopy metrics derived from terrestrial and airborne laser scanning in a Douglas-fir dominated forest stand},
      journal = {Trees - Structure and Function},
      publisher = {Springer Berlin / Heidelberg},
      year = {2010},
      volume = {24},
      pages = {819-832},
      note = {10.1007/s00468-010-0452-7},
      url = {http://dx.doi.org/10.1007/s00468-010-0452-7}
    }
    
    Hill, R. Going Undercover: Mapping Woodland Understorey From Leaf-On and Leaf-Off LIDAR Data 2007
    Vol. VOLUME XXXVI(PART 3 / W52)INTERNATIONAL ARCHIVES OF PHOTOGRAMMETRY,

    REMOTE SENSING AND SPATIAL INFORMATION SCIENCES, pp. 184-189 

    conference  
    BibTeX:
    @conference{hill07,
      author = {Hill, R.A.},
      title = {Going Undercover: Mapping Woodland Understorey From Leaf-On and Leaf-Off LIDAR Data},
      booktitle = {INTERNATIONAL ARCHIVES OF PHOTOGRAMMETRY,

    REMOTE SENSING AND SPATIAL INFORMATION SCIENCES}, year = {2007}, volume = {VOLUME XXXVI}, number = {PART 3 / W52}, pages = {184-189} }

    Hill, R.A., Hinsley, S.A. & Bellamy, P.E. Integrating multiple datasets for the remote quantification of woodland bird habitat quality 2004 International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXVI, Part 8/W2, pp. 248-253  inproceedings  
    BibTeX:
    @inproceedings{hill04,
      author = {Ross A. Hill and Shelley A. Hinsley and Paul E. Bellamy},
      title = {Integrating multiple datasets for the remote quantification of woodland bird habitat quality},
      booktitle = {International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXVI, Part 8/W2},
      year = {2004},
      pages = {248-253}
    }
    
    Hill, R.A., Smith, G.S., Fuller, R.M. & Veitch, N. Landscape modelling using airborne multi-spectral and laser scanning data 2002
    Vol. 23(11), pp. 2327-2334 
    article  
    Abstract: By integrating multi-spectral and elevation data from airborne sensors (CASI and ALTM) and adopting a parcel-based approach, a progression is achieved from land-cover classification to landscape modelling. This work involved data integration, per-parcel classification, knowledge-based correction and the derivation of landscape objects. For a 1 km2 study area, a 14 land-cover class vector dataset was generated in which the parcels relate to landscape objects and contain information on their structure and 'terrain' context. At a 1 m spatial resolution, the correspondence between land-cover mapped using the airborne sensor data and identified by Countryside Survey 2000 field surveyors was 88 $%$ .
    BibTeX:
    @article{hill02,
      author = {R. A. Hill and G. S. Smith and R. M. Fuller and N. Veitch},
      title = {Landscape modelling using airborne multi-spectral and laser scanning data},
      year = {2002},
      volume = {23},
      number = {11},
      pages = {2327-2334}
    }
    
    Hill, R. & Broughton, R. Mapping the understorey of decidouous woodland from leaf-on and leaf-off airborne LiDAR data: A case study in lowland Britain. 2009 Journal of Photogrammetry and Remote Sensing
    Vol. 64, pp. 223-233 
    article  
    BibTeX:
    @article{Hill2009,
      author = {Hill, R.A. and Broughton, R.K.},
      title = {Mapping the understorey of decidouous woodland from leaf-on and leaf-off airborne LiDAR data: A case study in lowland Britain.},
      journal = {Journal of Photogrammetry and Remote Sensing},
      year = {2009},
      volume = {64},
      pages = {223-233}
    }
    
    Hill, R. & Broughton, R. Mapping the understorey of deciduous woodland from leaf-on and leaf-off airborne LiDAR data: A case study in lowland Britain 2009 ISPRS Journal of Photogrammetry and Remote Sensing
    Vol. 64(2), pp. 223 - 233 
    article DOI URL 
    Abstract: This study examines the understorey information present in discrete-return LiDAR (Light Detection And Ranging) data acquired for temperate deciduous woodland in mid summer (leaf-on) and in early spring when the understorey had mostly leafed out, but the overstorey had only just begun budburst (referred to here as leaf-off). The woodland is ancient, semi-natural broadleaf and has a heterogeneous structure with a mostly closed canopy overstorey and a patchy understorey layer. In this study, the understorey was defined as suppressed trees and shrubs growing beneath an overstorey canopy. Forest mensuration data for the study site were examined to identify thresholds (taking the 95th percentile) for crown depth as a percentage of crown top height for the six overstorey tree species present. These data were used in association with a digital tree species map and leaf-on first return LiDAR data, to identify the possible depth of space available below the overstorey canopy in which an understorey layer could exist. The leaf-off last return LiDAR data were then examined to identify whether they contained information on where this space was occupied by suppressed trees or shrubs forming an understorey. Thus, understorey was mapped from the leaf-off last return data where the height was below the predicted crown depth. A height threshold of 1 m was applied to separate the ground vegetation layer from the understorey. The derived understorey model formed a discontinuous layer covering 46.4 ha (or 31% of the study site), with an average height of 2.64 m and a 77% correspondence with field data on the presence/absence of suppressed trees and shrubs (kappa 0.53). Because the first return data in leaf-on and leaf-off conditions were very similar (differing by an average of just 0.87 m), it was also possible to map the understorey layer using leaf-off data alone. The resultant understorey model covered 39.4 ha (or 26% of the study site), and had a 72% correspondence with field data on the presence/absence of suppressed trees and shrubs (kappa 0.45). This moderate reduction in the area of understorey mapped and associated accuracy came with a saving of half of all data acquisition and pre-processing costs. Whilst the understorey modelling presented here undoubtedly benefited from the specific timing of LiDAR data acquisition and from ancillary data available for the study site, the conclusions have resonance beyond this case study. Given that the understorey and overstorey canopies in lowland broadleaf woodland can merge into one another, the modelling of understorey information from discrete-return LiDAR data must consider overstorey canopy characteristics and laser penetration through the overstorey. It is not adequate in such circumstances to apply simple height thresholds to LiDAR height frequency distributions, as this is unlikely to distinguish whether a return has backscattered from the lower parts of the overstorey canopy or from near the surface of the understorey canopy.
    BibTeX:
    @article{Hill2009,
      author = {R.A. Hill and R.K. Broughton},
      title = {Mapping the understorey of deciduous woodland from leaf-on and leaf-off airborne LiDAR data: A case study in lowland Britain},
      journal = {ISPRS Journal of Photogrammetry and Remote Sensing},
      year = {2009},
      volume = {64},
      number = {2},
      pages = {223 - 233},
      url = {http://www.sciencedirect.com/science/article/B6VF4-4VDGTHG-1/2/728bb9f48d4f516deee2a5b881600d84},
      doi = {DOI: 10.1016/j.isprsjprs.2008.12.004}
    }
    
    Hill, R., Hinsley, S., Gaveau, D. & Bellamy, P. Predicting habitat quality for Great Tits (Parus major) with airborne laser scanning data. 2004 International Journal of Remote Sensing
    Vol. 25, pp. 4851-4855 
    article  
    BibTeX:
    @article{hill04_intj,
      author = {Hill, R.A. and Hinsley, S.A. and Gaveau, D.L.A. and Bellamy, P.E},
      title = {Predicting habitat quality for Great Tits (Parus major) with airborne laser scanning data.},
      journal = {International Journal of Remote Sensing},
      year = {2004},
      volume = {25},
      pages = {4851-4855}
    }
    
    Hodgson, M.E., Jensen, J., Raber, G., Tullis, J., Davis, B.A., Thompson, G. & Schuckmann, K. An Evaluation of Lidar-derived Elevation and Terrain Slope in Leaf-off Conditions 2005 Photogrammetric Engineering & Remote Sensing
    Vol. 71(7), pp. 817-823 
    article  
    BibTeX:
    @article{hodgson05,
      author = {Michael E. Hodgson and John Jensen and George Raber and Jason Tullis and Bruce A. Davis and Gary Thompson and Karen Schuckmann},
      title = {An Evaluation of Lidar-derived Elevation and Terrain Slope in Leaf-off Conditions},
      journal = {Photogrammetric Engineering & Remote Sensing},
      year = {2005},
      volume = {71},
      number = {7},
      pages = {817-823}
    }
    
    Hodgson, M.E., Jensen, J.R., Schmidt, L., Schill, S. & Davis, B. An evaluation of LIDAR- and IFSAR-derived digital elevation models in leaf-on conditions with USGS Level 1 and Level 2 DEMs 2003 Remote Sensing of Environment
    Vol. 84(2), pp. 295-308 
    article  
    Abstract: An assessment of four different remote sensing based methods for deriving digital elevation models (DEMs) was conducted in a flood-prone watershed in North Carolina. New airborne LIDAR (light detecting and ranging) and IFSAR (interferometric synthetic aperture radar (SAR)) data were collected and corresponding DEMs created. These new sources were compared to two methods: Gestalt Photomapper (GPM) and contour-to-grid, used by the U.S. Geological Survey (USGS) for creating DEMs. Survey-grade points (1470) for five different land cover classes were used as reference points. One unique aspect of this study was the LIDAR and IFSAR data were collected during leaf-on conditions. Analyses of absolute elevation accuracy and terrain slope were conducted. The LIDAR- and contour-to-grid derived DEMs exhibited the highest overall absolute elevation accuracies. Elevation accuracy was found to vary with land cover categories. Elevation accuracy also decreased with increasing slopes--but only for the scrub/shrub land cover category. Appreciable terrain slope errors for the reference points were found with all methods.
    BibTeX:
    @article{hodgson03,
      author = {Hodgson, Michael E. and Jensen, John R. and Schmidt, Laura and Schill, Steve and Davis, Bruce},
      title = {An evaluation of LIDAR- and IFSAR-derived digital elevation models in leaf-on conditions with USGS Level 1 and Level 2 DEMs},
      journal = {Remote Sensing of Environment},
      year = {2003},
      volume = {84},
      number = {2},
      pages = {295--308}
    }
    
    Hofton, M.A. & Blair, J.B. LASER PULSE CORRELATION: A METHOD FOR DETECTING SUBTLE TOPOGRAPHIC CHANGE USING LIDAR RETURN WAVEFORMS 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 181-184 
    article  
    Abstract: We present a technique for using the recorded laser return pulse as a raw observation to detect centimeter-level vertical topographic change from large footprint airborne and spaceborne laser altimetry. We use the correlation of waveforms from coincident footprints as an indication of the similarity in structure of the waveforms from epoch to epoch, and assume that low correlation is an indicator of vertical structure or elevation change. Thus, using vertically and horizontally geolocated waveforms as raw observables (i.e., waveforms tied to a common reference ellipsoid), we assess whether epoch-to-epoch vertical ground motion results in a decrease in the correlation of coincident waveforms over time, and whether this can be used to quantify the magnitude of the deformation. Results of computer models and an example over an area of eroded beachfront are described.
    BibTeX:
    @article{hofton01a,
      author = {Michelle A. Hofton and J. Bryan Blair},
      title = {LASER PULSE CORRELATION: A METHOD FOR DETECTING SUBTLE TOPOGRAPHIC CHANGE USING LIDAR RETURN WAVEFORMS},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {181-184}
    }
    
    Hofton, M.A., Minster, J.B. & Blair, J.B. Decomposition of Laser Altimeter Waveforms 2000 IEEE Transactions on Geoscience and Remote Sensing
    Vol. 38, pp. 1989-1996 
    article  
    BibTeX:
    @article{hofton00,
      author = {Michelle A. Hofton and Jean Bernard Minster and J. Bryan Blair},
      title = {Decomposition of Laser Altimeter Waveforms},
      journal = {IEEE Transactions on Geoscience and Remote Sensing},
      year = {2000},
      volume = {38},
      pages = {1989-1996}
    }
    
    Holben, B., Kimes, D. & Fraser, R.S. Directional reflectance response in AVHRR red and near-IR bands for three cover types and varying atmospheric conditions 1986 Remote Sensing of Environment
    Vol. 19(3), pp. 213-236 
    article  
    Abstract: Surface directional red and near-infrared reflectances of bare soil, orchard grass, and fescue were extracted from a multitemporal data set to correspond to NOAA-7 Advanced Very High Resolution Radiometer (AVHRR) scanning and illumination geometry at 30? latitude. Radiances were simulated at satellite altitude and a ratio vegetation index calculated. The results show that off-nadir directional reflectance measured at the surface in the red and near-IR portions of the spectrum are approximately maintained with AVHRR viewing and illumination characteristics. The two-channel reflectance response is such that the ratio vegetation index is more constant with scan angle and atmospheric conditions than individual channels. It is shown that inclusion of atmospheric and surface reflectance data can greatly improve interpretation of AVHRR data, when knowledge of the range of atmospheric conditions and approximate directional reflectances of major cover types are known.
    BibTeX:
    @article{Holben1986,
      author = {Holben, Brent and Kimes, Dan and Fraser, Robert S.},
      title = {Directional reflectance response in AVHRR red and near-IR bands for three cover types and varying atmospheric conditions},
      journal = {Remote Sensing of Environment},
      year = {1986},
      volume = {19},
      number = {3},
      pages = {213--236}
    }
    
    Holmgren, J., Nilsson, M. & Olsson, H. Simulating the effects of lidar scanning angle

    for estimation of mean tree height and

    canopy closure

    2003 Canadian Journal of Remote Sensing
    Vol. 29, pp. 623-632 
    article  
    Abstract: A three-dimensional simulation model was used for modeling the scanning angle effect when measuring tree

    height and canopy closure in boreal forest with a laser scanner. The height distribution of the laser returns and the

    proportion of laser returns from the canopy were simulated using ray-tracing applied to a computer modeled forest. The

    proportion of canopy returns is commonly used as a measure of canopy closure, and height percentiles are commonly used

    to estimate mean tree height. Laser scanner data and field measurements of tree position, tree height, crown diameter, and

    crown base height were used for validating the simulation model. The correlation coefficient between simulated and real

    laser height percentiles was 0.96 and the simulation model systematically overestimated the laser height percentiles by

    2.25 m. Simulations show that laser height percentiles and proportion of canopy returns changed more with an increased

    scanning angle for long crown species like spruce, compared with short crown species like pine. The change of height

    percentiles due to scanning angle was greater in forests with low stem numbers than with high stem numbers. The

    proportion of canopy returns was more affected by scanning angle than were the laser height percentiles.

    BibTeX:
    @article{holmgren03,
      author = {J. Holmgren and M. Nilsson and H. Olsson},
      title = {Simulating the effects of lidar scanning angle 

    for estimation of mean tree height and

    canopy closure}, journal = {Canadian Journal of Remote Sensing}, year = {2003}, volume = {29}, pages = {623-632} }

    Holmgren, J., Persson, ?.. & Söderman, U. Species identification of individual trees by combining high resolution LiDAR data with multi-spectral images 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1537-1552 
    article  
    Abstract: The objectives of this study were to identify useful predictive factors for tree species identification of individual trees and to compare classifications based on a combination of LiDAR data and multi-spectral images with classification by the use of each individual data source. Crown segments derived from LiDAR data were mapped to multi-spectral images for extraction of spectral data within individual tree crowns. Several features, related to height distribution of laser returns in the canopy, canopy shape, proportion of different types of laser returns, and intensity of laser returns, were derived from LiDAR data. Data from a test site in southern Sweden were used (lat. 58??30?????N, long. 13??40?????E). The forest consisted of Norway spruce (Picea abies), Scots pine (Pinus sylvestris), and deciduous trees. Classification into these three tree species groups was validated for 1711 trees that had been detected in LiDAR data within 14 field plots (sizes of 20??50??m2 or 80??80??m2). The LiDAR data were acquired by the TopEye MkII system (50 LiDAR measurements per??m2) and the multi-spectral images were taken by the Zeiss/Intergraph Digital Mapping Camera. The overall classification accuracy was 96% when both data sources were combined.
    BibTeX:
    @article{Holmgren2008,
      author = {Holmgren, J. and Persson, ?. and Söderman, U.},
      title = {Species identification of individual trees by combining high resolution LiDAR data with multi-spectral images},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1537-1552}
    }
    
    Holmgren, J. & Persson, A. Identifying species of individual trees using airborne laser scanner 2004 Remote Sensing of Environment
    Vol. 90, pp. 415-423 
    article  
    Abstract: Individual trees can be detected using high-density airborne laser scanner data. Also, variables characterizing the detected trees such as tree height, crown area, and crown base height can be measured. The Scandinavian boreal forest mainly consists of Norway spruce (Picea abies L. Karst.), Scots pine (Pinus sylvestris L.), and deciduous trees. It is possible to separate coniferous from deciduous trees using nearinfrared images, but pine and spruce give similar spectral signals. Airborne laser scanning, measuring structure and shape of tree crowns could be used for discriminating between spruce and pine. The aim of this study was to test classification of Scots pine versus Norway spruce on an individual tree level using features extracted from airborne laser scanning data. Field measurements were used for training and validation of the classification. The position of all trees on 12 rectangular plots (50 20 m 2) were measured in field and tree species was recorded. The dominating species (>80%) was Norway spruce for six of the plots and Scots pine for six plots. The field-measured trees were automatically linked to the laser-measured trees. The laser-detected trees on each plot were classified into species classes using all laserdetected trees on the other plots as training data. The portion correctly classified trees on all plots was 95%. Crown base height estimations of individual trees were also evaluated (r = 0.84). The classification results in this study demonstrate the ability to discriminate between pine and spruce using laser data. This method could be applied in an operational context. In the first step, a segmentation of individual tree crowns is performed using laser data. In the second step, tree species classification is performed based on the segments. Methods could be developed in the future that combine laser data with digital near-infrared photographs for classification with the three classes: Norway spruce, Scots pine, and deciduous trees.
    BibTeX:
    @article{holmgren04,
      author = {Johan Holmgren and Asa Persson},
      title = {Identifying species of individual trees using airborne laser scanner},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {90},
      pages = {415-423}
    }
    
    Hopkinson, C. The influence of lidar acquisition settings on canopy penetration and laser pulse return characteristics. 2006 Proceedings of the joint IGARSS and CSRS meeting, Denver, Colorado.  inproceedings  
    BibTeX:
    @inproceedings{hopkinson06_igarss,
      author = {Hopkinson, C.},
      title = {The influence of lidar acquisition settings on canopy penetration and laser pulse return characteristics.},
      booktitle = {Proceedings of the joint IGARSS and CSRS meeting, Denver, Colorado.},
      publisher = {Published on CDROM by the Geosciences and Remote Sensing Society (unpaginated).},
      year = {2006}
    }
    
    Hopkinson, C. & Chasmer, L. Testing LiDAR models of fractional cover across multiple forest ecozones 2009 Remote Sensing of Environment
    Vol. 113(1), pp. 275 - 288 
    article DOI  
    Abstract: Four LiDAR-based models of canopy fractional cover (FCLiDAR) have been tested against hemispherical photography fractional cover measurements (FCHP) and compared across five ecozones, eight forest species and multiple LiDAR survey configurations. The four models compared are based on: i) a canopy-to-total first returns ratio (FCLiDAR(FR)) method; ii) a canopy-to-total returns ratio (FCLiDAR(RR)); iii) an intensity return ratio (FCLiDAR(IR)); and iv) a Beer's Law modified (two-way transmission loss) intensity return ratio (FCLiDAR(BL)). It is found that for the entire dataset, the FCLiDAR(RR) model demonstrates the lowest overall predictive capability of overhead FC (annulus rings 1-4) (r2 = 0.70), with a slight improvement for the FCLiDAR(FR) model (r2 = 0.74). The intensity-based FCLiDAR(IR) model displays the best results (r2 = 0.78). However, the FCLiDAR(BL) model is considered generally more useful (r2 = 0.75) because the associated line of best fit passes through the origin, has a slope near unity and produces a mean estimate of FCHP within 5 Therefore, FCLiDAR(BL) requires the least calibration across a broad range of forest cover types. The FCLiDAR(FR) and FCLiDAR(RR) models, on the other hand, were found to be sensitive to variations in both canopy height and sensor pulse repetition frequency (or pulse power); i.e. changing the repetition frequency led to a systematic shift of up to 11% in the mean FCLiDAR(RR) estimates while it had no effect on the intensity-based FCLiDAR(IR) or FCLiDAR(BL) models. While the intensity-based models were generally more robust, all four models displayed at least some sensitivity to variations in canopy structural class, suggesting that some calibration of FCLiDAR might be necessary regardless of the model used. Short (< 2 m tall) or open canopy forest plots posed the greatest challenge to accurate FC estimation regardless of the model used.
    BibTeX:
    @article{Hopkinson2009,
      author = {Chris Hopkinson and Laura Chasmer},
      title = {Testing LiDAR models of fractional cover across multiple forest ecozones},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {1},
      pages = {275 - 288},
      doi = {DOI: 10.1016/j.rse.2008.09.012}
    }
    
    Hopkinson, C., Chasmer, L. & Hall, R. The uncertainty in conifer plantation growth prediction from multi-temporal lidar datasets 2008 Remote Sensing of Environment
    Vol. 112(3), pp. 1168 - 1180 
    article DOI  
    Abstract: An evaluation of the use of airborne lidar for multi-temporal forest height growth assessment in a temperate mature red pine (Pinus resinosa Ait.) plantation over a five-year period is presented. The objective was to evaluate the level of uncertainty in lidar-based growth estimates through time so that the optimal repeat interval necessary for statistically meaningful growth measurements could be evaluated. Four airborne lidar datasets displaying similar survey configuration parameters were collected between 2000 and 2005. Coincident with the 2002 and 2005 acquisitions, field mensuration for 126 trees within 19 plots was carried out. Field measurements of stem height were compared to both coincident plot-level laser pulse return (LPR) height percentile metrics and stand level raster canopy height models (CHM). The average plot-level field heights were found to be 23.8 m (standard deviation ([sigma]) = 0.4 m) for 2002 and 25.0 m ([sigma] = 0.6 m) for 2005, with an approximate annual growth rate of 0.4 m/yr ([sigma] = 0.5 m). The standard deviation uncertainty for field height growth estimates over the three year period was 41% at the plot-level (n = 19) and 92% at the individual tree level (n = 126). Of the lidar height percentile metrics tested, the 90th (L90), 95th (L95) and maximum (Lmax) LPR distribution heights demonstrated the highest overall correlations with field-measured tree height. While all lidar-based methods, including raster CHM comparison, tended to underestimate the field estimate of growth, Lmax provided the most robust overall direct estimate (0.32 m/yr, [sigma] = 0.37 m). A single factor analysis of variance demonstrated that there was no statistically significant difference between all plot-level field and Lmax mean growth rate estimates (P = 0.38) and, further, that there was no difference in Lmax growth rate estimates across the examined time intervals (P = 0.59). A power function relationship between time interval and the standard deviation of error in growth estimate demonstrated that over a one-year period, the growth uncertainty was in the range of 0.3 m (~ 100% of total growth) reducing to less than 0.1 m (~ 6% of total growth) after 5 years. Assuming a 10% uncertainty is acceptable for operational or research-based conifer plantation growth estimates, this can be achieved at a three-year time interval.
    BibTeX:
    @article{Hopkinson20081168,
      author = {Chris Hopkinson and Laura Chasmer and R.J. Hall},
      title = {The uncertainty in conifer plantation growth prediction from multi-temporal lidar datasets},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {3},
      pages = {1168 - 1180},
      doi = {DOI: 10.1016/j.rse.2007.07.020}
    }
    
    Hopkinson, C., Chasmer, L., Lim, K., Treitz, P. & Creed, I. Towards a universal lidar canopy height indicator 2006 Canadian Journal of Remote Sensing
    Vol. 32(2), pp. 139-152 
    article  
    Abstract: A light detection and ranging (lidar) canopy height study was conducted with 13 datasets collected using four

    different models of airborne laser terrain mapper (ALTM) sensors over 13 widely variable vegetation types ranging in

    average height from <1 m to 24 m at five sites across Canada between 2000 and 2005. The study demonstrates that the

    vertical standard deviation of all topographically detrended first and last laser pulse returns (LSD) is a robust estimator of

    canopy height (Ht) for a wide variety of vegetation types and heights and lidar survey configurations. After regressing Ht

    against LSD for 77 plots and transects, it was found that Ht could be predicted as a simple multiplication (M) of LSD (M =

    2.5, coefficient of determination (r2) = 0.95, root mean square error (RMSE) = 1.8 m, tail probability (p) < 0.01). For forest

    plots only, LSD was found to better predict average tree height (r2 = 0.80, RMSE = 2.1 m, p < 0.01) than Lorey?s height (r2 =

    0.59, RMSE = 3.0 m, p < 0.01). A test of the LSD canopy height model was performed using stand heights (HtFRI) from an

    independent forest resource inventory (FRI) for four vegetation classes. Results from the raw FRI and modelled stand height

    comparison displayed close to a 1:1 relationship (HtFRI = 0.97HtLSD, r2 = 0.73, RMSE = 4.7 m, p < 0.01, n = 38). All plot

    and transect canopy heights were also compared with the localized maxima of laser pulse returns (Lmax). For individual

    surveys over homogeneous vegetation types, Lmax generally provides a better canopy height indicator. Across all surveys and

    site types, however, LSD was almost always shown to have a more consistent relationship with actual canopy height. The

    only observed exception was in the case of forest plot level Lorey?s mean tree height. The advantages of using a multiplier

    of LSD to estimate canopy height are its apparent insensitivity to survey configuration and its demonstrated applicability to a

    range of vegetation types and height classes.

    BibTeX:
    @article{hopkinson06,
      author = {Chris Hopkinson and Laura Chasmer and Kevin Lim and Paul Treitz and Irena Creed},
      title = {Towards a universal lidar canopy height indicator},
      journal = {Canadian Journal of Remote Sensing},
      year = {2006},
      volume = {32},
      number = {2},
      pages = {139-152}
    }
    
    Huang, D., Knyazikhin, Y., Dickinson, R.E., Rautiainen, M., Stenberg, P., Disney, M., Lewis, P., Cescatti, A., Tian, Y., Verhoef, W., Martonchik, J.V. & Myneni, R.B. Canopy spectral invariants for remote sensing and model applications 2007 Remote Sensing of Environment
    Vol. 106(1), pp. 106-122 
    article  
    Abstract: The concept of canopy spectral invariants expresses the observation that simple algebraic combinations of leaf and canopy spectral transmittance and reflectance become wavelength independent and determine a small set of canopy structure specific variables. This set includes the canopy interceptance, the recollision and the escape probabilities. These variables specify an accurate relationship between the spectral response of a vegetation canopy to the incident solar radiation at the leaf and the canopy scale and allow for a simple and accurate parameterization for the partitioning of the incoming radiation into canopy transmission, reflection and absorption at any wavelength in the solar spectrum. This paper presents a solid theoretical basis for spectral invariant relationships reported in literature with an emphasis on their accuracies in describing the shortwave radiative properties of the three-dimensional vegetation canopies. The analysis of data on leaf and canopy spectral transmittance and reflectance collected during the international field campaign in Flakaliden, Sweden, June 25-July 4, 2002 supports the proposed theory. The results presented here are essential to both modeling and remote sensing communities because they allow the separation of the structural and radiometric components of the measured/modeled signal. The canopy spectral invariants offer a simple and accurate parameterization for the shortwave radiation block in many global models of climate, hydrology, biogeochemistry, and ecology. In remote sensing applications, the information content of hyperspectral data can be fully exploited if the wavelength-independent variables can be retrieved, for they can be more directly related to structural characteristics of the three-dimensional vegetation canopy.
    BibTeX:
    @article{Huang2007,
      author = {Huang, Dong and Knyazikhin, Yuri and Dickinson, Robert E. and Rautiainen, Miina and Stenberg, Pauline and Disney, Mathias and Lewis, Philip and Cescatti, Alessandro and Tian, Yuhong and Verhoef, Wout and Martonchik, John V. and Myneni, Ranga B.},
      title = {Canopy spectral invariants for remote sensing and model applications},
      journal = {Remote Sensing of Environment},
      year = {2007},
      volume = {106},
      number = {1},
      pages = {106--122}
    }
    
    Huber, P. Robust Statistics 1981   book  
    BibTeX:
    @book{huber,
      author = {P.J. Huber},
      title = {Robust Statistics},
      publisher = {Wiley, New York},
      year = {1981}
    }
    
    Hudak, A.T., Lefsky, M.A., Cohen, W.B. & Berterretche, M. Integration of lidar and Landsat ETM+ data for estimating and mapping forest canopy height 2002 Remote Sens. Environ.
    Vol. 82(2-3), pp. 397-416 
    article  
    Abstract: Light detection and ranging (lidar) data provide accurate measurements of forest canopy structure in the vertical plane; however, current lidar sensors have limited coverage in the horizontal plane. Landsat data provide extensive coverage of generalized forest structural classes in the horizontal plane but are relatively insensitive to variation in forest canopy height. It would, therefore, be desirable to integrate lidar and Landsat data to improve the measurement, mapping, and monitoring of forest structural attributes. We tested five aspatial and spatial methods for predicting canopy height, using an airborne lidar system (Aeroscan) and Landsat Enhanced Thematic Mapper (ETM+) data: regression, kriging, cokriging, and kriging and cokriging of regression residuals. Our 200-km2 study area in western Oregon encompassed Oregon State University's McDonaldØDunn Research Forest, which is broadly representative of the age and structural classes common in the region. We sampled a spatially continuous lidar coverage in eight systematic patterns to determine which lidar sampling strategy would optimize lidarØLandsat integration in western Oregon forests: transects sampled at 2000, 1000, 500, and 250 m frequencies, and points sampled at these same spatial frequencies. The aspatial regression model results, regardless of sampling strategy, preserved actual vegetation pattern, but underestimated taller canopies and overestimated shorter canopies. The spatial models, kriging and cokriging, produced less biased results than regression but poorly reproduced vegetation pattern, especially at the sparser (2000 and 1000 m) sampling frequencies. The spatial model predictions were more accurate than the regression model predictions at locations <200 m from sample locations. Cokriging, using the ETM+ panchromatic band as the secondary variable, proved slightly more accurate than kriging. The integrated models that kriged or cokriged regression residuals were preferable to either the aspatial or spatial models alone because they preserved the vegetation pattern like regression yet improved estimation accuracies above those predicted from the regression models alone. The 250-m point sampling strategy proved most optimal because it oversampled the landscape relative to the geostatistical range of actual spatial variation, as indicated by the sample semivariograms, while making the sample data volume more manageable. We concluded that an integrated modeling strategy is most suitable for estimating and mapping canopy height at locations unsampled by lidar, and that a 250-m discrete point sampling strategy most efficiently samples an intensively managed forested landscape in western Oregon.
    BibTeX:
    @article{hudak02,
      author = {Andrew T. Hudak and Michael A. Lefsky and Warren B. Cohen and Mercedes Berterretche},
      title = {Integration of lidar and Landsat ETM+ data for estimating and mapping forest canopy height},
      journal = {Remote Sens. Environ.},
      year = {2002},
      volume = {82},
      number = {2-3},
      pages = {397-416}
    }
    
    Hudak, A.T., Lefsky, M.A., Cohen, W.B. & Berterretche, M. INTEGRATION OF LIDAR AND LANDSAT ETM+ DATA 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 95-103 
    article  
    Abstract: Lidar data provide accurate measurements of forest canopy structure in the vertical plane however current lidar sensors have limited coverage in the horizontal plane. Landsat data provide extensive coverage of generalized forest structural classes in the horizontal plane but are relatively insensitive to variation in forest canopy height. It would therefore be desirable to integrate lidar and Landsat data to improve the measurement, mapping, and monitoring of forest structural attributes. We tested five aspatial and spatial methods for predicting canopy height, as measured by an airborne lidar system (Aeroscan), from Landsat ETM+ data: regression, kriging, cokriging, and kriging and cokriging of regression residuals. Our 200 km2 study area in western Oregon encompassed Oregon State University s McDonald-Dunn Research Forest, which is broadly representative of the age and structural classes common in the region. We sampled our continuous lidar coverage in eight systematic patterns to determine which lidar sampling strategy would optimize lidar-Landsat integration: transects sampled at 2000, 1000, 500 and 250 m frequencies, and points sampled at these same spatial frequencies. The aspatial regression model results, regardless of sampling strategy, preserved actual vegetation pattern, but underestimated taller canopies and overestimated shorter canopies. The spatial models, kriging and cokriging, produced less biased results than regression but poorly reproduced vegetation pattern. The integrated models that kriged or cokriged regression residuals were preferable to either the aspatial or spatial models alone, because they preserved the vegetation pattern like regression yet improved estimation accuracies above those predicted from the regression models alone. We concluded that in our study landscape, an integrated modeling strategy is most suitable for estimating and mapping canopy height at locations unsampled by lidar, and that a 250 m point sampling strategy would be more useful for lidar-Landsat ETM+ integration than sparser transect sampling strategies planned for satellite missions.
    BibTeX:
    @article{hudak01,
      author = {Andrew T. Hudak and Michael A. Lefsky and Warren B. Cohen and Mercedes Berterretche},
      title = {INTEGRATION OF LIDAR AND LANDSAT ETM+ DATA},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {95-103}
    }
    
    Huemmrich, K.F. The GeoSail model: a simple addition to the SAIL model to describe discontinuous canopy reflectance. 2001 Remote Sensing of Environment
    Vol. 75 (3), pp. 423-431 
    article  
    BibTeX:
    @article{huemmrich01,
      author = {Huemmrich, K. F.},
      title = {The GeoSail model: a simple addition to the SAIL model to describe discontinuous canopy reflectance.},
      journal = {Remote Sensing of Environment},
      year = {2001},
      volume = {75 (3)},
      pages = {423-431}
    }
    
    Huising, E.J. & Gomes Pereira, L.M. Errors and accuracy estimates of laser data acquired by various laser scanning systems for topographic applications 1998 ISPRS Journal of Photogrammetry and Remote Sensing
    Vol. 53(5), pp. 245-261 
    article  
    Abstract: The Survey Department of Rijkswaterstaat in The Netherlands makes extensive use of laser scanning for topographic measurements. An inventory of sources of errors indicates that errors may vary from 5 to 200 cm. The experience shows that errors related to the laser instrument, GPS and INS may frequently occur, resulting in local distortions, and planimetric and height shifts. Moreover, the results indicate that for flat terrain, having corrected for gross errors, an offset of less than 10 cm can often be obtained and standard deviations are generally well within 15 cm. For hilly and flat terrain densely covered by vegetation, accuracy estimates do not generally fulfil those required by Rijkswaterstaat. However, the use of an adequate strategy for data collection and processing will, to a great extent, improve the accuracy and fidelity of the results. Thus, research should be devoted to the design of appropriate strategies for data collection and processing.
    BibTeX:
    @article{Huising1998,
      author = {Huising, E. J. and Gomes Pereira, L. M.},
      title = {Errors and accuracy estimates of laser data acquired by various laser scanning systems for topographic applications},
      journal = {ISPRS Journal of Photogrammetry and Remote Sensing},
      year = {1998},
      volume = {53},
      number = {5},
      pages = {245--261}
    }
    
    Humphrey, J., Hawes, C., Peace, A., Ferris-Kaan, R. & Jukes, M. Relationships between insect diversity and habitat characteristics in plantation forests. 1999 Forest Ecology and Management
    Vol. 113, pp. 11-21 
    article  
    BibTeX:
    @article{humphrey99,
      author = {Humphrey, J.W and Hawes, C. and Peace, A.J. and Ferris-Kaan, R. and Jukes, M.R.},
      title = {Relationships between insect diversity and habitat characteristics in plantation forests.},
      journal = {Forest Ecology and Management},
      year = {1999},
      volume = {113},
      pages = {11-21}
    }
    
    Hurtt, G., Xiao, X., Keller, M., Palace, M., Asner, G.P., Braswell, R., Brond?zio, E.S., Cardoso, M., Carvalho, C.J.R., Fearon, M.G., Guild, L., Hagen, S., Hetrick, S., Moore, B., Nobre, C., Read, J.M., S?, T., Schloss, A., Vourlitis, G. & Wickel, A.J. IKONOS imagery for the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) 2003 Remote Sensing of Environment
    Vol. 88(1-2)IKONOS Fine Spatial Resolution Land Observation, pp. 111-127 
    article  
    Abstract: The LBA-ECO program is one of several international research components under the Brazilian-led Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA). The field-oriented research activities of this study are organized along transects and include a set of primary field sites, where the major objective is to study land-use change and ecosystem dynamics, and a smaller set of 15 operational eddy flux tower sites, where the major objective is to quantify net exchange of CO2 with the atmosphere. To supplement these studies and help to address issues of fine-scale spatial heterogeneity and scaling, high-resolution satellite imagery (IKONOS, 1-4 m) have been acquired over some of these study sites. This paper begins with a description of the acquisition strategy and IKONOS holdings for LBA. This section is followed with a review of some of the most promising new applications of these data in LBA.
    BibTeX:
    @article{Hurtt2003,
      author = {Hurtt, George and Xiao, Xiangming and Keller, Michael and Palace, Michael and Asner, Gregory P. and Braswell, Rob and Brond?zio, Eduardo S. and Cardoso, Manoel and Carvalho, Claudio J. R. and Fearon, Matthew G. and Guild, Liane and Hagen, Steve and Hetrick, Scott and Moore, Berrien and Nobre, Carlos and Read, Jane M. and S?, Tatiana and Schloss, Annette and Vourlitis, George and Wickel, Albertus J.},
      title = {IKONOS imagery for the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA)},
      booktitle = {IKONOS Fine Spatial Resolution Land Observation},
      journal = {Remote Sensing of Environment},
      year = {2003},
      volume = {88},
      number = {1-2},
      pages = {111--127}
    }
    
    Hyde, P., Dubayah, R., Peterson, B., Blair, J., Hofton, M., Hunsaker, C., Knox, R. & Walker, W. Mapping forest structure for wildlife habitat analysis using waveform lidar: Validation of montane ecosystems 2005 Remote Sensing of Environment
    Vol. 96(3-4), pp. 427-437 
    article  
    Abstract: Consistent and accurate measurements of forest structure at the landscape scale are required by forest ecologists and managers for a variety of applications. Lidar remote sensing has proven to be a valuable tool for measuring these attributes in many ecosystems, including tropical, boreal, and mid-latitude forests. However, there have been few studies in montane forests. Here, we examine the ability of a large footprint lidar system to retrieve forest structural attributes in the highly variable terrain and canopy conditions of the Sierra Nevada mountains in California. Specifically, we examined the impact of slope, elevation, aspect, canopy cover, crown shape, and the spatial arrangement of canopy-forming trees on the accuracy of a large footprint lidar system in retrieving canopy height, canopy cover, and biomass. We found good agreement between field and lidar measurements of height, cover, and biomass at the footprint level, and canopy height and biomass at the stand level. Differences between field and lidar measurements are mainly attributable to the spatial configuration of canopy elements and are less sensitive to topography, crown shape, or canopy cover. The accuracy of canopy cover retrieval was highly sensitive to estimates of ground cover reflectivity and to ground sampling density. The accuracy of biomass retrieval was also good, and comparable to previous efforts in other biomes.
    BibTeX:
    @article{Hyde2005,
      author = {Hyde, P. and Dubayah, R. and Peterson, B. and Blair, J.B. and Hofton, M. and Hunsaker, C. and Knox, R. and Walker, W.},
      title = {Mapping forest structure for wildlife habitat analysis using waveform lidar: Validation of montane ecosystems},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {96},
      number = {3-4},
      pages = {427--437}
    }
    
    Hyde, P., Dubayah, R., Peterson, B., Blair, J., Hofton, M., Hunsaker, C., Knox, R. & Walker, W. Mapping forest structure for wildlife habitat analysis using waveform lidar: Validation of montane ecosystems 2005 Remote Sensing of Environment
    Vol. 96(3-4), pp. 427-437 
    article  
    Abstract: Consistent and accurate measurements of forest structure at the landscape scale are required by forest ecologists and managers for a variety of applications. Lidar remote sensing has proven to be a valuable tool for measuring these attributes in many ecosystems, including tropical, boreal, and mid-latitude forests. However, there have been few studies in montane forests. Here, we examine the ability of a large footprint lidar system to retrieve forest structural attributes in the highly variable terrain and canopy conditions of the Sierra Nevada mountains in California. Specifically, we examined the impact of slope, elevation, aspect, canopy cover, crown shape, and the spatial arrangement of canopy-forming trees on the accuracy of a large footprint lidar system in retrieving canopy height, canopy cover, and biomass. We found good agreement between field and lidar measurements of height, cover, and biomass at the footprint level, and canopy height and biomass at the stand level. Differences between field and lidar measurements are mainly attributable to the spatial configuration of canopy elements and are less sensitive to topography, crown shape, or canopy cover. The accuracy of canopy cover retrieval was highly sensitive to estimates of ground cover reflectivity and to ground sampling density. The accuracy of biomass retrieval was also good, and comparable to previous efforts in other biomes.
    BibTeX:
    @article{Hyde2005a,
      author = {Hyde, P. and Dubayah, R. and Peterson, B. and Blair, J.B. and Hofton, M. and Hunsaker, C. and Knox, R. and Walker, W.},
      title = {Mapping forest structure for wildlife habitat analysis using waveform lidar: Validation of montane ecosystems},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {96},
      number = {3-4},
      pages = {427--437}
    }
    
    Hyde, P., Dubayah, R., Walker, W., Blair, J.B., Hofton, M. & Hunsaker, C. Mapping forest structure for wildlife habitat analysis using multi-sensor (LiDAR, SAR/InSAR, ETM+, Quickbird) synergy 2006 Remote Sensing of Environment
    Vol. 102(1-2), pp. 63-73 
    article  
    Abstract: Measurements of forest structure are important for wildlife habitat management. An optimal strategy for mapping forest structure would include detailed measurements of the vertical dimension, which are traditionally provided by field sampling, together with the broad spatial coverage afforded by remote sensing. While no single sensor is capable of delivering this at the present time, it should be possible to combine information from multiple sensors to achieve a reasonable approximation. In this study, we compare estimates of forest structural metrics derived from remote sensing to measurements obtained in the field (large tree maximum canopy height, mean canopy height, standard deviation canopy height, and biomass). We then statistically combine structural information from LiDAR, RaDAR, and passive optical sensors in an attempt to improve accuracy of our estimates. The results of this study indicate that LiDAR is the best single sensor for estimating canopy height and biomass. The addition of ETM+ metrics significantly improved LiDAR estimates of large tree structure, while Quickbird and InSAR/SAR improved estimates either marginally or not at all. The combination of all sensors was more accurate than LiDAR alone, but only marginally better than the combination of LiDAR and ETM+. Structure metrics from LiDAR and RaDAR are essentially redundant, as are ETM+ and Quickbird.
    BibTeX:
    @article{Hyde2006,
      author = {Hyde, Peter and Dubayah, Ralph and Walker, Wayne and Blair, J. Bryan and Hofton, Michelle and Hunsaker, Carolyn},
      title = {Mapping forest structure for wildlife habitat analysis using multi-sensor (LiDAR, SAR/InSAR, ETM+, Quickbird) synergy},
      journal = {Remote Sensing of Environment},
      year = {2006},
      volume = {102},
      number = {1-2},
      pages = {63--73}
    }
    
    Hyde, P., Dubayah, R., Walker, W., Blair, J.B., Hofton, M. & Hunsaker, C. Mapping forest structure for wildlife habitat analysis using multi-sensor (LiDAR, SAR/InSAR, ETM+, Quickbird) synergy 2006 Remote Sensing of Environment
    Vol. 102(1-2), pp. 63-73 
    article  
    Abstract: Measurements of forest structure are important for wildlife habitat management. An optimal strategy for mapping forest structure would include detailed measurements of the vertical dimension, which are traditionally provided by field sampling, together with the broad spatial coverage afforded by remote sensing. While no single sensor is capable of delivering this at the present time, it should be possible to combine information from multiple sensors to achieve a reasonable approximation. In this study, we compare estimates of forest structural metrics derived from remote sensing to measurements obtained in the field (large tree maximum canopy height, mean canopy height, standard deviation canopy height, and biomass). We then statistically combine structural information from LiDAR, RaDAR, and passive optical sensors in an attempt to improve accuracy of our estimates. The results of this study indicate that LiDAR is the best single sensor for estimating canopy height and biomass. The addition of ETM+ metrics significantly improved LiDAR estimates of large tree structure, while Quickbird and InSAR/SAR improved estimates either marginally or not at all. The combination of all sensors was more accurate than LiDAR alone, but only marginally better than the combination of LiDAR and ETM+. Structure metrics from LiDAR and RaDAR are essentially redundant, as are ETM+ and Quickbird.
    BibTeX:
    @article{Hyde2006a,
      author = {Hyde, Peter and Dubayah, Ralph and Walker, Wayne and Blair, J. Bryan and Hofton, Michelle and Hunsaker, Carolyn},
      title = {Mapping forest structure for wildlife habitat analysis using multi-sensor (LiDAR, SAR/InSAR, ETM+, Quickbird) synergy},
      journal = {Remote Sensing of Environment},
      year = {2006},
      volume = {102},
      number = {1-2},
      pages = {63--73}
    }
    
    Hyde, P., Nelson, R., Kimes, D. & Levine, E. Exploring LiDAR-RaDAR synergy--predicting aboveground biomass in a southwestern ponderosa pine forest using LiDAR, SAR and InSAR 2007 Remote Sensing of Environment
    Vol. 106(1), pp. 28-38 
    article  
    Abstract: Scanning Light Detecting and Ranging (LiDAR), Synthetic Aperture Radar (SAR) and Interferometric SAR (InSAR) were analyzed to determine (1) which of the three sensor systems most accurately predicted forest biomass, and (2) if LiDAR and SAR/InSAR data sets, jointly considered, produced more accurate, precise results relative to those same data sets considered separately. LiDAR ranging measurements, VHF-SAR cross-sectional returns, and X- and P-band cross-sectional returns and interferometric ranges were regressed with ground-estimated (from dbh) forest biomass in ponderosa pine forests in the southwestern United States. All models were cross-validated. Results indicated that the average canopy height measured by the scanning LiDAR produced the best predictive equation. The simple linear LiDAR equation explained 83% of the biomass variability (n = 52 plots) with a cross-validated root mean square error of 26.0 t/ha. Additional LiDAR metrics were not significant to the model. The GeoSAR P-band ([lambda] = 86 cm) cross-sectional return and the GeoSAR/InSAR canopy height (X-P) captured 30% of the forest biomass variation with an average predictive error of 52.5 t/ha. A second RaDAR-FOPEN collected VHF ([lambda] ~ 7.8 m) and cross-polarized P-band ([lambda] = 88 cm) cross-sectional returns, none of which proved useful for forest biomass estimation (cross-validated R2 = 0.09, RMSE = 63.7 t/ha). Joint consideration of LiDAR and RaDAR measurements produced a statistically significant, albeit small improvement in biomass estimation precision. The cross-validated R2 increased from 83% to 84% and the prediction error decreased from 26.0 t/ha to 24.9 t/ha when the GeoSAR X-P interferometric height is considered along with the average LiDAR canopy height. Inclusion of a third LiDAR metric, the 60th decile height, further increased the R2 to 85% and decreased the RMSE to 24.1 t/ha. On this 11 km2 ponderosa pine study area, LiDAR data proved most useful for predicting forest biomass. RaDAR ranging measurements did not improve the LiDAR estimates.
    BibTeX:
    @article{Hyde2007,
      author = {Hyde, Peter and Nelson, Ross and Kimes, Dan and Levine, Elissa},
      title = {Exploring LiDAR-RaDAR synergy--predicting aboveground biomass in a southwestern ponderosa pine forest using LiDAR, SAR and InSAR},
      journal = {Remote Sensing of Environment},
      year = {2007},
      volume = {106},
      number = {1},
      pages = {28--38}
    }
    
    Hyypp?, J., Hyypp?, H., Leckie, D., Gougeon, F., Yu, X. & Maltamo, M. Review of methods of small-footprint airborne laser scanning for extracting forest inventory data in boreal forests 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1339-1366 
    article  
    Abstract: Experiences from Nordic countries and Canada have shown that the retrieval of the stem volume and mean tree height of a tree or at stand level from laser scanner data performs as well as, or better than, photogrammetric methods, and better than other remote sensing methods. This paper reviews the methods of small-footprint airborne laser scanning for extracting forest inventory data, mainly in the boreal forest zone. The methods are divided into the following categories: extraction of terrain and canopy height model; feature extraction approaches (canopy height distribution and individual-tree-based techniques, techniques based on the synergetic use of aerial images and lidar, and other new approaches); tree species classification and forest growth using laser scanner; and the use of intensity and waveform data in forest information extraction. Despite this, the focus is on methods, some review of quality obtained, especially in the boreal forest area, is included. Several recommendations for future research are given to foster the methodology development.
    BibTeX:
    @article{hyyppae08,
      author = {Hyypp?, J. and Hyypp?, H. and Leckie, D. and Gougeon, F. and Yu, X. and Maltamo, M.},
      title = {Review of methods of small-footprint airborne laser scanning for extracting forest inventory data in boreal forests},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1339--1366}
    }
    
    Hyyppä, J. & Hallikainen, M. Applicability of Airborne Profiling Radar to Forest Inventory 1996 Remote Sens. Environ.
    Vol. 57, pp. 39-57 
    article  
    Abstract: In this work the applicability of airborne profiling radar to forest inventory was studied in detail. The radar stand profiles were collected by using a helicopter-borne ranging scatterometer, HUTSCAT (Helsinki University of Technology SCATterometer), which can probe the forest canopy from the top to the bottom due to its ranging capability. Several radar variables were analyzed from stand profiles, and compared with field-measured characteristics of 20 m by 20 m sample plots, by applying multivariate data analysis methods. It was shown that mean and dominant heights, height of the crown base line, and stem volume per hectare can be obtained with good accuracy. Furthermore, the ranging radar can measure mean and dominant tree heights more accurately than is usually obtained with conventional field measurements. As possible direct application, it is proposed that radar measurements would be employed with helicopter-borne ocular inventories in order to improve the estimation accuracy and to speed up the measurements.
    BibTeX:
    @article{hyyppa96,
      author = {Juha Hyyppä and Martti Hallikainen},
      title = {Applicability of Airborne Profiling Radar to Forest Inventory},
      journal = {Remote Sens. Environ.},
      year = {1996},
      volume = {57},
      pages = {39-57}
    }
    
    Hyyppä, J., Hyyppä, H., Inkinen, M., Engdahl, M., Linko, S. & Zhu, Y.-H. Accuracy comparison of various remote sensing data sources in the retrieval of forest stand attributes 1999 Forest Ecology and Management
    Vol. 128, pp. 109-120 
    article  
    Abstract: Recent advances in developing new airborne instruments and space-borne missions and in SAR technology, especially in interferometry and coherence estimation, have roused questions: can such new SAR data be utilized in operational forest inventory? What is the accuracy of different satellite data for forest inventory? This paper verifies the explanatory power and information contents of several remote sensing data sources on the retrieval of stem volume, basal area, and mean height, utilizing the following data: Landsat TM, Spot PAN and XS, ERS-1/2 PRI and SLC (coherence estimation), airborne data from imaging spectrometer AISA, radar-derived forest canopy profiles (obtained with HUTSCAT), and aerial photographs. Ground truth data included three different sets ranging from conventional forest inventory data to intensive field checking where one man-day was spent for assessing one stand. Multivariate and neural network methods were applied in data analysis. The results suggested that (1) radar-derived stand profiles obtained with 100 m spacing was the most accurate data source in this comparison and was of equivalent accuracy with conventional forest inventory for mean height and stem volume estimation, (2) aerial photographs (scale 1 : 20,000) gave comparable results with the imaging spectrometer AISA, (3) the satellite images used for the estimation in the decreasing explanation power were Spot XS, Spot PAN, Landsat TM, ERS SAR coherence, JERS SAR intensity images (PRI), and ERS SAR intensity images (PRI). It appears that optical images still include more information for forest inventory than radar images, (4) from all satellite radar methods, the coherence technique seemed to be superior to other methods.
    BibTeX:
    @article{hyyppae99b,
      author = {Juha Hyyppä and Hannu Hyyppä and Mikko Inkinen and Marcus Engdahl and Susan Linko and Yi-Hong Zhu},
      title = {Accuracy comparison of various remote sensing data sources in the retrieval of forest stand attributes},
      journal = {Forest Ecology and Management},
      year = {1999},
      volume = {128},
      pages = {109-120}
    }
    
    Hyyppä, J., Kelle, O., Lehikoinen, M. & Inkinen, M. A segmentation-based method to retrieve stem volume estimates from 3-D tree height models produced by laser scanners 2001 IEEE Transactions on Geoscience and Remote Sensing
    Vol. 39, pp. 969-975 
    article  
    Abstract: In the boreal forest zone and in many forest areas, there exist gaps between the forest crowns. For example, in Finland, more than 30% of the first pulse data of laser scanning reflect directly from the ground without any interaction with the canopy. By increasing the number of pulses, it is possible to have samples from each individual tree and also from the gaps between the trees. Basically, this means that several laser pulses can be recorded per m/sup 2/. This allows detailed investigation of forest areas and the creation of a three-dimensional (3D) tree height model. Tree height model can be calculated from the digital terrain and crown models both obtained with the laser scanner data. By analyzing the 3D tree height model by using image vision methods, e.g., segmentation, it is possible to locate individual trees, estimate individual tree heights, crown area, and, by using that data, to derive the stem diameter, number of stems, basal area, and stem volume. The advantage of the method is the capability to measure directly physical dimensions from the trees and use that information to calculate the needed stand attributes. This paper demonstrates for the first time that it is possible to accurately estimate standwise forest attributes, especially stem volume (biomass), using high-pulse-rate laser scanners to provide data, from which individual trees can be detected and characteristics of trees such as height, location, and crown dimensions can be determined. That information can be applied to provide estimates for larger areas (stands). Using the new method, the following standard errors were demonstrated for mean height, basal area and stem volume: 1.8 m (9.9%), 2.0 m/sup 2//ha (10.2%), and 18.5 m/sup 3//ha (10.5%), respectively.
    BibTeX:
    @article{hyyppae_seg01,
      author = {Juha Hyyppä and O. Kelle and M. Lehikoinen and M. Inkinen},
      title = {A segmentation-based method to retrieve stem volume estimates from 3-D tree height models produced by laser scanners},
      journal = {IEEE Transactions on Geoscience and Remote Sensing},
      year = {2001},
      volume = {39},
      pages = {969-975}
    }
    
    Hyyppä, J., Pyysalo, U., Hyyppä, H. & Samberg, A. ELEVATION ACCURACY OF LASER SCANNING-DERIVED DIGITAL TERRAIN AND TARGET MODELS IN FOREST ENVIRONMENT 2000 20th EARSeL Symposium and Workshops, Dresden, Germany, pp. 8p (in press)  article  
    Abstract: This paper evaluates and discusses the accuracy of laser scanner in DTM (digital terrain model) gen-eration and digital 3-D height model generation in forested areas. High-pulse-rate laser scanners are capable of detecting single trees in a boreal forest zone, since a significant amount of the laser pulses reflect directly from the ground without any interaction with the canopy. This allows for a detailed investigation of forest areas and the creation of a 3-dimensional tree height model. Special emphasis is laid on the optimisation of the selection of ground hits used for the creation of the DTM of future high-pulse-rate laser scanners. A novel DTM algorithm is depicted in detail. In order to develop the algorithm, five phases were created: 1) Calculation of the original reference surface, 2) removal of the vegetation from the reference surface, 3) classification of the original cloud of points, 4) calculation of the DTM based on the classified ground hits, and 5) interpolation of the missing points. A standard error of 15 cm was obtained for flat forest areas and the error increased with increasing terrain slope to the value of approximately 40 cm at the slope of 40 $%$ . The average standard error for forest area was about 22 cm. The laser-derived DTM of the forest road deviated from the true height by 8.5 cm only. An optimum performance for the DTM generation was ob-tained by averaging the ground hits which were located, at the maximum, 60 cm above the mini-mum terrain values. It was also shown that tree heights of individual trees in the dominating storey can be obtained with less than 1 m standard error.
    BibTeX:
    @article{hyyppa00,
      author = {J. Hyyppä and U. Pyysalo and H. Hyyppä and A. Samberg},
      title = {ELEVATION ACCURACY OF LASER SCANNING-DERIVED DIGITAL TERRAIN AND TARGET MODELS IN FOREST ENVIRONMENT},
      journal = {20th EARSeL Symposium and Workshops, Dresden, Germany},
      year = {2000},
      pages = {8p (in press)}
    }
    
    Hyyppä, J., Hyyppä, H., Litkey, P., Yu, X., Haggrén, H., Rönnholm, P., Pyysalo, U., Pitkänen, J. & Maltamo, M. ALGORITHMS AND METHODS OF AIRBORNE LASER SCANNING FOR FOREST

    MEASUREMENTS

    2004 International Archives of Photgrammetry, Remote Sensing and Spatial Information Sciences, Vol. XXXVI - 8/W2  inproceedings  
    BibTeX:
    @inproceedings{hyyppae_rev04,
      author = {Juha Hyyppä and Hannu Hyyppä and Paula Litkey and Xiaowei Yu and Henrik Haggrén and 

    Petri Rönnholm and Ulla Pyysalo and Juho Pitkänen and Matti Maltamo}, title = {ALGORITHMS AND METHODS OF AIRBORNE LASER SCANNING FOR FOREST

    MEASUREMENTS}, booktitle = {International Archives of Photgrammetry, Remote Sensing and Spatial Information Sciences, Vol. XXXVI - 8/W2}, year = {2004} }

    Hyyppä, J. & Inkinen, M. Detecting and estimating

    attributes for single trees using laser scanner.

    1999 Photogrammetric Journal of Finland
    Vol. 16, pp. 27-42 
    article  
    BibTeX:
    @article{hyyppae99a,
      author = {Hyyppä, Juha and Inkinen, M.},
      title = {Detecting and estimating 

    attributes for single trees using laser scanner.}, journal = {Photogrammetric Journal of Finland}, year = {1999}, volume = {16}, pages = {27-42} }

    Höfle, B. & Pfeifer, N. Correction of laser scanning intensity data: Data and model-driven approaches 2007 ISPRS Journal of Photogrammetry and Remote Sensing
    Vol. 62(6), pp. 415-433 
    article  
    Abstract: Most airborne and terrestrial laser scanning systems additionally record the received signal intensity for each measurement. Multiple studies show the potential of this intensity value for a great variety of applications (e.g. strip adjustment, forestry, glaciology), but also state problems if using the original recorded values. Three main factors, a) spherical loss, b) topographic and c) atmospheric effects, influence the backscatter of the emitted laser power, which leads to a noticeably heterogeneous representation of the received power. This paper describes two different methods for correcting the laser scanning intensity data for these known influences resulting in a value proportional to the reflectance of the scanned surface. The first approach - data-driven correction - uses predefined homogeneous areas to empirically estimate the best parameters (least-squares adjustment) for a given global correction function accounting for all range-dependent influences. The second approach - model-driven correction - corrects each intensity independently based on the physical principle of radar systems. The evaluation of both methods, based on homogeneous reflecting areas acquired at different heights in different missions, indicates a clear reduction of intensity variation, to 1/3.5 of the original variation, and offsets between flight strips to 1/10. The presented correction methods establish a great potential for laser scanning intensity to be used for surface classification and multi-temporal analyses.
    BibTeX:
    @article{hoefle07,
      author = {Höfle, Bernhard and Pfeifer, Norbert},
      title = {Correction of laser scanning intensity data: Data and model-driven approaches},
      journal = {ISPRS Journal of Photogrammetry and Remote Sensing},
      year = {2007},
      volume = {62},
      number = {6},
      pages = {415--433}
    }
    
    Imhoff, M. Radar backscatter and biomass saturation: ramifications for global biomass inventory 1995 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 33(2)Geoscience and Remote Sensing, IEEE Transactions on, pp. 511-518 
    article  
    Abstract: Two SAR and biomass data sets of forests with different canopy architectures were examined for commonalties regarding backscatter/biomass saturation. The SAR data were collected using the NASA/JPL AIRSAR at incidence angles between 40&deg; and 50&deg; for tropical broadleaf evergreen forests in Hawaii and coniferous forests in North America and Europe. Radar signal saturation limits with respect to biomass for both forest types were determined to be &ap;100 tons/ha for P-band (0.44 GHz), &ap;40 tons/ha for L-band (1.25 GHz), and &ap;20 tons/ha for C-band (5.3 GHz). The effect of the saturation limits on making global biomass inventories with SAR sensors was assessed by comparing the biomass saturation limits to a global vegetation type and biomass data base. C-band can be used to measure biomass in biomes covering 25% of the world's total ice-free vegetated surface area accounting for 4% of Earth's store of terrestrial phytomass. L- and P-band can be used to measure biomass in biomes covering 37% and 62% of the total vegetated surface area accounting for 8% and 19% of Earth's pool of terrestrial phytomass respectively. Biomes occupying approximately 38% of Earth's vegetated surface area containing 81% of the estimated total terrestrial phytomass have biomass densities above the saturation limit of current SAR systems (&gt;100 tons/ha for P-band). Since P-band radar systems cannot currently operate effectively from orbit, the use of SAR sensors for biomass surveys may be limited even further to the L-band threshold. Emphasis should be shifted toward using SAR to characterize forest regeneration and development up to the saturation limits shown in this article rather than attempting to measure biomass directly in heavy forests. The development of new and innovative technologies for measuring biomass in high density vegetation is encouraged
    BibTeX:
    @article{Imhoff1995,
      author = {Imhoff, M.L.},
      title = {Radar backscatter and biomass saturation: ramifications for global biomass inventory},
      booktitle = {Geoscience and Remote Sensing, IEEE Transactions on},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {1995},
      volume = {33},
      number = {2},
      pages = {511--518}
    }
    
    Ingram, J.C., Dawson, T.P. & Whittaker, R.J. Mapping tropical forest structure in southeastern Madagascar using remote sensing and artificial neural networks 2005 Remote Sensing of Environment
    Vol. 94(4), pp. 491-507 
    article  
    Abstract: Tropical forest condition has important implications for biodiversity, climate change and human needs. Structural features of forests can serve as useful indicators of forest condition and have the potential to be assessed with remotely sensed imagery, which can provide quantitative information on forest ecosystems at high temporal and spatial resolutions. Herein, we investigate the utility of remote sensing for assessing, predicting and mapping two important forest structural features, stem density and basal area, in tropical, littoral forests in southeastern Madagascar. We analysed the relationships of basal area and stem density measurements to the Normalised Difference Vegetation Index (NDVI) and radiance measurements in bands 3, 4, 5 and 7 from the Landsat Enhanced Thematic Mapper Plus (ETM+). Strong relationships were identified among all of the individual bands and field based measurements of basal area (p<0.01) while there were weak and insignificant relationships among spectral response and stem density measurements. NDVI was not significantly correlated with basal area but was strongly and significantly correlated with stem density (r=-0.69, p<0.01) when using a subset of the data, which represented extreme values. We used an artificial neural network (ANN) to predict basal area from radiance values in bands 3, 4, 5 and 7 and to produce a predictive map of basal area for the entire forest landscape. The ANNs produced strong and significant relationships between predicted and actual measures of basal area using a jackknife method (r=0.79, p<0.01) and when using a larger data set (r=0.82, p<0.01). The map of predicted basal area produced by the ANN was assessed in relation to a pre-existing map of forest condition derived from a semi-quantitative field assessment. The predictive map of basal area provided finer detail on stand structural heterogeneity, captured known climatic influences on forest structure and displayed trends of basal area associated with degree of human accessibility. These findings demonstrate the utility of ANNs for integrating satellite data from the Landsat ETM+ spectral bands 3, 4, 5 and 7 with limited field survey data to assess patterns in basal area at the landscape scale.
    BibTeX:
    @article{Ingram2005,
      author = {Ingram, J. Carter and Dawson, Terence P. and Whittaker, Robert J.},
      title = {Mapping tropical forest structure in southeastern Madagascar using remote sensing and artificial neural networks},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {94},
      number = {4},
      pages = {491--507}
    }
    
    Irish, J.L. & Lillycrop, W.J. Scanning laser mapping of the coastal zone: the SHOALS system 1999 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 54(2-3), pp. 123-129 
    article  
    Abstract: The SHOALS system uses lidar technology to remotely measure bathymetry and topography in the coastal zone. During five years of survey operations, SHOALS has demonstrated airborne lidar bathymetry's benefits to the coastal community by providing a cost-effective tool for comprehensive assessment of coastal projects. This paper discusses the application of lidar technology for water-depth measurement, specifically outlining the SHOALS system and introducing a SHOALS survey from Saco River, ME.
    BibTeX:
    @article{irish99,
      author = {Jennifer L. Irish and W. Jeff Lillycrop},
      title = {Scanning laser mapping of the coastal zone: the SHOALS system},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {1999},
      volume = {54},
      number = {2-3},
      pages = {123-129}
    }
    
    Izzawati, Wallington, E. & Woodhouse, I. Forest height retrieval from commercial X-band SAR products 2006 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 44(4)Geoscience and Remote Sensing, IEEE Transactions on, pp. 863-870 
    article  
    Abstract: This paper assesses the accuracy and reliability of tree height retrieval over coniferous plantations using X-band interferometry. Factors such as crown shape, density, tree height, incidence angle, and slope have been assessed and quantified using a simple polarimetric radar interferometry simulator to determine their impact on height retrieval. Results from model simulation show that the most important factors are: crown shape, plantation density, and tree height. Variation in viewing angle and small slopes (<30&deg;) appear to have only small effects. These results appear to be in reasonably good agreement with the retrieved tree height from airborne X-band Intermap data over coniferous plantations in the U.K.
    BibTeX:
    @article{Izzawati2006,
      author = {Izzawati and Wallington, E.D. and Woodhouse, I.H.},
      title = {Forest height retrieval from commercial X-band SAR products},
      booktitle = {Geoscience and Remote Sensing, IEEE Transactions on},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {2006},
      volume = {44},
      number = {4},
      pages = {863--870}
    }
    
    Jacquemoud, S. Inversion of the PROSPECT + SAIL canopy reflectance model from AVIRIS equivalent spectra: Theoretical study 1993 Remote Sensing of Environment
    Vol. 44(2-3), pp. 281-292 
    article  
    Abstract: The potentials and limits of estimating canopy parameters are investigated using only a reflectance spectrum in the optical domain, and the PROSPECT + SAIL model. Simulations are performed on AVIRIS (Airborne Visible / Infrared Imaging Spectrometer) equivalent spectra, corrected for the atmospheric effects. It is established that this model is numerically invertible. The sensitivity analysis of reflectance spectral features to changes in the values of canopy parameters (leaf mesophyll structure N, chlorophyll a + b concentration Cab, water depth Cw, leaf area index, LAI, and average leaf inclination angle [theta]1) suggests that the accuracy of the inversion procedure needs some constraints. The Cab and Cw parameters, which describe the leaf physiological status, can be generally retrieved with a reasonable accuracy; it is somewhat difficult to estimate the canopy geometrical parameters (LAI and [theta]1) separately. Determining the fraction of absorbed photosynthetic active radiation (APAR) with parameters derived from the inversion procedure is discussed.
    BibTeX:
    @article{jacquemoud93,
      author = {Jacquemoud, S.},
      title = {Inversion of the PROSPECT + SAIL canopy reflectance model from AVIRIS equivalent spectra: Theoretical study},
      journal = {Remote Sensing of Environment},
      year = {1993},
      volume = {44},
      number = {2-3},
      pages = {281--292}
    }
    
    Jacquemoud, S. & Baret, F. PROSPECT: A model of leaf optical properties spectra 1990 Remote Sensing of Environment
    Vol. 34(2), pp. 75-91 
    article  
    Abstract: PROSPECT is a radiative transfer model based of Allen's generalized "plate model" that represents the optical properties of plant leaves from 400 nm to 2500 nm. Scattering is described by a spectral refractive index (n) and a parameter characterizing the leaf mesophyll structure (N). Absorption is modeled using pigment concentration (Ca+b), water content (Cw), and the corresponding specific spectral absorption coefficients (Ka+b and Kw). The parameters n, Ka+b, and Kw have been fitted using experimental data corresponding to a wide range of plant types and status. PROSPECT has been tested successfully on independent data sets. Its inversion allows one to reconstruct, with reasonable accuracy, leaf reflectance, and transmittance features in the 400-2500 nm range by adjusting the three input variables N, Ca+b, and Cw.
    BibTeX:
    @article{jacquemoud90,
      author = {Jacquemoud, S. and Baret, F.},
      title = {PROSPECT: A model of leaf optical properties spectra},
      journal = {Remote Sensing of Environment},
      year = {1990},
      volume = {34},
      number = {2},
      pages = {75--91}
    }
    
    Jacquemoud, S., Baret, F., Andrieu, B., Danson, F.M. & Jaggard, K. Extraction of vegetation biophysical parameters by inversion of the PROSPECT + SAIL models on sugar beet canopy reflectance data. Application to TM and AVIRIS sensors 1995 Remote Sensing of Environment
    Vol. 52(3), pp. 163-172 
    article  
    Abstract: The PROSPECT leaf optical properties and SAIL canopy reflectance models were coupled and inverted using a set of 96 AVIRIS (Airborne Visible/Infrared Imaging Spectrometer) equivalent spectra gathered in afield experiment on sugar beet plots expressing a large range in leaf area index, chlorophyll concentration, and soil color. In a first attempt, the model accurately reproduced the spectral reflectance of vegetation, using six variables: chlorophyll a + b concentration (Cab), water depth (Cw), leaf mesophyll structure parameter (N), leaf area index (LAI), mean leaf inclination angle ([theta]l), and hot-spot size parameter (s). The four structural parameters (N, LAI, [tau]l, and s) were poorly estimated, indicating instability in the inversion process; however, the two biochemical parameters (Cab and Cw) were evaluated reasonably well, except over very bright soils. In a second attempt, three of the four structure variables were assigned a fixed value corresponding to the average observed in the experiment. Inversions performed to retrieve the remaining structure variable, leaf area index, and the two biochemical variables showed large improvements in the accuracy of LAI, but slightly poorer performance for Cab and Cw. Here again, poor results were obtained with very bright soils. The compensations observed between the LAI and Cab or Cw led us to evaluate the performance of two more-synthetic variables, canopy chlorophyll content or canopy water content, for these the inversions produced reasonable estimates. The application of this approach to Landsat TM (Thematic Mapper) data provided similar results, both for the spectrum reconstruction capability and for the retrieval of canopy biophysical characteristics.
    BibTeX:
    @article{jacquemoud95,
      author = {Jacquemoud, S. and Baret, F. and Andrieu, B. and Danson, F. M. and Jaggard, K.},
      title = {Extraction of vegetation biophysical parameters by inversion of the PROSPECT + SAIL models on sugar beet canopy reflectance data. Application to TM and AVIRIS sensors},
      journal = {Remote Sensing of Environment},
      year = {1995},
      volume = {52},
      number = {3},
      pages = {163--172}
    }
    
    Jason, S. & Bork, E. Characterization of diverse plant communities in Aspen Parkland rangeland using LiDAR data. 2007 Applied Vegetation Science
    Vol. 10, pp. 407-416 
    article  
    BibTeX:
    @article{Jason2007,
      author = {Jason, S. and Bork, E.W.},
      title = {Characterization of diverse plant communities in Aspen Parkland rangeland using LiDAR data.},
      journal = {Applied Vegetation Science},
      year = {2007},
      volume = {10},
      pages = {407-416}
    }
    
    Joerg, P.C., Morsdorf, F. & Zemp, M. Operational use of airborne laserscanning for glacier monitoring in Switzerland 2010 Geophysical Research Abstracts Vol. 12, EGU2010-750, 2010 EGU General Assembly  conference  
    BibTeX:
    @conference{joerg2010,
      author = {Philip Claudio Joerg and Felix Morsdorf and Michael Zemp},
      title = {Operational use of airborne laserscanning for glacier monitoring in Switzerland},
      booktitle = {Geophysical Research Abstracts Vol. 12, EGU2010-750, 2010 EGU General Assembly},
      year = {2010}
    }
    
    Jonckheere, I., Fleck, S., Nackaerts, K., Muys, B., Coppin, P., Weiss, M. & Baret, F. Review of methods for in situ leaf area index determination: Part I. Theories, sensors and hemispherical photography 2004 Agricultural and Forest Meteorology
    Vol. 121(1-2), pp. 19-35 
    article  
    BibTeX:
    @article{jonckheere04,
      author = {Jonckheere, Inge and Fleck, Stefan and Nackaerts, Kris and Muys, Bart and Coppin, Pol and Weiss, Marie and Baret, Frederic},
      title = {Review of methods for in situ leaf area index determination: Part I. Theories, sensors and hemispherical photography},
      journal = {Agricultural and Forest Meteorology},
      year = {2004},
      volume = {121},
      number = {1-2},
      pages = {19--35}
    }
    
    Jonckheere, I., Nackaerts, K., Muys, B. & Coppin, P. Assessment of automatic gap fraction estimation of forests from digital hemispherical photography 2005 Agricultural and Forest Meteorology
    Vol. 132(1-2), pp. 96-114 
    article  
    Abstract: Thresholding is a central part of the analysis of hemispherical images in terms of gap fraction and leaf area index (LAI), and the selection of optimal thresholds has remained a challenge over decades. The need for an objective, automatic, operator-independent thresholding method has long been of interest to scientists using hemispherical photography. This manuscript deals with the comparison of a wide variety of different well-known automatic thresholding techniques against the subjective manual method, using high-dynamic range digital hemispherical photographs. The performance of the different thresholding methods was evaluated based on: (1) visual inspection by means of a multi-criteria decision system and (2) quantitative analysis of the methods' sensitivity to an overall performance criterium. The automatic Ridler clustering method proved to be the most robust thresholding method for various canopy structure conditions. This automatic method might be the best solution for a fast, reliable and objective use of hemispherical photographs for gap fraction and LAI estimation in forest stands, given that the threshold setting is no longer manually performed. The fine-tuning potential of local thresholding methods to better address particular photographic limitations (e.g. over-exposure in a certain image region) is also presented.
    BibTeX:
    @article{jonckheere05,
      author = {Jonckheere, Inge and Nackaerts, Kris and Muys, Bart and Coppin, Pol},
      title = {Assessment of automatic gap fraction estimation of forests from digital hemispherical photography},
      journal = {Agricultural and Forest Meteorology},
      year = {2005},
      volume = {132},
      number = {1-2},
      pages = {96--114}
    }
    
    Jutzi, B., Neulist, J. & Stilla, U. SUB-PIXEL EDGE LOCALIZATION BASED ON LASER WAVEFORM ANALYSIS 2005 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXVI, pp. 109-115 
    article  
    BibTeX:
    @article{jutzi05b,
      author = {B. Jutzi and J. Neulist and U. Stilla},
      title = {SUB-PIXEL EDGE LOCALIZATION BASED ON LASER WAVEFORM ANALYSIS},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2005},
      volume = {XXXVI},
      pages = {109-115}
    }
    
    Jutzi, B. & Stilla, U. Erfassung und Analyse der zeitlichen Signalform bei gepulsten Lasersystemen 2005 pers. Mitteilung, pp. 11  article  
    BibTeX:
    @article{jutzi05,
      author = {Boris Jutzi and Uwe Stilla},
      title = {Erfassung und Analyse der zeitlichen Signalform bei gepulsten Lasersystemen},
      journal = {pers. Mitteilung},
      year = {2005},
      pages = {11}
    }
    
    Jutzi, B. & Stilla, U. Laser pulse analysis for reconstruction and classification of urban objects 2003 International Archives of Photogrammetry and Remote Sensing
    Vol. 34, pp. Part 3/W8, 151-156 
    article  
    BibTeX:
    @article{jutzi03,
      author = {B. Jutzi and U. Stilla},
      title = {Laser pulse analysis for reconstruction and classification of urban objects},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2003},
      volume = {34},
      pages = {Part 3/W8, 151-156}
    }
    
    K?tz, B., Schaepman, M., Morsdorf, F., Bowyer, P., Itten, K. & Allg?wer, B. Radiative transfer modeling within a heterogeneous canopy for estimation of forest fire fuel properties 2004 Remote Sensing of Environment
    Vol. 92(3)Forest Fire Prevention and Assessment, pp. 332-344 
    article URL 
    Abstract: Imaging spectrometer data were acquired over conifer stands to retrieve spatially distributed information on canopy structure and foliage water content, which may be used to assess fire risk and to manage the impact of forest fires. The study relied on a comprehensive field campaign using stratified systematic unaligned sampling ranging from full spectroradiometric characterization of the canopy to conventional measurements of biochemical and biophysical variables. Airborne imaging spectrometer data (DAIS7915 and ROSIS) were acquired parallel to the ground measurements, describing the canopy reflectance of the observed forest. Coniferous canopies are highly heterogeneous and thus the transfer of incident radiation within the canopy is dominated by its structure. We demonstrated the viability of radiative transfer representation and compared the performance of two hybrid canopy reflectance models, GeoSAIL and FLIGHT, within this heterogeneous medium. Despite the different nature and canopy representation of these models, they yielded similar results. Subsequently, the inversion of a hyperspectral GeoSAIL version demonstrated the feasibility of estimating structure and foliage water content of a coniferous canopy based on radiative transfer modeling. Estimates of the canopy variables showed reasonably accurate results and were validated through ground measurements.
    BibTeX:
    @article{Koetz2004,
      author = {K?tz, Benjamin and Schaepman, Michael and Morsdorf, Felix and Bowyer, Paul and Itten, Klaus and Allg?wer, Britta},
      title = {Radiative transfer modeling within a heterogeneous canopy for estimation of forest fire fuel properties},
      booktitle = {Forest Fire Prevention and Assessment},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {92},
      number = {3},
      pages = {332--344},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4CXDT8T-1/2/7d48075df197d282815d23e1f05ee207}
    }
    
    Kaartinen, H., Hyyppä, J., Gülch, E., Vosselman, G., Hyyppä, H., Matikainen, L., Hofmann, A., Mäder, U., Persson, Å., Söderman, U., Elmqvist, M., Ruiz, A., Dragoja, M., Flamanc, D., Maillet, G., Kersten, T., Carl, J., Hau, R., Wild, E., Frederiksen, L., Holmgaard, J. & Vester, K. Accuracy of 3D City Models: EuroSDR comparison 2005 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXVI, pp. 227-232 
    article  
    Abstract: The paper focuses on comparing accuracies obtained with photogrammetry and laser scanning in building extraction and partly com-

    pares results obtained with various methods. The objective of the EuroSDR Building Extraction comparison was to evaluate the

    quality, accuracy, feasibility and economical aspects of semi-automatic building extraction based on photogrammetric techniques

    with the emphasis on commercial and/or operative systems, semi-automatic and automatic building extraction techniques based on

    high density laser scanner data and semi-automatic and automatic building extraction techniques based on integration of laser scan-

    ner data and aerial images (hybrid technique). The project consists of three test sites by Finnish Geodetic Institute (FGI), namely

    Senaatti, Hermanni and Espoonlahti and one test site by Institut Geographique National (IGN), namely Amiens. For each test site fol-

    lowing data was provided to the partners: aerial images, camera calibration and image orientation information, ground control point

    coordinates and jpg images of point locations (not for Amiens), laser scanner data and cadastral map vectors of selected buildings.

    Participants were requested to create the vectors of 3D city models. 3D-models were obtained from 11 participants. Paper confirms

    with experiments that laser scanning is more suitable in deriving building heights, extracting planar roof faces and ridges of the roof

    whereas the photogrammetry and aerial images are more suitable in building outline and length determination. CyberCity, Stuttgart

    and TerraScan (performed by ICC) solutions provided the highest accuracy. There seemed to be a higher variation in the quality of

    other models depending on test site or remotely sensed information.

    BibTeX:
    @article{kaartinen05,
      author = {H. Kaartinen and J. Hyyppä and E. Gülch and G. Vosselman and H. Hyyppä and L. Matikainen and A.D. Hofmann and U. Mäder and Å. Persson and U. Söderman and M. Elmqvist and A. Ruiz and M. Dragoja and D. Flamanc and G. Maillet and T. Kersten and J. Carl and R. Hau and E. Wild and L. 

    Frederiksen and J. Holmgaard and K. Vester}, title = {Accuracy of 3D City Models: EuroSDR comparison}, journal = {International Archives of Photogrammetry and Remote Sensing}, year = {2005}, volume = {XXXVI}, pages = {227-232} }

    Kaasalainen, S., Ahokas, E., Hyyppa, J. & Suomalainen, J. Study of surface brightness from backscattered laser intensity: calibration of laser data 2005 Geoscience and Remote Sensing Letters, IEEE
    Vol. 2(3), pp. 255-259 
    article DOI  
    Abstract: Systematic laboratory measurements of laser backscatter intensity are presented for brightness calibration targets, and a calibration scheme for airborne laser scanner intensity data is proposed. Thus far, the use of these data has been partly hampered by the variability of the intensity with time, and no test fields have been available for airborne reflectance calibration. Portable brightness targets (tarps), with nominal reflectances from 5% to 70%, were manufactured, and, based on these measurements, found suitable for lidar reflectance standards. Furthermore, the variability of the recorded intensity from the tarps as a function of incidence angle was low. The measurements also provide new information on the surface albedo dependence of backscattering effects: as the surface brightness increases from 5% to 70%, the hotspot brightness peak amplitudes increase by 20% to 30%, and their apparent widths reduce to a half, which implies that hotspots could be used as an albedo discriminator.
    BibTeX:
    @article{kaasalainen05,
      author = {Kaasalainen, S. and Ahokas, E. and Hyyppa, J. and Suomalainen, J.},
      title = {Study of surface brightness from backscattered laser intensity: calibration of laser data},
      journal = {Geoscience and Remote Sensing Letters, IEEE},
      year = {2005},
      volume = {2},
      number = {3},
      pages = {255-259},
      doi = {http://dx.doi.org/10.1109/LGRS.2005.850534}
    }
    
    Kaasalainen, S., Hyyppa, H., Kukko, A., Litkey, P., Ahokas, E., Hyyppa, J., Lehner, H., Jaakkola, A., Suomalainen, J., Akujarvi, A., Kaasalainen, M. & Pyysalo, U. Radiometric Calibration of LIDAR Intensity With Commercially Available Reference Targets 2009 IEEE Transactions on Geoscience and Remote Sensing
    Vol. 47(2), pp. 588-598 
    article DOI  
    Abstract: We present a new approach for radiometric calibration of light detection and ranging (LIDAR) intensity data and demonstrate an application of this method to natural targets. The method is based on 1) using commercially available sand and gravel as reference targets and 2) the calibration of these reference targets in the laboratory conditions to know their backscatter properties. We have investigated the target properties crucial for accurate and consistent reflectance calibration and present a set of ideal targets easily available for calibration purposes. The first results from LIDAR-based brightness measurement of grass and sand show that the gravel-based calibration approach works in practice, is cost effective, and produces statistically meaningful results: Comparison of results from two separate airborne laser scanning campaigns shows that the relative calibration produces repeatable reflectance values.
    BibTeX:
    @article{Kaasalainen2009,
      author = {Kaasalainen, S. and Hyyppa, H. and Kukko, A. and Litkey, P. and Ahokas, E. and Hyyppa, J. and Lehner, H. and Jaakkola, A. and Suomalainen, J. and Akujarvi, A. and Kaasalainen, M. and Pyysalo, U.},
      title = {Radiometric Calibration of LIDAR Intensity With Commercially Available Reference Targets},
      journal = {IEEE Transactions on Geoscience and Remote Sensing},
      year = {2009},
      volume = {47},
      number = {2},
      pages = {588-598},
      doi = {http://dx.doi.org/10.1109/TGRS.2008.2003351}
    }
    
    Kaasalainen, S., Kukko, A., Lindroos, T., Litkey, P., Kaartinen, H., Hyyppa, J. & Ahokas, E. Brightness Measurements and Calibration With Airborne and Terrestrial Laser Scanners 2008 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 46(2), pp. 528-534 
    article DOI  
    Abstract: Brightness measurement with an airborne or terrestrial laser scanner is a new concept since the intensity information recorded by the laser scanner detectors has, thus far, not been used or implemented in surface brightness studies. This is partly due to the calibration problems and the lack of information on the behavior of laser light in the observation geometry where laser scanners operate. In addition, the 3-D position information has, thus far, been sufficient for surface modeling. We present a new type of empirical calibration scheme for laser scanner intensity developed with a terrestrial laser scanner in laboratory and field conditions using brightness targets and a calibrated reference panel. We compare the results with those obtained from airborne laser scanner flight campaigns using the same set of brightness targets. It turns out that the relative calibration of laser scanner intensity is possible using a calibrated grayscale but requires background information of the targets and the conditions in which the measurements are carried out. We also discuss the feasibility and uses of a laser-scanner-based intensity measurement in general.
    BibTeX:
    @article{Kaasalainen2008,
      author = {Kaasalainen, S. and Kukko, A. and Lindroos, T. and Litkey, P. and Kaartinen, H. and Hyyppa, J. and Ahokas, E.},
      title = {Brightness Measurements and Calibration With Airborne and Terrestrial Laser Scanners},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {2008},
      volume = {46},
      number = {2},
      pages = {528-534},
      doi = {http://dx.doi.org/10.1109/TGRS.2007.911366}
    }
    
    Kaasalainen, S., Lindroos, T. & Hyyppa, J. Toward Hyperspectral Lidar: Measurement of Spectral Backscatter Intensity With a Supercontinuum Laser Source 2007 Geoscience and Remote Sensing Letters, IEEE
    Vol. 4(2), pp. 211-215 
    article DOI  
    Abstract: We have tested the use of a supercontinuum laser source in laser-based spectral backscatter measurement. The calibration and first results with the prototype instrument are presented with a discussion of improvements and applications in laser-based hyperspectral remote sensing and laboratory measurements. This technique enables the spectral study of the backscatter effects and the calibration and test measurements for the purpose of airborne laser measurement. We also explore the prospect of using a supercontinuum laser source in a broadband (hyperspectral) lidar
    BibTeX:
    @article{kaasalainen07,
      author = {Kaasalainen, S. and Lindroos, T. and Hyyppa, J.},
      title = {Toward Hyperspectral Lidar: Measurement of Spectral Backscatter Intensity With a Supercontinuum Laser Source},
      journal = {Geoscience and Remote Sensing Letters, IEEE},
      year = {2007},
      volume = {4},
      number = {2},
      pages = {211-215},
      doi = {http://dx.doi.org/10.1109/LGRS.2006.888848}
    }
    
    Kalliovirta, J., Laasasenaho, J. & Kangas, A. Evaluation of the Laser-relascope 2005 Forest Ecology and Management
    Vol. 204(2-3), pp. 181-194 
    article  
    Abstract: The second prototype of a new measuring device, the Laser-relascope, was tested under typical forest conditions. The Laser-relascope is functionally a combination of a relascope and a dendrometer. It uses distance and angle information to determine the diameter of a tree. The distance between the device and a tree is measured with a laser instrument. In addition to a laser rangefinder, the Laser-relascope includes a variable-width slot with a fixed-length arm, an electronic compass, an electronic inclinometer, a data collection/processing unit, and a GPS receiver. In this study, diameters, heights, and distances (bearing and distance from the center of a sample point) of trees were measured. Furthermore, sample points can be located by using the GPS receiver.With the use of a Laser-relascope, diameter measurements were almost unbiased (overestimation 1.3 mm), with measuring distances of 1.4-15.0 m. The standard error was 8.2 mm. The accuracy was dependent on the distance, the slot width, measuring time of a tree, and the diameter at breast height (dbh). The individual's familiarity with the Laser-relascope also had an effect on the precision of diameter measurements. In height measurements, the device produced unbiased results. The standard error was 4.9 dm. Locations of trees could also be determined with good precision. The mean distance between the observed and correct location was 32 cm. The measurements of the height and location were not affected by experience with the device. The precision of volume estimation was dependent on the basal area and the time needed to measure a tree. Measuring a sample point took on average 15.5 min and the measuring of a single tree 85 s. Measuring time was dependent on basal area, visibility, and dominant species. The device can be used throughout the day with moderate strain. It is most suitable for near mature forests with good visibility.
    BibTeX:
    @article{kalliovirta05,
      author = {Kalliovirta, J. and Laasasenaho, J. and Kangas, A.},
      title = {Evaluation of the Laser-relascope},
      journal = {Forest Ecology and Management},
      year = {2005},
      volume = {204},
      number = {2-3},
      pages = {181--194}
    }
    
    Kasischke, E., Christensen, N.L., J. & Bourgeau-Chavez, L. Correlating radar backscatter with components of biomass in loblolly pine forests 1995 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 33(3)Geoscience and Remote Sensing, IEEE Transactions on, pp. 643-659 
    article  
    Abstract: A multifrequency, multipolarization airborne SAR data set was utilized to examine the relationship between radar backscatter and the aboveground biomass. This data set was also used to examine the potential of SAR to estimate aboveground biomass in these forests. The total aboveground biomass in the test stands used in this study ranged from &lt;1-50 kg m-2. Not only was total aboveground biomass considered, but the biomass of the tree boles, branches, and needles/leaves. Significant correlations were found in all three frequencies of radar imagery used in this study (C-, L- and P-band), At P- and L-bands, the greatest sensitivity to change in biomass occurred in the HH and VH polarized channels, while at C-band, the greatest sensitivity was in the VH polarized channel. The results of the correlation analyses support modeling studies which show the dominant scattering mechanisms from these pines should be double-bounce, ground-trunk scattering and canopy volume scattering. To produce equations to estimate biomass, a stepwise, multiple-linear regression approach was used, using all the radar channels as independent variables, and the log of the biomass components as the dependent variables. The results of this regression analysis produced equations with high coefficients of linear correlation and low standard errors of the regression equation for estimating total stand, bole and total stem biomass. Statistically-significant regression equations were also generated for large stem, small stem and needle/leaf biomass. Even though the biomass estimation algorithms had high correlation coefficients and low standard errors, when the predicted biomass estimates were expressed in arithmetic terms and compared to actual values, low levels of accuracy were found. A second method was developed using total stem biomass to estimate the other components, with total stem biomass being estimated from the radar image intensity values. This two-step method reduced the coefficient of variation to between 16 and 27% for all biomass components
    BibTeX:
    @article{Kasischke1995,
      author = {Kasischke, E.S. and Christensen, N.L., Jr. and Bourgeau-Chavez, L.L.},
      title = {Correlating radar backscatter with components of biomass in loblolly pine forests},
      booktitle = {Geoscience and Remote Sensing, IEEE Transactions on},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {1995},
      volume = {33},
      number = {3},
      pages = {643--659}
    }
    
    Katzenbeisser, R. ABOUT THE CALIBRATION OF LIDAR SENSORS 2003 ISPRS Workshop ?3-D Reconstruction form Airborne Laser-Scanner and InSAR data"
    Vol. Dresden 
    article  
    BibTeX:
    @article{katzenbeisser_calib03,
      author = {R. Katzenbeisser},
      title = {ABOUT THE CALIBRATION OF LIDAR SENSORS},
      journal = {ISPRS Workshop ?3-D Reconstruction form Airborne Laser-Scanner and InSAR data"},
      year = {2003},
      volume = {Dresden}
    }
    
    Katzenbeisser, R. Echo Detection 2003 Technical Note  article  
    BibTeX:
    @article{katzenbeisser_echo03,
      author = {R. Katzenbeisser},
      title = {Echo Detection},
      journal = {Technical Note},
      year = {2003}
    }
    
    Kergoat, L. A model for hydrological equilibrium of leaf area index on a global scale 1998 Journal of Hydrology
    Vol. 212-213, pp. 268-286 
    article  
    Abstract: In this paper, a model for hydrological equilibrium of leaf area index (LAI) is presented. The central assumption is that adaptation of vegetation to the local climate leads to a development of the canopy, which ensures a large light absorption but prevents severe soil water depletion. Particular attention has been paid to the processes which strengthen or weaken the basic LAI/evapotranspiration relationship, including soil moisture feedback on transpiration and evaporation, deciduousness of the canopy and interception losses. The annual water balance has been compared to stream flow data. A general agreement was found between simulated and observed run-off averaged over 28 large river basins. This shows that a water exchange scheme with explicit canopy processes can be used on a global scale. Vegetation aridity gradients are well defined by the hydrological equilibrium theory. An additional light availability constraint shows that the LAI, for wet tropics, some wet temperate and boreal areas, is not primarily water limited. An interesting point arises from an underestimation of the LAI and evapotranspiration in the rain forest margins and dry forests. This suggests that these areas are prone to recurrent droughts, and that drought resistance and avoidance strategies are of uppermost importance for vegetation function and therefore water cycle modelling. In particular, deep rooting may play a crucial role. The objective of modelling vegetation response to resources availability--here the water and light resources--is to improve our understanding of the biosphere as a resource-based system on a global scale, in the perspective of a change in atmospheric CO2 and corresponding climate modifications. The exact role of below-ground functioning, its links with carbon allocation, and especially the cost of deep rooting, emerge from this study as critical questions.
    BibTeX:
    @article{kergoat98,
      author = {Kergoat, Laurent},
      title = {A model for hydrological equilibrium of leaf area index on a global scale},
      journal = {Journal of Hydrology},
      year = {1998},
      volume = {212-213},
      pages = {268--286}
    }
    
    Kim, S., McGaughey, R.J., Andersen, H.-E. & Schreuder, G. Tree species differentiation using intensity data derived from leaf-on and leaf-off airborne laser scanner data 2009 Remote Sensing of Environment
    Vol. 113(8), pp. 1575 - 1586 
    article DOI  
    Abstract: Tree species identification is important for a variety of natural resource management and monitoring activities including riparian buffer characterization, wildfire risk assessment, biodiversity monitoring, and wildlife habitat assessment. Intensity data recorded for each laser point in a LIDAR system is related to the spectral reflectance of the target material and thus may be useful for differentiating materials and ultimately tree species. The aim of this study is to test if LIDAR intensity data can be used to differentiate tree species. Leaf-off and leaf-on LIDAR data were obtained in the Washington Park Arboretum, Seattle, Washington, USA. Field work was conducted to measure tree locations, tree species and heights, crown base heights, and crown diameters of individual trees for eight broadleaved species and seven coniferous species. LIDAR points from individual trees were identified using the field-measured tree location. Points from adjacent trees within a crown were excluded using a procedure to separate crown overlap. Mean intensity values of laser returns within individual tree crowns were compared between species. We found that the intensity values for different species were related not only to reflective properties of the vegetation, but also to a presence or absence of foliage and the arrangement of foliage and branches within individual tree crowns. The classification results for broadleaved and coniferous species using linear discriminant function with a cross validation suggests that the classification rate was higher using leaf-off data (83.4%) than using leaf-on data (73.1%), with highest (90.6%) when combining these two LIDAR data sets. The result also indicates that different ranges of intensity values between two LIDAR datasets didn't affect the result of discriminant functions. Overall results indicate that some species and species groups can be differentiated using LIDAR intensity data and implies the potential of combining two LIDAR datasets for one study.
    BibTeX:
    @article{Kim2009,
      author = {Sooyoung Kim and Robert J. McGaughey and Hans-Erik Andersen and Gerard Schreuder},
      title = {Tree species differentiation using intensity data derived from leaf-on and leaf-off airborne laser scanner data},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {8},
      pages = {1575 - 1586},
      doi = {DOI: 10.1016/j.rse.2009.03.017}
    }
    
    Kimes, D. Remote sensing of row crop structure and component temperatures using directional radiometric temperatures and inversion techniques 1983 Remote Sensing of Environment
    Vol. 13(1), pp. 33-55 
    article  
    Abstract: A physically based sensor response model of a row crop was used as the mathematical framework from which several inversion strategies were tested for extracting row structure information and component temperatures using a series of sensor view angles. The technique was evaluated on ground-based radiometric thermal infrared data of a cotton row crop that covered 48% of the ground in the vertical projection. The results showed that the accuracies of the predicted row heights and widths, vegetation temperatures, and soil temperatures of the cotton row crop were on the order of 5 cm (? 10% of mean values), 1?, and 2?C, respectively. The inversion techniques can be applied to directional sensor data from aircraft platforms and even space platforms if the effects of atmospheric absorption and emission can be corrected. In theory, such inversion techniques can be applied to a wide variety of vegetation types and thus can have significant implications for remote sensing research and applications in disciplines that deal with incomplete vegetation canopies.
    BibTeX:
    @article{Kimes1983,
      author = {Kimes, D.S.},
      title = {Remote sensing of row crop structure and component temperatures using directional radiometric temperatures and inversion techniques},
      journal = {Remote Sensing of Environment},
      year = {1983},
      volume = {13},
      number = {1},
      pages = {33--55}
    }
    
    Kimes, D. Effects of vegetation canopy structure on remotely sensed canopy temperatures 1980 Remote Sensing of Environment
    Vol. 10(3), pp. 165-174 
    article  
    Abstract: Remote sensing of vegetation temperatures is a promising technique for inferring plant water stress and yield on a large spatial scale. The effects of vegetation canopy structure on thermal infrared sensor response need to be understood before vegetation surface temperatures of canopies with low percentages of ground cover can be accurately inferred. The response of a sensor is a function of vegetation geometric structure, the vertical surface temperature distribution of the canopy components, and sensor view angle. Large deviations between the nadir sensor effective radiant temperature (ERT) and vegetation ERT for a soybean canopy were observed throughout the growing season. The nadir sensor ERT of a soybean canopy with 35% ground cover deviated from the vegetation ERT by as much as 11?C during the mid-day. These deviations were quantitatively explained as a function of canopy structure and soil temperature. Remote sensing techniques which uniquely determine the vegetation canopy temperature(s) from the sensor response need to be studied.
    BibTeX:
    @article{Kimes1980,
      author = {Kimes, D.S.},
      title = {Effects of vegetation canopy structure on remotely sensed canopy temperatures},
      journal = {Remote Sensing of Environment},
      year = {1980},
      volume = {10},
      number = {3},
      pages = {165--174}
    }
    
    Kimes, D. & Deering, D. Remote sensing of surface hemispherical reflectance (albedo) using pointable multispectral imaging spectroradiometers 1992 Remote Sensing of Environment
    Vol. 39(2), pp. 85-94 
    article  
    Abstract: Several techniques that use multiple off-nadir view angles taken in a single azimuth plane (called a string of data) to estimate hemispherical reflectance have been developed. The range of view angles that is required in order to obtain accurate inferences of hemispherical reflectance using string techniques was studied as applicable to the Moderate Resolution Imaging Spectroradiometer (MODIS) and the High Resolution Imaging Spectroradiometer (HIRIS). Full and half strings out to 60?, 45?, 30?, and 15? were tested on ground data of a wide range of cover types and sun angles. Both a visible and near infrared band (AVHRR Bands 1 and 2) were tested using a knowledge-based system called VEG. Using string techniques that calculate a single coefficient from an internal spectral data base, the results showed small errors for the full string ? 60? (less than 4% error), HIRIS like data (less than 5% error), and MODIS like data (less than 7% error). Much larger errors occur in those cases where long extrapolations must be calculated (e.g., strings to only 15? and 30?). Systems that view fore and aft out to 60? would be desirable to minimize errors, assuming atmospheric corrections could be made at these angles. HIRIS (views 60? in forward and 30? in aft directions) is a good compromise by viewing out to 60? in only one direction and increases the error by approximately 2% or less. MODIS (full string ? 45?) still has a relatively small error of approximately 5% or less. Sensor systems capable of only viewing in the fore or aft directions (half strings) as opposed to both directions (full strings) greatly increase the error.
    BibTeX:
    @article{Kimes1992,
      author = {Kimes, D.S and Deering, D.W},
      title = {Remote sensing of surface hemispherical reflectance (albedo) using pointable multispectral imaging spectroradiometers},
      journal = {Remote Sensing of Environment},
      year = {1992},
      volume = {39},
      number = {2},
      pages = {85--94}
    }
    
    Kimes, D., Gastellu-Etchegorry, J. & Est?ve, P. Recovery of forest canopy characteristics through inversion of a complex 3D model 2002 Remote Sensing of Environment
    Vol. 79(2-3), pp. 320-328 
    article  
    Abstract: Radiative transfer models for vegetation serve as a basis for extracting vegetation variables using directional/spectral data from modern-borne sensors (e.g., MODIS, MISR, POLDER, SeaWiFS). Only recently have significant efforts been made to provide operational algorithms to invert these models. These efforts have exposed a need to significantly improve the efficiency and accuracy of traditional methods for inverting these physically based models. In an effort to overcome the limitations of traditional inversion methods, a neural network method was designed and tested. In this study, a complex 3D model (Discrete Anisotropic Radiative Transfer, DART) was inverted for a wide range of simulated forest canopies using POLDER-like data. The model was inverted to recover three forest canopy variables: forest cover, leaf area index, and a soil reflectance parameter. The ranges of these variables were 0.4-1.0, 0.8-9.3, and 0.0-1.0, respectively. Two inversion methods were used -- a traditional inversion technique using a modified simplex method, and a neural network method in combination with an exhaustive variable selection technique. A comparison of the methods' efficiency, accuracy, and stability was made. The neural network method gave relatively accurate solutions to the inversion problem given a small subset of directional/spectral data using only one to five view angles. Using only nadir data, the root mean squared error (RMSE) for the forest cover, leaf area index, and the soil reflectance parameter were 0.025, 0.23, and 0.15, respectively, and using the "best" view directions (2-5) were 0.021, 0.21, and 0.11, respectively. In general, the neural network method was more accurate than the simplex method. The results from both methods showed that the addition of directional view angles, as opposed to only a nadir view, can significantly improve the accuracy of recovering forest canopy characteristics. The traditional simplex method is computationally intensive and may not be appropriate for many operational applications on a per-pixel basis for regional and global data. The neural network method was computationally efficient and can be applied on a per-pixel basis. In general, the neural network technique had significantly lower RMSE values at the low noise levels. However, at moderate noise levels, the simplex method was equal to the neural network method in RMSE values. At high noise levels, the simplex method had significantly lower RMSE values than the neural network method. The neural network approach can provide an accurate, efficient, and stable inversion method for radiative transfer models using directional/spectral data from modern-borne sensors.
    BibTeX:
    @article{Kimes2002,
      author = {Kimes, D. and Gastellu-Etchegorry, J. and Est?ve, P.},
      title = {Recovery of forest canopy characteristics through inversion of a complex 3D model},
      journal = {Remote Sensing of Environment},
      year = {2002},
      volume = {79},
      number = {2-3},
      pages = {320--328}
    }
    
    Kimes, D., Harrison, P. & Harrison, P. Extension of off-nadir view angles for directional sensor systems 1994 Remote Sensing of Environment
    Vol. 50(3), pp. 201-211 
    article  
    Abstract: A knowledge-based system called VEG was expanded to infer nadir or any off-nadir reflectance(s) of a vegetation target given any combination of other directional reflectance(s) of the target. VEG determines the best techniques to use in an array of techniques, applies the techniques to the target data, and provides a rigorous estimate of the accuracy of the inference(s). The knowledge-based system, VEG, facilitates the use of diverse knowledge bases to be incorporated into the inference techniques. In this study, VEG used additional information to make more accurate view-angle extension techniques than the traditional techniques that only use spectral data from the unknown target. VEG used spectral data and a normalized difference technique to infer the percentage of ground cover of the unknown target. This estimate of percentage of ground cover of the unknown target along with information on the sun angle were then used to search a historical data base for targets that match the unknown target in these characteristics. This data captured the general shape of the reflectance distribution of the unknown target. This historical information was used to estimate the coefficients of the techniques for the conditions at hand and to test the accuracy of the techniques. The tests used in this study were difficult ones. For example, techniques were tested that make long angular extensions using one, two, or four input view angles to predict an unknown nadir value. Furthermore, a wide variety of unknown targets were tested. The errors (?proportional rms) obtained were on the order of 0.15. In addition techniques were tested that use seven or nine multiple view angles to predict the entire hemispherical reflectance distribution of an unknown target. The accuracy of these tests was relatively good considering the relatively dynamic and noisy nature of directional reflectance distributions. The accuracy of the techniques in this study depends on the smoothness of the historical reflectance distributions and the amount of historical data available that closely matches the unknown target.
    BibTeX:
    @article{Kimes1994,
      author = {Kimes, D.S. and Harrison, P.A. and Harrison, P.R.},
      title = {Extension of off-nadir view angles for directional sensor systems},
      journal = {Remote Sensing of Environment},
      year = {1994},
      volume = {50},
      number = {3},
      pages = {201--211}
    }
    
    Kimes, D., Idso, S., Pinter Jr., P., Reginato, R. & Jackson, R. View angle effects in the radiometric measurement of plant canopy temperatures 1980 Remote Sensing of Environment
    Vol. 10(4), pp. 273-284 
    article  
    Abstract: The thermal infrared sensor response from a wheat canopy was extremely non-Lambertian because of spatial variations in energy flow processes; the effective radiant temperature of the sensor varied as much as 13?C with changing view angle. This variation of sensor response was accurately quantified (root-mean-square of deviations between theoretical and measured responses reduced to 1.1?C) as a function of vegetation canopy geometry, vertical temperature distribution of canopy components, and sensor view angle. The results have important implications for optimizing sensor view angles for remote sensing missions.
    BibTeX:
    @article{Kimes1980a,
      author = {Kimes, D.S. and Idso, S.B. and Pinter Jr., P.J. and Reginato, R.J. and Jackson, R.D.},
      title = {View angle effects in the radiometric measurement of plant canopy temperatures},
      journal = {Remote Sensing of Environment},
      year = {1980},
      volume = {10},
      number = {4},
      pages = {273--284}
    }
    
    Kimes, D., Irons, J., Levine, E. & Horning, N. Learning class descriptions from a data base of spectral reflectance of soil samples 1993 Remote Sensing of Environment
    Vol. 43(2), pp. 161-169 
    article  
    Abstract: A program was developed to learn class descriptions from positive and negative training examples of spectral reflectance data of bare soils. The program combined a form of learning referred to as "learning by example" with the generate-and-test paradigm to provide a robust learning environment that could handle error prone data. The program was tested by having it learn class descriptions of various categories of organic carbon content, iron oxide content, and particle size distribution in soils. These class descriptions were then used to classify an array of targets. The class descriptions in this program were comprised of a series of different relationships (greater-than, first-maximum, second-maximum, first-minimum, second-minimum, convex, and concave) between combinations of spectral bands. The program found the sequence of relationships between bands that contained the most important information to distinguish the classes. The concept being learned was a sequence of relationships that optimized the discrimination of a class. Training examples of spectral reflectance data of bare soils were taken from data of Stoner and Baumgardner (1981). Classes of any soil characteristic that is in the data base can be explored. The characteristics include organic carbon content, iron oxide content, particle size distribution, soil order, mineralogy, cation exchange capacity, drainage class, and Munsell color. Combinations of the first four characteristics were used to make class descriptions that were used to classify the soil samples into the five classes observed by Stoner and Baumgardner (1981). Other classes of organic carbon, iron oxide, drainage, and clay content were explored using this method. The program was tested by learning class descriptions of these classes and subsequently classifying an array of unknown soil data. The results showed a high classification accuracy of 77% for separating classes of high and low organic carbon content. Physical explanations for the class descriptions obtained were presented.
    BibTeX:
    @article{Kimes1993,
      author = {Kimes, D.S. and Irons, J.R. and Levine, E.R. and Horning, N.A.},
      title = {Learning class descriptions from a data base of spectral reflectance of soil samples},
      journal = {Remote Sensing of Environment},
      year = {1993},
      volume = {43},
      number = {2},
      pages = {161--169}
    }
    
    Kimes, D., Kerber, A. & Sellers, P. Spatial averaging errors in creating hemispherical reflectance (Albedo) maps from directional reflectance data 1993 Remote Sensing of Environment
    Vol. 45(1), pp. 85-94 
    article  
    Abstract: The problems in moving from a radiance measurement made for a particular sun-target-sensor geometry to an accurate estimate of the hemispherical reflectance are considerable. A knowledge-based system called VEG was used in this study to infer hemispherical reflectance. Given directional reflectance(s) and the sun angle, VEG selects the most suitable inference technique(s) and estimates the surface hemispherical reflectance with an estimate of the error. Ideally, VEG is applied to homogeneous vegetation. However, what is typically done in GCM (global circulation model) models and related studies is to obtain an average hemispherical reflectance on a square grid cell on the order of 200 km ? 200 km. All available directional data for a given cell are averaged (for each view direction), and then a particular technique for inferring hemispherical reflectance is applied to this averaged data. Any given grid cell can contain several surface types that directionally scatter radiation very differently. When averaging over a set of view angles, the resulting mean values may be atypical of the actual surface types that occur on the ground, and the resulting inferred hemispherical reflectance can be in error. These errors were explored by creating a simulated scene and applying VEG to estimate the area-averaged hemispherical reflectance using various sampling procedures. The reduction in the hemispherical reflectance errors provided by using VEG ranged from a factor of 2-4, depending on conditions. This improvement represents a shift from the calculation of a hemispherical reflectance product of relative value (errors of 20% or more), to a product that could be used quantitatively in global modeling applications, where the requirement is for errors to be limited to around 5-10%. The results suggest sampling and averaging strategies for creating hemispherical reflectance maps for photosynthetic, carbon cycle, and climate change studies.
    BibTeX:
    @article{Kimes1993a,
      author = {Kimes, D.S and Kerber, A.G and Sellers, P.J},
      title = {Spatial averaging errors in creating hemispherical reflectance (Albedo) maps from directional reflectance data},
      journal = {Remote Sensing of Environment},
      year = {1993},
      volume = {45},
      number = {1},
      pages = {85--94}
    }
    
    Kimes, D. & Kirchner, J. Irradiance measurement errors due to the assumption of a Lambertian reference panel 1982 Remote Sensing of Environment
    Vol. 12(2), pp. 141-149 
    article  
    Abstract: Total and diffuse global spectral irradiances, which are often required field measurements in remote sensing, are commonly obtained by measuring the radiance from a horizontal reference panel with assumed Lambertian properties. A technique is presented for determining the error in diurnal irradiance measurements that results from the non-Lambertian behavior of a reference panel under various irradiance conditions. Spectral biconical reflectance factors of a spray-painted barium sulfate panel, along with simulated sky radiance data for clear and hazy skies at six solar zenith angles, were used to calculate the estimated panel irradiances and true-irradiances for a nadir-looking sensor in two wavelength bands. The inherent errors in total spectral irradiance (0.68 [mu]m) for a clear sky were 0.60, 6.0, 13.0, and 27.0% for solar zenith angles of 0?, 45?, 60?, and 75?. The technique can be used to characterize the error of a specific panel used in field measurements and thus eliminate any ambiguity of the effects of the type, preparation, and aging of the paint.
    BibTeX:
    @article{Kimes1982,
      author = {Kimes, D.S. and Kirchner, J.A.},
      title = {Irradiance measurement errors due to the assumption of a Lambertian reference panel},
      journal = {Remote Sensing of Environment},
      year = {1982},
      volume = {12},
      number = {2},
      pages = {141--149}
    }
    
    Kimes, D., Markham, B., Tucker, C. & McMurtrey III, J. Temporal relationships between spectral response and agronomic variables of a corn canopy 1981 Remote Sensing of Environment
    Vol. 11, pp. 401-411 
    article  
    Abstract: There is growing interest in employing hand-held radiometry as a nondestructive research tool in lieu of or support of more tedious vegetation measurements. The objective of this study was to evaluate such techniques on corn. The spectral radiances from corn plots 1.8 m in diameter were measured using a three-band radiometer elevated 3.7 m above the ground. The three spectral bands used corresponded to NASA'S Landsat-D Thematic Mapper bands TM3 (0.63-0.69 [mu]m), TM4 (0.76-0.90 [mu]m), and TM5 (1.55-1.75 [mu]m). Periodically throughout the growing season a plot was selected and radiometrically measured then harvested for measurement of several agronomic variables. By the end of the growing season, a total of 43 plots had been measured with solar zenith angles ranging between 16 and 44?. Significant relationships were found between various combinations of the radiance data and the wet and dry total biomass, plant height, fraction of ground covered by plants, wet and dry green leaf biomass, green leaf area index, fraction of leaf chlorosis, and total plant water content. Some of these relationships were found to be redundant since several of the agronomic variables were highly correlated to one another. In addition, the TM5 band did not provide any marked improvement in the relationships to the agronomic variables. The relationships between the radiance data and agronomic variables represent a nondestructive remote sensing technique for researching the growth of corn canopies.
    BibTeX:
    @article{Kimes1981,
      author = {Kimes, D.S and Markham, B.L and Tucker, C.J and McMurtrey III, J.E},
      title = {Temporal relationships between spectral response and agronomic variables of a corn canopy},
      journal = {Remote Sensing of Environment},
      year = {1981},
      volume = {11},
      pages = {401--411}
    }
    
    Kimes, D., Nelson, R., Skole, D. & Salas, W. Accuracies in Mapping Secondary Tropical Forest Age from Sequential Satellite Imagery 1998 Remote Sensing of Environment
    Vol. 65(1), pp. 112-120 
    article  
    Abstract: Multitemporal satellite images have been used to differentiate, measure the areal extent of, and determine transitional probabilities among different secondary forest age classes in the tropics. In these studies, temporal gaps in the satellite archive are common due to difficulties associated with availability of cloud-free data, costs, temporal discontinuities between satellite sensors, etc. In this probability study, examples of multitemporal image sequences with data gaps are considered in order to illustrate error rates associated with estimating the age of secondary tropical forest. Results indicate that on the order of 8-32% of scene pixels may be misclassified with respect to age if land cover transitions which occur within the data gap(s) are ignored. Using secondary forest regeneration rates from the literature, calculations showed that these gap errors caused the above-ground biomass to be overestimated by 8-23%. The error rates are scene-dependent. The results are presented to flag a potentially significant source of error.
    BibTeX:
    @article{Kimes1998,
      author = {Kimes, D.S. and Nelson, R.F. and Skole, D.L. and Salas, W.A.},
      title = {Accuracies in Mapping Secondary Tropical Forest Age from Sequential Satellite Imagery},
      journal = {Remote Sensing of Environment},
      year = {1998},
      volume = {65},
      number = {1},
      pages = {112--120}
    }
    
    Kimes, D., Newcomb, W., Tucker, C., Zonneveld, I., Van Wijngaarden, W., De Leeuw, J. & Epema, G. Directional reflectance factor distributions for cover types of Northern Africa 1985 Remote Sensing of Environment
    Vol. 18(1), pp. 1-19 
    article  
    Abstract: Directional reflectance factors that spanned the entire exitance hemisphere were collected on the ground throughout the morning period for common cover types in Tunisia, Africa. NOAA 7/8 AVHRR bands 1 (0.58-0.68 [mu]m) and 2 (0.73-1.1 [mu]m) were used in data collection. The cover types reported were a plowed field, annual grassland, steppe grassland, hard wheat, salt plain, and irrigated wheat. Several of these cover types had geometric structures that are extreme as compared to those reported in the literature. Comparisons were made between the dynamics of the observed reflectance distributions and those reported in the literature. It was found that the dynamics of the measured data could be explained by a combination of soil and vegetation scattering components. The data and analysis further validated physical principles that cause the reflectance distribution dynamics as proposed by field and simulation studies in the literature. Finally, the normalized difference transformation [(Band 2 - Band 1)/(Band 1 + Band 2)], which is useful in monitoring vegetation cover, generally decreased the variation in signal with changing view angle. However, several exceptions were noted.
    BibTeX:
    @article{Kimes1985,
      author = {Kimes, D.S. and Newcomb, W.W. and Tucker, C.J. and Zonneveld, I.S. and Van Wijngaarden, W. and De Leeuw, J. and Epema, G.F.},
      title = {Directional reflectance factor distributions for cover types of Northern Africa},
      journal = {Remote Sensing of Environment},
      year = {1985},
      volume = {18},
      number = {1},
      pages = {1--19}
    }
    
    Kimes, D., Ranson, K., Sun, G. & Blair, J. Predicting lidar measured forest vertical structure from multi-angle spectral data 2006 Remote Sensing of Environment
    Vol. 100(4), pp. 503-511 
    article  
    Abstract: A capability to remotely measure the vertical and spatial distribution of forest structure is required for more accurate modeling of energy, carbon, water, and climate over regional, continental, and global scales. We examined the potential of using a multi-angle spectral sensor to predict forest vertical structure as measured by an airborne lidar system. Data were acquired from AirMISR (Airborne Multi-Angle Imaging Spectrometer) and airborne LVIS (Laser Vegetation Imaging Sensor) for a 7000 ha study site near Howland Maine, consisting of small plantations, multi-generation clearings and large natural forest stands. The LVIS data set provided a relatively direct measure of forest vertical structure at a fine scale (20 m diameter footprints). Multivariate linear regression and neural network models were developed to predict the LVIS forest energy height measures from 28 AirMISR multi-angle spectral radiance values. The best model accurately predicted the maximum canopy height (as measured from LVIS) using AirMISR data (rmse?=?0.92 m, R2?=?0.89). The models developed in this study achieved high accuracies over a study site with an elaborate patchwork of forest communities with exceptional diversity in forest structure. We conclude that models using MISR-like data are capable of accurately predicting the vertical structure of forest canopies.
    BibTeX:
    @article{Kimes2006,
      author = {Kimes, D.S. and Ranson, K.J. and Sun, G. and Blair, J.B.},
      title = {Predicting lidar measured forest vertical structure from multi-angle spectral data},
      journal = {Remote Sensing of Environment},
      year = {2006},
      volume = {100},
      number = {4},
      pages = {503--511}
    }
    
    Kimes, D. & Sellers, P. Inferring hemispherical reflectance of the earth's surface for global energy budgets from remotely sensed nadir or directional radiance values 1985 Remote Sensing of Environment
    Vol. 18(3), pp. 205-223 
    article  
    Abstract: The importance of the hemispherical reflectance (albedo) of terrestrial surfaces to biospheric and atmospheric processes is briefly reviewed. It is proposed that satellite-borne instruments represent the only practical means of obtaining global estimates of surface albedo data at reasonable time resolution, the problem being how to relate the nadir or directional reflectance observations obtained from such sensors to the integrated hemispherical reflectance. This paper discusses results measured at ground level in which NOAA satellite 7/8 AVHRR data, Bands 1 (0.58-0.68 [mu]m) and 2 (0.73-1.1 [mu]m), were used to investigate 1) the relationships between directional reflectances (spanning the entire reflecting hemisphere) and hemispherical reflectance (albedo) and 2) the effect of solar zenith angle and cover type on these relationships. Eleven natural vegetation surfaces ranging from bare soils to dense vegetation canopies were considered in the study. The results show that errors in inferring hemispherical reflectance from nadir reflectance can be as high as 45% for all cover types and solar zenith angles. By choosing a time of observation such that the solar zenith angle is between 30 and 40? the same error is reduced to less than 20% in both bands. For both bands a view angle of 60? off-nadir and ?90? from the solar azimuth reduces this error to less than 11% for all sun angles and cover types. A technique using two specific view angles reduces this error to less than 6% for both bands and for all sun angles and cover types. These techniques may yield considerable dividends in terms of more reliable estimation of hemispherical reflectance of natural surfaces.
    BibTeX:
    @article{Kimes1985a,
      author = {Kimes, D.S. and Sellers, P.J.},
      title = {Inferring hemispherical reflectance of the earth's surface for global energy budgets from remotely sensed nadir or directional radiance values},
      journal = {Remote Sensing of Environment},
      year = {1985},
      volume = {18},
      number = {3},
      pages = {205--223}
    }
    
    Kimes, D.S., Holben, B.N., Nickeson, J.E. & McKee, W.A. Extracting forest age in a Pacific Northwest forest from Thematic Mapper and topographic data 1996 Remote Sensing of Environment
    Vol. 56(2), pp. 133-140 
    article  
    Abstract: The feasibility of extracting forest age of young stands (< 50 yr) in a Pacific Northwest Forest using Landsat Thematic Mapper (TM) spectral bands and topographic information was explored using a neural network approach. Understanding the changes of forest fragmentation through time are important for assessing alterations in ecosystem processes (forest productivity, species diversity, nutrient cycling, carbon flux, hydrology, spread of pests, etc.) and wildlife habitat and populations. The study area was the H.J. Andrews Experimental Forest on the Blue River Ranger District of the Willamette National Forest in western Oregon. Timber harvesting has occurred in this forest over the past 45 years and has a recorded forest management history. The study area was extracted from a georeferenced TM scene acquired on 7 July 1991. A coincident digital terrain model (DTM) derived from digital topographic elevation data was also acquired. Using this DTM and an image processing software package, slope and aspect images were generated over the study area. Sites were chosen to cover the entire range of forest stand age and slope and aspect. The oldest recorded clearcut stands were logged in 1950. A number of sites were chosen as primary forest which had no recorded history of cutting. Various feed-forward neural networks trained with back propagation were tested to predict forest age from TM data and topographic data. The results demonstrated that neural networks can be used as an initial model for inferring forest age. The best network was a 6-->5-->1 structure with inputs of TM Bands 3, 4, and 5, elevation, slope and aspect. The rms values of the predicted forest age were on the order of 5 years. TM Bands 1, 2, 6, and 7 did not significantly add information to the network for learning forest age. Furthermore, the results suggest that topographic information (elevation, slope, and aspect) can be effectively utilized by a neural network approach. The results of the network approach were significantly better than corresponding linear systems.
    BibTeX:
    @article{Kimes1996,
      author = {Kimes, D. S. and Holben, B. N. and Nickeson, J. E. and McKee, W. A.},
      title = {Extracting forest age in a Pacific Northwest forest from Thematic Mapper and topographic data},
      journal = {Remote Sensing of Environment},
      year = {1996},
      volume = {56},
      number = {2},
      pages = {133--140}
    }
    
    Koch, B. & Friedlaender, H. Erste Erfahrungen zum Einsatz von Laserscannerdaten zur Erfassung von vertikalen und horizontalen Strukturen im Wald 1999   article  
    Abstract: Zielsetzung der Untersuchungen ist es zu pr"ufen, in welchem Umfang flugzeuggetragene Laserscannersysteme im Rahmen von Waldinventur und wald"okologischen Untersuchungen eingesetzt werden koennen. Hierbei sollen neue Methoden zur Informationsextraktion und -darstellung entwickelt und bestehende Algorithmen erprobt werden. Im Rahmen der Forstinventur sind insbesondere die automatische Messung von Baumh"ohen f"ur verschiedene Baumarten und die automatische Kronendelinierung von grossem Interesse, um daraus Inventurgroessen, wie Holzvolumen und Stammfl"ache u.a. abzuleiten. Im Hinblick auf die Wald"okosystemforschung und -kartierung ist dar"uber hinaus die Erfassung der Horizontal und Vertikalstrukturen sowie die Entwicklung von Kronenstrukturmodellen von Bedeutung. Neben der Informationsextraktion aus Laserscannerdaten wird im Rahmen des Untersuchungsprojektes eine Verkn"upfung von Laserscannerdaten mit optischen Daten, insbesondere den neuen hochaufl"osenden Daten, wie sie von Ikonos zur Verf"ugung gestellt werden, durchgef"uhrt, um auf der Basis der zus"atzlichen spektralen Information Aussagen zur Baumart und Vitalit"at in die forstlichen Modelle zur Datennutzung einbauen zu k"onnen. Langfristige Zielsetzung ist die Ableitung forstlicher und wald"okologischer Parameter durch Informationsextraktion aus kombinierten multispektralen Daten und Laserscannerdaten.
    BibTeX:
    @article{koch,
      author = {Barbara Koch and Hans Friedlaender},
      title = {Erste Erfahrungen zum Einsatz von Laserscannerdaten zur Erfassung von vertikalen und horizontalen Strukturen im Wald},
      year = {1999}
    }
    
    Koetz, B., Baret, F., Poilve, H. & Hill, J. Use of coupled canopy structure dynamic and radiative transfer models to estimate biophysical canopy characteristics 2005 Remote Sensing of Environment
    Vol. 95(1), pp. 115-124 
    article  
    Abstract: Leaf area index (LAI) is a key variable for the understanding of several eco-physiological processes within a vegetation canopy. The LAI could thus provide vital information for the management of the environment and agricultural practices when estimated continuously over time and space thanks to remote sensing sensors.This study proposed a method to estimate LAI spatial and temporal variation based on multi-temporal remote sensing observations processed using a simple semi-mechanistic canopy structure dynamic model (CSDM) coupled with a radiative transfer model (RTM). The CSDM described the temporal evolution of the LAI as function of the accumulated daily air temperature as measured from classical ground meteorological stations.The retrieval performances were evaluated for two different data sets: first, a data set simulated by the RTM but taking into account realistic measurement conditions and uncertainties resulting from different error sources; second, an experimental data set acquired over maize crops the Blue Earth City area (USA) in 1998. Results showed that the proposed approach improved significantly the retrieval performances for LAI mainly by smoothing the residual errors associated to each individual observation. In addition it provides a way to describe in a continuous manner the LAI time course from a limited number of observations during the growth cycle.
    BibTeX:
    @article{koetz05,
      author = {Koetz, Benjamin and Baret, Frederic and Poilve, Herve and Hill, Joachim},
      title = {Use of coupled canopy structure dynamic and radiative transfer models to estimate biophysical canopy characteristics},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {95},
      number = {1},
      pages = {115--124}
    }
    
    Koetz, B., Morsdorf, F., Kneubühler, M., Schaepman, M., Meier, E., Itten, K. & Allgöwer, B. Combination of imaging spectrometer data and high resolution LIDAR data by 3-D radiative transfer modeling 2004 R.O. Green (Ed.), AVIRIS workshop, Pasadena, CA, USA, 2004.  inproceedings  
    BibTeX:
    @inproceedings{koetz_aviris04,
      author = {Koetz, B. and Morsdorf, F and Kneubühler, M. and Schaepman, M. and Meier, E. and Itten, K. and Allgöwer, B.},
      title = {Combination of imaging spectrometer data and high resolution LIDAR data by 3-D radiative transfer modeling},
      booktitle = {R.O. Green (Ed.), AVIRIS workshop, Pasadena, CA, USA, 2004.},
      year = {2004}
    }
    
    Koetz, B., Morsdorf, F., van der Linden, S., Curt, T. & Allgöwer, B. Multi-source land cover classification for forest fire management based on imaging spectrometry and LiDAR data 2008 Forest Ecology and Management
    Vol. 256(3)Impacts of forest ecosystem management on greenhouse gas budgets, pp. 263-271 
    article  
    Abstract: Forest fire management practices are highly dependent on the proper monitoring of the spatial distribution of the natural and man-made fuel complexes at landscape level. Spatial patterns of fuel types as well as the three-dimensional structure and state of the vegetation are essential for the assessment and prediction of forest fire risk and fire behaviour. A combination of the two remote sensing systems, imaging spectrometry and light detection and ranging (LiDAR), is well suited to map fuel types and properties, especially within the complex wildland-urban interface. LiDAR observations sample the spatial information dimension providing explicit geometric information about the structure of the Earth's surface and super-imposed objects. Imaging spectrometry on the other hand samples the spectral dimension, which is sensitive for discrimination of surface types. As a non-parametric classifier support vector machines (SVM) are particularly well adapted to classify data of high dimensionality and from multiple sources as proposed in this work. The presented approach achieves an improved land cover mapping adapted to forest fire management needs. The map is based on a single SVM classifier combining the spectral and spatial information dimensions provided by imaging spectrometry and LiDAR.
    BibTeX:
    @article{Koetz2008,
      author = {Koetz, B. and Morsdorf, F. and van der Linden, S. and Curt, T. and Allgöwer, B.},
      title = {Multi-source land cover classification for forest fire management based on imaging spectrometry and LiDAR data},
      booktitle = {Impacts of forest ecosystem management on greenhouse gas budgets},
      journal = {Forest Ecology and Management},
      year = {2008},
      volume = {256},
      number = {3},
      pages = {263--271}
    }
    
    Koetz, B., Morsdorf, F., Schaepman, M., Meier, E., Itten, K. & Allgöwer, B. Specific Parameterization of a Boreal Forest for a 3-D Radiative Transfer Modelling Approach based on Imaging Spectrometer Data and High Resolution LIDAR Data 2003 M. Rast (Ed.), Second SPECTRA Workshop. ESA/ESTEC, Noordwijk.  inproceedings  
    BibTeX:
    @inproceedings{koetz_spectra03,
      author = {Koetz, B. and Morsdorf, F. and Schaepman, M. and Meier, E. and Itten, K. and Allgöwer, B.},
      title = {Specific Parameterization of a Boreal Forest for a 3-D Radiative Transfer Modelling Approach based on Imaging Spectrometer Data and High Resolution LIDAR Data},
      booktitle = {M. Rast (Ed.), Second SPECTRA Workshop. ESA/ESTEC, Noordwijk.},
      year = {2003}
    }
    
    Koetz, B., Morsdorf, F., Sun, G., Ranson, K.J., Itten, K. & Allgower, B. Inversion of a Lidar Waveform Model for Forest Biophysical Parameter Estimation 2006 IEEE Geoscience and Remote Sensing Letters
    Vol. 3, pp. 49-53 
    article  
    BibTeX:
    @article{koetz06,
      author = {Koetz, B. and Morsdorf, F. and Sun, G. and Ranson, K. J. and Itten, K. and Allgower, B.3},
      title = {Inversion of a Lidar Waveform Model for Forest Biophysical Parameter Estimation},
      journal = {IEEE Geoscience and Remote Sensing Letters},
      year = {2006},
      volume = {3},
      pages = {49-53}
    }
    
    Koetz, B., Schaepman, M., Morsdorf, F., Itten, K. & Allgöwer, B. Radiative Transfer Modeling within a Heterogeneous Canopy for Estimation of Forest Fire Fuel Properties 2004 Remote Sensing of Environment
    Vol. 92(3), pp. 332-344 
    article  
    BibTeX:
    @article{koetz04,
      author = {B. Koetz and M. Schaepman and F. Morsdorf and K. Itten and B. Allgöwer},
      title = {Radiative Transfer Modeling within a Heterogeneous Canopy for Estimation of Forest Fire Fuel Properties},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {92},
      number = {3},
      pages = {332-344}
    }
    
    Koetz, B., Sun, G., Morsdorf, F., Ranson, K., Kneubuhler, M., Itten, K. & Allgower, B. Fusion of imaging spectrometer and LIDAR data over combined radiative transfer models for forest canopy characterization 2007 Remote Sensing of Environment
    Vol. 106(4), pp. 449-459 
    article  
    Abstract: A comprehensive canopy characterization of forests is derived from the combined remote sensing signal of imaging spectrometry and large footprint LIDAR. The inversion of two linked physically based Radiative Transfer Models (RTM) provided the platform for synergistically exploiting the specific and independent information dimensions obtained by the two earth observation systems. Due to its measurement principle, LIght Detection And Ranging (LIDAR) is particularly suited to assess the horizontal and vertical canopy structure of forests, while the spectral measurements of imaging spectrometry are specifically rich on information for biophysical and -chemical canopy properties. In the presented approach, the specific information content inherent to the observations of the respective sensor was not only able to complement the canopy characterization, but also helped to solve the ill-posed problem of the RTM inversion. The theoretical feasibility of the proposed earth observation concept has been tested on a synthetic data set generated by a forest growth model for a wide range of forest stands. Robust estimates on forest canopy characteristics were achieved, ranging from maximal tree height, fractional cover (fcover), Leaf Area Index (LAI) to the foliage chlorophyll and water content. The introduction of prior information on the canopy structure derived from large footprint LIDAR observations significantly improved the retrieval performance relative to estimates based solely on spectral information.
    BibTeX:
    @article{koetz07,
      author = {Koetz, Benjamin and Sun, Guoqing and Morsdorf, Felix and Ranson, K.J. and Kneubuhler, Mathias and Itten, Klaus and Allgower, Britta},
      title = {Fusion of imaging spectrometer and LIDAR data over combined radiative transfer models for forest canopy characterization},
      journal = {Remote Sensing of Environment},
      year = {2007},
      volume = {106},
      number = {4},
      pages = {449--459}
    }
    
    Koetz, B., Sun, G., Morsdorf, F., Ranson, K.J., Kneubuehler, M., Itten, K. & Allgoewer, B. Inversion of combined Radiative Transfer Models for Imaging Spectrometer and LIDAR Data {2006} 2006 IEEE INTERNATIONAL GEOSCIENCE AND REMOTE SENSING SYMPOSIUM, VOLS 1-8, pp. {395-398}  article  
    BibTeX:
    @article{ISI:000260989400102,
      author = {Koetz, B. and Sun, G. and Morsdorf, F. and Ranson, K. J. and Kneubuehler, M. and Itten, K. and Allgoewer, B.},
      title = {Inversion of combined Radiative Transfer Models for Imaging Spectrometer and LIDAR Data},
      booktitle = {2006 IEEE INTERNATIONAL GEOSCIENCE AND REMOTE SENSING SYMPOSIUM, VOLS 1-8},
      year = {2006},
      pages = {395-398},
      note = {IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Denver, CO, JUL 31-AUG 04, 2006}
    }
    
    Kooistra, L., Wamelink, W., Schaepman-Strub, G., Schaepman, M., van Dobben, H., Aduaka, U. & Batelaan, O. Assessing and predicting biodiversity in a floodplain ecosystem: Assimilation of net primary production derived from imaging spectrometer data into a dynamic vegetation model 2008 Remote Sensing of Environment
    Vol. 112(5)Earth Observations for Terrestrial Biodiversity and Ecosystems Special Issue, pp. 2118-2130 
    article URL 
    Abstract: New concepts for river management in northwestern Europe are being developed which aim at both flood protection and nature conservation. As a result, methods are required that assess the effect of management activities on the biodiversity of floodplain ecosystems. In this paper, we show that dynamic vegetation models (DVMs) in combination with regional scale derived remote sensing products can be adopted to assess both current and future ecosystem development and biodiversity status of a complex floodplain ecosystem in the Netherlands. The dynamic vegetation model SMART2-SUMO2 in combination with the nature valuation model NTM3 predicting potential floristic diversity was applied to simulate the biodiversity status of the Millingerwaard floodplain along the river Rhine in the Netherlands. Estimates of net primary production (NPP) derived from airborne HyMap imaging spectrometer data were used for validation of the simulated NPP by the DVM at the time of data acquisition in 2004. Imaging spectrometer derived NPP was in good agreement with the SMART2-SUMO2 modeled results. The NTM3 derived nature valuation in 2004 expressed as plant diversity for the floodplain was high and well in agreement with field observations. In a next step, the DVM was re-initialized using imaging spectrometer derived NPP in 2004 and a forecast of plant diversity and biomass development in 2050 was made. A comparison was performed for three pre-defined floodplain management scenarios using a data-assimilation based approach as well as one without. Significant differences in biomass development can be observed between the scenarios. Predicted plant diversity for individual ecosystems in 2050 shows increased variability for forest ecosystems compared to grass ecosystems. This shows that floodplain management should take advantage of spatiotemporal dynamics of the floodplain as a basis for fostering the development of increased biodiversity. The results of this study demonstrate that imaging spectrometer derived products can be used for validation and initialization of DVMs.
    BibTeX:
    @article{Kooistra2008,
      author = {Kooistra, Lammert and Wamelink, Wieger and Schaepman-Strub, Gabriela and Schaepman, Michael and van Dobben, Han and Aduaka, Uchenna and Batelaan, Okke},
      title = {Assessing and predicting biodiversity in a floodplain ecosystem: Assimilation of net primary production derived from imaging spectrometer data into a dynamic vegetation model},
      booktitle = {Earth Observations for Terrestrial Biodiversity and Ecosystems Special Issue},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {5},
      pages = {2118--2130},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4S08YMY-2/2/f7bd31a4501e5f390adb6909ec89f64a}
    }
    
    Kotchenova, S.Y., Shabanov, N.V., Knyazikhin, Y., Davis, A.B., Dubayah, R. & Myneni, R.B. Modeling lidar waveforms with time-dependent stochastic radiative transfer theory for remote estimations of forest structure. 2003 Journal of Geophysical Research
    Vol. 108(D15), pp. 4484 
    article DOI  
    BibTeX:
    @article{kotchenova03,
      author = {S. Y. Kotchenova and N. V. Shabanov and Y. Knyazikhin and A. B. Davis and R. Dubayah and R. B. Myneni},
      title = {Modeling lidar waveforms with time-dependent stochastic radiative transfer theory for remote estimations of forest structure.},
      journal = {Journal of Geophysical Research},
      year = {2003},
      volume = {108},
      number = {D15},
      pages = {4484},
      doi = {http://dx.doi.org/10.1029/2002JD003288.}
    }
    
    Kotchenova, S.Y., Song, X., Shabanov, N.V., Potter, C.S., Knyazikhin, Y. & Myneni, R.B. Lidar remote sensing for modeling gross primary production of deciduous forests 2004 Remote Sensing of Environment
    Vol. 92(2), pp. 158-172 
    article  
    Abstract: The influence of foliage vertical distribution on vegetation gross primary production (GPP) is investigated in this study. A new photosynthesis model has been created that combines the standard sunlit/shaded leaf separation (two-leaf) and the multiple layer approaches and uses vertical foliage profiles measured by SLICER (the Scanning Lidar Imager of Canopies by Echo Recovery). Daily gross carbon assimilation rates calculated by this model were compared with the rates calculated by two other models, the two-leaf model and the combined two-leaf multilayer model utilizing uniform foliage profiles. The comparison was made over a wide range of profiles and weather conditions for two mixed deciduous forest stands in eastern Maryland, measured by SLICER in September 1995. Incident radiation pattern, environmental parameters and total amounts of sunlit and shaded leaves were the same for all three models. The difference was in the distributions of radiation and sunlit/shaded leaves inside the canopy. For the combined models, these distributions were calculated based on the vertical foliage profiles, while for the two-leaf model, empirical equations were used to account for the average amounts of absorbed radiation. The simulations showed that: (1) the use of a uniform foliage distribution instead of the actual one results in large differences in the calculated GPP values, up to 46.4% and 50.7% for the days with partial and total cloud cover; (2) the performance of the two-leaf model is extremely sensitive to the absorbed radiation pattern, its disagreement with the proposed model becomes insignificant when the average amounts of absorbed radiation are the same; (3) days with partial cloud cover and a greater fraction of diffuse radiation are characterized by higher GPP rates. These findings highlight the importance of vertical foliage profile and separate treatments of diffuse and direct radiation for photosynthesis modeling.
    BibTeX:
    @article{kotechenova04,
      author = {Kotchenova, Svetlana Y. and Song, Xiangdong and Shabanov, Nikolay V. and Potter, Christopher S. and Knyazikhin, Yuri and Myneni, Ranga B.},
      title = {Lidar remote sensing for modeling gross primary production of deciduous forests},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {92},
      number = {2},
      pages = {158-172}
    }
    
    Kraus, K. & Pfeifer, N. Advanced DTM Generation from LIDAR Data 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 23-35 
    article  
    Abstract: The introduction of laser scanning has triggered o a revolution in topographic terrain capturing, especially in the generation of digital terrain models (DTM). In this article refined methods for the restitution of airborne LIDAR data are presented which have been developed at the Institute of Photogrammetry and Remote Sensing (Institut ftextregisteredur Photogrammetrie und Fernerkundung, I.P.F.) at Vienna University of Technology. First, a technique for the calibration of laser scanner data is introduced. The (height) discrepancies between overlapping strips, as well as control points with known co-ordinates are utilised for a simultaneous adjustment and transformation of all strips into a state wide co-ordinate system. The next step of LIDAR data processing are the filtering (elimination of vegetation and building points, generally o -terrain points) and the interpolation of the (bald earth) surface. The method, developed at the I.P.F., distinguishes itself in the integration of filtering and terrain interpolation in one process (advantage: even in steep terrain ground points are classified correctly) as well as in the application of data pyramids (advantage: even in very dense forest areas and on large buildings, o -terrain points are eliminated). In order to generate a terrain model with high geo-morphological quality, methods are required for deriving structural line information (e.g. break lines) from laser scanner data. The first method which will be presented, proceeds by a simulation of rain fall over the preliminary DTM (water flow analysis). This yields an identification of the pits with their pit base and the outflow (overflow) point. Subsequently, the terrain shape is changed in order to eliminate the pits. In a further method 3D break lines are derived from the original laser scanner points. The precondition is that the ground plan of the break line is known approximately. The result of this step are 3D-splines which are integrated in the hybrid DTM, combining raster and vector data.
    BibTeX:
    @article{kraus01,
      author = {K. Kraus and N. Pfeifer},
      title = {Advanced DTM Generation from LIDAR Data},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {23-35}
    }
    
    Kraus, K. & Pfeifer, N. Determination of terrain models in wooded areas with airborne laser scanner data 1998 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 53, pp. 193-203 
    article  
    Abstract: Large-scale terrain measurement in wooded areas was an unsolved problem up to now. Laser scanning solves this problem to a large extent. In this article, the characteristics of laser scanning will be compared to photogrammetry with reference to a big pilot project. Laser scanning supplies data with a skew distribution of errors because a portion of the supplied points is not on the terrain but on the treetops. Thus, the usual interpolation and filtering has to be adapted to this new data type. We will report on the implementation of this new method. The results are in accordance with the expectations. The geomorphologic quality of the contours, computed from a terrain model derived from laser scanning, needs to be improved. Solutions are still to be found.
    BibTeX:
    @article{kraus98,
      author = {K. Kraus and N. Pfeifer},
      title = {Determination of terrain models in wooded areas with airborne laser scanner data},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {1998},
      volume = {53},
      pages = {193-203}
    }
    
    Kuusk, A., Kuusk, J. & Lang, M. A dataset for the validation of reflectance models 2009 Remote Sensing of Environment
    Vol. 113(5), pp. 889 - 892 
    article DOI URL 
    Abstract: Three mature stands at the forest test site J?rvselja, Estonia were extensively measured for using as a validation dataset for heterogeneous canopy reflectance models. In order to enable the reconstruction of the 3-D architecture of these 100 ? 100 m2 test plots, individual tree positions and crown dimensions were inventoried. In addition, leaf, needle, stem bark and branch bark visible and near-infrared (VNIR) reflectance spectra, and VNIR reflectance spectra of ground vegetation were measured. This in situ dataset is supported by atmospherically and radiometrically corrected Mode 3 CHRIS reflectance spectra for three view directions, and top of canopy VNIR nadir spectra from airborne measurements. Details of measurements, instruments in use, data processing, and access to data are described in a technical report which is available on-line.
    BibTeX:
    @article{Kuusk2009889,
      author = {Andres Kuusk and Joel Kuusk and Mait Lang},
      title = {A dataset for the validation of reflectance models},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {5},
      pages = {889 - 892},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4VNCC54-3/2/712d200190ada98be5192b9c409fc373},
      doi = {DOI: 10.1016/j.rse.2009.01.005}
    }
    
    Kuusk, A., Nilson, T., Kuusk, J. & Lang, M. Reflectance spectra of RAMI forest stands in Estonia: Simulations and measurements 2010 Remote Sensing of Environment
    Vol. 114(12), pp. 2962 - 2969 
    article DOI URL 
    Abstract: Simulated reflectance spectra of three mature hemiboreal forests are compared to top-of-canopy reflectance factor from helicopter measurements in the spectral range of 400-1050 nm. Most of the input parameters of the forest reflectance model FRT used in the simulations have been measured in situ. The same data were used in the fourth phase of the Radiation Transfer Model Intercomparison (RAMI). The reasons of the discrepancies between simulated and measured spectra are analyzed.
    BibTeX:
    @article{Kuusk20102962,
      author = {Andres Kuusk and Tiit Nilson and Joel Kuusk and Mait Lang},
      title = {Reflectance spectra of RAMI forest stands in Estonia: Simulations and measurements},
      journal = {Remote Sensing of Environment},
      year = {2010},
      volume = {114},
      number = {12},
      pages = {2962 - 2969},
      url = {http://www.sciencedirect.com/science/article/B6V6V-50X30Y5-1/2/e0e0af675c9aacc9374665f15deacbae},
      doi = {DOI: 10.1016/j.rse.2010.07.014}
    }
    
    Kvalseth, T.O. Cautionary note about $R^2$ 1985 American Statistician
    Vol. 39, pp. 279-285 
    article  
    BibTeX:
    @article{kvalseth85,
      author = {Kvalseth, T. O.},
      title = {Cautionary note about $R^2$},
      journal = {American Statistician},
      year = {1985},
      volume = {39},
      pages = {279-285}
    }
    
    Kötz, B., Schaepman, M., Morsdorf, F., Bowyer, P., Itten, K. & Allgöwer, B. Scaling-up based on Radiative Transfer Modeling in a Pine (Pinus Montana ssp. arborea) dominated Canopy for Forest Fire Fuel Properties Mapping using ImagingSpectrometer Data 2003 EARSEL - 4th International Workshop: Remote Sensing and GIS applications for Forest Fire Management, Ghent.  inproceedings  
    BibTeX:
    @inproceedings{koetz_earsel03,
      author = {Kötz, B. and Schaepman, M. and Morsdorf, F. and Bowyer, P. and Itten, K. and Allgöwer, B.},
      title = {Scaling-up based on Radiative Transfer Modeling in a Pine (Pinus Montana ssp. arborea) dominated Canopy for Forest Fire Fuel Properties Mapping using ImagingSpectrometer Data},
      booktitle = {EARSEL - 4th International Workshop: Remote Sensing and GIS applications for Forest Fire Management, Ghent.},
      year = {2003}
    }
    
    Kötz, B., Schaepman, M., Morsdorf, F., Bowyer, P., Itten, K. & Allgöwer, B. Multiresolution Imaging Spectroscopy Resolving the Structure of HeterogeneousCanopies for Forest Fire Fuel Properties Mapping 2003 IGARSS 2003, Toulouse.  inproceedings  
    BibTeX:
    @inproceedings{koetz_igarss03,
      author = {Kötz, B. and Schaepman, M. and Morsdorf, F. and Bowyer, P. and Itten, K and Allgöwer, B.},
      title = {Multiresolution Imaging Spectroscopy Resolving the Structure of HeterogeneousCanopies for Forest Fire Fuel Properties Mapping},
      booktitle = {IGARSS 2003, Toulouse.},
      year = {2003}
    }
    
    Lafon, V., Froidefond, J., Lahet, F. & Castaing, P. SPOT shallow water bathymetry of a moderately turbid tidal inlet

    based on field measurements

    2002 Remote Sensing of Environment
    Vol. 81, pp. 136-148 
    article  
    BibTeX:
    @article{lafon02,
      author = {V. Lafon and J.M. Froidefond and F. Lahet and P. Castaing},
      title = {SPOT shallow water bathymetry of a moderately turbid tidal inlet

    based on field measurements}, journal = {Remote Sensing of Environment}, year = {2002}, volume = {81}, pages = {136-148} }

    Lang, M., Nilson, T., Kuusk, A., Kiviste, A. & Hordo, M. The performance of foliage mass and crown radius models in forming the input of a forest reflectance model: A test on forest growth sample plots and Landsat 7 ETM+ images 2007 Remote Sensing of Environment
    Vol. 110(4), pp. 445 - 457 
    article DOI URL 
    Abstract: Several published foliage mass and crown radius regression models were tested on the preparation of the input for the reflectance model of Kuusk and Nilson [Kuusk, A. and Nilson, T. (2000), A directional multispectral forest reflectance model. Remote Sensing of Environment, 72(2):244-252.] for 246 forest growth sample plots in Estonia. In each test, foliage mass and crown radius for trees in the sample plots were predicted with a particular pair of allometric regression models. The forest reflectance model was then run using the estimated foliage mass and crown radius values. Reflectance factors were simulated and compared with the reflectance values obtained from three atmospherically corrected Landsat 7 Enhanced Thematic Mapper (ETM+) scenes. The statistics of linear regression between the simulated and measured reflectance factors were used to assess the performance of foliage and crown radius models. The hypothesis was that the best allometric regression models should provide the best fit in reflectance. The strongest correlation between the simulated and measured reflectance factors was found in the short-wave infrared band (ETM + 5) for all the images. The highest R2 = 0.71 was observed in Picea abies dominated stands. No excellent combination of foliage mass and crown radius functions was found, but the ranking based on determination coefficients showed that some linear crown radius models are not applicable to our data. Processing of raster images, reflectance measurement for small sample plots, usage of tree-species-specific fixed parameters (specific leaf area, etc.), and the ignored influence of phenology introduced additional variation into the relationships between simulated and measured reflectance factors. Further studies are needed, but these preliminary results demonstrate that the proposed method could serve as an effective way of testing the performance of foliage mass and canopy cover regressions.
    BibTeX:
    @article{Lang2007445,
      author = {Mait Lang and Tiit Nilson and Andres Kuusk and Andres Kiviste and Maris Hordo},
      title = {The performance of foliage mass and crown radius models in forming the input of a forest reflectance model: A test on forest growth sample plots and Landsat 7 ETM+ images},
      journal = {Remote Sensing of Environment},
      year = {2007},
      volume = {110},
      number = {4},
      pages = {445 - 457},
      note = {ForestSAT Special Issue, ForestSAT 2005 Conference #Operational##tools##in##forestry##using##remote##sensing##techniques#},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4NYJS2W-1/2/7e1090d0bc6bfe21185f705de19c7f29},
      doi = {DOI: 10.1016/j.rse.2006.11.030}
    }
    
    Latham, P., Zuuring, H. & Coble, D. A method for quantifying vertical forest structure. 1998 Forest Ecology and Management
    Vol. 104, pp. 157-170 
    article  
    BibTeX:
    @article{latham98,
      author = {Latham, P.A. and Zuuring, H.R. and Coble, D.W.},
      title = {A method for quantifying vertical forest structure.},
      journal = {Forest Ecology and Management},
      year = {1998},
      volume = {104},
      pages = {157-170}
    }
    
    Latypov, D. Estimating relative lidar accuracy information from overlapping flight lines 2002 ISPRS Journal of Photogrammetry and Remote Sensing
    Vol. 56(4), pp. 236-245 
    article  
    Abstract: A pure statistical method for estimating relative lidar accuracy by comparing overlapping lidar datasets is described. It has been designed for commercial, fast turnaround, high-volume data production environment and has the following features. It operates on raw data and no building of grid or TIN is required. The method performs accuracy computations on statistical samples that are orders of magnitude larger than ones used in other methods reported in the literature, thus allowing detailed error analysis. Finally, the method provides a lot of relative accuracy information even when no ground control points are available. Software implementation of the method has been written and extensively tested on almost 100 Gb worth of data. Robust and fully automated, it has become an important quality control tool for data processing at TerraPoint.The method begins with the definition of a relative accuracy estimate, which is generalized from being a measure of point-to-point closeness to a measure of surface-to-surface closeness. Thus, a problem of matching the individual points in the overlapping datasets is eliminated. The generalized accuracy estimate is a function of surface size and flatness. Sampling overlap area by surfaces of different size allows one to discriminate between the random, systematic and locally systematic errors. The relative accuracy in the traditional sense of using only some tie points is a limiting case of the generalized one and can also be computed. The concepts and ideas of the method are illustrated by examples from real-life lidar projects.
    BibTeX:
    @article{latypov02,
      author = {Latypov, Damir},
      title = {Estimating relative lidar accuracy information from overlapping flight lines},
      journal = {ISPRS Journal of Photogrammetry and Remote Sensing},
      year = {2002},
      volume = {56},
      number = {4},
      pages = {236--245}
    }
    
    Lauber, K. & Wagner, G. Flora Helvetica. Flora der Schweiz 1996 Bern, Stuttgart, Wien, Paul Haupt Verlag, pp. 1613  article  
    BibTeX:
    @article{lauber96,
      author = {K. Lauber and G. Wagner},
      title = {Flora Helvetica. Flora der Schweiz},
      journal = {Bern, Stuttgart, Wien, Paul Haupt Verlag},
      year = {1996},
      pages = {1613}
    }
    
    Le Toan, T., Beaudoin, A., Riom, J. & Guyon, D. Relating forest biomass to SAR data 1992 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 30(2)Geoscience and Remote Sensing, IEEE Transactions on, pp. 403-411 
    article  
    Abstract: The authors present the results of an experiment defined to demonstrate the use of radar to retrieve forest biomass. The SAR data were acquired by the NASA/JPL SAR over the Landes pine forest during the 1989 MAESTRO-1 campaign. The SAR data, after calibration, were analyzed together with ground data collected on forest stands from a young stage (eight years) to a mature stage (46 years). The dynamic range of the radar backscatter intensity from forest was found to be greatest at P-band and decreased with increasing frequencies. Cross-polarized backscatter intensity yielded the best sensitivities to variations of forest biomass. L-band data confirmed past results on good correlation with forest parameters. The most striking observation was the strong correlation of P-band backscatter intensity to forest biomass
    BibTeX:
    @article{LeToan1992,
      author = {Le Toan, T. and Beaudoin, A. and Riom, J. and Guyon, D.},
      title = {Relating forest biomass to SAR data},
      booktitle = {Geoscience and Remote Sensing, IEEE Transactions on},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {1992},
      volume = {30},
      number = {2},
      pages = {403--411}
    }
    
    Leckie, D., Gougeon, F., Hill, D., Quinn, R., Armstrong, L. & Shreenan, R. Combined high-density lidar and multispectral

    imagery for individual tree crown analysis

    2003 Canadian Journal of Remote Sensing
    Vol. 29, pp. 633-649 
    article  
    BibTeX:
    @article{leckie03,
      author = {Don Leckie and Francois Gougeon and David Hill and Rick Quinn and Lynne Armstrong and and Roger Shreenan},
      title = {Combined high-density lidar and multispectral 

    imagery for individual tree crown analysis}, journal = {Canadian Journal of Remote Sensing}, year = {2003}, volume = {29}, pages = {633-649} }

    Leckie, D.G., Gougeon, F.A., Tinis, S., Nelson, T., Burnett, C.N. & Paradine, D. Automated tree recognition in old growth conifer stands with high resolution digital imagery 2004 Remote Sensing of Environment
    Vol. 94(3), pp. 311-326 
    article  
    Abstract: Automated individual tree isolation and species determination with high resolution multispectral imagery is becoming a viable forest survey tool. Application to old growth conifer forests offer unique technical issues including high variability in tree size and dominance, strong tree shading and obscuration, and varying ages and states of health. The capabilities of individual tree analysis are examined with two acquisitions of 70-cm resolution CASI imagery over a hemlock, amabilis fir, and cedar dominated old growth site on the west coast of Canada. Trees were delineated using the valley following approach of the Individual Tree Crown (ITC) software suite, classified according to species (hemlock, amabilis fir, and cedar) using object-based spectral classification and tested on a tree-for-tree basis against data derived from ground plots.Tree-for-tree isolation and species classification accuracy assessment, although often sobering, is important for portraying the overall effectiveness of species composition mapping using single tree approaches. This accuracy considers not only how well each tree is classified, but how well each automated isolation represents a true tree and its species. Omissions and commissions need to be included in overall species accuracy assessment. A structure of rules for defining isolation accuracy is developed and used. An example is given of a new approach to accuracy analysis incorporating both isolation and classification results (automated tree recognition) and the issues this presents.The automated tree isolation performed well on those trees that could be visually identified on the imagery using ground measured stem maps (approximately 50-60% of trees had a good match between manual and automated delineations). There were few omissions. Commission errors, i.e., automated isolations not associated with a delineated ground reference tree, were a problem (25%) usually associated with spurious higher intensity areas within shaded regions, which get confused in the process of trying to isolate shaded trees. Difficulty in classifying species was caused by: variability of the spectral signatures of the old growth trees within the same species, tree health, and trees partly or fully shaded by other trees. To accommodate this variability, several signatures were used to represent each species including shaded trees. Species could not be determined for the shaded cases or for the unhealthy trees and therefore two combined classes, a shaded class and unhealthy class with all species included, were used for further analysis. Species classification accuracy of the trees for which there was a good automated isolation match was 72%, 60%, and 40% for the non-shaded healthy hemlock, balsam, and cedar trees for the 1996 data. Equivalent accuracy for the 1998 imagery was 59% for hemlock, 80% for balsam, with only a few cedar trees being well isolated. If all other matches were considered an error in classification, species classification was poor (approximately 45% for balsam and hemlock, 25% for cedar). However, species classification accuracies incorporating the good isolation matches and trees for which there was a match of an isolations and reference tree but the match was not considered good were moderate (60%, 57%, and 38% for hemlock, balsam, and cedar from the 1996 data; 62%, 61%, and 89%, respectively, for the 1998 imagery).Automated tree isolation and species classification of old growth forests is difficult, but nevertheless in this example useful results were obtained.
    BibTeX:
    @article{leckie04,
      author = {Donald G. Leckie and Francois A. Gougeon and Sally Tinis and Trisalyn Nelson and Charles N. Burnett and Dennis Paradine},
      title = {Automated tree recognition in old growth conifer stands with high resolution digital imagery},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {94},
      number = {3},
      pages = {311-326}
    }
    
    Lee, B.S., Alexander, M.E., Hawkes, B.C., Lynham, T.J., Stocks, B.J. & Englefield, P. Information systems in support of wildland fire management decision making in Canada 2002 Computers and Electronics in Agriculture
    Vol. 37(1-3), pp. 185-198 
    article  
    Abstract: This paper provides an overview of four national forest fire management information systems currently used in Canada. The Canadian forest fire danger rating system (CFFDRS) is a non-spatial system, which provides the science framework for fire danger rating in Canada. The spatial fire management system (sFMS) is a geographic information system based fire management information system that implements two core subsystems of the CFFDRS, along with other models and systems. The sFMS is the spatial engine that has been used to implement both of Canada's national forest fire management information systems, the Canadian wildland fire information system (CWFIS) and the fire monitoring, mapping and modeling system (Fire M3). The CWFIS is Canada's national fire management information system; it presents daily information on fire weather, fire behavior potential and selected upper atmospheric conditions. Fire M3 integrates the use of satellite technology for monitoring and mapping large fire occurrence in Canada. Fire M3 also incorporates information from CWFIS to model the impacts of large forest fires based on fire weather conditions and potential fire behavior.
    BibTeX:
    @article{Lee2002,
      author = {Lee, B. S. and Alexander, M. E. and Hawkes, B. C. and Lynham, T. J. and Stocks, B. J. and Englefield, P.},
      title = {Information systems in support of wildland fire management decision making in Canada},
      journal = {Computers and Electronics in Agriculture},
      year = {2002},
      volume = {37},
      number = {1-3},
      pages = {185--198}
    }
    
    Lee, K.-S., Cohen, W.B., Kennedy, R.E., Maiersperger, T.K. & Gower, S.T. Hyperspectral versus multispectral data for estimating leaf area index in four different biomes 2004 Remote Sensing of Environment
    Vol. 91(3-4), pp. 508-520 
    article  
    Abstract: Motivated by the increasing importance of hyperspectral remote sensing data, this study sought to determine whether current-generation narrow-band hyperspectral remote sensing data could better track vegetation leaf area index (LAI) than traditional broad-band multispectral data. The study takes advantage of a unique dataset, wherein field measurements of LAI were acquired at the same general time and grain size as both Landsat ETM+ and AVIRIS (Airborne Visible/Infrared Imaging Spectrometer) imagery in four different biomes. Biome types sampled included row-crop agriculture, tallgrass prairie, mixed hardwood-conifer forest, and boreal conifer forest. The effects of bandwidth, band placement, and number of bands were isolated from radiometric quality by comparing regression models derived from individual AVIRIS channels with those derived from simulated ETM+ and MODIS channels using the AVIRIS data. Models with selected subsets of individual AVIRIS channels performed better to predict LAI than those based on the broadband datasets, although the potential to overfit models using the large number of available AVIRIS bands is a concern. Models based on actual ETM+ data were generally stronger than those based on simulated ETM+ data, suggesting that, for predicting LAI, ETM+ data suffer no penalty for having lower radiometric quality. NDVI was generally not sensitive to LAI at the four sites. Band placement of broad-band sensors (e.g., simulated ETM+ and MODIS) did not affect relationships with LAI, suggesting that there is no inherent advantage to MODIS spectral properties over those of ETM+ for estimating LAI. Spectral channels in the red-edge and shortwave-infrared regions were generally more important than those in the near-infrared for predicting LAI.
    BibTeX:
    @article{lee04,
      author = {Lee, Kyu-Sung and Cohen, Warren B. and Kennedy, Robert E. and Maiersperger, Thomas K. and Gower, Stith T.},
      title = {Hyperspectral versus multispectral data for estimating leaf area index in four different biomes},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {91},
      number = {3-4},
      pages = {508--520}
    }
    
    Leersnijder, R. PINOGRAM: a pine growth area model 1992 School: Wageningen Agricultural University, The Netherlands.  phdthesis  
    BibTeX:
    @phdthesis{leersnijder92,
      author = {Leersnijder, R.P.},
      title = {PINOGRAM: a pine growth area model},
      school = {Wageningen Agricultural University, The Netherlands.},
      year = {1992}
    }
    
    Lefsky, M. Lidar Remote Sensing of Forests with the Geoscience Laser Altimeter System. 2005 Keynote at the Silviscan Conference, Blacksburg, Virginia.  conference  
    BibTeX:
    @conference{lefsky2005_talk,
      author = {Michael Lefsky},
      title = {Lidar Remote Sensing of Forests with the Geoscience Laser Altimeter System.},
      booktitle = {Keynote at the Silviscan Conference, Blacksburg, Virginia.},
      year = {2005}
    }
    
    Lefsky, M.A. A global forest canopy height map from the Moderate Resolution Imaging Spectroradiometer and the Geoscience Laser Altimeter System 2010 Geophys. Res. Lett.
    Vol. 37, pp. L15401 
    article DOI  
    BibTeX:
    @article{Lefsky2010,
      author = {Lefsky, M. A.},
      title = {A global forest canopy height map from the Moderate Resolution Imaging Spectroradiometer and the Geoscience Laser Altimeter System},
      journal = {Geophys. Res. Lett.},
      year = {2010},
      volume = {37},
      pages = {L15401},
      doi = {http://dx.doi.org/10.1029/2010GL043622.}
    }
    
    Lefsky, M.A., Cohen, W.B., Acker, S.A., Parker, G.G., Spies, T.A. & Harding, D. Lidar Remote Sensing of the Canopy Structure and Biophysical Properties of Douglas-Fir Western Hemlock Forests 1999 Remote Sensing of Environment
    Vol. 70, pp. 339-361 
    article  
    Abstract: Scanning lidar remote sensing systems have recently become available for use in ecological applications. Unlike conventional microwave and optical sensors, lidar sensors directly measure the distribution of vegetation material along the vertical axis and can be used to provide three-dimensional, or volumetric, characterizations of vegetation structure. Ecological applications of scanning lidar have hitherto used one-dimensional indices to characterize canopy height. A novel three-dimensional analysis of lidar waveforms was developed to characterize the total volume and spatial organization of vegetation material and empty space within the forest canopy. These aspects of the physical structure of canopies have been infrequently measured, from either field or remote methods. We applied this analysis to 22 plots in Douglas-fir/western hemlock stands on the west slope of the Cascades Range in Oregon. Each plot had coincident lidar data and field measurements of stand structure. We compared results from the novel analysis to two earlier meth-ods of canopy description. Using the indices of canopy structure from all three methods of description as independent variables in a stepwise multiple regression, we were able to make nonasymptotic predictions of biomass and leaf area index (LAI) over a wide range, up to 1200 Mg/ha of biomass and an LAI of 12, with 90 $%$ and 75 $%$ of variance explained, respectively. Furthermore, we were able to make accurate estimates of other stand structure attributes, including the mean and standard deviation of diameter at breast height, the number of stems greater than 100 cm in diameter, and independent estimates of the basal area of Douglas-fir and western hemcharacterize lock. These measurements can be directly related to indices of forest stand structural complexity, such as those developed for old-growth forest characterization. Indices of canopy structure developed using the novel, threedimensional analysis accounted for most of the variables used in predictive equations generated by the stepwise multiple regression.
    BibTeX:
    @article{lefsky99,
      author = {M. A. Lefsky and W. B. Cohen and S. A. Acker and G. G. Parker and T. A. Spies and D. Harding},
      title = {Lidar Remote Sensing of the Canopy Structure and Biophysical Properties of Douglas-Fir Western Hemlock Forests},
      journal = {Remote Sensing of Environment},
      year = {1999},
      volume = {70},
      pages = {339-361}
    }
    
    Lefsky, M.A., Cohen, W.B., Parker, G.G. & Harding, D.J. Lidar Remote Sensing for Ecosystem Studies 2002 BioScience
    Vol. 52(1), pp. 19-30 
    article  
    Abstract: LIDAR, AN EMERGING REMOTE SENSING TECHNOLOGY THAT DIRECTLY MEASURES THE THREE-DIMENSIONAL DISTRIBUTION OF PLANT CANOPIES, CAN ACCURATELY ESTIMATE VEGETATION STRUCTURAL ATTRIBUTES AND SHOULD BE OF PARTICULAR INTEREST TO FOREST, LANDSCAPE, AND GLOBAL ECOLOGISTS
    BibTeX:
    @article{lefsky02,
      author = {Michael A. Lefsky and Warren B. Cohen and Geoffrey G. Parker and David J. Harding},
      title = {Lidar Remote Sensing for Ecosystem Studies},
      journal = {BioScience},
      year = {2002},
      volume = {52},
      number = {1},
      pages = {19-30}
    }
    
    Lefsky, M.A., Harding, D., Cohen, W.B., Parker, G. & Shugart, H.H. Surface Lidar Remote Sensing of Basal Area and Biomass in Deciduous Forests of Eastern Maryland, USA 1999 Remote Sensing of Environment
    Vol. 67, pp. 83-98 
    article  
    Abstract: A method of predicting two forest stand structure attributes, basal area and aboveground biomass, from measurements of forest vertical structure was developed and tested using field and remotely sensed canopy structure measurements. Coincident estimates of the vertical distribution of canopy surface area (the canopy height profile), and field-measured stand structure attributes were acquired for two data sets. The chronosequence data set consists of 48 plots in stands distributed within 25 miles of Annapolis, MD, with canopy height profiles measured in the field using the optical-quadrat method. The stem-map data set consists of 75 plots subsetted from a single 32 ha stem-mapped stand, with measurements of their canopy height profiles made using the SLICER (Scanning Lidar Imager of Canopies by Echo Recovery) instrument, an airborne surface lidar system. Four height indices, maximum, median, mean, and quadratic mean canopy height (QMCH) were calculated from the canopy height profiles. Regressions between the indices and stand basal area and biomass were developed using the chronosequence data set. The regression equations developed from the chronosequence data set were then applied to height indices calculated from the remotely sensed canopy height profiles from the stem map data set, and the ability of the regression equations to predict the stem map plot's stand structure attributes was then evaluated. The QMCH was found to explain the most variance in the chronosequence data set's stand structure attributes, and to most accurately predict the values of the same attributes in the stem map data set. For the chronosequence data set, the QMCH predicted 70 $%$ of variance in stand basal area, and 80 $%$ of variance in aboveground biomass, and remained nonasymptotic with basal areas up to 50 m2/ha, and aboveground biomass values up to 450 Mg/ha. When applied to the stem-map data set, the regression equations resulted in basal areas that were, on average, underestimated by 2.1 m2 ha21, and biomass values were underestimated by 16 Mg ha21, and explained 37 $%$ and 33 $%$ of variance, respectively. Differences in the magnitude of the coefficients of determination were due to the wider range of stand conditions found in the chronosequence data set; the standard deviation of residual values were lower in the stem map data set than on the chronosequence data sets. Stepwise multiple regression was performed to predict the two stand structure attributes using the canopy height profile data directly as independent variables, but they did not improve the accuracy of the estimates over the height index approach.
    BibTeX:
    @article{lefsky99b,
      author = {Michael A. Lefsky and D. Harding and W. B. Cohen and G. Parker and H. H. Shugart},
      title = {Surface Lidar Remote Sensing of Basal Area and Biomass in Deciduous Forests of Eastern Maryland, USA},
      journal = {Remote Sensing of Environment},
      year = {1999},
      volume = {67},
      pages = {83-98}
    }
    
    Lefsky, M., Cohen, W.B., Harding, D.J., Parker, G.G., Acker, S.A. & Gower, S.T. Lidar Remote Sensing of Aboveground Biomass in Three Biomes 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 150-160 
    article  
    Abstract: Estimation of the amount of carbon stored in forests is a key challenge for understanding the global carbon cycle, one which remote sensing is expected to help address. However, direct estimation of carbon storage in moderate to high biomass forests is difficult for conventional optical and radar sensors. Lidar (light detection and ranging) instruments measure the vertical structure of forests and thus hold great promise for remotely sensing the quantity and spatial organization of forest biomass. In this study, we compare the relationships between lidar-measured canopy structure and coincident field measurements of aboveground biomass at sites in the temperate deciduous, temperate coniferous, and boreal coniferous biomes. A single simplified regression for all three sites is compared with equations derived for each site individually. The simplified equation explains 84 $%$ of variance in aboveground biomass (p<0.0001) and shows no statistically significant bias in its predictions for any individual site.
    BibTeX:
    @article{lefsky01c,
      author = {M.A. Lefsky and Warren B. Cohen and David J. Harding and Geoffery G. Parker and Steven A. Acker and S. Thomas Gower},
      title = {Lidar Remote Sensing of Aboveground Biomass in Three Biomes},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {150-160}
    }
    
    Lewis, P. & Disney, M. Spectral invariants and scattering across multiple scales from within-leaf to canopy 2007 Remote Sensing of Environment
    Vol. 109(2), pp. 196-206 
    article  
    Abstract: Spectral invariants can be considered fundamental descriptors of the impact of canopy structure on canopy scattering where the scattering objects are large compared with the wavelength of radiation. The paper uses the concept of canopy spectral invariants to explore scaling relationships within canopy scattering. A new approximation to the leaf-level PROSPECT scattering model of Jacquemoud and Baret [Jacquemoud, S., & Baret, F. (1990). PROSPECT: A model of leaf optical properties spectra. Remote Sensing of Environment, 34, 75-91.] is developed by applying the spectral invariant approach to leaf internal scattering, in a similar manner to that which has been used to describe canopy-level scattering. We show that it is possible to express both the canopy- and leaf-level single scattering albedo as a function of canopy spectral invariants. This approach provides a framework through which structural information can be maintained in a self-consistent manner across multiple scales from leaf- to canopy-level scattering, at least for the simple canopy architectures considered. It is demonstrated that the nesting of scales described in these relationships implies limits to the retrieval of absolute concentrations of any biochemical constituents or absolute quantities of the amount of scattering material from hyperspectral observations of total scattering. The implication is that in general it may not be possible to separate the components of structural and biochemical influences on measured total scattering signals.
    BibTeX:
    @article{Lewis2007,
      author = {Lewis, P. and Disney, M.},
      title = {Spectral invariants and scattering across multiple scales from within-leaf to canopy},
      journal = {Remote Sensing of Environment},
      year = {2007},
      volume = {109},
      number = {2},
      pages = {196--206}
    }
    
    Lim, K., Treitz, P., Baldwin, K., Morrison, I. & Green, J. Lidar remote sensing of biophysical properties of tolerant northern hardwood forests 2003 Canadian Journal of Remote Sensing
    Vol. 29(5), pp. 658-678 
    article  
    Abstract: Previous forest research using time-of-flight lidar data has primarily focused on forest ecosystems with conifers as the predominant tree type. In this study, small-footprint time-of-flight lidar data were used to estimate biophysical properties of tolerant hardwood forests composed predominantly of mature sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britton) in the Turkey Lakes Watershed (TLW) near Sault Ste. Marie, Ontario. Ground reference data were collected during the first two weeks of July 2000 for 49 circular sample plots, each 0.04 ha (or 400 m 2) in area. Lidar data were acquired on 24 August 2000 using an Optech ALTM 1225 (Optech Incorporated, Toronto, Ont.). Ten biophysical forest metrics were derived for each plot: (1) maximum tree height (hmax), (2) Lorey?s mean tree height (hLorey), (3) mean diameter at breast height (DBH), (4) total basal area (BA), (5) percent canopy openness (CO%), (6) leaf area index (LAI), (7) ellipsoidal crown closure (CC), (8) total aboveground biomass (BIO), (9) total wood volume (VOL), and (10) stem density (SD). Likewise, three laser height metrics were derived for each plot: (1) maximum laser height (Lhmax), (2) mean laser height (Lhmean), and (3) mean laser height calculated from lidar returns filtered based on a threshold applied to the intensity return values (LhIR). The results demonstrate that for each forest with a given stand structure, there exists one or more laser height metrics derived from lidar data that are capable of providing an estimate of various biophysical properties. Lhmax was the best estimator of hmax (r 2 = 0.79) and h Lorey (r 2 = 0.87); Lh IR was the best estimator of BA (r 2 = 0.85), BIO (r2 = 0.85), and VOL (r2 = 0.87); and Lh mean was the best estimator of CC (r 2 = 0.89), DBH (r2 = 0.63), CO% (r 2 = 0.76), LAI (r2 = 0.80), and SD (r2 = 0.86). The results illustrate the potential for laser height metrics to estimate (i) plot heights and stem densities, (ii) aboveground biomass and volume, and (iii) canopy-related measures.
    BibTeX:
    @article{lim03,
      author = {Kevin Lim and Paul Treitz and Ken Baldwin and Ian Morrison and Jim Green},
      title = {Lidar remote sensing of biophysical properties of tolerant northern hardwood forests},
      journal = {Canadian Journal of Remote Sensing},
      year = {2003},
      volume = {29},
      number = {5},
      pages = {658-678}
    }
    
    Lim, K., Treitz, P., Wulder, M., St-Onge, B. & Flood, M. LiDAR remote sensing of forest structure 2002 Progress in Physical Geography  article  
    Abstract: Light detection and ranging (LiDAR) technology provides horizontal and vertical information at high spatial resolutions and vertical accuracies. Forest attributes such as canopy height can be directly retrieved from LiDAR data. Direct retrieval of canopy height provides opportunities to model above ground biomass and canopy volume. Access to the vertical nature of forest ecosystems also offers new opportunities for enhanced forest monitoring, management and planning.
    BibTeX:
    @article{lim_ppg02,
      author = {Kevin Lim and Paul Treitz and Mike Wulder and Benoit St-Onge and Martin Flood},
      title = {LiDAR remote sensing of forest structure},
      journal = {Progress in Physical Geography},
      year = {2002}
    }
    
    Linn, R., Reisner, J., Colman, J.J. & Winterkamp, J. Studying wildfire behavior using FIRETEC 2002 International Journal of Wildland Fire
    Vol. 11, pp. 233-246 
    article  
    BibTeX:
    @article{linn02,
      author = {Linn, R. and Reisner, J. and Colman, J. J. and J. Winterkamp},
      title = {Studying wildfire behavior using FIRETEC},
      journal = {International Journal of Wildland Fire},
      year = {2002},
      volume = {11},
      pages = {233-246}
    }
    
    Linn, R., Winterkamp, J., Colman, J., Edminster, C. & Bailey, J. Modeling interactions between fire and atmosphere in discrete element fuel beds. 2005 International Journal of Wildland Fire
    Vol. 14, pp. 37-48 
    article  
    BibTeX:
    @article{linn2005,
      author = {Linn, R.R. and Winterkamp, J. and Colman, J.J. and Edminster, C. and Bailey, J.},
      title = {Modeling interactions between fire and atmosphere in discrete element fuel beds.},
      journal = {International Journal of Wildland Fire},
      year = {2005},
      volume = {14},
      pages = {37-48}
    }
    
    Lithopoulos, E. The Applanix Approach to GPS/INS Integration 1999 Photogrammetric Week
    Vol. Wichmann Verlag, Heidelberg 
    article  
    BibTeX:
    @article{lithopoulos99,
      author = {Erik Lithopoulos},
      title = {The Applanix Approach to GPS/INS Integration},
      journal = {Photogrammetric Week},
      year = {1999},
      volume = {Wichmann Verlag, Heidelberg}
    }
    
    Lobell, D.B. & Asner, G.P. Cropland distributions from temporal unmixing of MODIS data 2004 Remote Sensing of Environment
    Vol. 93(3), pp. 412-422 
    article  
    Abstract: Knowledge of the distribution of crop types is important for land management and trade decisions, and is needed to constrain remotely sensed estimates of variables, such as crop stress and productivity. The Moderate Resolution Imaging Spectroradiometer (MODIS) offers a unique combination of spectral, temporal, and spatial resolution compared to previous global sensors, making it a good candidate for large-scale crop type mapping. However, because of subpixel heterogeneity, the application of traditional hard classification approaches to MODIS data may result in significant errors in crop area estimation. We developed and tested a linear unmixing approach with MODIS that estimates subpixel fractions of crop area based on the temporal signature of reflectance throughout the growing season. In this method, termed probabilistic temporal unmixing (PTU), endmember sets were constructed using Landsat data to identify pure pixels, and uncertainty resulting from endmember variability was quantified using Monte Carlo simulation. This approach was evaluated using Landsat classification maps in two intensive agricultural regions, the Yaqui Valley (YV) of Mexico and the Southern Great Plains (SGP). Performance of the mixture model varied depending on the scale of comparison, with R2 ranging from roughly 50% for estimating crop area within individual pixels to greater than 80% for crop cover within areas over 10 km2. The results of this study demonstrate the importance of subpixel heterogeneity in cropland systems, and the potential of temporal unmixing to provide accurate and rapid assessments of land cover distributions using coarse resolution sensors, such as MODIS.
    BibTeX:
    @article{Lobell2004,
      author = {Lobell, David B. and Asner, Gregory P.},
      title = {Cropland distributions from temporal unmixing of MODIS data},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {93},
      number = {3},
      pages = {412--422}
    }
    
    Lovell, J., Jupp, D., Culvenor, D. & Coops, N. Using airborne and ground-based ranging lidar to measure canopy structure in Australian forests 2003 Canadian Journal of Remote Sensing
    Vol. 29(5), pp. 607-622 
    article  
    Abstract: Airborne and ground-based lidars are useful tools to probe the structure of forest canopies. Such information is not readily available from other remote sensing methods but is essential for modern forest inventory in which growth models and ecological assessment are becoming increasingly important. This study was undertaken to investigate the capacity of current airborne and ground-based ranging systems to provide data from which useful forest inventory parameters can be derived. Additional data collected included standard forest inventory, hemispherical photography, and optical point-quadrat sampling. Four contrasting study sites were established within an existing study area in the Bago and Maragle State Forests, New South Wales, Australia. A simple and standard set of models was fitted to the data to establish consistency between methods and current practice. Methods to reduce the bias induced by interaction of the size of the airborne laser scanner (ALS) footprint and thresholding used in ranging systems are demonstrated by the use of first and last returns and the intensity of the returns. A measure analogous to predominant height was calculated from an average of a number of the highest ALS returns within an area. This estimate agreed with field measured predominant heights within the uncertainty of the measurements. Data from a ground-based scanning rangefinder system were used to model leaf area index (LAI). These LAI estimates coincided with those from hemispherical canopy photographs. The validation work presented in this paper justifies further development of the instrumentation and analyses to combine results from multi-angular systems with data from airborne systems to alleviate some of the problems associated with the vertical view. Current laser ranging systems can be used to derive canopy structural parameters such as height, cover, and foliage profile provided information based on multiple returns or the intensity of returns is used to minimize the bias induced by the size of the footprint and the detection threshold.
    BibTeX:
    @article{lovell03,
      author = {J.L. Lovell and D.L.B. Jupp and D.S. Culvenor and N.C. Coops},
      title = {Using airborne and ground-based ranging lidar to measure canopy structure in Australian forests},
      journal = {Canadian Journal of Remote Sensing},
      year = {2003},
      volume = {29},
      number = {5},
      pages = {607-622}
    }
    
    Lovell, J., Jupp, D., Newnham, G., Coops, N. & Culvenor, D. Simulation study for finding optimal lidar acquisition parameters for forest height retrieval 2005 Forest Ecology and Management
    Vol. 214(1-3), pp. 398-412 
    article  
    Abstract: Accurate and cost-effective measurements of forest inventory parameters are an essential input to forest management practice. Of these parameters, height has been shown to be valuable in the estimation of stem volume and site quality. The accuracy of height estimates from lidar data depends critically on the operational characteristics of the airborne instrument and the resulting sampling density relative to the individual tree spacing within the stand. Using a simulated lidar dataset for a forest plantation with varying stem density it was found that mean nearest neighbour spacing of the lidar point samples is linearly related to retrieved predominant height. The results also indicated that the accuracy of height retrieval may be poorer at the edge of the lidar swath due to uneven spacing of the sample points. Given the significant cost of lidar data acquisition, it is crucial that data acquisition planning maximizes the benefit of the data retrieved. The information gained through simulations such as those detailed in this paper may assist attaining this maximum benefit by identifying lidar operational parameters that produce sufficiently accurate results while minimizing cost.
    BibTeX:
    @article{lovell05,
      author = {Lovell, J.L. and Jupp, D.L.B. and Newnham, G.J. and Coops, N.C. and Culvenor, D.S.},
      title = {Simulation study for finding optimal lidar acquisition parameters for forest height retrieval},
      journal = {Forest Ecology and Management},
      year = {2005},
      volume = {214},
      number = {1-3},
      pages = {398--412}
    }
    
    Lucas, R.M., Lee, A.C. & Bunting, P.J. Retrieving forest biomass through integration of CASI and LiDAR data 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1553-1577 
    article  
    Abstract: To increase understanding of forest carbon cycles and stocks, estimates of total and component (e.g. leaf, branch and trunk) biomass at a range of scales are desirable. Focusing on mixed species forests in central south-east Queensland, two different approaches to the retrieval of biomass from small footprint Light Detection and Ranging (LiDAR) and Compact Airborne Spectrographic Imager (CASI) hyperspectral data were developed and compared. In the first, stems were located using a LiDAR crown openness index, and each was associated with crowns delineated and identified to species using CASI data. The component biomass for individual trees was then estimated using LiDAR-derived height and stem diameter as input to species-specific allometric equations. When summed to give total above-ground biomass (AGB) and aggregated to the plot level, these estimates showed a reasonable correspondence with ground (plot-based) estimates (r 2??=??0.56, RSE??=??25.3??Mg??ha-1, n??=??21) given the complex forest being assessed. In the second approach, a Jackknife linear regression utilizing six LiDAR strata heights and crown cover at the plot-scale produced more robust estimates of AGB that showed a closer correspondence with plot-scale ground data (r 2??=??0.90, RSE??=??11.8??Mg??ha-1, n??=??31). AGB aggregated from the tree-level and Jackknife regression plot-based AGB estimates (for 270 plots???each of 0.25??ha) compared well for more mature homogeneous and open forests. However, at the tree level, AGB was overestimated in taller forests dominated by trees with large spreading crowns, and underestimated AGB where an understorey with a high density of stems occurred. The study demonstrated options for quantifying component biomass and AGB through integration of LiDAR and CASI data but highlighted the requirement for methods that give improved estimation of tree density (by size class distributions) and species occurrence in complex forests.
    BibTeX:
    @article{Lucas2008,
      author = {Lucas, R. M. and Lee, A. C. and Bunting, P. J.},
      title = {Retrieving forest biomass through integration of CASI and LiDAR data},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1553--1577}
    }
    
    Luethy, J. & Stengele, R. Mapping of Switzerland - Challenges and Experiences 2005 ISPRS WG III/3, III/4, V/3 Workshop "Laser scanning 2005", Enschede, the Netherlands, September 12-14  conference  
    BibTeX:
    @conference{luethy05,
      author = {Luethy, J. and Stengele, R.},
      title = {Mapping of Switzerland - Challenges and Experiences},
      booktitle = {ISPRS WG III/3, III/4, V/3 Workshop "Laser scanning 2005", Enschede, the Netherlands, September 12-14},
      year = {2005}
    }
    
    Maas, H.G., Bienert, A., Scheller, S. & Keane, E. Automatic forest inventory parameter determination from terrestrial laser scanner data 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1579-1593 
    article  
    Abstract: Terrestrial laser scanners find rapidly growing interest in photogrammetry as efficient tools for fast and reliable three-dimensional (3D) point cloud data acquisition. They have opened a wide range of application fields within a short period of time. Beyond interactive measurement in 3D point clouds, techniques for the automatic detection of objects and the determination of geometric parameters form a high priority research issue. With the quality of 3D point clouds generated by laser scanners and the automation potential in data processing, terrestrial laser scanning is also becoming a useful tool for forest inventory. This paper presents a brief review of current laser scanner systems from a technological point of view and discusses different scanner technologies and system parameters regarding their suitability for forestry applications. Methods for the automatic detection of trees in terrestrial laser scanner data as well as the automatic determination of diameter at breast height (DBH), tree height and 3D stem profiles are outlined. Reliability and precision of the techniques are analysed on the basis of several pilot studies. In these pilot studies more than 97% of the trees could be detected correctly, and DBH could be determined with a precision of about 1.8??cm.
    BibTeX:
    @article{Maas2008,
      author = {Maas, H. G. and Bienert, A. and Scheller, S. and Keane, E.},
      title = {Automatic forest inventory parameter determination from terrestrial laser scanner data},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1579--1593}
    }
    
    Maas, H.-G. Methods for Measuring Height and Planimetry Discrepancies in Airborne Laserscanner Data 2002 Photogrammetric Engineering & Remote Sensing
    Vol. 68(9), pp. 933-940 
    article  
    Abstract: Airborne laserscanning (or lidar) has become a very important technique for the acquisition of digital terrain model data. Beyond this, the technique is increasingly being used for the acquisition of point clouds for 3D modeling of a wide range of objects, such as buildings, vegetation, or electrical power lines. As an active technique, airborne laserscanning offers a high reliability even over terrain with poor image contrast. The precision of the technique is often specified to be on the order of one to two decimeters. By reason of its primary use in digital terrain modeling, examinations of the precision potential of airborne laserscanning have so far been concentrated on the height precision. With the use of the technique for general 3D reconstruction tasks and the increasing resolution of laserscanner systems, the planimetric precision of laserscanner point clouds becomes an important issue. In addition to errors in the laser distance meter and the deflecting mirror system, the error budget of airborne laserscanning instruments is strongly influenced by the GPS/INS systems used for sensor pose (position and orientation) determination. Errors of these systems often lead to the deformation of laserscanner data strips and may become evident as discrepancies in the overlap region between neighboring strips in a block of laserscanner data. The paper presents least-squares matching implemented on a TIN structure as a general tool for the determination of laser-scanner strip discrepancies in all three coordinate directions, using both height and reflectance data. Practical problems of applying matching techniques to 2.5D laserscanner point clouds are discussed and solved, and the success of the technique is shown on the basis of several datasets. Applying least-squares matching techniques to dense laserscanner data in a TIN structure, strip discrepancies can be determined with centimeter precision for the height coordinate and decimeter precision for the planimetric coordinates.
    BibTeX:
    @article{maas02,
      author = {Hans-Gerd Maas},
      title = {Methods for Measuring Height and Planimetry Discrepancies in Airborne Laserscanner Data},
      journal = {Photogrammetric Engineering & Remote Sensing},
      year = {2002},
      volume = {68},
      number = {9},
      pages = {933-940}
    }
    
    Maas, H.-G. On the use of pulse reflectance data for laserscanner strip adjustment 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 53-65 
    article  
    Abstract: The precision of airborne laserscanner data is strongly influenced by the limited accuracy potential of the integrated GPS/INS pose determination system. Errors of kinematic GPS height determination will often be in the order of one to two decimeters and propagate directly into the height coordinates of digital surface models, digital terrain models and 3-D object models derived from these data. The planimetric accuracy of ground points is influenced by the kinematic GPS accuracy as well as by drift effects of the INS system and is in the order of a few decimeters. Errors become evident at check points or as discrepancies between neighboring strips of laserscanner data. Vice versa, these discrepancies can be used to apply corrections to laserscanner data in a strip adjustment procedure. Tie points for laserscanner strip adjustment can be determined with high precision by least-squares matching applied to the original non-interpolated ground point clouds organized in stripwise TINs. This procedure provides useful results in regions with sufficient surface slopes in both coordinate directions, but fails over flat terrain if both height and planimetry coordinate discrepancies are to be determined. In such situations, image contrast in the laserscanner pulse reflectance data, simultaneously recorded by some laserscanner systems and perfectly co-registered with the height data in the TIN structure, can replace non-existent height contrast and provide a solution. The paper describes the extension of least-squares-matching to the alternative use of height and reflectance values of irregularly distributed laserscanner points for the determination of laserscanner strip discrepancies in flat regions with existing local image intensity contrast. The practical applicability and precision potential of the technique will be discussed.
    BibTeX:
    @article{maas01,
      author = {Hans-Gerd Maas},
      title = {On the use of pulse reflectance data for laserscanner strip adjustment},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {53-65}
    }
    
    Maas, H.-G. Least-Squares Matching with Airborne Laserscanning Data in a TIN Structure 2000 International Archives of Photogrammetry and Remote Sensing
    Vol. 33(3a), pp. 548-555 
    article  
    Abstract: A number of tasks in airborne laserscanning require the establishment of correspondences between point data from neighbouring strips, or referencing between point clouds and object models. These tasks may be solved by interpolating laserscanner data, which are usually irregularly distributed 21/2-D points, to a regular grid and applying standard photogrammetric matching techniques. Instead, the paper presents a formulation of least squares matching based on the original data points in a triangulated irregular network structure, thus avoiding degrading effects caused by the interpolation. The technique determines shifts in all three coordinate directions together with their covariance matrix. It can be shown that applying matching techniques to laserscanner data causes large systematic errors of the shift parameters in the case of partial occlusions. The presented formulation on the basis of a TIN structure allows for manifold extensions to solve this problem. The technique and a number of extensions have been implemented and applied to the measurement of strip errors in an airborne laser scanner dataset with moderate point density, consisting of 20 strips including crossing strips. The paper shows the results from this test, discusses the advantages of the presented technique and the limitations of matching techniques applied to laserscanner data. Special attention has to be paid to problems caused by height discontinuities in the data and by the fact that the design matrix in least squares matching is derived from observations with stochastic properties. The latter leads to precision figures that are usually much too optimistic. A detailed analysis of the design matrix and extensive testing lead to better funded precision figures for the standard deviation of the obtained shift parameters. These are in the order of one centimeter in height direction and one decimeter in horizontal direction, corresponding to about 1/20th of the average point spacing.
    BibTeX:
    @article{maasTIN00,
      author = {Hans-Gerd Maas},
      title = {Least-Squares Matching with Airborne Laserscanning Data in a TIN Structure},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2000},
      volume = {33},
      number = {3a},
      pages = {548-555}
    }
    
    Maas, H.-G. THE POTENTIAL OF HEIGHT TEXTURE MEASURES FOR THE SEGMENTATION OF AIRBORNE LASERSCANNER DATA 1999 Fourth International Airborne Remote Sensing Conference and Exhibition
    Vol. 21st Canadian Symposium on Remote Sensing, pp. Ottawa, Ontario, Canada 
    article  
    Abstract: Airborne laserscanning is being used for an increasing number of mapping and GIS data acquisition tasks. Besides the original purpose of digital terrain model generation, new applications arise in the automatic detection and modeling of objects such as buildings or vegetation for the generation of 3-D city models. A crucial prerequisite for the automatic extraction of objects on the Earth's surface from las-erscanner height data is the segmentation of datasets. Besides the height itself, height texture defined by local variations of the height is a significant feature of objects to be rec-ognized. The paper shows the potential of the analysis of height texture for the automatic segmentation of dense laserscanner datasets and the detection of objects in the segmented data. Based on the definition and computation of a number of texture measures used as bands in a classification approach, objects like buildings, single trees, ground vegetation and roads can be recognized. The technique was applied to a FLI-MAP laserscanner dataset with an average point density of more than five points per squaremeter, acquired over a village in The Netherlands. In a maximum likelihood classification based on the absolute height and several texture measures derived from it, a classification accuracy of 98% could be achieved. Based on the result of the segmentation, all buildings of the scene and most single trees could be automatically detected.
    BibTeX:
    @article{maas99a,
      author = {Hans-Gerd Maas},
      title = {THE POTENTIAL OF HEIGHT TEXTURE MEASURES FOR THE SEGMENTATION OF AIRBORNE LASERSCANNER DATA},
      journal = {Fourth International Airborne Remote Sensing Conference and Exhibition},
      year = {1999},
      volume = {21st Canadian Symposium on Remote Sensing},
      pages = {Ottawa, Ontario, Canada}
    }
    
    Maas, H.-G. & Vosselman, G. Two algorithms for extracting building models from raw laser altimetry data 1999 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 54(2-3), pp. 153-163 
    article  
    Abstract: Two new techniques for the determination of building models from laser altimetry data are presented. Both techniques work on the original laser scanner data points without the requirement of an interpolation to a regular grid. Available ground plan information may be used, but is not required. Closed solutions for the determination of the parameters of a standard gable roof type building model based on invariant moments of 2 1/2-D point clouds are shown. In addition, the analysis of deviations between point cloud and model does allow for modelling asymmetries such as dorms on a gable roof. By intersecting planar faces nonparametric buildings with more complex roof types can also be modelled. The techniques were applied to a FLI-MAP laser scanner dataset covering an area of 500???????250 m2 with a density of more than 5 points/m2. Within this region, all but one building could be modelled. An analysis of the variance of the parameters within a group of buildings indicates a precision in the range of 0.1?????0.2 m.
    BibTeX:
    @article{maas99b,
      author = {Hans-Gerd Maas and George Vosselman},
      title = {Two algorithms for extracting building models from raw laser altimetry data},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {1999},
      volume = {54},
      number = {2-3},
      pages = {153-163}
    }
    
    MacArthur, R.H. & Horn, H.S. Foliage profile by vertical measurements. 1969 Ecology
    Vol. 50, pp. 802-804 
    article  
    BibTeX:
    @article{macarthur69,
      author = {MacArthur, R. H. and Horn, H. S.},
      title = {Foliage profile by vertical measurements.},
      journal = {Ecology},
      year = {1969},
      volume = {50},
      pages = {802-804}
    }
    
    MacDonald, J.S., Ustin, S.L. & Schaepman, M.E. The contributions of Dr. Alexander F.H. Goetz to imaging spectrometry 2009 Remote Sensing of Environment
    Vol. 113(Supplement 1)Imaging Spectroscopy Special Issue, pp. S2-S4 
    article URL 
    Abstract: Hyperspectral remote sensing is the definitive optical tool for increasing knowledge and understanding of the Earth's surface. Contiguous high-resolution spectrometry provides a new dimension in mapping capability because of the potential for quantitative measurement of surface biogeochemistry. Alexander Goetz provided the vision and leadership that has produced nearly all critical developments in this field. He was among the first to recognize that spectrometry would change optical remote sensing from qualitative observations to quantitative physical measurements. His significant accomplishments over the last 25?years include development of critical image processing and atmospheric correction software, spectrometers that made it possible to move research out of the lab and into the field environment, and the development of NASA's airborne imaging spectrometer program. This special issue is dedicated to Dr. Goetz and his accomplishments.
    BibTeX:
    @article{MacDonald2009,
      author = {MacDonald, John S. and Ustin, Susan L. and Schaepman, Michael E.},
      title = {The contributions of Dr. Alexander F.H. Goetz to imaging spectrometry},
      booktitle = {Imaging Spectroscopy Special Issue},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {Supplement 1},
      pages = {S2--S4},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4W1SGHY-2/2/3517b95e7c6649b3803d317392ae04fd}
    }
    
    Macelloni, G., Paloscia, S., Pampaloni, P., Marliani, F. & Gai, M. The relationship between the backscattering coefficient and the biomass of narrow and broad leaf crops 2001 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 39(4)Geoscience and Remote Sensing, IEEE Transactions on, pp. 873-884 
    article  
    Abstract: The influence of the shape and dimensions of plant constituents on the backscattering of agricultural vegetation is investigated. Multifrequency multitemporal polarimetric data, collected at C- and L-bands by means of airborne and satellite synthetic aperture radar (SAR), showed that the relations between the backscattering of crops and the vegetation biomass depend on plant type, and that there are different trends for &ldquo;narrow&rdquo; and &ldquo;broad&rdquo; leaf crops. In the latter crops, backscattering increases with an increase in the biomass, especially at L-band. This behavior is typical of media in which scattering is dominant, whereas on &ldquo;narrow leaf&rdquo; plants, the trend is flat or decreasing, denoting a major contribution of absorption. Theoretical simulations obtained with a discrete element radiative transfer model have confirmed that a different backscattering of crops with the same biomass may be due to plant geometry
    BibTeX:
    @article{Macelloni2001,
      author = {Macelloni, G. and Paloscia, S. and Pampaloni, P. and Marliani, F. and Gai, M.},
      title = {The relationship between the backscattering coefficient and the biomass of narrow and broad leaf crops},
      booktitle = {Geoscience and Remote Sensing, IEEE Transactions on},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {2001},
      volume = {39},
      number = {4},
      pages = {873--884}
    }
    
    MacLean, D. Forest management strategies to reduce spruce budworm damage in the Fundy Model Forest. 1996 Forestry Chronicle
    Vol. 72, pp. 399-405 
    article  
    BibTeX:
    @article{maclean96,
      author = {MacLean, D.A.},
      title = {Forest management strategies to reduce spruce budworm damage in the Fundy Model Forest.},
      journal = {Forestry Chronicle},
      year = {1996},
      volume = {72},
      pages = {399-405}
    }
    
    Magnussen, S., Gougeon, F.A., Leckie, D. & Wulder, M. Predicting tree heights from a combination of LIDAR canopy heights and digital stem counts 1999 Remote Sensing and Forest Monitoring, Rogow, Poland
    Vol. Conference Proceedings 
    article  
    Abstract: Tree heights can be derived from LIDAR (Light Detection And Ranging) data of canopy heights when estimates of the expected number ( hit N ) of 'tree top' hits exists. Then, the topmost hit N canopy heights can be considered as proxies of tree height. This simple concept is demonstrated in a thinning trial with 39-year-old Douglas-fir. The probability of a LIDAR pulse hitting a tree top is governed by the number and size of 'tree tops'. Counts of trees with a sunlit crown were derived from Compact Airborne Spectrographic Imager images with 55 x 55 cm pixels. Pairing this count with an assumed 'tree top' size of 3 pixels suggested an average of 6 'tree top' hits in a 400 m2 plot. Extreme value distributions fitted to expected 'tree-top' hits generated various statistics of predicted dominant and codominant tree heights. Our approach lowered the average discrepancy between mean canopy and Lorey's mean tree height from 20 $%$ to a non-significant 3 $%$ (P=0.09). Ground-based tree-counts improved the results slightly.
    BibTeX:
    @article{magnussen,
      author = {S. Magnussen and Francois A. Gougeon and D. Leckie and M. Wulder},
      title = {Predicting tree heights from a combination of LIDAR canopy heights and digital stem counts},
      journal = {Remote Sensing and Forest Monitoring, Rogow, Poland},
      year = {1999},
      volume = {Conference Proceedings}
    }
    
    Magnussen, S., Næsset, E. & Wulder, M. Efficient multiresolution spatial predictions for large data arrays 2007 Remote Sensing of Environment
    Vol. 109(4), pp. 451 - 463 
    article DOI  
    Abstract: Imputations of missing values and optimal smoothing with massive data arrays poses a computational challenge since ordinary kriging becomes infeasible. Imputation and smoothing with standard algorithms like inverse distance weighted nearest neighbour interpolation (IDW) and interpolation on triangulated irregular networks (TIN/IP) fail to incorporate the spatial structure and ignore information beyond the neighbourhood. Multiresolution spatial models (MRSM) or approximate kriging methods adapted to handling massive data sets can be expected to do better than IDW and TIN/IP in terms of mean square errors of prediction (MSEP). We illustrate a MRSM that is efficient, computationally fast, and easy to implement. In two forestry examples with imputation of LiDAR range values the MRSM achieved a lower MSEP than IDW, TIN/IP, and fixed ranked kriging. MRSM appear as especially attractive for the construction of a DTM from last return LiDAR pulses. A third example demonstrates MRSM for efficient smoothing.
    BibTeX:
    @article{Magnussen2007451,
      author = {S. Magnussen and E. Næsset and M.A. Wulder},
      title = {Efficient multiresolution spatial predictions for large data arrays},
      journal = {Remote Sensing of Environment},
      year = {2007},
      volume = {109},
      number = {4},
      pages = {451 - 463},
      doi = {DOI: 10.1016/j.rse.2007.01.018}
    }
    
    Malenovsk?, Z., Homolov?, L., Hanu?, J., Kaplan, V., Dolansk?, T. & Yanez, L. Structural parametrization of Norway spruce trees in radiative transfer of high spatial resolution. 2008 Nordic Network on Physically based remote sensing of forests - PHYSENSE, University of Helsinky, Finland,  inproceedings  
    BibTeX:
    @inproceedings{malenovsky2008,
      author = {Malenovsk?, Z. and Homolov?, L. and Hanu?, J. and Kaplan, V. and Dolansk?, T. and Yanez, L.},
      title = {Structural parametrization of Norway spruce trees in radiative transfer of high spatial resolution.},
      booktitle = {Nordic Network on Physically based remote sensing of forests - PHYSENSE, University of Helsinky, Finland,},
      year = {2008}
    }
    
    Malenovsk?, Z., Martin, E., Homolov?, L., Gastellu-Etchegorry, J.-P., Zurita-Milla, R., Schaepman, M.E., Pokorn?, R., Clevers, J.G. & Cudl?n, P. Influence of woody elements of a Norway spruce canopy on nadir reflectance simulated by the DART model at very high spatial resolution 2008 Remote Sensing of Environment
    Vol. 112(1), pp. 1-18 
    article URL 
    Abstract: A detailed sensitivity analysis investigating the effect of woody elements introduced into the Discrete Anisotropic Radiative Transfer (DART) model on the nadir bidirectional reflectance factor (BRF) for a simulated Norway spruce canopy was performed at a very high spatial resolution (modelling resolution 0.2?m, output pixel size 0.4?m). We used such a high resolution to be able to parameterize DART in an appropriate way and subsequently to gain detailed understanding of the influence of woody elements contributing to the radiative transfer within heterogeneous canopies. Three scenarios were studied by modelling the Norway spruce canopy as being composed of i) leaves, ii) leaves, trunks and first order branches, and finally iii) leaves, trunks, first order branches and small woody twigs simulated using mixed cells (i.e. cells approximated as composition of leaves and/or twigs turbid medium, and large woody constituents). The simulation of each scenario was performed for 10 different canopy closures (CC?=?50-95%, in steps of 5%), 25 leaf area index (LAI?=?3.0-15.0?m2 m-?2, in steps of 0.5?m2 m-?2), and in four spectral bands (centred at 559, 671, 727, and 783?nm, with a FWHM of 10?nm). The influence of woody elements was evaluated separately for both, sunlit and shaded parts of the simulated forest canopy, respectively. The DART results were verified by quantifying the simulated nadir BRF of each scenario with measured Airborne Imaging Spectroradiometer (AISA) Eagle data (pixel size of 0.4?m). These imaging spectrometer data were acquired over the same Norway spruce stand that was used to parameterise the DART model. The Norway spruce canopy modelled using the DART model consisted of foliage as well as foliage including robust woody constituents (i.e. trunks and branches). All results showed similar nadir BRF for the simulated wavelengths. The incorporation of small woody parts in DART caused the canopy reflectance to decrease about 4% in the near-infrared (NIR), 2% in the red edge (RE) and less than 1% in the green band. The canopy BRF of the red band increased by about 2%. Subsequently, the sensitivity on accounting for woody elements for two spectral vegetation indices, the normalized difference vegetation index (NDVI) and the angular vegetation index (AVI), was evaluated. Finally, we conclude on the importance of including woody elements in radiative transfer based approaches and discuss the applicability of the vegetation indices as well as the physically based inversion approaches to retrieve the forest canopy LAI at very high spatial resolution.
    BibTeX:
    @article{Malenovsky2008,
      author = {Malenovsk?, Zbynek and Martin, Emmanuel and Homolov?, Lucie and Gastellu-Etchegorry, Jean-Philippe and Zurita-Milla, Ra?l and Schaepman, Michael E. and Pokorn?, Radek and Clevers, Jan G.P.W. and Cudl?n, Pavel},
      title = {Influence of woody elements of a Norway spruce canopy on nadir reflectance simulated by the DART model at very high spatial resolution},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {1},
      pages = {1--18},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4PYYGC0-1/2/d49fa73041c5c37e9dbb46c0e8881a76}
    }
    
    Malenovsky, Z., Albrechtova, J., Lhotakova, Z., Zurita Milla, R., Clevers, J., Schaepman, M. & Cudlin, P. Applicability of the PROSPECT model for Norway spruce needles 2006 International Journal of Remote Sensing
    Vol. 27(24/20), pp. 5315-5340 
    article  
    BibTeX:
    @article{malenovsky06,
      author = {Malenovsky, Z. and Albrechtova, J. and Lhotakova, Z. and Zurita Milla, R. and Clevers, J.G.P.W. and Schaepman, M.E. and Cudlin, P.},
      title = {Applicability of the PROSPECT model for Norway spruce needles},
      journal = {International Journal of Remote Sensing},
      year = {2006},
      volume = {27},
      number = {24/20},
      pages = {5315-5340}
    }
    
    Mallet, C. & Bretar, F. Full-waveform topographic lidar: State-of-the-art 2009 ISPRS Journal of Photogrammetry and Remote Sensing
    Vol. 64(1), pp. 1-16 
    article  
    Abstract: Airborne laser scanning (ALS) is an active remote sensing technique providing range data as 3D point clouds. This paper aims at presenting a survey of the literature related to such techniques, with emphasis on the new sensors called full-waveform lidar systems. Indeed, an emitted laser pulse interacts with complex natural and man-made objects leading to a temporal distortion of the returned energy profile. The new technology of full-waveform laser scanning systems permits one to digitize the complete waveform of each backscattered pulse. Full-waveform lidar data give more control to an end user in the interpretation process of the physical measurement and provide additional information about the structure and the physical backscattering characteristics of the illuminated surfaces. In this paper, the theoretical principles of full-waveform airborne laser scanning are first described. Afterwards, a review of the main sensors as well as signal processing techniques are presented. We then discuss the interpretation of full-waveform measures with special interest on vegetated and urban areas.
    BibTeX:
    @article{Mallet2009,
      author = {Mallet, Cl?ment and Bretar, Fr?d?ric},
      title = {Full-waveform topographic lidar: State-of-the-art},
      journal = {ISPRS Journal of Photogrammetry and Remote Sensing},
      year = {2009},
      volume = {64},
      number = {1},
      pages = {1--16}
    }
    
    Maltamo, M., Eerikainen, K., Pitkaenen, J., Hyyppä, J. & Vehmasa, M. Estimation of timber volume and stem density based on scanning laser altimetry and expected tree size distribution functions 2004 Remote Sensing of Environment
    Vol. 90, pp. 319-330 
    article  
    Abstract: Laser scanners of small footprint diameter and high sampling density provide possibility to obtain accurate height information on the forest canopy. When applying tree crown segmentation methods, individual single trees can be recognised and tree height as well as crown area can be detected. Detection of suppressed trees from a height model based on laser scanning is difficult; however, it is possible to predict these trees by using theoretical distribution functions. In this study, two different methods are used to predict small trees. In the first method, the parameter prediction method is utilised with the complete Weibull distribution, the parameters of which are predicted with separate parameter prediction models; thus, small trees are determined from the predicted tree height distribution. In the second method, the twoparameter left-truncated Weibull distribution is fitted to the detected tree height distribution. The results are presented by using timber volume and stem density as predicted stand characteristics. The results showed that the root mean square error (RMSE) for the timber volume is about 25% when using only information obtained from laser scanning, whereas the RMSE for the number of stems per ha is about 75%. Predictions for both characteristics are also highly biased and the underestimates are 24% and 62%, respectively. The use of the parameter prediction method to describe small trees improved the accuracy considerably; the RMSE figures for estimates of timber volume and number of stems are 16.0% and 49.2%, respectively. The bias for the estimates is also decreased to 6.3% for timber volume and 8.2% for the number of stems. When a left-truncated height distribution is used to predict the heights of the missing small trees, the RMSEs for the estimates of timber volume and number of stems are 22.5% and 72.7%, respectively. In the case of the timber volume, the reliability figures for both the original laser scanning-based estimates and for the estimates that also contain small trees are comparable to those obtained by conventional compartment-wise Finnish field inventories.
    BibTeX:
    @article{maltamo04,
      author = {M. Maltamo and K. Eerikainen and J. Pitkaenen and J. Hyyppä and M. Vehmasa},
      title = {Estimation of timber volume and stem density based on scanning laser altimetry and expected tree size distribution functions},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {90},
      pages = {319-330}
    }
    
    Maltamo, M., Packal?n, P., Yu, X., Eerik?inen, K., Hyypp?, J. & Pitk?nen, J. Identifying and quantifying structural characteristics of heterogeneous boreal forests using laser scanner data. 2005 Forest Ecology and Management
    Vol. 216, pp. 41-50 
    article  
    BibTeX:
    @article{Maltamo2005,
      author = {Maltamo, M. and Packal?n, P. and Yu, X. and Eerik?inen, K. and Hyypp?, J. and Pitk?nen, J.},
      title = {Identifying and quantifying structural characteristics of heterogeneous boreal forests using laser scanner data.},
      journal = {Forest Ecology and Management},
      year = {2005},
      volume = {216},
      pages = {41-50}
    }
    
    Maltamo, M., Packalan, P., Yu, X., Eerikainen, K., Hyyppä, J. & Pitkainen, J. Identifying and quantifying structural characteristics of heterogeneous boreal forests using laser scanner data 2005 Forest Ecology and Management
    Vol. 216(1-3), pp. 41-50 
    article  
    BibTeX:
    @article{maltamo05,
      author = {Maltamo, M. and Packalan, P. and Yu, X. and Eerikainen, K. and Hyyppä, J. and Pitkainen, J.},
      title = {Identifying and quantifying structural characteristics of heterogeneous boreal forests using laser scanner data},
      journal = {Forest Ecology and Management},
      year = {2005},
      volume = {216},
      number = {1-3},
      pages = {41--50}
    }
    
    Malthus, T. & Karpouzli, E. Integrating field and high spatial resolution satellite based methods for monitoring shallow submersed aquatic habitats in the Sound of Eriskay, Scotland, UK 2003 International Journal of Remote Sensing
    Vol. 24(13), pp. 2585-2593 
    article  
    BibTeX:
    @article{malthus03,
      author = {Malthus, T.J. and Karpouzli, E.},
      title = {Integrating field and high spatial resolution satellite based methods for monitoring shallow submersed aquatic habitats in the Sound of Eriskay, Scotland, UK},
      journal = {International Journal of Remote Sensing},
      year = {2003},
      volume = {24},
      number = {13},
      pages = {2585-2593}
    }
    
    Margerit, J. & Séro-Guillaume, O. Modeling forest fires. Part II: Reduction to two-dimensional models and simulation of propagation 2002 International Journal of Heat and Mass Transfer
    Vol. 45, pp. 1723-1737 
    article  
    BibTeX:
    @article{sero02b,
      author = {J. Margerit and O. Séro-Guillaume},
      title = {Modeling forest fires. Part II: Reduction to two-dimensional models and simulation of propagation},
      journal = {International Journal of Heat and Mass Transfer},
      year = {2002},
      volume = {45},
      pages = {1723-1737}
    }
    
    Martens, S.N., Ustin, S.L. & Rousseau, R.A. Estimation of tree canopy leaf area index by gap fraction analysis 1993 Forest Ecology and Management
    Vol. 61(1-2), pp. 91-108 
    article  
    BibTeX:
    @article{martens93,
      author = {Scott N. Martens and Susan L. Ustin and Robert A. Rousseau},
      title = {Estimation of tree canopy leaf area index by gap fraction analysis},
      journal = {Forest Ecology and Management},
      year = {1993},
      volume = {61},
      number = {1-2},
      pages = {91-108}
    }
    
    Martinuzzi, S., Vierling, L.A., Gould, W.A., Falkowski, M.J., Evans, J.S., Hudak, A.T. & Vierling, K.T. Mapping snags and understory shrubs for a LiDAR-based assessment of wildlife habitat suitability 2009 Remote Sensing of Environment
    Vol. 113(12), pp. 2533 - 2546 
    article DOI URL 
    Abstract: The lack of maps depicting forest three-dimensional structure, particularly as pertaining to snags and understory shrub species distribution, is a major limitation for managing wildlife habitat in forests. Developing new techniques to remotely map snags and understory shrubs is therefore an important need. To address this, we first evaluated the use of LiDAR data for mapping the presence/absence of understory shrub species and different snag diameter classes important for birds (i.e. >= 15 cm, >= 25 cm and >= 30 cm) in a 30,000 ha mixed-conifer forest in Northern Idaho (USA). We used forest inventory plots, LiDAR-derived metrics, and the Random Forest algorithm to achieve classification accuracies of 83% for the understory shrubs and 86% to 88% for the different snag diameter classes. Second, we evaluated the use of LiDAR data for mapping wildlife habitat suitability using four avian species (one flycatcher and three woodpeckers) as case studies. For this, we integrated LiDAR-derived products of forest structure with available models of habitat suitability to derive a variety of species-habitat associations (and therefore habitat suitability patterns) across the study area. We found that the value of LiDAR resided in the ability to quantify 1) ecological variables that are known to influence the distribution of understory vegetation and snags, such as canopy cover, topography, and forest succession, and 2) direct structural metrics that indicate or suggest the presence of shrubs and snags, such as the percent of vegetation returns in the lower strata of the canopy (for the shrubs) and the vertical heterogeneity of the forest canopy (for the snags). When applied to wildlife habitat assessment, these new LiDAR-based maps refined habitat predictions in ways not previously attainable using other remote sensing technologies. This study highlights new value of LiDAR in characterizing key forest structure components important for wildlife, and warrants further applications to other forested environments and wildlife species.
    BibTeX:
    @article{Martinuzzi2009,
      author = {Sebasti?n Martinuzzi and Lee A. Vierling and William A. Gould and Michael J. Falkowski and Jeffrey S. Evans and Andrew T. Hudak and Kerri T. Vierling},
      title = {Mapping snags and understory shrubs for a LiDAR-based assessment of wildlife habitat suitability},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {12},
      pages = {2533 - 2546},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4XBF8TC-1/2/19da9703af63af7e2e7e9b1b2a2cb615},
      doi = {DOI: 10.1016/j.rse.2009.07.002}
    }
    
    Mbow, C., Goita, K. & Benie, G.B. Spectral indices and fire behavior simulation for fire risk assessment in savanna ecosystems 2004 Remote Sensing of Environment
    Vol. 91(1), pp. 1-13 
    article  
    Abstract: The lack of information on the vegetation status before the use of fire as a management tool in protected areas leads to drastic destruction of the natural vegetation and biodiversity. This paper describes the use of spectral indices and simulation of savanna burning to assess risk of intensive fire propagation in a National Park (Niokolo Koba, Senegal, West Africa). Spectral parameters corresponding to thematic information (wetness, brightness, and greenness) were retrieved using an orthogonal transformation, the Tasseled Cap approach on LANDSAT-ETM images. Wetness and brightness indices were normalized ([sigma]=1 and MEAN=0) and then combined in a simple semi-empirical algorithm of fire risk levels discrimination. These two indices are proven to reflect qualitatively both fuel moisture and its distribution, which constitute the most foreseen determinants of fire propagation in savanna areas. The fire risk assessment algorithm (FIRA algorithm) was used to produce a fire risk map at the beginning of the management fire implement period. In parallel, a fire area simulator (FARSITE) developed by USDA was used with randomly spaced fire sources to determine areas which can be potentially burned in the study site. These simulated burned areas and the FIRA algorithm results were cross-compared to a real fire scars dated at the end of the same burning period and to land cover map. A great consistency was found between the different sources of information. More than 85% of fire prone areas identified by the FIRA algorithm or simulated by FARSITE were located in trees-shrub, woodland, and shrub savannas. These cover types included also 95% of real fire scars. Almost 88% and 84% of real fire scars were found in the risk zones determined by the FIRA algorithm and the simulated burned areas by FARSITE, respectively. The method used is simple and suited for an operational use for management fire implementation in savanna ecosystems.
    BibTeX:
    @article{mbow04,
      author = {Mbow, Cheikh and Goita, Kalifa and Benie, Goze B.},
      title = {Spectral indices and fire behavior simulation for fire risk assessment in savanna ecosystems},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {91},
      number = {1},
      pages = {1--13}
    }
    
    McIntosh, K. & Krupnik, A. Integration of laser-derived DSMs and matched image edges for generating an accurate surface model 2002 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 53(3), pp. 167-176 
    article  
    Abstract: Airborne laser altimetry is a highly efficient and accurate method of obtaining data for the determination of visible surface topography. With minimal processing, the laser data can provide coordinates of points on the visible surface with high spatial frequency and precision. Although this technology has benefits compared to photogrammetric techniques, there are limiting factors due to the laser data having no structural and textural information. These limitations are significant in low-density laser data and may be overcome by utilizing both laser altimetry and photogrammetrically derived data in the surface determination process. The research described in this paper has been undertaken to accurately determine the visible surface in urban areas using airborne laser scanner data and digital aerial images. Edges detected and matched in aerial images are used to refine the digital surface model (DSM) produced from airborne laser scanner data. The laser data and the edge information are merged to exploit the benefits of each dataset, facilitating the generation of an accurate surface model. This model provides a better representation of surface discontinuities, especially building walls. The paper presents the algorithms developed and shows that the surface accuracy is improved by 49 $%$ and 15 $%$ for the two tested areas, respectively.
    BibTeX:
    @article{mcintosh02,
      author = {Kerry McIntosh and Amnon Krupnik},
      title = {Integration of laser-derived DSMs and matched image edges for generating an accurate surface model},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {2002},
      volume = {53},
      number = {3},
      pages = {167-176}
    }
    
    McLachlan, G. & Peel, D. Finite Mixture Models 2000   book  
    BibTeX:
    @book{McLachlan2000,
      author = {McLachlan, G., and D. Peel},
      title = {Finite Mixture Models},
      publisher = {John Wiley & Sons Inc.},
      year = {2000}
    }
    
    Means, J.E., Acker, S.A., Fitt, B.J., Renslow, M., Emerson, L. & Hendrix, C. Predicting Forest Stand Characteristics with Airborne Scanning Lidar 2000 Photogrammetric Engineering & Remote Sensing
    Vol. 66(11), pp. 1367-1371 
    article  
    Abstract: Currently, commercial forestry applications of airborne scanning lidar are limited to geo-technical applications such as creation of digital terrain models for layout of roads or logging systems. We investigated the feasibility of predicting characteristics of forest stands with lidar data in a university-industry partnership. Lidar lends itself well to such applications because it allows direct measurement of important structural characteristics of height and canopy closure. We found that lidar data can be used to predict the stand characteristics of height, basal area, and volume quite well. The potential for commercial applications appears bright. Lidar data can be used to estimate stand characteristics over large areas or entire forests. After the process is streamlined, it should be possible to provide maps of height, basal area, and volume in such areas within a few weeks of the lidar collection flight.
    BibTeX:
    @article{means00,
      author = {Joseph E. Means and Steven A. Acker and Brandon J. Fitt and Michael Renslow and Lisa Emerson and Chad Hendrix},
      title = {Predicting Forest Stand Characteristics with Airborne Scanning Lidar},
      journal = {Photogrammetric Engineering & Remote Sensing},
      year = {2000},
      volume = {66},
      number = {11},
      pages = {1367-1371}
    }
    
    Means, J.E., Acker, S.A., Harding, D.J., Blair, J.B., Lefsky, M.A., Cohen, W.B., Harmon, M.E. & McKee, W.A. Use of Large-Footprint Scanning Airborne Lidar To Estimate Forest Stand Characteristics in the Western Cascades of Oregon 1999 Remote Sensing of Environment
    Vol. 67, pp. 298-308 
    article  
    Abstract: A scanning lidar, a relatively new type of sensor which explicitly measures canopy height, was used to measure structure of conifer forests in the Pacific Northwest. SLICER (Scanning Lidar Imager of Canopies by Echo Recovery), an airborne pulsed laser developed by NASA which scans a swath of five 10-m diameter footprints along the aircraft's flightpath, captures the power of the reflected laser pulse as a function of height from the top of the canopy to the ground. Ground measurements of forest stand structure were collected on 26 plots with coincident SLICER data. Height, basal area, total biomass, and leaf biomass as estimated from field data could be predicted from SLICER-derived metrics with r2 values of 0.95, 0.96, 0.96, and 0.84, respectively. These relationships were strong up to a height of 52 m, basal area of 132 m2/ha and total biomass of 1300 Mg/ha. In light of these strong relationships, large-footprint, airborne scanning lidar shows promise for characterizing stand structure for management and research purposes.
    BibTeX:
    @article{means,
      author = {Joseph E. Means and Steven A. Acker and David J. Harding and J. Bryan Blair and Michael A. Lefsky and Warren B. Cohen and Mark E. Harmon and W. Arthur McKee},
      title = {Use of Large-Footprint Scanning Airborne Lidar To Estimate Forest Stand Characteristics in the Western Cascades of Oregon},
      journal = {Remote Sensing of Environment},
      year = {1999},
      volume = {67},
      pages = {298-308}
    }
    
    Mercer, D.E. & Prestemon, J.P. Comparing production function models for wildfire risk analysis in the wildland-urban interface 2005 Forest Policy and Economics
    Vol. 7(5)Economic and Policy Perspectives of the Wildland-Urban Interface, pp. 782-795 
    article  
    Abstract: Wildfires create damages in the wildland-urban interface (WUI) that total hundreds of millions of dollars annually in the United States. Understanding how fires are produced in built-up areas near and within fire prone landscapes requires evaluating and quantifying the roles that humans play in fire regimes. We outline a typology of wildfire production functions (WPFs) and empirically estimate three broad classes of WPFs: fire event (ignitions), fire aggregate extent, and a combination function of fire effect and aggregate extent (an intensity-weighted aggregate extent model). Our case study is Florida, which contains an abundance of both wildland and human populations. We find that socio-economic variables play statistically significant roles in all three estimated production functions. At the county level, we find that population and poverty are usually positively related to annual wildfire area and intensity-weighted fire area, while unemployment is negatively related to ignitions, area, and intensity-weighted wildfire area. Poverty is found to be negatively related to wildfire ignitions, while the number of police are correlated with fewer ignitions. These results suggest that managers and decision makers should be aware of socio-economic variables and consider them in their wildland fire management decisions in the wildland-urban interface. Our results also emphasize the importance of including such variables in statistical models of wildfire risk in the WUI.
    BibTeX:
    @article{Mercer2005,
      author = {Mercer, D. Evan and Prestemon, Jeffrey P.},
      title = {Comparing production function models for wildfire risk analysis in the wildland-urban interface},
      booktitle = {Economic and Policy Perspectives of the Wildland-Urban Interface},
      journal = {Forest Policy and Economics},
      year = {2005},
      volume = {7},
      number = {5},
      pages = {782--795}
    }
    
    Meroni, M., Colombo, R. & Panigada, C. Inversion of a radiative transfer model with hyperspectral observations for LAI mapping in poplar plantations 2004 Remote Sensing of Environment
    Vol. 92(2), pp. 195-206 
    article  
    Abstract: The potential of radiative transfer modelling and inversion techniques for operational uses is investigated in order to retrieve leaf area index in a poplar plantation. The 1-D bidirectional canopy reflectance model SAIL, coupled with the leaf optical properties model PROSPECT, was inverted with hyperspectral airborne DAIS data by means of an iterative method. The root mean square error in LAI estimation was determined against in situ measurements in order to evaluate the impact of different inversion strategies on the LAI retrieval accuracy. These included the selection of an optimal spectral sampling set, the exploitation of prior knowledge in the inversion process and the use of multiview angle data. We claim that the best configuration is achieved by exploiting multiview DAIS data and prior knowledge information about the model variables (RMSE of 0.39 m2 m-2). It is also shown that the use of prior knowledge and the selection of a limited number of bands forming the optimal spectral sampling are instrumental in increasing the accuracy of the inversion process. Our analysis confirms the operational potential of model inversion for biophysical parameter retrieval.
    BibTeX:
    @article{meroni04,
      author = {Meroni, M. and Colombo, R. and Panigada, C.},
      title = {Inversion of a radiative transfer model with hyperspectral observations for LAI mapping in poplar plantations},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {92},
      number = {2},
      pages = {195--206}
    }
    
    Mesarch, M.A., Walter-Shea, E.A., Asner, G.P., Middleton, E.M. & Chan, S.S. A Revised Measurement Methodology for Conifer Needles Spectral Optical Properties: Evaluating the Influence of Gaps between Elements 1999 Remote Sensing of Environment
    Vol. 68(2), pp. 177-192 
    article  
    Abstract: Gaps are unavoidable when compositing small or narrow plant parts (e.g., conifer needles, twigs, narrow leaves, and leaflets) on sample holders in preparation for measuring spectral optical properties. The Daughtry et al. (1989) (A new technique to measure the spectral properties of conifer needles. Remote Sens. Environ. 27:81-91.) method of measuring conifer needle optical properties utilizes a relatively large gap fraction (approximately 0.3-0.6) and needles painted black on one surface of the sample from which the gap fraction of the sample is indirectly determined. Following this protocol typically results in distortions in optical properties, including underestimates in transmittance (sometimes negative values), and only one surface of the sample can be measured. The objectives of this article are to: 1) evaluate the influence of gaps between sample elements (conifer needles, twigs, narrow leaves and leaflets) on optical properties calculated with the published equations from Daughtry et al. (1989) and 2) revise the original Daughtry et al. method for optical property measurements by using an image-analysis to directly measure the gap fraction and use both surfaces of the sample. We achieve these objectives by reviewing the theory and investigating the effects of gaps by measurements of an inert photographic film material, fir needles, and mesquite leaflets. Tests to estimate the transmittance of film samples (film) and foliage (fir needles, mesquite leaflets) indicate that a relatively small gap fraction (less than 0.20) reduces the occurrence of computed negative transmittance values, reduces the variation in computed values, and yields values expected for the "true" or "nongap" transmittance. Employing the image analysis along with reduced gap fractions decreased the variance of measurements and permitted measurements of both surfaces per sample, thus reducing the time required by making half as many samples as originally required by Daughtry et al.
    BibTeX:
    @article{Mesarch1999,
      author = {Mesarch, Mark A. and Walter-Shea, Elizabeth A. and Asner, Gregory P. and Middleton, Elizabeth M. and Chan, Stephen S.},
      title = {A Revised Measurement Methodology for Conifer Needles Spectral Optical Properties: Evaluating the Influence of Gaps between Elements},
      journal = {Remote Sensing of Environment},
      year = {1999},
      volume = {68},
      number = {2},
      pages = {177--192}
    }
    
    Michel, P., Jenkins, J., Mason, N., Dickinson, K.J.M. & Jamieson, I.G. Assessing the ecological application of lasergrammetric techniques to measure fine-scale vegetation structure. 2008 Ecological Informatics
    Vol. 3, pp. 309-320 
    article  
    BibTeX:
    @article{Michel2008,
      author = {Michel, P. and Jenkins, J. and Mason, N. and Dickinson, K. J. M. and Jamieson, I. G.},
      title = {Assessing the ecological application of lasergrammetric techniques to measure fine-scale vegetation structure.},
      journal = {Ecological Informatics},
      year = {2008},
      volume = {3},
      pages = {309-320}
    }
    
    Miller, J.D., Danzer, S.R., Watts, J.M., Stone, S. & Yool, S.R. Cluster analysis of structural stage classes to map wildland fuels in a Madrean ecosystem 2003 Journal of Environmental Management
    Vol. 68(3), pp. 239-252 
    article  
    Abstract: Geospatial information technology is changing the nature of fire mapping science and management. Geographic information systems (GIS) and global positioning system technology coupled with remotely sensed data provide powerful tools for mapping, assessing, and understanding the complex spatial phenomena of wildland fuels and fire hazard. The effectiveness of these technologies for fire management still depends on good baseline fuels data since techniques have yet to be developed to directly interrogate understory fuels with remotely sensed data. We couple field data collections with GIS, remote sensing, and hierarchical clustering to characterize and map the variability of wildland fuels within and across vegetation types. One hundred fifty six fuel plots were sampled in eight vegetation types ranging in elevation from 1150 to 2600 m surrounding a Madrean &lsquo;sky island&rsquo; mountain range in the southwestern US. Fuel plots within individual vegetation types were divided into classes representing various stages of structural development with unique fuel load characteristics using a hierarchical clustering method. Two Landsat satellite images were then classified into vegetation/fuel classes using a hybrid unsupervised/supervised approach. A back-classification accuracy assessment, which uses the same pixels to test as used to train the classifier, produced an overall Kappa of 50% for the vegetation/fuels map. The map with fuel classes within vegetation type collapsed into single classes was verified with an independent dataset, yielding an overall Kappa of 80
    BibTeX:
    @article{Miller2003,
      author = {Miller, Jay D. and Danzer, Shelley R. and Watts, Joseph M. and Stone, Sheridan and Yool, Stephen R.},
      title = {Cluster analysis of structural stage classes to map wildland fuels in a Madrean ecosystem},
      journal = {Journal of Environmental Management},
      year = {2003},
      volume = {68},
      number = {3},
      pages = {239--252}
    }
    
    Miller, J.D. & Yool, S.R. Modeling fire in semi-desert grassland/oak woodland: The spatial implications 2002 Ecological Modelling
    Vol. 153(3), pp. 229-245 
    article  
    Abstract: Fire-evolved forests that historically had high fire return intervals (FARSITE to the level of detail in the fuels data, both spatially and quantitatively, to better understand requirements for mapping fuels to produce accurate fire simulations. Simulated fires generated using site specific fuel models mapped at 30 m and degraded to 210 m were compared to fires simulated using standard generic Northern Forest Fire Laboratory (NFFL) fuel types. Eight classes of surface fuels were mapped by classification of satellite imagery with an overall accuracy of 0.78. A percent tree canopy cover map was created from digital orthophotos using a linear regression model with an Radj2=0.93 of field sampled percent canopy cover data to a tree canopy shadow model. The dominant site specific fuel model (63% cover) was found to agree with the most suitable NFFL fuel model. Site specific fuel models mapped at fine resolution were found to produce statistically smaller fire areas than those produced with generic fuel models mapped at a fine scale and site specific fuels mapped at a coarse scale. In the worst case scenario (low fuel moistures and high wind speeds) the average fire size was about 20% larger with the fuel map using NFFL fuel models than with the fine scale map using site specific fuel models.
    BibTeX:
    @article{miller02,
      author = {Miller, Jay D. and Yool, Stephen R.},
      title = {Modeling fire in semi-desert grassland/oak woodland: The spatial implications},
      journal = {Ecological Modelling},
      year = {2002},
      volume = {153},
      number = {3},
      pages = {229--245}
    }
    
    Miller, J.D. & Yool, S.R. Mapping forest post-fire canopy consumption in several overstory types using multi-temporal Landsat TM and ETM data 2002 Remote Sensing of Environment
    Vol. 82(2-3), pp. 481-496 
    article  
    Abstract: To facilitate the identification of appropriate post-fire watershed treatments and minimize erosion effects after socio-economically important fires, Interagency Burned Area Emergency Rehabilitation (BAER) teams produce initial timely estimates of the fire perimeter and classifications of burn severity, forest mortality, and vegetation mortality. Accurate, cost-effective, and minimal time-consuming methods of mapping fire are desirable to assist rehabilitation efforts immediately after containment of the fire. BAER teams often derive their products by manually interpreting color infrared aerial photos and/or field analysis. Automated classification of multispectral satellite data are examined to determine whether they can provide improved accuracy over manually digitized aerial photographs. In addition, pre-fire vegetation data are incorporated to determine whether further gains in accuracy of mapped canopy consumption can be made. BAER team classifications from the Cerro Grande Fire were compared to estimates of overstory consumption produced using a pre-fire vegetation classification, and a change detection algorithm using bands 4 and 7 from July 1997 pre-fire Landsat Thematic Mapper (TM) and July 2000 post-fire Enhanced Thematic Mapper (ETM) data. BAER team classifications are highly correlated to overstory consumption and should produce high Kappa statistics when verified using the same dataset. Our three-class supervised classification of the change image incorporating a pre-fire vegetation classification yielded the highest Kappa at 0.86. A three-class unsupervised classification of the change image yielded a lower Kappa of 0.72. BAER team classifications yielded Kappas ranging from 0.38 to 0.63 using the same verification dataset.
    BibTeX:
    @article{Miller2002,
      author = {Miller, Jay D. and Yool, Stephen R.},
      title = {Mapping forest post-fire canopy consumption in several overstory types using multi-temporal Landsat TM and ETM data},
      journal = {Remote Sensing of Environment},
      year = {2002},
      volume = {82},
      number = {2-3},
      pages = {481--496}
    }
    
    Milton, E.J., Schaepman, M.E., Anderson, K., Kneub?hler, M. & Fox, N. Progress in field spectroscopy 2009 Remote Sensing of Environment
    Vol. 113(Supplement 1)Imaging Spectroscopy Special Issue, pp. S92-S109 
    article URL 
    Abstract: This paper reviews developments in the science of field spectroscopy, focusing on the last twenty?years in particular. During this period field spectroscopy has become established as an important technique for characterising the reflectance of natural surfaces in situ, for supporting the vicarious calibration of airborne and satellite sensors, and for providing a means of scaling-up measurements from small areas (e.g. leaves, rocks) to composite scenes (e.g. vegetation canopies), and ultimately to pixels. This paper describes the physical basis of the subject and evaluates the different methods and instruments which have been employed across a range of studies. The development and use of field goniometers is described, and related to methods for estimating the bidirectional reflectance distribution function (BRDF) from directional reflectance measurements in the field. The paper also considers the practical aspects of field spectroscopy, and identifies a number of factors affecting the useability of field spectroradiometers, including the weight and cost of the instruments, limitations of some commonly used methodologies and practical issues such as the legibility of displays and limited battery life. The prospects for the future of field spectroscopy are considered in relation to the increasingly important contribution that field spectral data will make to EO-based global measurement and monitoring systems, specifically through their assimilation into numerical models. However, for this to be achieved it is essential that the data are of high quality, with stated levels of accuracy and uncertainty, and that common protocols are developed and maintained to ensure the long-term value of field spectroscopic data. The importance of employing a precise terminology for describing the geometric configuration of measurements is highlighted in relation to issues of repeatability and reproducibility. Through such refinements in methodology, field spectroscopy will establish its credentials as a reliable method of environmental measurement, underpinning quantitative Earth observation and its applications in the environmental and Earth sciences.
    BibTeX:
    @article{Milton2009,
      author = {Milton, Edward J. and Schaepman, Michael E. and Anderson, Karen and Kneub?hler, Mathias and Fox, Nigel},
      title = {Progress in field spectroscopy},
      booktitle = {Imaging Spectroscopy Special Issue},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {Supplement 1},
      pages = {S92--S109},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4PSJT3R-1/2/1f6cf30222e1e5b467c6161e6eb6817d}
    }
    
    Mitchell, P. & Kirby, K. Ecological effects of forestry practices in long-established woodland and their implications for nature conservation. 1989 Oxford Forestry Institute, Oxford.  article  
    BibTeX:
    @article{Mitchell1989,
      author = {Mitchell, P.L. and Kirby, K.J.},
      title = {Ecological effects of forestry practices in long-established woodland and their implications for nature conservation.},
      journal = {Oxford Forestry Institute, Oxford.},
      year = {1989}
    }
    
    Moffiet, T., Mengersen, K., Witte, C., King, R. & Denham, R. Airborne laser scanning: Exploratory data analysis indicates potential variables for classification of individual trees or forest stands according to species 2005 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 59, pp. 289-309 
    article  
    BibTeX:
    @article{moffiet05,
      author = {T. Moffiet and K. Mengersen and C. Witte and R. King and R. Denham},
      title = {Airborne laser scanning: Exploratory data analysis indicates potential variables for classification of individual trees or forest stands according to species},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {2005},
      volume = {59},
      pages = {289-309}
    }
    
    Moorthy, I., Miller, J.R. & Noland, T.L. Estimating chlorophyll concentration in conifer needles with hyperspectral data: An assessment at the needle and canopy level 2008 Remote Sensing of Environment
    Vol. 112(6), pp. 2824-2838 
    article  
    Abstract: This investigation quantitatively links chlorophyll a?+?b (chl?a?+?b) concentration, a physiological marker of forest health condition, to hyperspectral observations of Jack Pine (Pinus banksiana), a dominant Boreal forest species. Compact Airborne Spectrographic Imager (CASI) observations, in the visible-near infrared domain, were acquired over eight selected Jack Pine sites, near Sudbury, Ontario, between June and September of 2001. Supplementing the airborne campaigns was concurrent on-site collection of foliage samples for laboratory spectral and chemical measurements. The study first connected needle-level optical properties with pigment concentration through the inversion of radiative transfer models, LIBERTY and PROSPECT. Next, a chlorophyll sensitive optical index (R750/R710), was "scaled-up" using SAILH, a turbid medium canopy model, to estimate total pigment content at the canopy-level. Due to the potential confounding effects of open canopy structure and foliage clumping, the analysis accordingly focused on high spatial resolution CASI imagery (1?m) to visually target tree crowns, while accounting for shadowed areas. Chl?a?+?b concentration estimation from airborne spectral data using coupled leaf and canopy models was shown to be feasible with a root mean square error of 5.3?[mu]g/cm2, for a pigment range of 25.7 to 45.9?[mu]g/cm2. Such predictive algorithms using airborne-level data provide the methodology to be potentially scaled-up to satellite-level hyperspectral platforms for large scale monitoring of vegetation productivity and forest stand condition.
    BibTeX:
    @article{Moorthy2008,
      author = {Moorthy, Inian and Miller, John R. and Noland, Thomas L.},
      title = {Estimating chlorophyll concentration in conifer needles with hyperspectral data: An assessment at the needle and canopy level},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {6},
      pages = {2824--2838}
    }
    
    Morris, R.D., von Toussaint, U. & Cheeseman, P.C. HIGH RESOLUTION SURFACE GEOMETRY AND ALBEDO BY COMBINING LASER ALTIMETRY AND VISIBLE IMAGES 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 105-111 
    article  
    Abstract: The need for accurate geometric and radiometric information over large areas has become increasingly important. Laser al- timetry is one of the key technologies for obtaining this geometric information. However, there are important application areas where the observing platform has its orbit constrained by the other instruments it is carrying, and so the spatial resolution that can be recorded by the laser altimeter is limited. In this paper we show how information recorded by one of the other instruments commonly carried, a high-resolution imaging camera, can be combined with the laser altimeter measurements to give a high resolution estimate both of the surface geometry and its re ectance properties. This estimate has an accuracy unavailable from other interpolation methods. We present the results from combining synthetic laser altimeter measurements on a coarse grid with images generated from a surface model to re-create the surface model.
    BibTeX:
    @article{morris01,
      author = {Robin D. Morris and Udo von Toussaint and Peter C. Cheeseman},
      title = {HIGH RESOLUTION SURFACE GEOMETRY AND ALBEDO BY COMBINING LASER ALTIMETRY AND VISIBLE IMAGES},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {105-111}
    }
    
    Morsdorf, F. Sensitivity of airborne laser scanning data to sensor and survey configurations - a modelling study. in preparation IEEE Transactions on Geoscience and Remote Sensing  article  
    BibTeX:
    @article{morsdorf09c,
      author = {Felix Morsdorf},
      title = {Sensitivity of airborne laser scanning data to sensor and survey configurations - a modelling study.},
      journal = {IEEE Transactions on Geoscience and Remote Sensing},
      year = {in preparation}
    }
    
    Morsdorf, F. LIDAR Remote Sensing for Estimation of Biophysical Vegetation Parameters 12.01.2007 School: University of Zürich, Zürich, Switzerland.  phdthesis  
    BibTeX:
    @phdthesis{morsdorf_phd,
      author = {Felix Morsdorf},
      title = {LIDAR Remote Sensing for Estimation of Biophysical Vegetation Parameters},
      school = {University of Zürich, Zürich, Switzerland.},
      year = {12.01.2007}
    }
    
    Morsdorf, F., Frey, O., Koetz, B. & Meier, E. Ray Tracing for Modeling of Small Footprint

    Airborne Laser Scanning Returns.

    2007 International Archives of Photogrammetry and Remote Sensing

    Volume XXXVI, Part 3 / W52, pp. 294-299. 

    inproceedings  
    BibTeX:
    @inproceedings{Morsdorf2007,
      author = {Morsdorf, F. and Frey, O. and Koetz, B. and Meier, E.},
      title = {Ray Tracing for Modeling of Small Footprint 

    Airborne Laser Scanning Returns.}, booktitle = {International Archives of Photogrammetry and Remote Sensing

    Volume XXXVI, Part 3 / W52}, year = {2007}, pages = {294-299.} }

    Morsdorf, F., Frey, O., Meier, E., Itten, K. & Allgöwer, B. Assessment on the influence of flying height and scan angle on biophysical vegetation products

    derived from airborne laser scanning

    2006 3d Remote Sensing in Forestry, 14-15. Feb. 2006, Vienna, Austria  conference  
    BibTeX:
    @conference{morsdorf06_vienna,
      author = {Felix Morsdorf and Othmar Frey and Erich Meier and K.I. Itten and Britta Allgöwer},
      title = {Assessment on the influence of flying height and scan angle on biophysical vegetation products 

    derived from airborne laser scanning}, booktitle = {3d Remote Sensing in Forestry, 14-15. Feb. 2006, Vienna, Austria}, year = {2006} }

    Morsdorf, F., Frey, O., Meier, E., Itten, K.I. & Allgöwer, B. Assessment of the influence of flying altitude and scan angle on biophysical vegetation products derived from airborne laser scanning 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1387-1406 
    article  
    Abstract: Airborne Laser Scanning (ALS) has been established as a valuable tool for the estimation of biophysical vegetation properties such as tree height, crown width, fractional cover and leaf area index (LAI). It is expected that the conditions of data acquisition, such as viewing geometry and sensor configuration influence the value of these parameters. In order to gain knowledge about these different conditions, we test for the sensitivity of vegetation products for viewing geometry, namely flying altitude and scanning (incidence) angle. Based on two methodologies for single tree extraction and derivation of fractional cover and LAI previously developed and published by our group, we evaluate how these variables change with either flying altitude or scanning angle. These are the two parameters which often need to be optimized towards the best compromise between point density and area covered with a single flight line, in order to reduce acquisition costs. Our test-site in the Swiss National Park was sampled with two nominal flying altitudes, 500 and 900??m above ground. Incidence angle and local incidence angle were computed based on the digital terrain model using a simple backward geocoding procedure. We divided the raw laser returns into several different incident angle classes based on the flight path data; the TopoSys Falcon II system used in this study has a maximum scan angle of ??7.15??. We compared the derived biophysical properties from each of these classes with field measurements based on tachymeter measurements and hemispherical photographs, which were geolocated using differential GPS. It was found that with increasing flying height the well-known underestimation of tree height increases. A similar behaviour can be observed for fractional cover; its respective values decrease with higher flying height. The minimum distance between first and last echo increases from 1.2 metres for 500??m AGL to more than 3 metres for 900??m AGL, which does alter return statistics. The behaviour for incidence angles is not so evident, probably due to the small scanning angle of the system used. fCover seems to be most affected by incidence angles, with significantly higher differences for locations further away from nadir. As expected, incidence angle appears to be of higher importance for vegetation density parameters than local incidence angle.
    BibTeX:
    @article{morsdorf08,
      author = {Morsdorf, F. and Frey, O. and Meier, E. and Itten, K. I. and Allgöwer, B.},
      title = {Assessment of the influence of flying altitude and scan angle on biophysical vegetation products derived from airborne laser scanning},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1387--1406}
    }
    
    Morsdorf, F., Koetz, B., Meier, E., Itten, K. & Allg?wer, B. The potential of discrete return, small footprint airborne laser scanning data for vegetation density estimation 2005
    Vol. VOLUME XXXVI, PART 3/W19(ISSN 1682-1777)International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences 
    inproceedings  
    BibTeX:
    @inproceedings{morsdorf05_isprs,
      author = {Felix Morsdorf and Benjamin Koetz and Erich Meier and K.I. Itten and Britta Allg?wer},
      title = {The potential of discrete return, small footprint airborne laser scanning data for vegetation density estimation},
      booktitle = {International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences},
      year = {2005},
      volume = {VOLUME XXXVI, PART 3/W19},
      number = {ISSN 1682-1777}
    }
    
    Morsdorf, F., Kötz, B., Itten, K., Isenegger, D. & Allgöwer, B. Sensitivity of a Forest Fire Behavior Model to High Resolution Remote Sensing Data 2005 EARSeL 5th International workshop on Remote Sensing and GIS Applications to Forest Fire Management: Fire Effects Assessment. Zaragoza, Spain.  conference  
    BibTeX:
    @conference{morsdorf05a,
      author = {Felix Morsdorf and Benjamin Kötz and Klaus Itten and Daniel Isenegger and Britta Allgöwer},
      title = {Sensitivity of a Forest Fire Behavior Model to High Resolution Remote Sensing Data},
      booktitle = {EARSeL 5th International workshop on Remote Sensing and GIS Applications to Forest Fire Management: Fire Effects Assessment. Zaragoza, Spain.},
      year = {2005}
    }
    
    Morsdorf, F., Kötz, B., Meier, E., Itten, K. & Allgöwer, B. Estimation of LAI and fractional cover from small footprint airborne laser scanning data based on gap fraction 2006 Remote Sensing of Environment
    Vol. 104(1), pp. 50-61 
    article  
    Abstract: We evaluate the potential of deriving fractional cover (fCover) and leaf area index (LAI) from discrete return, small footprint airborne laser scanning (ALS) data. fCover was computed as the fraction of laser vegetation hits over the number of total laser echoes per unit area. Analogous to the concept of contact frequency, an effective LAI proxy was estimated by a fraction of first and last echo types inside the canopy. Validation was carried out using 83 hemispherical photographs georeferenced to centimeter accuracy by differential GPS, for which the respective gap fractions were computed over a range of zenith angles using the Gap Light Analyzer (GLA). LAI was computed by GLA from gap fraction estimations at zenith angles of 0-60[deg]. For ALS data, different data trap sizes were used to compute fCover and LAI proxy, the range of radii was 2-25[no-break space]m. For fCover, a data trap size of 2[no-break space]m radius was used, whereas for LAI a radius of 15 m provided best results. fCover was estimated both from first and last echo data, with first echo data overestimating field fCover and last echo data underestimating field fCover. A multiple regression of fCover derived from both echo types with field fCover showed no increase of R2 compared to the regression of first echo data, and thus, we only used first echo data for fCover estimation. R2 for the fCover regression was 0.73, with an RMSE of 0.18. For the ALS LAI proxy, R2 was lower, at 0.69, while the RMSE was 0.01. For LAI larger radii (~ 15[no-break space]m ) provided best results for our canopy types, which is due to the importance of a larger range of zenith angles (0-60[deg]) in LAI estimation from hemispherical photographs. Based on the regression results, maps of fCover and LAI were computed for our study area and compared qualitatively to equivalent maps based on imaging spectrometry, revealing similar spatial patterns and ranges of values.
    BibTeX:
    @article{morsdorf06,
      author = {Morsdorf, Felix and Kötz, Benjamin and Meier, Erich and Itten, K.I. and Allgöwer, Britta},
      title = {Estimation of LAI and fractional cover from small footprint airborne laser scanning data based on gap fraction},
      journal = {Remote Sensing of Environment},
      year = {2006},
      volume = {104},
      number = {1},
      pages = {50--61}
    }
    
    Morsdorf, F., M?rell, A., Koetz, B., Cassagne, N., Pimont, F., Rigolot, E. & Allg?wer, B. Discrimination of vegetation strata in a multi-layered Mediterranean forest ecosystem using height and intensity information derived from airborne laser scanning 2010 Remote Sensing of Environment
    Vol. 114(7), pp. 1403 - 1415 
    article DOI URL 
    Abstract: Height and intensity information derived from Airborne Laser Scanning (ALS) was used to obtain a quantitative vertical stratification of vegetation in a multi-layered Mediterranean ecosystem. A new methodology for the separation of different vegetation strata was implemented using supervised classification of a two-dimensional feature space spanned by ALS return height (terrain corrected) and intensity. The classification was carried out using Gaussian mixture models tuned on a control plot. The approach was validated using extensive field measurements from treated plots, ranging from single vegetation strata to a more complex multi-layered ecosystem. Plot-level canopy profiles derived from ALS and from a geometric reconstruction based on field measurements were in very good agreement, with correlation coefficients ranging from 0.73 (for complex, 3-layered) to 0.96 (simple, single-layered). In addition, it was possible to derive plot-level information on layer height, vertical extent and coverage with absolute accuracies of some decimetres (simple plots) to a meter (complex plots) for both height and vertical extent and about 10 to 15% for layer coverage. The approach was then used to derive maps of the layer height, vertical extent and percentage of ground cover for a larger area, and classification accuracy was evaluated on a per-pixel basis. The method performed best for single-layered plots or dominant layers on multi-layered plots, obtaining an overall accuracy of 80 to 90%. For subdominant layers in the more complex plots, accuracies obtained were as low as 48%. Our results demonstrate the possibility of deriving qualitative (presence and absence of specific vegetation layers) and quantitative, physical data (height, vertical extent and ground cover) describing the vertical structure of complex multi-layered forest ecosystems using ALS-based height and intensity information.
    BibTeX:
    @article{Morsdorf2010,
      author = {Felix Morsdorf and Anders M?rell and Benjamin Koetz and Nathalie Cassagne and Francois Pimont and Eric Rigolot and Britta Allg?wer},
      title = {Discrimination of vegetation strata in a multi-layered Mediterranean forest ecosystem using height and intensity information derived from airborne laser scanning},
      journal = {Remote Sensing of Environment},
      year = {2010},
      volume = {114},
      number = {7},
      pages = {1403 - 1415},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4YR37N6-2/2/bef1a113cee6afafbdf922f397383ffd},
      doi = {DOI: 10.1016/j.rse.2010.01.023}
    }
    
    Morsdorf, F., Marell, A., Rigolot, E. & Allgöwer, B. A role for airborne laser scanning data in vertical stratification of multilayered ecosystems 2009 International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXVIII, Part 3 / W8., pp. 141-146  inproceedings  
    BibTeX:
    @inproceedings{morsdorf_2009_ign,
      author = {Felix Morsdorf and Anders Marell and Eric Rigolot and Britta Allgöwer},
      title = {A role for airborne laser scanning data in vertical stratification of multilayered ecosystems},
      booktitle = {International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXVIII, Part 3 / W8.},
      year = {2009},
      pages = {141-146}
    }
    
    Morsdorf, F., Meier, E., Allgöwer, B. & Nüesch, D. Cluster-Analyse von LIDAR-Vektordaten zur Erfassung geomatrischer Eigenschaften von einzelnen Bäumen 2004 Photogrammetrie Fernerkundung Geoinformation(4), pp. 259-268  article  
    BibTeX:
    @article{morsdorf_pfg04,
      author = {Felix Morsdorf and Erich Meier and Britta Allgöwer and Daniel Nüesch},
      title = {Cluster-Analyse von LIDAR-Vektordaten zur Erfassung geomatrischer Eigenschaften von einzelnen Bäumen},
      journal = {Photogrammetrie Fernerkundung Geoinformation},
      year = {2004},
      number = {4},
      pages = {259-268}
    }
    
    Morsdorf, F., Meier, E., Allgöwer, B. & Nüesch, D. Clustering in Airborne Laser Scanning Raw Data for Segmentation of Single Trees 2003 Proceedings of the ISPRS working group III/3 workshop "3-D reconstruction from airborne laserscanner and InSAR data" Dresden, Germany 8-10 October 2003, ISSN 1682-1750 VOLUME XXXIV, PART 3/W13  inproceedings  
    BibTeX:
    @inproceedings{conf_dresden03,
      author = {Felix Morsdorf and Erich Meier and Britta Allgöwer and Daniel Nüesch},
      title = {Clustering in Airborne Laser Scanning Raw Data for Segmentation of Single Trees},
      booktitle = {Proceedings of the ISPRS working group III/3 workshop "3-D reconstruction from airborne laserscanner and InSAR data" Dresden, Germany 8-10 October 2003, ISSN 1682-1750 VOLUME XXXIV, PART 3/W13},
      year = {2003}
    }
    
    Morsdorf, F., Meier, E., Koetz, B., Itten, K. & Allgöwer, B. High Resolution Airborne Laser Scanning for Forest Fuel Type Mapping 2003 EARSEL - 4th International Workshop: Remote Sensing and GIS applications for Forest Fire Management  inproceedings  
    BibTeX:
    @inproceedings{morsdorf_earsel03,
      author = {Felix Morsdorf and Erich Meier and Benjamin Koetz and K.I. Itten and Britta Allgöwer},
      title = {High Resolution Airborne Laser Scanning for Forest Fuel Type Mapping},
      booktitle = {EARSEL - 4th International Workshop: Remote Sensing and GIS applications for Forest Fire Management},
      year = {2003}
    }
    
    Morsdorf, F., Meier, E., Koetz, B., Nüesch, D., Itten, K. & Allgöwer, B. The potential of high resolution airborne laser scanning for deriving geometric properties of single trees 2003 EGS - AGU - EUG Joint Assembly, Nice, France.  inproceedings  
    BibTeX:
    @inproceedings{morsdorf_egs03,
      author = {Morsdorf, Felix and Meier, E. and Koetz, B. and Nüesch, D. and Itten, K. and Allgöwer, B.},
      title = {The potential of high resolution airborne laser scanning for deriving geometric properties of single trees},
      booktitle = {EGS - AGU - EUG Joint Assembly, Nice, France.},
      year = {2003}
    }
    
    Morsdorf, F., Meier, E., Kötz, B., Itten, K.I., Dobbertin, M. & Allgöwer, B. LIDAR-based geometric reconstruction of boreal type forest stands at single tree level for forest and wildland fire management 2004 Remote Sensing of Environment
    Vol. 3(92), pp. 353-362 
    article  
    BibTeX:
    @article{morsdorf04,
      author = {Felix Morsdorf and Erich Meier and Benjamin Kötz and Klaus I. Itten and Matthias Dobbertin and Britta Allgöwer},
      title = {LIDAR-based geometric reconstruction of boreal type forest stands at single tree level for forest and wildland fire management},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {3},
      number = {92},
      pages = {353-362}
    }
    
    Morsdorf, F., Nichol, C., Malthus, T., Patenaude, G. & Woodhouse, I. Modelling multi-spectral LIDAR vegetation backscatter - assessing structural and physiological information content 2008 Silvilaser, Edinburgh, UK  conference  
    BibTeX:
    @conference{morsdorf08b,
      author = {Felix Morsdorf and Caroline Nichol and T.J. Malthus and G. Patenaude and I.H. Woodhouse},
      title = {Modelling multi-spectral LIDAR vegetation backscatter - assessing structural and physiological information content},
      booktitle = {Silvilaser, Edinburgh, UK},
      year = {2008}
    }
    
    Morsdorf, F., Nichol, C., Malthus, T. & Woodhouse, I.H. Assessing forest structural and physiological information content of multi-spectral LiDAR waveforms by radiative transfer modelling 2009 Remote Sensing of Environment
    Vol. 113(10), pp. 2152 - 2163 
    article DOI  
    Abstract: The concept for a multi-spectral, full-waveform canopy LiDAR instrument was tested by simulating return waveforms using a model providing ecological sound tree structure (TREEGROW) and a model of leaf optical properties (PROSPECT). The proposed instrument will take measurements at four different wavelengths, which were chosen according to physiological processes altering leaf reflectance and transmittance. The modelling was used to assess both the structural and physiological information content such an instrument could provide, especially whether the normally structure-dominated return waveform would pick up small changes in reflectance at the leaf level. Multi-spectral waveforms were simulated for models of single Scots pine trees of different ages and at different stages of the growing season, including chlorophyll concentration induced changes in leaf optical properties. It was shown that the LiDAR waveforms would not only capture the tree height information, but would also pick up the seasonal and vertical variation of NDVI computed from two of the four MSCL wavelengths inside the tree canopy. The instrument concept was further tested in a simulation of a virtual forest stand constructed of 74 trees of different ages according to measurements taken on a field site being 20 by 20 meter in size. A total of 1521 NDVI profiles were computed and mean NDVI corrected backscatter was compared to the actual canopy profile of the virtual stand. The profiles picked up the seasonal variation of chlorophyll within the canopy, while the return of ground remained unchanged from June to September. Thus, it was shown that a MSCL instrument would be able to separately pick up the physiology of canopy and understorey and/or soil. It was found that occlusion would mask the lower parts of the canopy volume within the stand and the seasonal variation of this occlusion effect was quantified, being larger in September, when the absorption of canopy elements is higher. In addition, it could be demonstrated that a new multi-wavelength LiDAR predictor variable was able to significantly improve the retrieval accuracy of photosynthetically active biomass opposed to using a single-wavelength LiDAR alone.
    BibTeX:
    @article{Morsdorf2009,
      author = {Felix Morsdorf and Caroline Nichol and Timothy Malthus and Iain H. Woodhouse},
      title = {Assessing forest structural and physiological information content of multi-spectral LiDAR waveforms by radiative transfer modelling},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {10},
      pages = {2152 - 2163},
      doi = {DOI: 10.1016/j.rse.2009.05.019}
    }
    
    Morsdorf, F. & Volmer, S. LIVE@WEB.COM - Using CBIR technology in interactive Web-TV {2002} MULTIMEDIA 2001, PROCEEDINGS, pp. {189-197}  article  
    Abstract: The increasing amount of internet based television broadcasts has lead to new approachs to interactivity in TV programs. We developed a system which is able to supply the viewer of the program upon interaction with information relating to the program, only based on the low-level visual content of the scene. This aim is achieved by comparing signatures describing the visual content of single frames of the video with a remote database of signatures derived from known videos. The database actually links the visual information contained in the signatures to some second-level information interesting for the user. Two main problems in extending CBIR technology to videos must be overcome, one is the extraction of the visual information out of the highly redundant video material, and the other is reducing the matching time of the system enough to allow for web-based interactivity.
    BibTeX:
    @article{ISI:000175262500019,
      author = {Morsdorf, F and Volmer, S},
      title = {LIVE@WEB.COM - Using CBIR technology in interactive Web-TV},
      booktitle = {MULTIMEDIA 2001, PROCEEDINGS},
      year = {2002},
      pages = {189-197},
      note = {6th Eurographics Workshop on Multimedia, MANCHESTER, ENGLAND, SEP 08-09, 2001}
    }
    
    Morvan, D. & Dupuy, J.L. Modeling of fire spread through a forest fuel bed using a multiphase formulation 2001 Combustion and Flame
    Vol. 127(1-2), pp. 1981-1994 
    article  
    Abstract: We describe a multiphase formulation to study numerically the propagation of a line fire in a forest fuel bed. One of the objectives of these studies is the improvement of knowledge on the fundamental physical mechanisms that control the propagation of forest fires. In complement of the experimental approach, this simulation tool can also be used for the development of simplified operational models used for instance for the prediction of the rate of spread (ROS) of wildland fires. The decomposition of solid fuel constituting a forest fuel bed as well as the multiple interactions with the gas phase are represented by adopting a multiphase formulation. This approach consists in solving the conservation equations (mass, momentum, energy) averaged in a control volume at a scale sufficient to contain several solid particles in the surrounding gas mixture. After a presentation of the equations and closure sub-models used in this approach, some numerical results obtained for the propagation of a line fire in a pine needles litter are presented and compared with experimental data obtained in laboratory. These results show that the rate of spread of fire in the fuel bed is primarily controlled by the radiative heat transfer. By increasing the fuel load (with a constant packing ratio), the results show the existence of two modes of propagation. A first area where the ROS varies linearly with the fuel load followed of a second where the ROS becomes independent of the load. By introducing the optical thickness characterizing the fuel bed, this difference in mode of propagation was interpreted like the demonstration of two modes of radiative transfer (optically thin and thick, respectively). The analysis of the distributions of the mass fractions of fuel and oxidant present in the gas mixture integrated through the depth of the fuel bed shows that the propagation velocity could also be limited by the lack of oxygen or fuel available in the ignited zone to maintain the pilot flame.
    BibTeX:
    @article{Morvan2001,
      author = {Morvan, D. and Dupuy, J. L.},
      title = {Modeling of fire spread through a forest fuel bed using a multiphase formulation},
      journal = {Combustion and Flame},
      year = {2001},
      volume = {127},
      number = {1-2},
      pages = {1981--1994}
    }
    
    Mougin, E., Proisy, C., Marty, G., Fromard, F., Puig, H., Betoulle, J. & Rudant, J. Multifrequency and multipolarization radar backscattering from mangrove forests 1999 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 37(1)Geoscience and Remote Sensing, IEEE Transactions on, pp. 94-102 
    article  
    Abstract: The authors examine the dependence between multifrequency/multipolarization synthetic aperture radar (SAR) data and mangrove forest parameters. AIRSAR data at P-, L-, and C-band were acquired over French Guiana in June 1993. Structural parameters, namely, tree height, tree diameter at breast height (DBH), tree density, basal area, and total above-ground biomass were estimated in 12 stands representative of different mangrove forest stages. At the study site, total biomass ranges from about 5 to 437 tons of dry matter per ha (t DM ha-1). Strong relationships were found between most forest parameters and radar data, with P-HV showing the greatest sensitivity to total biomass. Estimation of the forest parameters was performed through multiple stepwise regression techniques. While &sigma;0 at P-HV saturated at about 160 t DM ha-1, the use of several frequencies and polarizations allowed total biomass to be accurately estimated up to about 240 t DM ha-1. Furthermore, the use of polarization ratios at different frequencies has provided useful information about the penetration capability of the radar wave as well as the dominant mechanisms occurring between the radar wave and the mangrove canopy
    BibTeX:
    @article{Mougin1999,
      author = {Mougin, E. and Proisy, C. and Marty, G. and Fromard, F. and Puig, H. and Betoulle, J.L. and Rudant, J.P.},
      title = {Multifrequency and multipolarization radar backscattering from mangrove forests},
      booktitle = {Geoscience and Remote Sensing, IEEE Transactions on},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {1999},
      volume = {37},
      number = {1},
      pages = {94--102}
    }
    
    Mougin, E., Proisy, C., Marty, G., Fromard, F., Puig, H., Betoulle, J. & Rudant, J. Multifrequency and multipolarization radar backscattering from mangrove forests 1999 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 37(1)Geoscience and Remote Sensing, IEEE Transactions on, pp. 94-102 
    article  
    Abstract: The authors examine the dependence between multifrequency/multipolarization synthetic aperture radar (SAR) data and mangrove forest parameters. AIRSAR data at P-, L-, and C-band were acquired over French Guiana in June 1993. Structural parameters, namely, tree height, tree diameter at breast height (DBH), tree density, basal area, and total above-ground biomass were estimated in 12 stands representative of different mangrove forest stages. At the study site, total biomass ranges from about 5 to 437 tons of dry matter per ha (t DM ha-1). Strong relationships were found between most forest parameters and radar data, with P-HV showing the greatest sensitivity to total biomass. Estimation of the forest parameters was performed through multiple stepwise regression techniques. While &sigma;0 at P-HV saturated at about 160 t DM ha-1, the use of several frequencies and polarizations allowed total biomass to be accurately estimated up to about 240 t DM ha-1. Furthermore, the use of polarization ratios at different frequencies has provided useful information about the penetration capability of the radar wave as well as the dominant mechanisms occurring between the radar wave and the mangrove canopy
    BibTeX:
    @article{Mougin1999a,
      author = {Mougin, E. and Proisy, C. and Marty, G. and Fromard, F. and Puig, H. and Betoulle, J.L. and Rudant, J.P.},
      title = {Multifrequency and multipolarization radar backscattering from mangrove forests},
      booktitle = {Geoscience and Remote Sensing, IEEE Transactions on},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {1999},
      volume = {37},
      number = {1},
      pages = {94--102}
    }
    
    Murakami, H., Nakagawa, K., Hasegawa, H., Shibata, T. & Iwanami, E. Change detection of buildings using an airborne laser scanner 1999 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 54(2-3), pp. 148-152 
    article  
    Abstract: This study employed an airborne laser scanner to detect changes of buildings by acquiring a digital surface model (DSM) data of urban areas. Simple comparison between DSM data sets acquired at different occasions successfully detected building changes without omission errors. A CCD array image simultaneously acquired with the DSM data was also automatically orthorectified with the DSM data and indicated to help revise the building database efficiently.
    BibTeX:
    @article{murakami99,
      author = {Hiroshi Murakami and Katsuto Nakagawa and Hiroyuki Hasegawa and Taku Shibata and Eiji Iwanami},
      title = {Change detection of buildings using an airborne laser scanner},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {1999},
      volume = {54},
      number = {2-3},
      pages = {148-152}
    }
    
    Mutlu, M., Popescu, S.C., Stripling, C. & Spencer, T. Mapping surface fuel models using lidar and multispectral data fusion for fire behavior 2008 Remote Sensing of Environment
    Vol. 112(1), pp. 274-285 
    article URL 
    Abstract: Wild-land fires have become intense and more frequent all over the world. Improving the accuracy of mapping fuel models is essential for fuel management decisions and explicit fire behavior prediction for real-time support of suppression tactics and logistics decisions. The overall aim of this paper is to develop the use of lidar (LIght Detection and Ranging) remote sensing to accurately and effectively assess fuel models in East Texas. More specific goals include: (1) developing lidar derived products and the methodology to use them for assessing fuel models; (2) investigating the use of several techniques for data fusion of lidar and multispectral imagery for assessing fuel models; (3) investigating the gain in fuels mapping accuracy when using lidar as opposed to QuickBird imagery alone; and (4) producing spatially explicit digital fuel maps. Estimates of fuel models were compared with in-situ data collected over 62 plots. We employ a unique approach to classify fuel models using a combination of lidar height bins and multispectral image data. Different image processing approaches for fusing lidar and multispectral data, such as the Minimum Noise Fraction (MNF) and Principle Component Analysis (PCA), were used to improve the overall accuracy of image classification. Supervised image classification methods provided better accuracy (90.10%) with the fusion of airborne lidar data with QuickBird data than with QuickBird imagery alone (76.52%). According to our results, lidar derived data provide accurate estimates of surface fuel parameters efficiently and accurately over extensive areas of forests. This study demonstrates the importance of using accurate maps of fuel models derived using new lidar remote sensing techniques.
    BibTeX:
    @article{Mutlu2008,
      author = {Mutlu, Muge and Popescu, Sorin C. and Stripling, Curt and Spencer, Tom},
      title = {Mapping surface fuel models using lidar and multispectral data fusion for fire behavior},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {1},
      pages = {274--285},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4P8H8CN-2/2/8798e4a5c560bc521ba4e54fc0b9baf5}
    }
    
    Myneni, R., Nemani, R. & Running, S. Estimation of global leaf area index and absorbed PAR using radiative transfer models. 1997 IEEE Transactions on Geoscience and Remote Sensing
    Vol. 35, pp. 1380-1393 
    article  
    BibTeX:
    @article{myneni97,
      author = {R.B. Myneni and R.R. Nemani and S.W. Running},
      title = {Estimation of global leaf area index and absorbed PAR using radiative transfer models.},
      journal = {IEEE Transactions on Geoscience and Remote Sensing},
      year = {1997},
      volume = {35},
      pages = {1380-1393}
    }
    
    Myneni, R.B., Maggion, S., Iaquinta, J., Privette, J.L., Gobron, N., Pinty, B., Kimes, D.S., Verstraete, M.M. & Williams, D.L. Optical remote sensing of vegetation: Modeling, caveats, and algorithms 1995 Remote Sensing of Environment
    Vol. 51(1)Remote Sensing of Land Surface for Studies of Global Chage, pp. 169-188 
    article  
    Abstract: The state-of-the-art on radiative transfer modeling in vegetation canopies arul the application of such models to the interpretation and analysis of remotely sensed optical data is summarized. Modeling of top-of-the-atmosphere and top-of-the-canopy radiance field is developed as boundary value problems in radiative transfer. The parameterization of the constituent functions with simple models and/or empirical data is outlined together with numerical solution methods and examples of results of model validation. Caveats in the assignment of signal characteristics to surface properties are itemized and discussed with example results. Algorithms to estimate surface properties from remote observations are classified as spectral vegetation indices, model inversion, expert systems, neural networks, and genetic algorithms. Their applicability is also discussed.
    BibTeX:
    @article{Myneni1995,
      author = {Myneni, R. B. and Maggion, S. and Iaquinta, J. and Privette, J. L. and Gobron, N. and Pinty, B. and Kimes, D. S. and Verstraete, M. M. and Williams, D. L.},
      title = {Optical remote sensing of vegetation: Modeling, caveats, and algorithms},
      booktitle = {Remote Sensing of Land Surface for Studies of Global Chage},
      journal = {Remote Sensing of Environment},
      year = {1995},
      volume = {51},
      number = {1},
      pages = {169--188}
    }
    
    Nelson, R. Modeling Forest Canopy Heights: The Effects of Canopy Shape 1997 Remote Sens. Environ.
    Vol. 60, pp. 327-334 
    article  
    Abstract: Three-dimensional models that represent the top-of-canopy forest height structure were developed to simulate airborne laser profiling responses along forested transects. The simulator which produced these 3-D models constructed individual tree crowns according to a tree's total height, height to first branch, crown diameter, and crown shape (cone, parabola, ellipse, sphere, or a random assortment of these shapes), and then inserted these crowns into a fixed-area plot using mapped stand (x,y) coordinates. This two-dimensional array of forest canopy heights was randomly transected to simulate measurements by an airborne ranging laser. These simulated laser measurements were regressed with ground reference measures to develop predictive linear relationships. The assumed crown shape had a significant impact on 1) simulated laser measurements of height and 2) estimates of basal area, woody volume, and above-ground dry biomass derived via simulation. As canopy shape progressed from a conic form to a more spheric structure, average canopy height, canopy profile area, and canopy volume increased, canopy height variation decreased, and coefficients of variability were stable or decreased. In Costa Rican tropical forests, simulated laser measurements of average height, canopy profile area, and canopy volume increased 8-10 $%$ when a parabolic rather than a conic shape was assumed. An elliptic canopy was 16-18 $%$ taller, on average, than a conic canopy, and a spheric canopy was 23-25 $%$ taller. The effect of these height increases and height variability changes can profoundly affect basal area, volume, and biomass estimates, but the degree to which these estimates are affected is study-area-dependent. Since canopy shape may significantly affect such estimates, canopy shapes should be noted when field data are collected for purposes of height simulation. If canopy shapes are not noted and are unknown, an assumption of an elliptical shape is suggested in order to mitigate potentially large errors which may be incurred using a generic assumption of a cone or sphere.
    BibTeX:
    @article{nelson97,
      author = {Ross Nelson},
      title = {Modeling Forest Canopy Heights: The Effects of Canopy Shape},
      journal = {Remote Sens. Environ.},
      year = {1997},
      volume = {60},
      pages = {327-334}
    }
    
    Ni, W., Li, X., Woodcock, C., Caetano, M. & Strahler, A. An analytical

    hybrid GORT model for bidirectional reflectance over discontinuous plant canopies.

    1999 IEEE Transactions on Geoscience and Remote Sensing
    Vol. 37, pp. 987-999 
    article  
    BibTeX:
    @article{ni99,
      author = {Ni, W.G. and Li, X.W. and Woodcock, C.E. and Caetano, M.R. and Strahler, A.H.},
      title = {An analytical 

    hybrid GORT model for bidirectional reflectance over discontinuous plant canopies.}, journal = {IEEE Transactions on Geoscience and Remote Sensing}, year = {1999}, volume = {37}, pages = {987-999} }

    Ni-Meister, W., Jupp, D.L.B. & Dubayah, R. Modeling Lidar Waveforms in Heterogeneous and Discrete Canopies 2001 IEEE Transactions on Geoscience and Remote Sensing
    Vol. 39(9), pp. 1943-1958 
    article  
    BibTeX:
    @article{ni01,
      author = {Wenge Ni-Meister and David L. B. Jupp and Ralph Dubayah},
      title = {Modeling Lidar Waveforms in Heterogeneous and Discrete Canopies},
      journal = {IEEE Transactions on Geoscience and Remote Sensing},
      year = {2001},
      volume = {39},
      number = {9},
      pages = {1943-1958}
    }
    
    Nichol, C.J., Huemmrich, K.F., Black, T.A., Paul G. Jarvis, C.L.W., Grace, J. & Hall, F.G. Remote sensing of photosynthetic-light-use efficiency of boreal forests 2000 Agricultural and Forest Meteorology
    Vol. 101, pp. 131-142 
    article  
    Abstract: Using a helicopter-mounted portable spectroradiometer and continuous eddy covariance data we were able to evaluate the

    photochemical re?ectance index (PRI) as an indicator of canopy photosynthetic light-use ef?ciency (LUE) in four boreal

    forest species during the Boreal Ecosystem Atmosphere experiment (BOREAS). PRI was calculated from narrow waveband

    re?ectance data and correlated with LUE calculated from eddy covariance data. Signi?cant linear correlations were found

    between PRI and LUE when the four species were grouped together and when divided into functional type: coniferous

    and deciduous. Data from the helicopter-mounted spectroradiometer were then averaged to represent data generated by the

    Airborne Visible Infrared Imaging Spectrometer (AVIRIS). We calculated PRI from these data and relationships with canopy

    LUE were investigated. The relationship between PRI and LUE was weakened for deciduous species but strengthened for

    the coniferous species. The robust nature of this relationship suggests that relative photosynthetic rates may be derived from

    remotely-sensed re?ectance measurements.

    BibTeX:
    @article{nichol00,
      author = {Caroline J. Nichol and Karl F. Huemmrich and T. Andrew Black and Paul G. Jarvis, 

    Charles L. Walthall and John Grace and Forrest G. Hall}, title = {Remote sensing of photosynthetic-light-use efficiency of boreal forests}, journal = {Agricultural and Forest Meteorology}, year = {2000}, volume = {101}, pages = {131-142} }

    Nichol, C.J., Lloyd, J., Shibistova, O., Arneth, A., Röser, C., Knohl, A., Matsubara, S. & Grace, J. Remote sensing of photosynthetic-light-use efficiency of a Siberian boreal forest 2002 Tellus
    Vol. 54B(5), pp. 677-687 
    article  
    BibTeX:
    @article{nichol02,
      author = {Caroline J. Nichol and Jon Lloyd and Olga Shibistova and Almut Arneth and Carola Röser and Alexander Knohl and Shizue Matsubara and John Grace},
      title = {Remote sensing of photosynthetic-light-use efficiency of a Siberian boreal forest},
      journal = {Tellus},
      year = {2002},
      volume = {54B},
      number = {5},
      pages = {677-687}
    }
    
    Nilson, T. Inversion of gap frequency data in forest stands 1999 Agricultural and Forest Meteorology
    Vol. 98-99, pp. 437-448 
    article  
    Abstract: The inversion of gap proportion data for canopy structure variables has been widely used in plant canopy analysers. However, the results for most forest canopies tend to be biased, due to the foliage clustering at different structural levels. To invert the gap frequency data in forest stands for the canopy leaf area index, new gap fraction formulas are proposed capable of taking explicitly into account the clustering of foliage into crowns as one of the most important clustering levels. The formulas are based on the given mathematical expressions for the crown shape and on the Poisson or binomial tree distribution patterns.
    BibTeX:
    @article{nilson99,
      author = {Tiit Nilson},
      title = {Inversion of gap frequency data in forest stands},
      journal = {Agricultural and Forest Meteorology},
      year = {1999},
      volume = {98-99},
      pages = {437-448}
    }
    
    Nilson, T. & Kuusk, A. Improved algorithm for estimating canopy indices from gap fraction data in forest canopies 2004 Agricultural and Forest Meteorology
    Vol. 124(3-4), pp. 157-169 
    article  
    Abstract: An algorithm has been proposed to estimate the leaf area index (LAI) and canopy closure of forest canopies from the distribution of gap fraction measured by an LAI-2000 plant canopy analyser by inverting a forest gap fraction theoretical formula. The algorithm is based on the idea that the canopy closure is estimated from the reading of canopy analyser in the near-zenith ring. However, the measured gap fraction, especially at the near-zenith view directions, is subject to random variations due to insufficient spatial sampling. For that reason a regularisation of the inverse problem is proposed, based on the idea that the random fluctuations of the gap fraction can be described by means of their expansion by eigenvectors and eigenvalues of the covariance matrix. An algorithm to simulate the eigenvectors and eigenvalues and to evaluate the random coefficients of the expansion has been presented. Another novel feature of the algorithm is that it provides an opportunity to correct for the shadowing effect of tree trunks in the gap fraction data. To apply the algorithm, estimates for certain inventory data on the stand under study are needed, such as the mean tree height, crown depth, breast-height trunk diameter and stem number. The application of the algorithm appears to be efficient when the respective stand data can be obtained from a forestry database or at least their expert estimates are available. A few examples demonstrating fairly good performance of the algorithm, especially in relatively open boreal and sub-boreal forests, have been given.
    BibTeX:
    @article{nilson04,
      author = {Tiit Nilson and Andres Kuusk},
      title = {Improved algorithm for estimating canopy indices from gap fraction data in forest canopies},
      journal = {Agricultural and Forest Meteorology},
      year = {2004},
      volume = {124},
      number = {3-4},
      pages = {157-169}
    }
    
    Nilsson, M. Estimation of Tree Heights and Stand Volume Using an Airborne Lidar System 1996 Remote Sensing of Environment
    Vol. 56, pp. 1-7 
    article  
    Abstract: The use of an airborne lidar system for estimating tree heights and stand volume was investigated. A helicopterborne laser was tested in a coastal Scots pine stand where mean height was approximately 12.5 m. The laser equipment operated in a scanning mode and different laser footprints and sampling densities were tested at three independent registration times: one in June, one in October, and one in December. The tested footprints, measured at the ground, were between 0.75 m and 3.0 m in diameter. The results showed that the mean tree height was underestimated by 2.1-3.7 m. Optimal laser footprint size was found to change across data acquisition times.
    BibTeX:
    @article{nilsson96,
      author = {Mats Nilsson},
      title = {Estimation of Tree Heights and Stand Volume Using an Airborne Lidar System},
      journal = {Remote Sensing of Environment},
      year = {1996},
      volume = {56},
      pages = {1-7}
    }
    
    Nobis, M. & Hunziker, U. Automatic thresholding for hemispherical canopy-photographs based on edge detection 2005 Agricultural and Forest Meteorology
    Vol. 128(3-4), pp. 243-250 
    article  
    Abstract: The analysis of hemispherical photographs is nowadays an established method for assessing light indirectly and describing canopy structures. In this article, we present an automatic threshold algorithm for separating canopy and sky by edge detection. The algorithm was evaluated under different canopy conditions by comparing its results for canopy openness, fractal dimension and diffuse transmittance with those from multiple manual thresholding and direct measurements of the percent photosynthetic photon flux density (PPFD). We show that the automatic threshold algorithm is appropriate to replace the widely used manual interactive processing. It also improves the accuracy of results, especially in comparison with single manual thresholding. Whereas manual threshold setting has often been criticised as subjective and a major source of error the less time-consuming edge detection approach is objective, reproducible and can be applied to a large number of images.
    BibTeX:
    @article{nobis05,
      author = {Nobis, Michael and Hunziker, Urs},
      title = {Automatic thresholding for hemispherical canopy-photographs based on edge detection},
      journal = {Agricultural and Forest Meteorology},
      year = {2005},
      volume = {128},
      number = {3-4},
      pages = {243--250}
    }
    
    North, P.R.J. Estimation of fAPAR, LAI, and vegetation fractional cover from ATSR-2 imagery 2002 Remote Sensing of Environment
    Vol. 80(1), pp. 114-121 
    article  
    Abstract: We examine methodologies for estimation of vegetation cover, leaf area index (LAI), and fraction of absorbed photosynthetically active radiation (fAPAR), considering the spectral sampling and dual-view capability of the ATSR-2 sensor. A set of simulated ATSR-2 reflectance measurements and corresponding vegetation parameters is defined using a Monte Carlo ray-tracing model. The case of semiarid vegetation is considered allowing for varying fractional cover, structure, and presence of standing litter. The error in estimation of vegetation properties using vegetation indices, linear spectral unmixing, and model inversion is compared over this dataset, quantified by a measure of signal to noise (S/N). For the estimation of fAPAR, the NDVI gave best S/N among vegetation indices (S/N 4.5). Linear mixture modelling based on library spectra showed considerable improvement over vegetation indices for estimation of total vegetation cover. LAI is not retrieved with much accuracy by any method in the presence of standing litter and variable fractional cover. Model inversion has potential to be the most accurate method for retrieving all parameters, but only if the model approximates reality within 15%. Overall, the S/N in estimating parameters by any method is considerably lower than the S/N in instrument calibration (20/1). Use of the dual-view showed potential to improve estimates, but requires accurate registration.
    BibTeX:
    @article{north02,
      author = {North, Peter R. J.},
      title = {Estimation of fAPAR, LAI, and vegetation fractional cover from ATSR-2 imagery},
      journal = {Remote Sensing of Environment},
      year = {2002},
      volume = {80},
      number = {1},
      pages = {114--121}
    }
    
    Næsset, E. Effects of different sensors, flying altitudes, and pulse repetition frequencies on forest canopy metrics and biophysical stand properties derived from small-footprint airborne laser data 2009 Remote Sensing of Environment
    Vol. 113(1), pp. 148 - 159 
    article DOI  
    Abstract: Canopy height distributions were created from small-footprint airborne laser scanner (ALS) data collected over 40 field sample plots with size 1000 m2 located in mature conifer forest. ALS data were collected with two different instruments, i.e., the ALTM 1233 and ALTM 3100 laser scanners (Optech Inc.). The ALTM 1233 data were acquired at a flying altitude of 1200 m and a pulse repetition frequency (PRF) of 33 kHz. Three different acquisitions were carried out with ALTM 3100, i.e., (1) a flying altitude of 1100 m and a PRF of 50 kHz, (2) a flying altitude of 1100 m and a PRF of 100 kHz, and (3) a flying altitude of 2000 m and a PRF of 50 kHz. Height percentiles, mean and maximum height values, coefficients of variation of the heights, and canopy density at different height intervals above the ground were derived from the four different ALS datasets and for single + first and last echoes of the ALS data separately. The ALS-derived height- and density variables were assessed in pair-wise comparisons to evaluate the effects of (a) instrument, (b) flying altitude, and (c) PRF. A systematic shift in height values of up to 0.3 m between sensors when the first echoes were compared was demonstrated. Also the density-related variables differed significantly between the two instruments. Comparisons of flying altitudes and PRFs revealed upwards shifted canopy height distributions for the highest flying altitude (2000 m) and the lowest PRF (50 kHz). The distribution of echoes on different echo categories, i.e., single and multiple (first and last) echoes, differed significantly between acquisitions. The proportion of multiple echoes decreased with increasing flying altitude and PRF. Different echo categories have different properties since it is likely that single echoes tend to occur in the densest parts of the tree crowns, i.e., near the apex where the concentration of biological matter is highest and distance to the ground is largest. To assess the influence of instrument, flying altitude, and PRF on biophysical properties derived from ALS data, regression analysis was carried out to relate ALS-derived metrics to mean tree height (hL) and timber volume (V). Cross validation revealed only minor differences in precision for the different ALS acquisitions, but systematic differences between acquisitions of up to 2.5% for hL and 10.7% for V were found when comparing data from different acquisitions.
    BibTeX:
    @article{Naesset2009a,
      author = {Erik Næsset},
      title = {Effects of different sensors, flying altitudes, and pulse repetition frequencies on forest canopy metrics and biophysical stand properties derived from small-footprint airborne laser data},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {1},
      pages = {148 - 159},
      doi = {DOI: 10.1016/j.rse.2008.09.001}
    }
    
    Næsset, E. Influence of terrain model smoothing and flight and sensor configurations on detection of small pioneer trees in the boreal-alpine transition zone utilizing height metrics derived from airborne scanning lasers 2009 Remote Sensing of Environment
    Vol. 113(10), pp. 2210 - 2223 
    article DOI  
    Abstract: It has been suggested that airborne laser scanning (ALS) with high point densities could be used to monitor changes in the alpine tree line. The overall goal of this study was to assess the influence of ALS sensor and flight configurations on the ability to detect small trees in the alpine tree line and on the estimation of their heights. The study was conducted in a sub-alpine/alpine environment in southeast Norway. 342 small trees (0.11-5.20 m tall) of Norway spruce, Scots pine, and downy birch were precisely georeferenced and measured in field. ALS data acquired with two different instruments and at different flying altitudes (700-1130 m a.g.l.) with different pulse repetition frequencies (100, 125, and 166 kHz) were collected with a point density of all echoes of 7.7-11.0 m- 2. For each acquisition, three different terrain models were used to process the ALS point clouds in order to assess the effects of different preprocessing parameters on the ability to detect small trees. Regardless of acquisition and terrain model, positive height values were found for 91% of the taller trees (> 1 m). For smaller trees (< 1 m), 29-61% of the trees displayed positive height values. For the lowest repetition frequencies (100 and 125 kHz) in particular, the portion of trees with positive laser height values increased significantly with increasing terrain smoothing. For the highest repetition frequency there were no differences between smoothing levels, likely because of large ALS measurement errors at low laser pulse energy levels causing a large portion of the laser echoes to be discarded during terrain modeling. Error analysis revealed large commission errors when detecting small trees. The commissions consisted of objects like terrain structures, rocks, and hummocks having positive height values. The magnitude of commissions ranged from 709 to 8948% of the true tree numbers and tended to increase with increasing levels of terrain smoothing and with acquisitions according to increasing point densities. The accuracy of tree height derived from the ALS data indicated a systematic underestimation of true tree height by 0.35 to 1.47 m, depending on acquisition, terrain model, and tree species. The underestimation also increased with increasing tree height. The standard deviation for the differences between laser-derived and field-measured tree heights was 0.16-0.57 m. Because there are significant effects of sensor and flight configurations on tree height estimation, field calibration of tree heights at each point of time is required when using airborne lasers for tree growth monitoring.
    BibTeX:
    @article{Naesset2009b,
      author = {Erik Næsset},
      title = {Influence of terrain model smoothing and flight and sensor configurations on detection of small pioneer trees in the boreal-alpine transition zone utilizing height metrics derived from airborne scanning lasers},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {10},
      pages = {2210 - 2223},
      doi = {DOI: 10.1016/j.rse.2009.06.003}
    }
    
    Næsset, E. Accuracy of forest inventory using airborne laser-scanning: evaluating the first Nordic full-scale operational project 2004 Scandinavian Journal of Forest Research
    Vol. 19, pp. 554-557 
    article  
    BibTeX:
    @article{naesset2004_forinv,
      author = {Næsset, E.},
      title = {Accuracy of forest inventory using airborne laser-scanning: evaluating the first Nordic full-scale operational project},
      journal = {Scandinavian Journal of Forest Research},
      year = {2004},
      volume = {19},
      pages = {554-557}
    }
    
    Næsset, E. Effects of different flying altitudes on biophysical stand properties estimated from canopy height and density measured with a small-footprint airborne scanning laser 2004 Remote Sensing of Environment
    Vol. 91(2), pp. 243 - 255 
    article DOI  
    Abstract: Canopy height distributions were created from small-footprint airborne laser scanner data collected over 133 georeferenced field sample plots and 56 forest stands located in young and mature forest. The plot size was 300-400 m2 and the average stand size was 1.7 ha. Spruce and pine were the dominant tree species. Canopy height distributions were created from both first and last pulse data. The laser data were acquired from two different flying altitudes, i.e., 530-540 and 840-850 m above ground. Height percentiles, mean and maximum height values, coefficients of variation of the heights, and canopy density at different height intervals above the ground were computed from the laser-derived canopy height distributions. Corresponding metrics derived from the two different flying altitudes were compared. Only 1 of 54 metrics derived from the first pulse data differed significantly between flying altitudes. For the last pulse data, the mean values of the height percentiles were up to 50 cm higher than the corresponding values of the low-altitude data. The high-altitude data yielded significantly higher values for most of the canopy density measures. The standard deviation for the differences between high and low flying altitude for each of the metrics was estimated. The standard deviations for the height percentiles ranged from 0.07 to 0.30 cm in the forest stands, indicating a large degree of stability between repeated flight overpasses. The effect of variable flying altitude on mean tree height (hL), stand basal area (G), and stand volume (V) estimated from the laser-derived height and density measures using a two-stage inventory procedure was assessed by randomly combining laser data from the two flying altitudes for each individual sample plot and forest stand. The sample plots were used as training data to calibrate the models. The random assignment was repeated 10,000 times. The results of the 10,000 trials indicated that the precision of the estimated values of hL, G, and V was robust against alterations in flying altitude.
    BibTeX:
    @article{Naesset2004a,
      author = {Erik Næsset},
      title = {Effects of different flying altitudes on biophysical stand properties estimated from canopy height and density measured with a small-footprint airborne scanning laser},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {91},
      number = {2},
      pages = {243 - 255},
      doi = {DOI: 10.1016/j.rse.2004.03.009}
    }
    
    Næsset, E. Predicting forest stand characteristics with airborne scanning laser using a practical two-stage procedure and field data 2002 Remote Sensing of Environment
    Vol. 80(1), pp. 88 - 99 
    article DOI  
    Abstract: The mean tree height, dominant height, mean diameter, stem number, basal area, and timber volume of 144 georeferenced field sample plots were estimated from various canopy height and canopy density metrics derived by means of a small-footprint laser scanner over young and mature forest stands using regression analysis. The sample plots were distributed systematically throughout a 1000-ha study area, and the size of each plot was 200 m2. On the average, the distance between transmitted laser pulses was 0.9 m on the ground. The plots were divided into three strata according to age class and site quality. The stratum-specific regressions explained 82-95%, 74-93%, 39-78%, 50-68%, 69-89%, and 80-93% of the variability in ground-truth mean height, dominant height, mean diameter, stem number, basal area, and volume, respectively. A proposed practical two-stage procedure for prediction of corresponding characteristics of entire forest stands was tested. Sixty-one stands within the study area, with an average size of 1.6 ha each, were divided into 200 m2 regular grid cells. The six examined characteristics were predicted for each grid cell from the corresponding laser data utilizing the estimated regression equations. Average values for each stand was computed. Most stand level predictions were unbiased (P>.05). Standard deviations of the differences between predicted and ground-truth values of mean height, dominant height, mean diameter, stem number, basal area, and volume were 0.61-1.17 m, 0.70-1.33 m, 1.37-1.61 cm, 16.9-22.2% (128-400 ha-1), 8.6-11.7% (2.33-2.54 m2 ha-1), and 11.4-14.2% (18.3-31.9 m3 ha-1), respectively.
    BibTeX:
    @article{Naesset2002,
      author = {Erik Næsset},
      title = {Predicting forest stand characteristics with airborne scanning laser using a practical two-stage procedure and field data},
      journal = {Remote Sensing of Environment},
      year = {2002},
      volume = {80},
      number = {1},
      pages = {88 - 99},
      doi = {DOI: 10.1016/S0034-4257(01)00290-5}
    }
    
    Næsset, E. Estimating timber volume of forest stands using airborne laser scanner data 1997 Remote Sensing of Environment
    Vol. 61(2), pp. 246 - 253 
    article DOI  
    Abstract: The stand volumes of 36 Norway spruce (Pieea abies Karst.) and Scots pine (Pinus sylvestris L.) stands were derived from various tree canopy height metrics and canopy cover density measured by means of an airborne laser scanner. On average, the laser transmitted 1350-1910 pulses per stand and recorded 505-1070 canopy hits with corresponding estimates of canopy height. Ground truth stand volume was regressed against mean stand height, the mean height of all laser pulses within a stand, and canopy cover density as determined from the laser data. The coefficients of determination were in the range between 0.456 and 0.887. The coefficients of variation ranged from 17.2% to 43.3
    BibTeX:
    @article{Naesset1997246,
      author = {Erik Næsset},
      title = {Estimating timber volume of forest stands using airborne laser scanner data},
      journal = {Remote Sensing of Environment},
      year = {1997},
      volume = {61},
      number = {2},
      pages = {246 - 253},
      doi = {DOI: 10.1016/S0034-4257(97)00041-2}
    }
    
    Næsset, E. & Bjerknes, K.-O. Estimating tree heights and number of stems in young forest stands using airborne laser scanner data 2001 Remote Sensing of Environment
    Vol. 78(3), pp. 328 - 340 
    article DOI  
    Abstract: The mean heights of dominant trees and the stem numbers of 39 plots of 200 m2 each were derived from various canopy height metrics and canopy density measured by means of a small-footprint airborne laser scanner over young forest stands with tree heights <6 m. On the average, the laser transmitted 12,019 pulses ha-1. Ground-truth values were regressed against laser-derived canopy height metrics and density. The regressions explained 83% and 42% of the variability in ground-truth mean height and stem number, respectively. Cross-validation of the regressions revealed standard deviations of the differences between predicted and ground-truth values of mean height and stem number of 0.57 m (15%) and 1209 ha-1 (28.8%), respectively. A proposed practical two-stage procedure for prediction of mean height of dominant trees in forest stands was tested. One hundred and seventy-four sample plots were distributed systematically throughout a 1000-ha forest area. Twenty-nine of the plots were sited in young stands with tree heights <11.5 m. In the first stage, mean height of dominant trees of the 29 plots were regressed against laser-derived canopy height metrics and density. In the second stage, the selected regression was used to predict mean height of 12 selected test stands. The prediction revealed a bias of 0.23 m (3.5%) (P>.05) and a standard deviation of the differences between predicted and ground-truth mean height of 0.56 m (8.4%).
    BibTeX:
    @article{Naesset2001328,
      author = {Erik Næsset and Kjell-Olav Bjerknes},
      title = {Estimating tree heights and number of stems in young forest stands using airborne laser scanner data},
      journal = {Remote Sensing of Environment},
      year = {2001},
      volume = {78},
      number = {3},
      pages = {328 - 340},
      doi = {DOI: 10.1016/S0034-4257(01)00228-0}
    }
    
    Næsset, E., Bollands?s, O.M. & Gobakken, T. Comparing regression methods in estimation of biophysical properties of forest stands from two different inventories using laser scanner data 2005 Remote Sensing of Environment
    Vol. 94(4), pp. 541 - 553 
    article DOI  
    Abstract: Mean tree height, dominant height, mean diameter, stem number, basal area, and timber volume of 233 field sample plots were estimated from various canopy height and canopy density metrics-- derived by means of a small-footprint laser scanner over young and mature forest stands-- using ordinary least-squares (OLS) regression analysis, seemingly unrelated regression (SUR), and partial least-squares (PLS) regression. The sample plots were distributed systematically throughout two separate inventory areas with size 1000 and 6500 ha, respectively. The plots were divided into three predefined strata. Separate regression models were estimated for each inventory as well as common models utilizing the plots of both inventories simultaneously. In the models estimated by combining data from the two areas, the statistical effect of inventory was found to be significant (p<0.05) in the mean height models only. A total of 115 test stands and plots with size 0.3-11.7 ha were used to validate the estimated regression models. The bias and standard deviations (parenthesized) of the differences between predicted and ground reference values of mean height, dominant height, mean diameter, stem number, basal area, and volume were -5.5% to 4.7% (3.1-7.3%), -6.0% to 0.4% (2.9-8.2%), -0.2% to 7.9% (5.5-15.8%), -21.3% to 12.5% (13.4-29.3%), -7.3% to 8.4% (7.1-13.6%), and -3.9% to 10.1% (8.3-14.9%), respectively. It was revealed that only minor discrepancies occurred between the three investigated estimation techniques. None of the techniques provided predicted values that were superior to the other techniques over all combinations of strata and variables.
    BibTeX:
    @article{Naesset2005541,
      author = {Erik Næsset and Ole Martin Bollands?s and Terje Gobakken},
      title = {Comparing regression methods in estimation of biophysical properties of forest stands from two different inventories using laser scanner data},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {94},
      number = {4},
      pages = {541 - 553},
      doi = {DOI: 10.1016/j.rse.2004.11.010}
    }
    
    Næsset, E. & Gobakken, T. Estimation of above- and below-ground biomass across regions of the boreal forest zone using airborne laser 2008 Remote Sensing of Environment
    Vol. 112(6), pp. 3079 - 3090 
    article DOI  
    Abstract: Regression models relating variables derived from airborne laser scanning (ALS) to above-ground and below-ground biomass were estimated for 1395 sample plots in young and mature coniferous forest located in ten different areas within the boreal forest zone of Norway. The sample plots were measured as part of large-scale operational forest inventories. Four different ALS instruments were used and point density varied from 0.7 to 1.2 m- 2. One variable related to canopy height and one related to canopy density were used as independent variables in the regressions. The statistical effects of area and age class were assessed by including dummy variables in the models. Tree species composition was treated as continuous variables. The proportion of explained variability was 88% for above- and 85% for below-ground biomass models. For given combinations of ALS-derived variables, the differences between the areas were up to 32% for above-ground biomass and 38% for below-ground biomass. The proportion of spruce had a significant impact on both the estimated models. The proportion of broadleaves had a significant effect on above-ground biomass only, while the effect of age class was significant only in the below-ground biomass model. Because of local effects on the biomass-ALS data relationships, it is indicated by this study that sample plots distributed over the entire area would be needed when using ALS for regional or national biomass monitoring.
    BibTeX:
    @article{Naesset20083079,
      author = {Erik Næsset and Terje Gobakken},
      title = {Estimation of above- and below-ground biomass across regions of the boreal forest zone using airborne laser},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {6},
      pages = {3079 - 3090},
      doi = {DOI: 10.1016/j.rse.2008.03.004}
    }
    
    Næsset, E. & Gobakken, T. Estimating forest growth using canopy metrics derived from airborne laser scanner data 2005 Remote Sensing of Environment
    Vol. 96(3-4), pp. 453 - 465 
    article DOI  
    Abstract: Canopy height distributions were created from small-footprint airborne laser scanner data with a sampling density of 0.9-1.2 m- 2 collected over 133 georeferenced field sample plots and 56 forest stands located in young and mature forest. The plot size was 300-400 m2 and the average stand size was 1.7 ha. Spruce and pine were the dominant tree species. Canopy height distributions were created from both first and last pulse data. The laser data were acquired in 1999 and 2001. Height percentiles, mean and maximum height values, coefficients of variation of the heights, and canopy density at different height intervals above the ground were computed from the laser-derived canopy height distributions. Corresponding metrics derived from the 1999 and 2001 laser datasets were compared. Forty-five of 54 metrics derived from the first pulse data changed their values significantly due to forest growth. The upper height percentiles increased their values more than the field-based height growth estimates. The 50 and 90 height percentiles increased by 0.4-1.3 m whereas the field-estimated mean height increased by 0.2-0.9 m. Metrics derived from the last pulse data were less influenced by growth. Mean tree height (hL), basal area (G), and volume (V) were regressed against the laser-derived variables to predict corresponding values of hL, G, and V based on the 1999 and 2001 laser data, respectively. Forest growth was estimated as the difference between the 2001 and 1999 estimates. Laser data were able to predict a significant growth in all the three biophysical variables over the 2-year period. However, the accuracy of the predictions was poor. In most cases the predictions were biased and the precision was low. Finally, several key issues of particular relevance to laser-based monitoring of forest growth are discussed.
    BibTeX:
    @article{Naesset2005453,
      author = {Erik Næsset and Terje Gobakken},
      title = {Estimating forest growth using canopy metrics derived from airborne laser scanner data},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {96},
      number = {3-4},
      pages = {453 - 465},
      doi = {DOI: 10.1016/j.rse.2005.04.001}
    }
    
    Næsset, E. & Nelson, R. Using airborne laser scanning to monitor tree migration in the boreal-alpine transition zone 2007 Remote Sensing of Environment
    Vol. 110(3), pp. 357 - 369 
    article DOI  
    Abstract: The boreal tree line is expected to advance upwards into the mountains and northwards into the tundra due to global warming. The major objective of this study was to find out if it is possible to use high-resolution airborne laser scanner data to detect very small trees -- the pioneers that are pushing the tree line up into the mountains and out onto the tundra. The study was conducted in a sub-alpine/alpine environment in southeast Norway. A total of 342 small trees of Norway spruce, Scots pine, and downy birch with tree heights ranging from 0.11 to 5.20 m were precisely georeferenced and measured in field. Laser data were collected with a pulse density of 7.7 m- 2. Three different terrain models were used to process the airborne laser point cloud in order to assess the effects of different pre-processing parameters on small tree detection. Greater than 91% of all trees > 1 m tall registered positive laser height values regardless of terrain model. For smaller trees (< 1 m), positive height values were found in 5-73% of the cases, depending on the terrain model considered. For this group of trees, the highest rate of trees with positive height values was found for spruce. The more smoothed the terrain model was, the larger the portion of the trees that had positive laser height values. The accuracy of tree height derived from the laser data indicated a systematic underestimation of true tree height by 0.40 to 1.01 m. The standard deviation for the differences between laser-derived and field-measured tree heights was 0.11-0.73 m. Commission errors, i.e., the detection of terrain objects -- rocks, hummocks -- as trees, increased significantly as terrain smoothing increased. Thus, if no classification of objects into classes like small trees and terrain objects is possible, many non-tree objects with a positive height value cannot be separated from those actually being trees. In a monitoring context, i.e., repeated measurements over time, we argue that most other objects like terrain structures, rocks, and hummocks will remain stable over time while the trees will change as they grow and new trees are established. Thus, this study indicates that, given a high laser pulse density and a certain density of newly established trees, it would be possible to detect a sufficient portion of newly established trees over a 10 years period to claim that tree migration is taking place.
    BibTeX:
    @article{Naesset2007357,
      author = {Erik Næsset and Ross Nelson},
      title = {Using airborne laser scanning to monitor tree migration in the boreal-alpine transition zone},
      journal = {Remote Sensing of Environment},
      year = {2007},
      volume = {110},
      number = {3},
      pages = {357 - 369},
      doi = {DOI: 10.1016/j.rse.2007.03.004}
    }
    
    Næsset, E. & Okland, T. Estimating tree height and tree crown properties using airborne scanning laser in a boreal nature reserve 2002 Remote Sensing of Environment
    Vol. 79(1), pp. 105-115 
    article  
    Abstract: Tree height, the height from the ground surface to the tree crown, and the crown length as a proportion of tree height of individual trees were derived from various canopy height metrics measured by a small-footprint airborne laser scanner flown over a boreal forest reserve. The average spacing on the ground of the laser pulses ranged from 0.66 to 1.29 m. Ground-truth values were regressed against laser-derived canopy height metrics. The regressions explained 75%, 53%, and 51% of the variability in ground-truth tree height, height to the crown, and relative crown length, respectively. Cross-validation of the regressions revealed standard deviations of the differences between predicted and ground-truth values of 3.15 m (17.6%), 2.19 m (39.1%), and 10.48% (14.9% of ground-truth mean), respectively. On 10 plots with size 50 m2 in the boreal forest reserve and on 27 plots with size 200 m2 in a managed spruce forest, mean tree height, average height from the ground surface to the crown, and average relative crown length were regressed against laser canopy height metrics. The coefficients of determination (R2) ranged from .47 to .91. Cross-validation revealed a precision of 1.49 m (7.6%), 1.24-1.52 m (20.9-23.3%), and 6.32-7.11% (8.8-10.9% of ground-truth mean) for mean tree height, average height to the crown, and average relative crown length, respectively. At least, mean tree height can be determined more accurately from laser data than by current methods.
    BibTeX:
    @article{naesset02b,
      author = {Næsset, Erik and Okland, Tonje},
      title = {Estimating tree height and tree crown properties using airborne scanning laser in a boreal nature reserve},
      journal = {Remote Sensing of Environment},
      year = {2002},
      volume = {79},
      number = {1},
      pages = {105--115}
    }
    
    Næsset, E. & Okland, T. Estimating tree height and tree crown properties using airborne scanning laser in a boreal nature reserve 2002 Remote Sensing of Environment
    Vol. 79(1), pp. 105 - 115 
    article DOI  
    Abstract: Tree height, the height from the ground surface to the tree crown, and the crown length as a proportion of tree height of individual trees were derived from various canopy height metrics measured by a small-footprint airborne laser scanner flown over a boreal forest reserve. The average spacing on the ground of the laser pulses ranged from 0.66 to 1.29 m. Ground-truth values were regressed against laser-derived canopy height metrics. The regressions explained 75%, 53%, and 51% of the variability in ground-truth tree height, height to the crown, and relative crown length, respectively. Cross-validation of the regressions revealed standard deviations of the differences between predicted and ground-truth values of 3.15 m (17.6%), 2.19 m (39.1%), and 10.48% (14.9% of ground-truth mean), respectively. On 10 plots with size 50 m2 in the boreal forest reserve and on 27 plots with size 200 m2 in a managed spruce forest, mean tree height, average height from the ground surface to the crown, and average relative crown length were regressed against laser canopy height metrics. The coefficients of determination (R2) ranged from .47 to .91. Cross-validation revealed a precision of 1.49 m (7.6%), 1.24-1.52 m (20.9-23.3%), and 6.32-7.11% (8.8-10.9% of ground-truth mean) for mean tree height, average height to the crown, and average relative crown length, respectively. At least, mean tree height can be determined more accurately from laser data than by current methods.
    BibTeX:
    @article{Naesset2002105,
      author = {Erik Næsset and Tonje Okland},
      title = {Estimating tree height and tree crown properties using airborne scanning laser in a boreal nature reserve},
      journal = {Remote Sensing of Environment},
      year = {2002},
      volume = {79},
      number = {1},
      pages = {105 - 115},
      doi = {DOI: 10.1016/S0034-4257(01)00243-7}
    }
    
    Okuda, T., Suzuki, M., Numata, S., Yoshida, K., Nishimura, S., Adachi, N., Niiyama, K., Manokaran, N. & Hashim, M. Estimation of aboveground biomass in logged and primary lowland rainforests using 3-D photogrammetric analysis 2004 Forest Ecology and Management
    Vol. 203(1-3), pp. 63-75 
    article  
    Abstract: We estimated the total aboveground tree biomass (TAGB) in an old-growth primary forest and in a regenerating forest that had been selectively logged in 1958, both within the tropical rainforest of the Pasoh Forest Reserve in Peninsular Malaysia. This was achieved by comparing aerial photographs with data obtained previously from destructive sampling in the same area. Aerial photographs were taken above the primary and logged forest plots in 1997. The heights of the canopy-forming trees were estimated in both plots by means of aerial triangulation and were regressed against the diameter at breast height (DBH) of the corresponding trees measured during ground surveys. The resulting allometric relationship between tree height and DBH let us estimate TAGB: in the primary forest, TAGB was 310 Mg ha-1, which was ca. 10-12% smaller than the value estimated by means of destructive sampling conducted in the 1970s. The estimated TAGB of the logged forest was 274 Mg ha-1, which was significantly smaller than that of the primary forest (P P laser profiling system that can quantify changes in the forest's vertical structure or volume to estimate biomass and its variation in dense evergreen forests.
    BibTeX:
    @article{okuda04,
      author = {Okuda, Toshinori and Suzuki, Mariko and Numata, Sinya and Yoshida, Keiichiro and Nishimura, Sen and Adachi, Naoki and Niiyama, Kaoru and Manokaran, N. and Hashim, Mazlan},
      title = {Estimation of aboveground biomass in logged and primary lowland rainforests using 3-D photogrammetric analysis},
      journal = {Forest Ecology and Management},
      year = {2004},
      volume = {203},
      number = {1-3},
      pages = {63--75}
    }
    
    Omasa, K., Hosoi, F. & Konishi, A. 3D lidar imaging for detecting and understanding plant

    responses and canopy structure

    2007 Journal of Experimental Botany
    Vol. `58, pp. 881-898 
    article  
    BibTeX:
    @article{omasa07,
      author = {Kenji Omasa and Fumiki Hosoi and Atsumi Konishi},
      title = {3D lidar imaging for detecting and understanding plant 

    responses and canopy structure}, journal = {Journal of Experimental Botany}, year = {2007}, volume = {`58}, pages = {881-898} }

    Orka, H.O., Næsset, E. & Bollandsas, O.M. Classifying species of individual trees by intensity and structure features derived from airborne laser scanner data 2009 Remote Sensing of Environment
    Vol. 113(6), pp. 1163 - 1174 
    article DOI  
    Abstract: The objective of this study was to identify candidate features derived from airborne laser scanner (ALS) data suitable to discriminate between coniferous and deciduous tree species. Both features related to structure and intensity were considered. The study was conducted on 197 Norway spruce and 180 birch trees (leaves on conditions) in a boreal forest reserve in Norway. The ALS sensor used was capable of recording multiple echoes. The point density was 6.6 m- 2. Laser echoes located within the vertical projection of the tree crowns, which were assumed to be circular and defined according to field measurements, were attributed to three categories: #first##echoes##of##many#, #single##echoes#, or #last##echoes##of##many##echoes#. They were denoted FIRST, SINGLE, and LAST, respectively. In tree species classification using ALS data features should be independent of tree heights. We found that many features were dependent on tree height and that this dependency influenced selection of candidate features. When we accounted for this dependency, it was revealed that FIRST and SINGLE echoes were located higher and LAST echoes lower in the birch crowns than in spruce crowns. The intensity features of the FIRST echoes differed more between species than corresponding features of the other echo categories. For the FIRST echoes the intensity values tended to be higher for birch than spruce. When using the various features for species classification, maximum overall classification accuracies of 77% and 73% were obtained for structural and intensity features, respectively. Combining candidate features related to structure and intensity resulted in an overall classification accuracy of 88%.
    BibTeX:
    @article{Orka2009,
      author = {Hans Ole Orka and Erik Næsset and Ole Martin Bollandsas},
      title = {Classifying species of individual trees by intensity and structure features derived from airborne laser scanner data},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {6},
      pages = {1163 - 1174},
      doi = {DOI: 10.1016/j.rse.2009.02.002}
    }
    
    Parker, G.G., Lefsky, M.A. & Harding, D.J. Light transmittance in forest canopies determined using airborne laser altimetry and in-canopy quantum measurements 2001 Remote Sens. Environ.
    Vol. 76, pp. 298-309 
    article  
    Abstract: The vertical distribution of light transmittance was derived from field and laser altimeter observations taken in the same canopies of five forests of several ages (young to mature) and canopy types (eastern broadleaved and western tall conifer). Vertical transmittances were derived remotely from the Scanning Lidar Imager of Canopies by Echo Recovery (SLICER) laser altimeter and in the field from measurements of Photosynthetically Active Radiation (PAR) made within the canopy using quantum sensors suspended from the gondola of a tower crane or atop small balloons. Derived numerical characteristics of mean transmittance profiles (the rate of attenuation, whole canopy transmittance, and the radiation-effective height) were similar for both methods across the sites. Measures of the variance and skewness of transmittance also showed similar patterns for corresponding heights between methods. The two methods exhibited greater correspondence in the eastern stands than in the western ones; differences in the interaction between canopy organization and the sensor characteristics between the stand types might explain this. The narrower, more isolated crowns of the western stands permit a deeper penetration into the canopy of nadir-directed laser light than of direct solar radiation from typical elevation angles. Transects of light transmittance in two stands demonstrate that the SLICER sensor can capture meaningful functional variation. Additionally, for one stand with numerous overlapping transects we constructed a three-dimensional view of the transmittance field. Using geostatistics, we demonstrated that the spatial covariance measured in the horizontal plane varied as a function of height. These results suggest a means to remotely assess an important functional characteristic of vegetation, providing a capacity for process-based ecological studies at large scales.
    BibTeX:
    @article{parker01,
      author = {Geoffrey G. Parker and Michael A. Lefsky and David J. Harding},
      title = {Light transmittance in forest canopies determined using airborne laser altimetry and in-canopy quantum measurements},
      journal = {Remote Sens. Environ.},
      year = {2001},
      volume = {76},
      pages = {298-309}
    }
    
    Parker, G.G. & Russ, M.E. The canopy surface and stand development: assessing forest canopy structure and complexity with near-surface altimetry 2004 Forest Ecology and Management
    Vol. 189(1-3), pp. 307-315 
    article  
    Abstract: A first-return laser rangefinder deployed from a low-flying helicopter provided inexpensive, repeatable, and high-resolution measurements of the shape of the outer forest canopy in stands of four successional stages on the Maryland coastal plain. The traces of canopy height in these stands revealed structural characteristics such as cover, maximum and mean heights which were consistent with corresponding ground measurements. Differences in the statistics on canopy structure corresponded to general developmental trends in these stands, including the development of maximum height and surface rugosity. Furthermore, some of the outer canopy statistics related to measures of internal organization, such as the shape of the foliage height profile and the leaf area index. These observations suggest that such measurements could be used readily to classify stand structure and developmental stage, and to deduce some aspects of internal organization of vegetation.
    BibTeX:
    @article{parker04,
      author = {Parker, Geoffrey G. and Russ, Mary E.},
      title = {The canopy surface and stand development: assessing forest canopy structure and complexity with near-surface altimetry},
      journal = {Forest Ecology and Management},
      year = {2004},
      volume = {189},
      number = {1-3},
      pages = {307--315}
    }
    
    Patenaude, G., Hill, R., Milne, R., Gaveau, D., Briggs, B. & Dawson, T. Quantifying forest above ground carbon content using LiDAR remote sensing 2004 Remote Sensing of Environment
    Vol. 93(3), pp. 368-380 
    article  
    Abstract: The UNFCCC and interest in the source of the missing terrestrial carbon sink are prompting research and development into methods for carbon accounting in forest ecosystems. Here we present a canopy height quantile-based approach for quantifying above ground carbon content (AGCC) in a temperate deciduous woodland, by means of a discrete-return, small-footprint airborne LiDAR. Fieldwork was conducted in Monks Wood National Nature Reserve UK to estimate the AGCC of five stands from forest mensuration and allometric relations. In parallel, a digital canopy height model (DCHM) and a digital terrain model (DTM) were derived from elevation measurements obtained by means of an Optech Airborne Laser Terrain Mapper 1210. A quantile-based approach was adopted to select a representative statistic of height distributions per plot. A forestry yield model was selected as a basis to estimate stemwood volume per plot from these heights metrics. Agreement of r=0.74 at the plot level was achieved between ground-based AGCC estimates and those derived from the DCHM. Using a 20?20 m grids superposed to the DCHM, the AGCC was estimated at the stand level and at the woodland level. At the stand level, the agreement between the plot data upscaled in proportion to area and the LiDAR estimates was r=0.85. At the woodland level, LiDAR estimates were nearly 24% lower than those from the upscaled plot data. This suggests that field-based approaches alone may not be adequate for carbon accounting in heterogeneous forests. Conversely, the LiDAR 20?20 m grid approach has an enhanced capability of monitoring the natural variability of AGCC across the woodland.
    BibTeX:
    @article{Patenaude2004,
      author = {Patenaude, G. and Hill, R.A and Milne, R. and Gaveau, D.L.A. and Briggs, B.B.J. and Dawson, T.P.},
      title = {Quantifying forest above ground carbon content using LiDAR remote sensing},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {93},
      number = {3},
      pages = {368--380}
    }
    
    Patenaude, G., Milne, R., Van Oijen, M., Rowland, C.S. & Hill, R.A. Integrating remote sensing datasets into ecological modelling: a Bayesian approach 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1295-1315 
    article  
    Abstract: Process-based models have been used to simulate 3-dimensional complexities of forest ecosystems and their temporal changes, but their extensive data requirement and complex parameterisation have often limited their use for practical management applications. Increasingly, information retrieved using remote sensing techniques can help in model parameterisation and data collection by providing spatially and temporally resolved forest information. In this paper, we illustrate the potential of Bayesian calibration for integrating such data sources to simulate forest production. As an example, we use the 3-PG model combined with hyperspectral, LiDAR, SAR and field-based data to simulate the growth of UK Corsican pine stands. Hyperspectral, LiDAR and SAR data are used to estimate LAI dynamics, tree height and above ground biomass, respectively, while the Bayesian calibration provides estimates of uncertainties to model parameters and outputs. The Bayesian calibration contrasts with goodness-of-fit approaches, which do not provide uncertainties to parameters and model outputs. Parameters and the data used in the calibration process are presented in the form of probability distributions, reflecting our degree of certainty about them. After the calibration, the distributions are updated. To approximate posterior distributions (of outputs and parameters), a Markov Chain Monte Carlo sampling approach is used (25 000 steps). A sensitivity analysis is also conducted between parameters and outputs. Overall, the results illustrate the potential of a Bayesian framework for truly integrative work, both in the consideration of field-based and remotely sensed datasets available and in estimating parameter and model output uncertainties.
    BibTeX:
    @article{Patenaude2008,
      author = {Patenaude, G. and Milne, R. and Van Oijen, M. and Rowland, C. S. and Hill, R. A.},
      title = {Integrating remote sensing datasets into ecological modelling: a Bayesian approach},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1295--1315}
    }
    
    Pedlosky, J. Geophysical Fluid Dynamics 1992   book  
    BibTeX:
    @book{pedlosky,
      author = {Joseph Pedlosky},
      title = {Geophysical Fluid Dynamics},
      publisher = {Springer},
      year = {1992}
    }
    
    Pekkarinen, A. Image segment-based spectral features in the estimation of timber volume 2002 Remote Sens. Environ.
    Vol. 82(2-3), pp. 349-359 
    article  
    Abstract: Plot- and stand-level errors associated with satellite image-based multisource forest inventory (MSFI) applications have been relatively high. The reasons suggested for that are related to the limited spatial resolution of the image material. The introduction of very high spatial resolution (VHR) images to MSFI applications should, therefore, diminish these errors. The use of VHR images is, however, problematic, because pixel-by-pixel analysis methods are no longer applicable. The paper presents an image segment-based approach to the determination of feature extraction and image analysis units. The study was carried out in Southern Finland and employed a spectrally averaged imaging spectrometer (AISA) image and field data gathered from sample plots. A two-phase segmentation method was applied and a large number of segment-based spectral features was extracted and used as input to a feature selection procedure. Forward selection based on an improvement of RMSE was applied. The performance of segment-based features (SF) was compared to that of reference features (RF) extracted from square-shaped windows. The estimation results revealed that even though the applied segmentation method succeeded well in the determination of units of feature extraction and image analysis, the differences between the performance of SF and RF were small and the plot-level estimation errors remained high. The study suggests that large estimation errors are due to the local nature of the field data and may be diminished using data that is representative at the segment level.
    BibTeX:
    @article{pekkarinen02,
      author = {Anssi Pekkarinen},
      title = {Image segment-based spectral features in the estimation of timber volume},
      journal = {Remote Sens. Environ.},
      year = {2002},
      volume = {82},
      number = {2-3},
      pages = {349-359}
    }
    
    Peltoniemi, J.I., Kaasalainen, S., N?r?nen, J., Rautiainen, M., Stenberg, P., Smolander, H., Smolander, S. & Voipio, P. BRDF measurement of understory vegetation in pine forests: dwarf shrubs, lichen, and moss 2005 Remote Sensing of Environment
    Vol. 94(3), pp. 343-354 
    article  
    Abstract: The spectral and directional reflection properties of pine forest understory in Suonenjoki, Finland were measured using a newly developed transportable field goniospectrometer under direct sunlight or plant lamp. The samples represent the most typical types in Finnish forests. Large differences between species were found. Wax-leaved shrubs such as lingonberry and blueberry proved to be strong forward scatterers, whereas lichen and soft-leaved dwarf shrubs such as heather were strong backscatterers. The measured moss showed both forward and backscattering features. There were variations among the samples of the same species, but many typical features appeared consistent and reproducible. Both "pure" and mixed samples were measured, the latter showing smoother behavior than the former, that is, the strongest forward and backward features are downscaled. The results provide a starting point for an empirical understory model and a basis for development and validation of a theoretical model.
    BibTeX:
    @article{Peltoniemi2005,
      author = {Peltoniemi, Jouni I. and Kaasalainen, Sanna and N?r?nen, Jyri and Rautiainen, Miina and Stenberg, Pauline and Smolander, Heikki and Smolander, Sampo and Voipio, Pekka},
      title = {BRDF measurement of understory vegetation in pine forests: dwarf shrubs, lichen, and moss},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {94},
      number = {3},
      pages = {343--354}
    }
    
    Peltoniemi, J.I., Kaasalainen, S., Naranen, J., Rautiainen, M., Stenberg, P., Smolander, H., Smolander, S. & Voipio, P. BRDF measurement of understory vegetation in pine forests: dwarf shrubs, lichen, and moss 2005 Remote Sensing of Environment
    Vol. 94(3), pp. 343-354 
    article  
    Abstract: The spectral and directional reflection properties of pine forest understory in Suonenjoki, Finland were measured using a newly developed transportable field goniospectrometer under direct sunlight or plant lamp. The samples represent the most typical types in Finnish forests. Large differences between species were found. Wax-leaved shrubs such as lingonberry and blueberry proved to be strong forward scatterers, whereas lichen and soft-leaved dwarf shrubs such as heather were strong backscatterers. The measured moss showed both forward and backscattering features. There were variations among the samples of the same species, but many typical features appeared consistent and reproducible. Both "pure" and mixed samples were measured, the latter showing smoother behavior than the former, that is, the strongest forward and backward features are downscaled. The results provide a starting point for an empirical understory model and a basis for development and validation of a theoretical model.
    BibTeX:
    @article{peltoniemi05,
      author = {Peltoniemi, Jouni I. and Kaasalainen, Sanna and Naranen, Jyri and Rautiainen, Miina and Stenberg, Pauline and Smolander, Heikki and Smolander, Sampo and Voipio, Pekka},
      title = {BRDF measurement of understory vegetation in pine forests: dwarf shrubs, lichen, and moss},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {94},
      number = {3},
      pages = {343--354}
    }
    
    Pereira, L.M.G. & Wicherson, R.J. Suitability of laser data for deriving geographical information A case study in the context of management of fluvial zones 1999 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 54(2-3), pp. 105-114 
    article  
    Abstract: In the Netherlands, around 40 $%$ of the territory is below sea level. Rivers that flow through this land have to be constantly monitored to avoid flooding. To this end, terrain information is needed. At present, the relief information is acquired by means of photogrammetry, which makes the information expensive. Furthermore, it is estimated that at least 4 years are needed to collect the relief information of all river zones. A cheaper and faster alternative appears to be the use of laser measurements acquired from an aircraft. Thus, it is of great importance to determine if the user requirements, concerning information needed and related quality, can be fulfilled by high-density laser measurements. In this article, we assess the feasibility of using laser data to help generate a hydrodynamic model. This is needed to determine the effect of high water levels and of earthworks, such as removal of sand in river areas. The conclusion of this study is that as far as the test area is concerned, which appears to be a good representative of the fluvial regions in the Netherlands, the laser data allow one to recover the relief information needed for river management with the desired quality.
    BibTeX:
    @article{pereira99,
      author = {L. M. Gomes Pereira and R. J. Wicherson},
      title = {Suitability of laser data for deriving geographical information A case study in the context of management of fluvial zones},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {1999},
      volume = {54},
      number = {2-3},
      pages = {105-114}
    }
    
    Persson, ., Söderman, U., Töpel, J. & Ahlberg, S. Visualization and analysis of full-waveform airborne laser scanner data 2005 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXVI 
    article  
    BibTeX:
    @article{persson05,
      author = { Persson and U. Söderman and J. Töpel and S. Ahlberg},
      title = {Visualization and analysis of full-waveform airborne laser scanner data},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2005},
      volume = {XXXVI}
    }
    
    Persson, A., Holmgren, J. & Söderman, U. Detecting and Measuring Individual Trees Using an Airborne Laser Scanner 2002 Photogrammetric Engineering & Remote Sensing
    Vol. 68(9), pp. 925-932 
    article  
    Abstract: High-resolution airborne laser scanner data offer the possibility to detect and measure individual trees. In this study, an algorithm which estimated position, height, and crown diameter of individual trees was validated with field measurements. Because all the trees in this study were measured on the ground with high accuracy, their positions could be linked with laser measurements, making validation on an individual tree basis possible. In total, 71 percent of the trees were correctly detected using laser scanner data. Because a large portion of the undetected trees had a small stem diameter, 91 percent of the total stem volume was detected. Height and crown diameter of detected trees could be estimated with a root-mean-square error (RMSE) of 0.63 m and 0.61 m, respectively. Stem diameter was estimated, using laser measured tree height and crown diameter, with an RMSE of 3.8 cm. Different laser beam diameters (0.26 to 3.68 m) were also tested, the smallest beam size showing a better detection rate in dense forest. However, estimates of tree height and crown diameter were not affected much by different beam size.
    BibTeX:
    @article{persson02,
      author = {Asa Persson and Johan Holmgren and Ulf Söderman},
      title = {Detecting and Measuring Individual Trees Using an Airborne Laser Scanner},
      journal = {Photogrammetric Engineering & Remote Sensing},
      year = {2002},
      volume = {68},
      number = {9},
      pages = {925-932}
    }
    
    Peterson, B., Hyde, P., Hofton, M., Dubayah, R., Fites-Kaufman, J., Hunsaker, C. & Blair, J. Deriving canopy structure for fire modeling from LIDAR 2003 EARSEL - 4th International Workshop: Remote Sensing and GIS applications for Forest Fire Management, Ghent.  article  
    BibTeX:
    @article{petersonghent,
      author = {B. Peterson and P. Hyde and M. Hofton and R. Dubayah and J. Fites-Kaufman and C. Hunsaker and J.B. Blair},
      title = {Deriving canopy structure for fire modeling from LIDAR},
      journal = {EARSEL - 4th International Workshop: Remote Sensing and GIS applications for Forest Fire Management, Ghent.},
      year = {2003}
    }
    
    Peterson, B., Ni-Meister, W., Blair, J., Hofton, M., Hyde, P. & Dubayah, R. MODELING LIDAR WAVEFORMS USING A RADIATIVE TRANSFER MODEL 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 121-124 
    article  
    Abstract: In the past, obtaining reliable measurements of key forest canopy metrics has been difficult, even after the development of remote sensing technology. Fortunately, next-generation lidar systems are proving to be useful tools for deriving critical canopy measurements, such as height, structure and biomass. These studies have all focused on empirical comparisons between basic lidar-derived and field-sampled measurements. The results of these studies have shown that lidar remote sensing instruments can successfully measure forest canopy characteristics. However, physically-based remote sensing models are necessary to more fully understand and interpret the interactions of the laser energy with the forest canopy. In this study the Geometric Optical and Radiative Transfer (GORT) model is used to model lidar waveforms. GORT is capable of modeling lidar returns from canopies with clumped multiple layers and multiple species. For this study, GORT was used to model waveforms over the Sierra National Forest in California. Field data input into GORT are a representative sample of the different vegetation types found in the forest. The modeled waveforms are then validated against actual lidar data collected by the Laser Vegetation Imaging Sensor (LVIS) which mapped the area in October 1999. By modeling lidar waveforms based on the physical principles of radiative transfer, GORT fills a missing link between the remotely sensed and actual canopy structure. The results of this study will also aid in future large-scale land surface mapping by developing a link between lidar and other remote sensing data.
    BibTeX:
    @article{peterson01,
      author = {B. Peterson and W. Ni-Meister and J.B. Blair and M.A. Hofton and P. Hyde and R. Dubayah},
      title = {MODELING LIDAR WAVEFORMS USING A RADIATIVE TRANSFER MODEL},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {121-124}
    }
    
    Petzold, B., Reiss, P. & Stüssel, W. Laser scanning - surveying and mapping agencies are using a new technique for the derivation of digital terrain models 1999 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 54(2-3), pp. 95-104 
    article  
    Abstract: A user group of the Surveying and Mapping Agencies (SMA) of the Federal States of Germany tested several datasets for the derivation of high-quality Digital Terrain Models (DTM) which were collected by laser scanning. Since the results were very promising, a standard procedure for verification and handling of the data was proposed. Because the ground points that are delivered by the contractor are the result of an automated filtering process, final editing is necessary to correct remaining misclassifications. This can be carried out using photogrammetric stereo models or through comparison of the results with large scale topographic maps. Both approaches lead to a high-quality DTM with much shorter production time and less costs as compared to the photogrammetric methods used up to now.
    BibTeX:
    @article{petzold99,
      author = {Bettina Petzold and Peter Reiss and Wolfgang Stüssel},
      title = {Laser scanning - surveying and mapping agencies are using a new technique for the derivation of digital terrain models},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {1999},
      volume = {54},
      number = {2-3},
      pages = {95-104}
    }
    
    Pfeifer, N., Kraus, K. & Küstli, A. Restitution of airborne laser scanner data in wooded regions 1999 GIS Geo-Information-Systems, Journal for Spatial Information and Decision Making
    Vol. 12, pp. 18-21 
    article  
    Abstract: Data from air-borne laser scanners provide the chance of accurate digital terrain modelling in forested areas. As a considerable portion of the laser rays is reflected before reaching the ground, a filtering technique sensible for many positive outliers is needed. Linear prediction extended with iterative robust estimation is a promising method for these requirements. In this paper we present the experiences with this algorithm, its implementation and examples.
    BibTeX:
    @article{pfeifer99,
      author = {Norbert Pfeifer and Karl Kraus and Andre Küstli},
      title = {Restitution of airborne laser scanner data in wooded regions},
      journal = {GIS Geo-Information-Systems, Journal for Spatial Information and Decision Making},
      year = {1999},
      volume = {12},
      pages = {18-21}
    }
    
    Pfeifer, N., Stadler, P. & Briese, C. DERIVATION OF DIGITAL TERRAIN MODELS IN THE SCOP++ ENVIRONMENT 2001 OEEPE Workshop on Airborne Laserscanning and Interferometric SAR for Digital Elevation Models, Stockholm  article  
    Abstract: Airborne laser scanning is widely used for the derivation of terrain information in wooded or open areas but also for the production of building models in cities. For this, the generation of a digital terrain model (DTM) is also required. In this paper the filtering and classification of laser scanner data with iterative robust linear prediction in a hierarchical fashion using data pyramids is described. The coarse-to-fine approach is advantageous because it strengthens the robustness of the method and makes it faster. The results for test data sets of the OEEPE are presented.
    BibTeX:
    @article{pfeifer01,
      author = {Norbert Pfeifer and Philipp Stadler and Christian Briese},
      title = {DERIVATION OF DIGITAL TERRAIN MODELS IN THE SCOP++ ENVIRONMENT},
      journal = {OEEPE Workshop on Airborne Laserscanning and Interferometric SAR for Digital Elevation Models, Stockholm},
      year = {2001}
    }
    
    Pimont, F., Linn, R., Dupuy, J. & Morvan, D. Effects of vegetation description parameters on forest fire behavior with FIRETEC. 2006 Forest Ecology and Management
    Vol. 234, pp. 120-134 
    article  
    BibTeX:
    @article{pimont06,
      author = {Pimont, F. and Linn, R.R. and Dupuy, J.L. and Morvan, D.},
      title = {Effects of vegetation description parameters on forest fire behavior with FIRETEC.},
      journal = {Forest Ecology and Management},
      year = {2006},
      volume = {234},
      pages = {120-134}
    }
    
    Popescu, S.C. & Wynne, R.H. Seeing the Trees in the Forest: Using Lidar and Multispectral Data Fusion with Local Filtering and Variable Window Size for Estimating Tree Height 2004 Photogrammetric Engineering & Remote Sensing
    Vol. 70, pp. 589-604 
    article  
    BibTeX:
    @article{popescu04,
      author = {Sorin C. Popescu and Randolph H. Wynne},
      title = {Seeing the Trees in the Forest: Using Lidar and Multispectral Data Fusion with Local Filtering and Variable Window Size for Estimating Tree Height},
      journal = {Photogrammetric Engineering & Remote Sensing},
      year = {2004},
      volume = {70},
      pages = {589-604}
    }
    
    Popescu, S.C., Wynne, R.H. & Nelson, R.F. Measuring individual tree crown diameter with

    lidar and assessing its influence on estimating

    forest volume and biomass

    2003 Canadian Journal of Remote Sensing
    Vol. 29, pp. 564-577 
    article  
    Abstract: The main objective of this study was to develop reliable processing and analysis techniques to facilitate the use of

    small-footprint lidar data for estimating tree crown diameter by measuring individual trees identifiable on the three-

    dimensional lidar surface. In addition, the study explored the importance of the lidar-derived crown diameter for estimating

    tree volume and biomass. The lidar dataset was acquired over deciduous, coniferous, and mixed stands of varying age

    classes and settings typical of the southeastern United States. For identifying individual trees, lidar processing techniques

    used data fusion with multispectral optical data and local filtering with both square and circular windows of variable size.

    The crown diameter was calculated as the average of two values measured along two perpendicular directions from the

    location of each tree top by fitting a fourth-degree polynomial on both profiles. The lidar-derived tree measurements were

    used with regression models and cross-validation to estimate plot level field-measured crown diameter. Linear regression

    was also used to compare plot level tree volume and biomass estimation with and without lidar-derived crown diameter

    measures from individual trees. Results for estimating crown diameter were similar for both pines and deciduous trees, with

    R2 values of 0.62?0.63 for the dominant trees (root mean square error (RMSE) 1.36 to 1.41 m). Lidar-measured crown

    diameter improved R2 values for volume and biomass estimation by up to 0.25 for both pines and deciduous plots (RMSE

    improved by up to 8 m3/ha for volume and 7 Mg/ha for biomass). For the pine plots, average crown diameter alone

    explained 78% of the variance associated with biomass (RMSE 31.28 Mg/ha) and 83% of the variance for volume (RMSE

    47.90 m3/ha).

    BibTeX:
    @article{popescu03,
      author = {Sorin C. Popescu and Randolph H. Wynne and Ross F. Nelson},
      title = {Measuring individual tree crown diameter with 

    lidar and assessing its influence on estimating

    forest volume and biomass}, journal = {Canadian Journal of Remote Sensing}, year = {2003}, volume = {29}, pages = {564-577} }

    Popescu, S.C., Wynne, R.H. & Nelson, R.F. Estimating plot-level tree heights with lidar: local filtering with a canopy-height based variable window size 2002 Computers and Electronics in Agriculture
    Vol. 37(1-3), pp. 71-95 
    article  
    Abstract: In recent years, the use of airborne lidar technology to measure forest biophysical characteristics has been rapidly increasing. This paper discusses processing algorithms for deriving the terrain model and estimating tree heights by using a multiple return, high-density, small-footprint lidar data set. The lidar data were acquired over deciduous, coniferous, and mixed stands of varying age classes and settings typical of the southeastern US. The specific objectives were: (1) to develop and test algorithms to estimate plot level tree height using lidar data, and (2) to investigate how ground measurements can help in the processing phase of lidar data for tree height assessment. The study area is located in the Piedmont physiographic province of Virginia, USA and includes a portion of the Appomattox-Buckingham State Forest (37[deg]25&prime;N, 78[deg]41&prime;W). Two lidar processing algorithms are discussed--the first based on single tree crown identification using a variable window size for local filtering, and the second based on the height of all laser pulses within the area covered by the ground truth data. Height estimates resulted from processing lidar data with both algorithms were compared to field measurements obtained with a plot design following the USDA Forest Service Forest Inventory and Analysis (FIA) field data layout. Linear regression was used to develop equations relating lidar-estimated parameters with field inventories for each of the FIA plots. As expected, the maximum height on each plot was predicted with the highest accuracy (R2 values of 85 and 90%, for the first and the second algorithm, respectively). The variable window size algorithm performed better for predicting heights of dominant and co-dominant trees (R2 values 84-85%), with a diameter at breast height (dbh) larger than 12.7 cm (5 in), when compared with the algorithm based on all laser heights (R2 values 57-73%). The use of field-based height thresholds when processing lidar data did not bring significant gains in explaining the total variation associated with tree height. The technique of local filtering with a variable window size considers fundamental forest biometrics relationships and overall proved to give better results than the technique of all laser shots.
    BibTeX:
    @article{popescu02,
      author = {Popescu, Sorin C. and Wynne, Randolph H. and Nelson, Ross F.},
      title = {Estimating plot-level tree heights with lidar: local filtering with a canopy-height based variable window size},
      journal = {Computers and Electronics in Agriculture},
      year = {2002},
      volume = {37},
      number = {1-3},
      pages = {71--95}
    }
    
    Popescu, S.C. & Zhao, K. A voxel-based lidar method for estimating crown base height for deciduous and pine trees 2008 Remote Sensing of Environment
    Vol. 112(3), pp. 767-781 
    article URL 
    Abstract: The overall goal of this study was to develop methods for assessing crown base height for individual trees using airborne lidar data in forest settings typical for the southeastern United States. More specific objectives are to: (1) develop new lidar-derived features as multiband height bins and processing techniques for characterizing the vertical structure of individual tree crowns; (2) investigate several techniques for filtering and analyzing vertical profiles of individual trees to derive crown base height, such as Fourier and wavelet filtering, polynomial fit, and percentile analysis; (3) assess the accuracy of estimating crown base height for individual trees, and (4) investigate which type of lidar data, point frequency or intensity, provides the most accurate estimate of crown base height. A lidar software application, TreeVaW, was used to locate individual trees and to obtain per tree measurements of height and crown width. Tree locations were used with lidar height bins to derive the vertical structure of tree crowns and measurements of crown base height. Lidar-derived crown base heights of individual trees were compared to field observations for 117 trees, including 94 pines and 23 deciduous trees. Linear regression models were able to explain up to 80% of the variability associated with crown base height for individual trees. Fourier filtering used for smoothing the vertical crown profile consistently provided the best results when estimating crown base height.
    BibTeX:
    @article{Popescu2008,
      author = {Popescu, Sorin C. and Zhao, Kaiguang},
      title = {A voxel-based lidar method for estimating crown base height for deciduous and pine trees},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {3},
      pages = {767--781},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4PDSYYJ-2/2/b8da66180b16464318dd4319b82f68f7}
    }
    
    Pouliot, D.A., King, D.J., Bell, F.W. & Pitt, D.G. Automated tree crown detection and delineation in high-resolution digital camera imagery of coniferous forest regeneration 2002 Remote Sens. Environ.
    Vol. 82(2-3), pp. 322-334 
    article  
    Abstract: Ensuring successful forest regeneration requires an effective monitoring program to collect information regarding the status of young crop trees and nearby competing vegetation. Current field-based assessment methodology provides the needed information, but is costly, and therefore assessment frequency is low. This often allows undesirable forest structures to develop that do not coincide with management objectives. Remote sensing techniques provide a potentially low-cost alternative to field-based assessment, but require the development of methods to easily and accurately extract the required information. Automated tree detection and delineation algorithms may be an effective means to accomplish this task. In this study, a tree detectionØdelineation algorithm designed specifically for high-resolution digital imagery of 6-year-old trees is presented and rigorously evaluated. The algorithm is based on the analysis of local transects extending outward from a potential tree apex. The crown boundary is estimated using the point of maximum rate of change in the transect data and a rule base is applied to ensure that the point is contextually suitable. This transect approach is implemented in both the tree-detection and crown-delineation phases. The tree-detection algorithm refines the results of an initial local maximum filter by providing an outline for each detected tree and retaining only one local maximum value within this outline. The crown-delineation algorithm is similar to the detection algorithm, but applies a different rule set in creating a more detailed crown outline. Results show that the algorithm's tree-detection accuracy was better than that using commonly applied fixed-window local maximum filters; it achieved a best result of 91%. For the crown-delineation algorithm, measured diameters from delineated crowns were within 17.9% of field measurements of diameter at the crown base on an individual tree basis and within 3% when averaged for the study. Tests of image pixel spacings from 5 to 30 cm showed that tree-detection accuracy was stable except at the lowest (30-cm) resolution where errors were unacceptable. Delineated crown-diameter accuracy was more sensitive to image resolution, decreasing consistently and nonlinearly with increasing pixel spacing. These results highlight the need for very high resolution imagery in automated object-based analysis of forest regeneration.
    BibTeX:
    @article{pouliot02,
      author = {D. A. Pouliot and D. J. King and F. W. Bell and D. G. Pitt},
      title = {Automated tree crown detection and delineation in high-resolution digital camera imagery of coniferous forest regeneration},
      journal = {Remote Sens. Environ.},
      year = {2002},
      volume = {82},
      number = {2-3},
      pages = {322-334}
    }
    
    Privette, J.L., Asner, G.P., Conel, J., Huemmrich, K.F., Olson, R., Rango, A., Rahman, A.F., Thome, K. & Walter-Shea, E.A. The EOS Prototype Validation Exercise (PROVE) at Jornada: Overview and Lessons Learned 2000 Remote Sensing of Environment
    Vol. 74(1), pp. 1-12 
    article  
    Abstract: The Earth Observing System (EOS) instrument teams must validate the operational products they produce from the Terra spacecraft data. As a pilot for future validation activities, four EOS teams (MODIS, MISR, ASTER, and Landsat-7) and community experts conducted an 11-day field campaign in May 1997 near Las Cruces, NM. The goals of the Prototype Validation Exercise (PROVE) included (1) gaining experience in the collection and use of field data for EOS product validation; (2) developing coordination, measurement, and data-archiving protocols; and (3) compiling a synoptic land and atmospheric data set for testing algorithms. PROVE was held at the USDA-Agricultural Research Service's (ARS) Jornada Experimental Range, an expansive desert plateau hosting a complex mosaic of grasses and shrubs. Most macroscopic variables affecting the radiation environment were measured with ground, air-borne (including AVIRIS and laser altimeter), and space-borne sensors (including AVHRR, Landsat TM, SPOT, POLDER, and GOES). The Oak Ridge Distributed Active Archive Center (DAAC) then used campaign data sets to prototype Mercury, its Internet-based data harvesting and distribution system. This article provides general information about PROVE and assesses the progress made toward the campaign goals. Primary successes included the rapid campaign formulation and execution, measurement protocol development, and the significant collection, reduction, and sharing of data among participants. However, the PROVE data were used primarily for arid-land research and model validation rather than for validating satellite products, and the data were slow to reach the DAAC and hence public domain. The lessons learned included: (1) validation campaigns can be rapidly organized and implemented if there are focused objectives and on-site facilities and expertise; (2) data needs, organization, storage, and access issues must be addressed at the onset of campaign planning; and (3) the end-to-end data collection, release, and publication environment may need to be readdressed by program managers, funding agencies, and journal editors if rapid and comprehensive validation of operational satellite products is to occur.
    BibTeX:
    @article{Privette2000,
      author = {Privette, J. L. and Asner, G. P. and Conel, J. and Huemmrich, K. F. and Olson, R. and Rango, A. and Rahman, A. F. and Thome, K. and Walter-Shea, E. A.},
      title = {The EOS Prototype Validation Exercise (PROVE) at Jornada: Overview and Lessons Learned},
      journal = {Remote Sensing of Environment},
      year = {2000},
      volume = {74},
      number = {1},
      pages = {1--12}
    }
    
    Pyysalo, U. & Hyyppä, H. Reconstructing Tree Crowns from Laser Scanner Data for Feature Extraction 2002 ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria, pp. B-218 ff (4 pages)  inproceedings  
    Abstract: The objective of this study was to carry out reconstruction of single tree crowns from laser scanner data to use the obtained vector model for feature extraction. The reconstruction was implemented in several stages. First, pulses which have reflected from each tree were marked off from the original point cloud. Ground points were then separated from all points using digital terrain model and analysing the histogram of terrain height values. In the next stage canopy was described with vector polygons, and the location of the trunk was estimated. With respect to the location of the trunk, tree points were transferred from (xyz)-co-ordinate system to the polarco- ordinate system (a,r,h), and features were estimated from the vector model. Evaluation of the reconstruction was performed choosing a test area and processing 50 single trees, and comparing results to the field measurements. In the study it was found that dense laser scanner data detail describes the upper canopy of forest and therefore is suitable for tree height information extraction. The lower crown was found less detail measured with laser scanner and parameters extracted from that part were less accurate, but trend setting. Obtained distance profile seemed to give tendency for the tree specie.
    BibTeX:
    @inproceedings{pyysalo02,
      author = {Ulla Pyysalo and Hannu Hyyppä},
      title = {Reconstructing Tree Crowns from Laser Scanner Data for Feature Extraction},
      booktitle = {ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria},
      year = {2002},
      pages = {B-218 ff (4 pages)}
    }
    
    Qi, J., Kerr, Y.H., Moran, M.S., Weltz, M., Huete, A.R., Sorooshian, S. & Bryant, R. Leaf Area Index Estimates Using Remotely Sensed Data and BRDF Models in a Semiarid Region 2000 Remote Sensing of Environment
    Vol. 73(1), pp. 18-30 
    article  
    Abstract: The amount and spatial and temporal dynamics of vegetation are important information in environmental studies and agricultural practices. There has been a great deal of interest in estimating vegetation parameters and their spatial and temporal extent using remotely sensed imagery. There are primarily two approaches to estimating vegetation parameters such as leaf area index (LAI). The first one is associated with computation of spectral vegetation indices (SVI) from radiometric measurements. This approach uses an empirical or modeled LAI-SVI relation between remotely sensed variables such as SVI and biophysical variables such as LAI. The major limitation of this empirical approach is that there is no single LAI-SVI equation (with a set of coefficients) that can be applied to remote-sensing images of different surface types. The second approach involves using bidirectional reflectance distribution function (BRDF) models. It inverts a BRDF model with radiometric measurements to estimate LAI using an optimization procedure. Although this approach has a theoretical basis and is potentially applicable to varying surface types, its primary limitation is the lengthy computation time and difficulty of obtaining the required input parameters by the model. In this study, we present a strategy that combines BRDF models and conventional LAI-SVI approaches to circumvent these limitations. The proposed strategy was implemented in three sequential steps. In the first step, a BRDF model was inverted with a limited number of data points or pixels to produce a training data set consisting of leaf area index and associated pixel values. In the second step, the training data set passed through a quality control procedure to remove outliers from the inversion procedure. In the final step, the training data set was used either to fit an LAI-SVI equation or to train a neural fuzzy system. The best fit equation or the trained fuzzy system was then applied to large-scale remote-sensing imagery to map spatial LAI distribution. This approach was applied to Landsat TM imagery acquired in the semiarid southeast Arizona and AVHRR imagery over the Hapex-Sahel experimental sites near Niamy, Niger. The results were compared with limited ground-based LAI measurements and suggested that the proposed approach produced reasonable estimates of leaf area index over large areas in semiarid regions. This study was not intended to show accuracy improvement of LAI estimation from remotely sensed data. Rather, it provides an alternative that is simple and requires little knowledge of study target and few ground measurements.
    BibTeX:
    @article{qi00,
      author = {Qi, J. and Kerr, Y. H. and Moran, M. S. and Weltz, M. and Huete, A. R. and Sorooshian, S. and Bryant, R.},
      title = {Leaf Area Index Estimates Using Remotely Sensed Data and BRDF Models in a Semiarid Region},
      journal = {Remote Sensing of Environment},
      year = {2000},
      volume = {73},
      number = {1},
      pages = {18--30}
    }
    
    Quaife, T., Lewis, P., De Kauwe, M., Williams, M., Law, B.E., Disney, M. & Bowyer, P. Assimilating canopy reflectance data into an ecosystem model with an Ensemble Kalman Filter 2008 Remote Sensing of Environment
    Vol. 112(4)Remote Sensing Data Assimilation Special Issue, pp. 1347-1364 
    article  
    Abstract: An Ensemble Kalman Filter (EnKF) is used to assimilate canopy reflectance data into an ecosystem model. We demonstrate the use of an augmented state vector approach to enable a canopy reflectance model to be used as a non-linear observation operator. A key feature of data assimilation (DA) schemes, such as the EnKF, is that they incorporate information on uncertainty in both the model and the observations to provide a best estimate of the true state of a system. In addition, estimates of uncertainty in the model outputs (given the observed data) are calculated, which is crucial in assessing the utility of model predictions. Results are compared against eddy-covariance observations of CO2 fluxes collected over three years at a pine forest site. The assimilation of 500?m spatial resolution MODIS reflectance data significantly improves estimates of Gross Primary Production (GPP) and Net Ecosystem Productivity (NEP) from the model, with clear reduction in the resulting uncertainty of estimated fluxes. However, foliar biomass tends to be over-estimated compared with measurements. Issues regarding this over-estimate, as well as the various assumptions underlying the assimilation of reflectance data are discussed.
    BibTeX:
    @article{Quaife2008,
      author = {Quaife, Tristan and Lewis, Philip and De Kauwe, Martin and Williams, Mathew and Law, Beverly E. and Disney, Mathias and Bowyer, Paul},
      title = {Assimilating canopy reflectance data into an ecosystem model with an Ensemble Kalman Filter},
      booktitle = {Remote Sensing Data Assimilation Special Issue},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {4},
      pages = {1347--1364}
    }
    
    Rall, J. & Knox, R. Spectral Ratio Biospheric LIDAR. 2004 22nd International Laser Radar Conference (ILRC 2004), Proceedings of the

    Conference held 12-16 July 2004 in Matera, Italy. ESA SP-561. Paris: European Space Agency, p.831. 

    inproceedings  
    BibTeX:
    @inproceedings{rall04,
      author = {Rall, J. and Knox, R.G.},
      title = {Spectral Ratio Biospheric LIDAR.},
      booktitle = {22nd International Laser Radar Conference (ILRC 2004), Proceedings of the 

    Conference held 12-16 July 2004 in Matera, Italy. ESA SP-561. Paris: European Space Agency, p.831.}, year = {2004} }

    Rall, J. & Knox, R. Spectral ratio biospheric lidar 2004 Geoscience and Remote Sensing Symposium, 2004. IGARSS '04. Proceedings. 2004 IEEE International
    Vol. 3, pp. 1951-1954 vol.3 
    article DOI  
    Abstract: A new active vegetation index measurement technique has been developed and demonstrated using low power laser diodes to make horizontal-path lidar measurements of nearby deciduous foliage. The two wavelength laser transmitter operates within and adjacent to the 680 nm absorption feature exhibited by all chlorophyll containing vegetation. Measurements from early October through late November 2003 are presented and the results are discussed
    BibTeX:
    @article{rall04_igarrs,
      author = {Rall, J.A.R. and Knox, R.G.},
      title = {Spectral ratio biospheric lidar},
      journal = {Geoscience and Remote Sensing Symposium, 2004. IGARSS '04. Proceedings. 2004 IEEE International},
      year = {2004},
      volume = {3},
      pages = {1951-1954 vol.3},
      doi = {http://dx.doi.org/10.1109/IGARSS.2004.1370726}
    }
    
    Rango, A., Chopping, M., Ritchie, J., Havstad, K., Kustas, W. & Schmugge, T. Morphological Characteristics of Shrub Coppice Dunes in Desert Grasslands of Southern New Mexico derived from Scanning LIDAR 2000 Remote Sensing of Environment
    Vol. 74(1), pp. 26-44 
    article  
    Abstract: Since the 1880s rangeland vegetation in southern New Mexico has changed dramatically over widespread areas, typically with shrublands displacing native grasslands. Coincident with these changes in vegetation dominance are increases in soil erosion, stream channel cutting, and shrub coppice dune formation on sandy soils. Where marked transitions in vegetation type from grassland to honey mesquite shrubland have occurred, the local topography has been transformed with previously flat mesa becoming rolling duneland. The size, distribution, and morphological characteristics of these dunes have an important impact on fluxes of energy and nutrients at the surface; they also render the land far less useful as grazing land for domestic livestock. These shrub coppice dunes and the mesquite shrubs that grow on them may be considered roughness elements. Quantifying their morphology is important for the calculation of aerodynamic roughness length and displacement height. This article tests the ability of active scanning laser remote sensing techniques to provide accurate estimates of the three-dimensional shapes and areal distributions of dune and interdune areas. It shows that scanning laser with a footprint diameter of 0.38 m and a sampling interval of 1.5 m to 2 m can be used to measure the morphological characteristics of shrub coppice dunes in the desert grasslands of southern New Mexico with acceptable accuracy and precision for a range of uses, including important geomorphological and hydrological applications. The use of scanning laser systems together with optical multispectral data is shown to be highly synergistic, providing information that is not easily obtainable via other surveying methods.
    BibTeX:
    @article{Rango2000,
      author = {Rango, A. and Chopping, M. and Ritchie, J. and Havstad, K. and Kustas, W. and Schmugge, T.},
      title = {Morphological Characteristics of Shrub Coppice Dunes in Desert Grasslands of Southern New Mexico derived from Scanning LIDAR},
      journal = {Remote Sensing of Environment},
      year = {2000},
      volume = {74},
      number = {1},
      pages = {26--44}
    }
    
    Rautiainen, M., Lang, M., M?ttus, M., Kuusk, A., Nilson, T., Kuusk, J. & L?kk, T. Multi-angular reflectance properties of a hemiboreal forest: An analysis using CHRIS PROBA data 2008 Remote Sensing of Environment
    Vol. 112(5), pp. 2627 - 2642 
    article DOI URL 
    Abstract: Forest types differ in their hyperspectral anisotropy patterns mainly due to species-specific geometrical structure, spatial arrangement of canopies and subsequent shadow patterns. This paper examines the multi-angular, hyperspectral reflectance properties of typical hemiboreal forests during summer time using three simultaneous CHRIS PROBA (mode 3) scenes and stand inventory data from the J?rvselja Training and Experimental Forestry District in southeastern Estonia. We investigated the magnitude and reasons for the differences in the anisotropy patterns of deciduous and coniferous stands at three backward viewing angles. A forest reflectance model (FRT) was used as a tool to provide a theoretical basis to the discussion, and to estimate the directional contribution of scattering from crowns and ground to total stand reflectance for the two forest types. The FRT model simulated successfully the HDRF (hemispherical-directional reflectance factor) curves of the study stands to match those obtained from the CHRIS image, yet it produced a smaller and less wavelength-dependent angular reflectance effect than was observed in the satellite image. The main results of this study provide new information for separating the spectral contribution of the forest floor (or understory layer) from the tree canopy layer: (1) the red edge domain was identified to have the largest contribution from forest understory, and (2) the more oblique the viewing angle, the smaller the contribution from the understory. In addition, coniferous stands were observed to have a specific angular effect at the red and red edge domain, possibly as a result of the hierarchical structure and arrangement of coniferous canopies.
    BibTeX:
    @article{Rautiainen20082627,
      author = {Miina Rautiainen and Mait Lang and Matti M?ttus and Andres Kuusk and Tiit Nilson and Joel Kuusk and T?nu L?kk},
      title = {Multi-angular reflectance properties of a hemiboreal forest: An analysis using CHRIS PROBA data},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {5},
      pages = {2627 - 2642},
      note = {Earth Observations for Terrestrial Biodiversity and Ecosystems Special Issue},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4RTCPT8-2/2/d602f8d7f8aa360e8fd2f22a4038ad63},
      doi = {DOI: 10.1016/j.rse.2007.12.005}
    }
    
    Rautiainen, M. & Stenberg, P. Application of photon recollision probability in coniferous canopy reflectance simulations Remote Sensing of Environment
    Vol. In Press, Corrected Proof, pp. - 
    article  
    Abstract: A new semi-physical forest reflectance model, PARAS, is presented in the paper. PARAS is a simple parameterization model for taking into account the effect of within-shoot scattering on coniferous canopy reflectance. Multiple scattering at the small scale represented by a shoot is a conifer-specific characteristic which causes the spectral signature of coniferous forests to differ from that of broadleaved forests. This has for long led to problems in remote sensing of canopy structural variables in coniferous dominated regions. The PARAS model uses a relationship between photon recollision probability and leaf area index (LAI) for simulating forest reflectance. The recollision probability is a measurable, wavelength independent variable which is defined as the probability with which a photon scattered in the canopy interacts with a phytoelement again. In this study, we present application results using PARAS in simulating reflectance of coniferous forests for approximately 800 Scots pine and Norway spruce dominated stands. The results of this study clearly indicate that a major improvement in simulating canopy reflectance in near-infrared (NIR) is achieved by simply accounting for the within-shoot scattering. In other words, the low NIR reflectance observed in coniferous areas is mainly due to within-shoot scattering. In the red wavelength the effect of within-shoot scattering was not pronounced due to the high level of needle absorption in the red range. To conclude the paper, further application possibilities of the presented parameterization model are discussed.
    BibTeX:
    @article{rautiainen05,
      author = {Rautiainen, Miina and Stenberg, Pauline},
      title = {Application of photon recollision probability in coniferous canopy reflectance simulations},
      journal = {Remote Sensing of Environment},
      volume = {In Press, Corrected Proof},
      pages = {--}
    }
    
    Rautiainen, M., Stenberg, P., Nilson, T. & Kuusk, A. The effect of crown shape on the reflectance of coniferous stands 2004 Remote Sensing of Environment
    Vol. 89(1), pp. 41-52 
    article  
    Abstract: The Kuusk-Nilson forest reflectance model was used to study the effect of crown shape on the reflectance of Scots pine and Norway spruce stands. In the first part of the study, we examined spruce and pine stands with an age range of 20-100 years and compared their simulated hemispherical-directional reflectance factors (HDRFs) at nadir in red (661 nm), NIR (838 nm) and MIR (1677 nm) when crowns were modeled as ellipsoids or cones. In all the cases, when a stand was modeled with conical crowns, it had a smaller reflectance factor than the same stand with ellipsoidal crowns.To analyze the sensitivity of HDRF on crown shape, in the second part of the study we simulated the angular distributions of HDRF of two pine stands with different leaf area index (LAI) and canopy closure values at 661 nm assuming four different crown shapes (cone, cylinder, ellipsoid, and cylinder bottom, cone top) and separated the components forming the HDRF. Considerable difference in the HDRF between the four crown shapes was observed: The larger the crown volume, the higher the canopy reflectance at similar LAI and canopy closure. A comparison of the two stands revealed that in denser stands (with a higher canopy closure) single scattering from tree crowns was responsible for the difference in HDRF between the different crown shapes, whereas in stands with a smaller canopy closure the single scattering from ground dominated the HDRF. Finally, the role of crown shape for the retrieval of LAI by inversion from remotely sensed data is discussed.
    BibTeX:
    @article{rautiainen04,
      author = {Rautiainen, Miina and Stenberg, Pauline and Nilson, Tiit and Kuusk, Andres},
      title = {The effect of crown shape on the reflectance of coniferous stands},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {89},
      number = {1},
      pages = {41--52}
    }
    
    Reitberger, J., Krzystek, P. & Stilla, U. Analysis of full waveform LIDAR data for the classification of deciduous and coniferous trees 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1407-1431 
    article  
    Abstract: The paper describes a methodology for tree species classification using features that are derived from small-footprint full waveform Light Detection and Ranging (LIDAR) data. First, 3-dimensional coordinates of the laser beam reflections, the intensity, and the pulse width are extracted by a waveform decomposition, which fits a series of Gaussian pulses to the waveform. Since multiple reflections are detected, and even overlapping pulse reflections are distinguished, a much higher point density is achieved compared to the conventional first/last-pulse technique. Secondly, tree crowns are delineated from the canopy height model (CHM) using the watershed algorithm. The CHM posts are equally spaced and robustly interpolated from the highest reflections in the canopy. Thirdly, tree features computed from the 3-dimensional coordinates of the reflections, the intensity and the pulse width are used to detect coniferous and deciduous trees by an unsupervised classification. The methodology is applied to datasets that have been captured with the TopEye MK II scanner and the Riegl LMS-Q560 scanner in the Bavarian Forest National Park in leaf-on and leaf-off conditions for Norway spruces, European beeches and Sycamore maples. The classification, which groups the data into two clusters (coniferous, deciduous), leads in the best case to an overall accuracy of 85% in a leaf-on situation and 96% in a leaf-off situation.
    BibTeX:
    @article{Reitberger2008,
      author = {Reitberger, J. and Krzystek, P. and Stilla, U.},
      title = {Analysis of full waveform LIDAR data for the classification of deciduous and coniferous trees},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1407--1431}
    }
    
    Reulke, R., Becker, S., Haala, N. & Tempelmann, U. Determination and improvement of spatial resolution of the CCD-line-scanner system ADS40 2006 ISPRS Journal of Photogrammetry and Remote Sensing
    Vol. 60(2), pp. 81-90 
    article  
    Abstract: Images that are collected for mapping purposes from airborne or space-borne sensors have to cover large areas by great image swaths at a high spatial resolution. These demands can be fulfilled by push-broom scanners featuring staggered line arrays, which are constructed from two identical CCD lines shifted against each other by half a pixel in line direction. Practical applications of such arrays in remote sensing include SPOT, and in the airborne environment the Airborne Digital Sensor, or ADS40, from Leica Geosystems. Furthermore, image restoration methods for enhancing the image quality can be applied to improve image quality and resolution. This paper presents an approach of high resolution image restitution from staggered lines and practical results with ADS40 high resolution panchromatic images.
    BibTeX:
    @article{reulke06,
      author = {Reulke, R. and Becker, S. and Haala, N. and Tempelmann, U.},
      title = {Determination and improvement of spatial resolution of the CCD-line-scanner system ADS40},
      journal = {ISPRS Journal of Photogrammetry and Remote Sensing},
      year = {2006},
      volume = {60},
      number = {2},
      pages = {81--90}
    }
    
    Reutebuch, S.E., McGaughey, R.J., Andersen, H.-E. & Carson, W.W. Accuracy of a high-resolution lidar terrain model

    under a conifer forest canopy

    2003 Canadian Journal of Remote Sensing
    Vol. 29, pp. 527-535 
    article  
    BibTeX:
    @article{reutebuch03,
      author = {Stephen E. Reutebuch and Robert J. McGaughey and Hans-Erik Andersen and Ward W. Carson},
      title = {Accuracy of a high-resolution lidar terrain model 

    under a conifer forest canopy}, journal = {Canadian Journal of Remote Sensing}, year = {2003}, volume = {29}, pages = {527-535} }

    Riano, D., Chuvieco, E., Condes, S., Gonzalez-Matesanz, J. & Ustin, S.L. Generation of crown bulk density for Pinus sylvestris L. from lidar 2004 Remote Sensing of Environment
    Vol. 92(3), pp. 345-352 
    article  
    BibTeX:
    @article{riano_cbd,
      author = {Riano, David and Chuvieco, Emilio and Condes, Sonia and Gonzalez-Matesanz, Javier and Ustin, Susan L.},
      title = {Generation of crown bulk density for Pinus sylvestris L. from lidar},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {92},
      number = {3},
      pages = {345--352}
    }
    
    Riano, D., Meier, E., Allgöwer, B. & Chuvieco, E. GENERATION OF VEGETATION HEIGHT, VEGETATION COVER AND CROWN BULK DENSITY FROM AIRBORNE LASER SCANNING DATA 2002   article  
    Abstract: Vegetation height, vegetation cover and crown bulk density, that are critical for fire behavior modeling, were produced from airborne laser scanning (LIDAR). High-density laser scanning data, 1.5 m across track and 0.11 m along track, were provided by Toposys, a German company specialized in LIDAR data. Raw data containing x, y and z (above sea level) coordinates were used to produce an algorithm for estimating these forest parameters. The algorithm was based on a cluster analysis used to discriminate crown base height. As a result two groups of heights were obtained, identifying both tree and understory parameters. Validation of the method is being carried out.
    BibTeX:
    @article{riano02,
      author = {David Riano and Erich Meier and Britta Allgöwer and Emilio Chuvieco},
      title = {GENERATION OF VEGETATION HEIGHT, VEGETATION COVER AND CROWN BULK DENSITY FROM AIRBORNE LASER SCANNING DATA},
      year = {2002}
    }
    
    Riano, D., Meier, E., Allgöwer, B., Chuvieco, E. & Ustin, S.L. Modeling airborne laser scanning data for the spatial generation of critical forest parameters in fire behavior modeling 2003 Remote Sensing of Environment
    Vol. 86(2), pp. 177-186 
    article  
    Abstract: Methods for using airborne laser scanning to retrieve forest parameters that are critical for fire behavior modeling are presented. A model for the automatic extraction of forest information is demonstrated to provide spatial coverage of the study area, making it possible to produce 3-D inputs to improve fire behavior models. The Toposys I airborne laser system recorded the last return of each footprint (0.30-0.38m) over a 2 km by 190 m flightline. Raw data were transformed into height above the surface, eliminating the effect of terrain on vegetation height, and allowing separation of ground surface and crown heights. Data were defined as ground elevation if heights were less than 0.6 m. A cluster analysis was used to discriminate crown base height, allowing identification of both tree and understory canopy heights. Tree height was defined as the 99 percentile of the tree crown height group, while crown base height was the 1 percentile of the tree crown height group. Tree cover was estimated from the fraction of total tree laser hits relative to the total number of laser hits. Surface canopy height was computed as the 99 percentile of the surface canopy group. Surface canopy cover is equal to the fraction of total surface canopy hits relative to the total number of hits, once the canopy height profile was corrected. Crown bulk density was obtained from foliage biomass estimate and crown volume, using an empirical equation for foliage biomass. Crown volume was estimated as the crown area times the crown height after a correction for mean canopy cover.
    BibTeX:
    @article{riano03,
      author = {David Riano and Erich Meier and Britta Allgöwer and Emilio Chuvieco and Susan L. Ustin},
      title = {Modeling airborne laser scanning data for the spatial generation of critical forest parameters in fire behavior modeling},
      journal = {Remote Sensing of Environment},
      year = {2003},
      volume = {86},
      number = {2},
      pages = {177-186}
    }
    
    Riano, D., Valladares, F., Condes, S. & Chuvieco, E. Estimation of leaf area index and covered ground from airborne laser scanner (Lidar) in two contrasting forests 2004 Agricultural and Forest Meteorology
    Vol. 124(3-4), pp. 269-275 
    article  
    BibTeX:
    @article{riano_lai,
      author = {Riano, David and Valladares, Fernando and Condes, Sonia and Chuvieco, Emilio},
      title = {Estimation of leaf area index and covered ground from airborne laser scanner (Lidar) in two contrasting forests},
      journal = {Agricultural and Forest Meteorology},
      year = {2004},
      volume = {124},
      number = {3-4},
      pages = {269--275}
    }
    
    Risch, A.C., Heiri, C. & Bugmann, H. Simulating structural forest patterns with a forest gap model: a model evaluation 2005 Ecological Modelling
    Vol. 181(2-3), pp. 161-172 
    article  
    Abstract: Ecological models can be characterized by their degree of generality, reality and precision. Any model, being a deliberate simplification of reality, cannot excel in all three aspects. Forest gap models have been widely used for studying tree population dynamics, but their predictions have not often been tested for their local precision, but rather for their broad agreement with descriptions of near-natural vegetation. The objectives of our study were (1) to evaluate the performance of the forest gap model ForClim, which had been developed striving for generality and realism, in simulating the long-term development of structural features in Swiss mountain forests; and (2) to examine whether and how the model needs to be changed to improve its precision for a specific site. We used long-term forest data (45 years) from three different forest types in the Swiss National Park. Initial simulation runs for the most dominant forest type in the study area failed to reproduce the observed structural patterns. A detailed analysis of the growth performance of individual trees led to the conclusion that a modified height-diameter function was required, which presumably increases the generality of the model. The new model structure led to simulated stand features that were broadly consistent with observations. After, in addition, taking local variations of model parameters (on mortality, browsing, and seedling establishment rates) into account, we were able to considerably improve the performance of ForClim in simulating the structural features of the different mountain forest stands. We suggest that from the point of view of its revised structure, the ForClim model is principally suitable for site-specific applications, but local precision can only be achieved by site-specific parameter estimation procedures. We conclude that model evaluation and validation as conducted in this study could be quite useful for increasing the reliability of simulations performed with this class of models.
    BibTeX:
    @article{Risch2005,
      author = {Risch, Anita C. and Heiri, Caroline and Bugmann, Harald},
      title = {Simulating structural forest patterns with a forest gap model: a model evaluation},
      journal = {Ecological Modelling},
      year = {2005},
      volume = {181},
      number = {2-3},
      pages = {161--172}
    }
    
    Rodriguez, E., Morris, C., Belz, J., Chapin, E., Martin, J., Daffer, W. & Hensley, S. An assessment of the SRTM topographic products. 2005   techreport  
    BibTeX:
    @techreport{rodriguez05,
      author = {Rodriguez, E. and C.S. Morris and J.E. Belz and E.C. Chapin and J.M. Martin and W. Daffer and S. Hensley},
      title = {An assessment of the SRTM topographic products.},
      year = {2005}
    }
    
    Roggero, M. Object Segmentation with Region Growing and Principal Component Analysis 2002 ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria, pp. A-289 ff (6 pages)  inproceedings  
    Abstract: The paper considers the problem of object segmentation and shape recognition in discrete noisy data. Two different algorithms combine region growing techniques with principal component analysis. The proposed algorithms are applied to a data set from airborne laser scanners.
    BibTeX:
    @inproceedings{roggero02a,
      author = {Marco Roggero},
      title = {Object Segmentation with Region Growing and Principal Component Analysis},
      booktitle = {ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria},
      year = {2002},
      pages = {A-289 ff (6 pages)}
    }
    
    Roggero, M. AIRBORNE LASER SCANNING: CLUSTERING IN RAW DATA 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 227-232 
    article  
    Abstract: We implemented a strategy for terrain, vegetation and building detection, based on laser range data only. The result was obtained by working on raw data, so we were able to take advantage of the full resolution potential of laser scanning. The detection of objects was performed in two stages: first, elevated objects and ground are separated, and then the objects are classified as vegetation or buildings. Work is still in progress, about the extraction and classification of entities. A comparative analysis of the first pulse, the last pulse and intensity data can improve the result of clustering. Results obtained in different environments with one-meter grid laser data are shown; we have tested the algorithm on city areas, countryside, river bed, landslides, mountains and wooded terrain.
    BibTeX:
    @article{roggero01,
      author = {Marco Roggero},
      title = {AIRBORNE LASER SCANNING: CLUSTERING IN RAW DATA},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {227-232}
    }
    
    Rosette, J.A.B., North, P.R.J. & Suarez, J.C. Vegetation height estimates for a mixed temperate forest using satellite laser altimetry 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1475-1493 
    article  
    Abstract: Data from the Geoscience Laser Altimeter System (GLAS) aboard the Ice Cloud and land Elevation Satellite (ICESat) offer an unprecedented opportunity for canopy height retrieval at a regional to global scale. The data also provide useful information for forest stand level assessment at coincident locations. In this study height indices from light detection and ranging (LiDAR) waveforms were explored as a means of extracting canopy height; these were examined with reference to a mixed temperate forest in Gloucestershire, UK, containing planted stands with a mean age of 51 years and mean maximum height of 26.6??m. A method based on using a terrain index (TI; maximum minus minimum elevations from a 7??7 subset 10-m resolution digital terrain model (DTM)) to adjust the waveform extent (WE; signal begin minus signal end) produced an R 2 value of 0.89 when regressed against field measurements of maximum canopy height at footprint locations (field height??=??0.91(WE-TI)+4.86; root mean squared error (RMSE)??=??2.99??m, coefficient significance p&lt;0.001, intercept significance p&gt;0.01). Multiple regression performed on both WE and TI with field measurements produced an R 2 of 0.90 and an RMSE of 2.86??m (field height??=??1.0208WE-0.7310TI; coefficient significance p&lt;0.001, intercept not significant). Maximum canopy height estimates using an automated approach to ground return identification based on iterative fitting of Gaussian peaks (GP1_2MAXAMP) to the waveform explained 74% of variance when compared to field measurements (field height??=??1.05(GP1_2MAXAMP); RMSE??=??4.53??m, coefficient significance p&lt;0.001, intercept not significant). The ability of satellite LiDAR to retrieve data for such a complex and diverse area further indicates the potential of this technique for both carbon accounting and forest management.
    BibTeX:
    @article{Rosette2008,
      author = {Rosette, J. A. B. and North, P. R. J. and Suarez, J. C.},
      title = {Vegetation height estimates for a mixed temperate forest using satellite laser altimetry},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1475--1493}
    }
    
    Rosette, J., North, P. & Suarez, J. Vegetation height estimates for a mixed temperate forest using satellite laser altimetry 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1475-1494 
    article  
    BibTeX:
    @article{rosette08,
      author = {J.A.B. Rosette and P.R.J. North and J.C. Suarez},
      title = {Vegetation height estimates for a mixed temperate forest using satellite laser altimetry},
      journal = {International Journal of Remote Sensing},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1475-1494}
    }
    
    Rothermel, R.C. A mathematical model for predicting fire spread in wildland fuels. 1972 Research Paper INT- 115
    Vol. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station., pp. 40p 
    article  
    BibTeX:
    @article{rothermel,
      author = {Rothermel, R. C.},
      title = {A mathematical model for predicting fire spread in wildland fuels.},
      journal = {Research Paper INT- 115},
      year = {1972},
      volume = {Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range 

    Experiment Station.}, pages = {40p} }

    Russell, W.H. & McBride, J.R. Landscape scale vegetation-type conversion and fire hazard in the San Francisco bay area open spaces 2003 Landscape and Urban Planning
    Vol. 64(4), pp. 201-208 
    article  
    Abstract: Successional pressures resulting from fire suppression and reduced grazing have resulted in vegetation-type conversion in the open spaces surrounding the urbanized areas of the San Francisco bay area. Coverage of various vegetation types were sampled on seven sites using a chronosequence of remote images in order to measure change over time. Results suggest a significant conversion of grassland to shrubland dominated by Baccharis pilularison five of the seven sites sampled. An increase in Pseudotsuga menziesii coverage was also measured on the sites where it was present. Increases fuel and fire hazard were determined through field sampling and use of the FARSITE fire area simulator. A significant increase in biomass resulting from succession of grass-dominated to shrub-dominated communities was evident. In addition, results from the FARSITE simulations indicated significantly higher fire-line intensity, and flame length associated with shrublands over all other vegetation types sampled. These results indicate that the replacement of grass dominated with shrub-dominated landscapes has increased the probability of high intensity fires.
    BibTeX:
    @article{russell03,
      author = {Russell, William H. and McBride, Joe R.},
      title = {Landscape scale vegetation-type conversion and fire hazard in the San Francisco bay area open spaces},
      journal = {Landscape and Urban Planning},
      year = {2003},
      volume = {64},
      number = {4},
      pages = {201--208}
    }
    
    Saatchi, S. & Moghaddam, M. Estimation of crown and stem water content and biomass of boreal forest using polarimetric SAR imagery 2000 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 38(2)Geoscience and Remote Sensing, IEEE Transactions on, pp. 697-709 
    article  
    Abstract: Characterization of boreal forests in ecosystem models requires temporal and spatial distributions of water content and biomass over local and regional scales. The authors report on the use of a semi-empirical algorithm for deriving these parameters from polarimetric synthetic aperture radar (SAR) measurements. The algorithm is based on a two layer radar backscatter model that stratifies the forest canopy into crown and stem layers and separates the structural and biometric attributes of forest stands. The structural parameters are estimated by training the model with SAR image data over dominant coniferous and deciduous stands in the boreal forest such as jack pine, black spruce, and aspen. The algorithm is then applied on AIRSAR images collected during the Boreal Ecosystem Atmospheric Study (BOREAS) over the boreal forest of Canada. The results are verified using biometry measurements during BOREAS-intensive field campaigns. Field data relating the water content of tree components to dry biomass are used to modify the coefficients of the algorithm for crown and stem biomass. The algorithm was then applied over the entire image generating biomass maps. A set of 18 test sites within the imaged area was used to assess the accuracy of the biomass maps. The accuracy of biomass estimation is also investigated by choosing different combinations of polarization and frequency channels of the AIRSAR system. It is shown that polarimetric data from P-band and L-band channels provide similar accuracy for estimating the above-ground biomass for boreal forest types. In general, the use of P-band channels can provide better estimates of stem biomass, while L-band channels can estimate the crown biomass more accurately
    BibTeX:
    @article{Saatchi2000,
      author = {Saatchi, S.S. and Moghaddam, M.},
      title = {Estimation of crown and stem water content and biomass of boreal forest using polarimetric SAR imagery},
      booktitle = {Geoscience and Remote Sensing, IEEE Transactions on},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {2000},
      volume = {38},
      number = {2},
      pages = {697--709}
    }
    
    Saatchi, S. & Moghaddam, M. Estimation of crown and stem water content and biomass of boreal forest using polarimetric SAR imagery 2000 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 38(2)Geoscience and Remote Sensing, IEEE Transactions on, pp. 697-709 
    article  
    Abstract: Characterization of boreal forests in ecosystem models requires temporal and spatial distributions of water content and biomass over local and regional scales. The authors report on the use of a semi-empirical algorithm for deriving these parameters from polarimetric synthetic aperture radar (SAR) measurements. The algorithm is based on a two layer radar backscatter model that stratifies the forest canopy into crown and stem layers and separates the structural and biometric attributes of forest stands. The structural parameters are estimated by training the model with SAR image data over dominant coniferous and deciduous stands in the boreal forest such as jack pine, black spruce, and aspen. The algorithm is then applied on AIRSAR images collected during the Boreal Ecosystem Atmospheric Study (BOREAS) over the boreal forest of Canada. The results are verified using biometry measurements during BOREAS-intensive field campaigns. Field data relating the water content of tree components to dry biomass are used to modify the coefficients of the algorithm for crown and stem biomass. The algorithm was then applied over the entire image generating biomass maps. A set of 18 test sites within the imaged area was used to assess the accuracy of the biomass maps. The accuracy of biomass estimation is also investigated by choosing different combinations of polarization and frequency channels of the AIRSAR system. It is shown that polarimetric data from P-band and L-band channels provide similar accuracy for estimating the above-ground biomass for boreal forest types. In general, the use of P-band channels can provide better estimates of stem biomass, while L-band channels can estimate the crown biomass more accurately
    BibTeX:
    @article{Saatchi2000a,
      author = {Saatchi, S.S. and Moghaddam, M.},
      title = {Estimation of crown and stem water content and biomass of boreal forest using polarimetric SAR imagery},
      booktitle = {Geoscience and Remote Sensing, IEEE Transactions on},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {2000},
      volume = {38},
      number = {2},
      pages = {697--709}
    }
    
    Saito, Y., Saito, R., Kawahara, T.D., Nomura, A. & Takeda, S. Development and performance characteristics of laser-induced fluorescence imaging lidar for forestry applications 2000 Forest Ecology and Management
    Vol. 128(1-2), pp. 129-137 
    article  
    Abstract: A laser-induced fluorescence (LIF) imaging lidar was developed to monitor and measure the chemical activities and status of trees and forests. A unique feature of the lidar system was the usage and combination of a nano-second pulse laser and a gated image intensified CCD camera as an imaging detector. The system performance was checked using a ginkgo tree located at a distance of 60 m from the system. By operating the high sensitivity image intensifier with a short time duration of 100 ns, the LIF images of the tree were successfully obtained not only at night but also during the day. The ratio of the LIF image at 740 nm to that at 685 nm could be effective to estimate the chlorophyll concentration inside the leaves. It was shown that the system has the potential for macroscale monitoring of trees remotely and nondestructively.
    BibTeX:
    @article{saito00,
      author = {Saito, Yasunori and Saito, Ryuta and Kawahara, Takuya D. and Nomura, Akio and Takeda, Satomi},
      title = {Development and performance characteristics of laser-induced fluorescence imaging lidar for forestry applications},
      journal = {Forest Ecology and Management},
      year = {2000},
      volume = {128},
      number = {1-2},
      pages = {129--137}
    }
    
    Sandberg, D., Ottmar, R. & Cushon, G. Characterizing fuels in the 21st Century. 2001 International Journal of Wildland Fire
    Vol. 10, pp. 381-387 
    article  
    BibTeX:
    @article{sandberg01,
      author = {Sandberg, D.V. and Ottmar, R.D. and Cushon, G.H.},
      title = {Characterizing fuels in the 21st Century.},
      journal = {International Journal of Wildland Fire},
      year = {2001},
      volume = {10},
      pages = {381-387}
    }
    
    Schaaf, C.B., Gao, F., Strahler, A.H., Lucht, W., Li, X., Tsang, T., Strugnell, N.C., Zhang, X., Jin, Y., Muller, J.-P., Lewis, P., Barnsley, M., Hobson, P., Disney, M., Roberts, G., Dunderdale, M., Doll, C., d'Entremont, R.P., Hu, B., Liang, S., Privette, J.L. & Roy, D. First operational BRDF, albedo nadir reflectance products from MODIS 2002 Remote Sensing of Environment
    Vol. 83(1-2), pp. 135-148 
    article  
    Abstract: With the launch of NASA's Terra satellite and the MODerate Resolution Imaging Spectroradiometer (MODIS), operational Bidirectional Reflectance Distribution Function (BRDF) and albedo products are now being made available to the scientific community. The MODIS BRDF/Albedo algorithm makes use of a semiempirical kernel-driven bidirectional reflectance model and multidate, multispectral data to provide global 1-km gridded and tiled products of the land surface every 16 days. These products include directional hemispherical albedo (black-sky albedo), bihemispherical albedo (white-sky albedo), Nadir BRDF-Adjusted surface Reflectances (NBAR), model parameters describing the BRDF, and extensive quality assurance information. The algorithm has been consistently producing albedo and NBAR for the public since July 2000. Initial evaluations indicate a stable BRDF/Albedo Product, where, for example, the spatial and temporal progression of phenological characteristics is easily detected in the NBAR and albedo results. These early beta and provisional products auger well for the routine production of stable MODIS-derived BRDF parameters, nadir reflectances, and albedos for use by the global observation and modeling communities.
    BibTeX:
    @article{Schaaf2002,
      author = {Schaaf, Crystal B. and Gao, Feng and Strahler, Alan H. and Lucht, Wolfgang and Li, Xiaowen and Tsang, Trevor and Strugnell, Nicholas C. and Zhang, Xiaoyang and Jin, Yufang and Muller, Jan-Peter and Lewis, Philip and Barnsley, Michael and Hobson, Paul and Disney, Mathias and Roberts, Gareth and Dunderdale, Michael and Doll, Christopher and d'Entremont, Robert P. and Hu, Baoxin and Liang, Shunlin and Privette, Jeffrey L. and Roy, David},
      title = {First operational BRDF, albedo nadir reflectance products from MODIS},
      journal = {Remote Sensing of Environment},
      year = {2002},
      volume = {83},
      number = {1-2},
      pages = {135--148}
    }
    
    Schaepman, M., Kneubühler, M., Koetz, B., Schlaepfer, D., Morsdorf, F., Meier, E., Allgöwer, B. & Itten, K. Validation and calibration of ENVISAT/MERIS Level 1 and 2 products over land 2003 EARSEL - 23rd annual Symposium, Ghent.  inproceedings  
    BibTeX:
    @inproceedings{schaepman_earsel03,
      author = {Schaepman, M. and Kneubühler, M. and Koetz, B. and Schlaepfer, D. and Morsdorf, F. and Meier, E. and Allgöwer, B. and Itten, K.},
      title = {Validation and calibration of ENVISAT/MERIS Level 1 and 2 products over land},
      booktitle = {EARSEL - 23rd annual Symposium, Ghent.},
      year = {2003}
    }
    
    Schaepman, M.E., Ustin, S.L., Plaza, A.J., Painter, T.H., Verrelst, J. & Liang, S. Earth system science related imaging spectroscopy--An assessment 2009 Remote Sensing of Environment
    Vol. 113(Supplement 1)Imaging Spectroscopy Special Issue, pp. S123-S137 
    article URL 
    Abstract: The science of spectroscopy has existed for more than three centuries, and imaging spectroscopy for the Earth system for three decades. We first discuss the historical background of spectroscopy, followed by imaging spectroscopy, introducing a common definition for the latter. The relevance of imaging spectroscopy is then assessed using a comprehensive review of the cited literature. Instruments, technological advancements and (pre-)processing approaches are discussed to set the scene for application related advancements. We demonstrate these efforts using four examples that represent progress due to imaging spectroscopy, namely (i) bridging scaling gaps from molecules to ecosystems using coupled radiative transfer models (ii) assessing surface heterogeneity including clumping, (iii) physical based (inversion) modeling, and iv) assessing interaction of light with the Earth surface. Recent advances of imaging spectroscopy contributions to the Earth system sciences are discussed. We conclude by summarizing the achievements of thirty years of imaging spectroscopy and strongly recommend this community to increase its efforts to convince relevant stakeholders of the urgency to acquire the highest quality imaging spectrometer data for Earth observation from operational satellites capable of collecting consistent data for climatically-relevant periods of time.
    BibTeX:
    @article{Schaepman2009,
      author = {Schaepman, Michael E. and Ustin, Susan L. and Plaza, Antonio J. and Painter, Thomas H. and Verrelst, Jochem and Liang, Shunlin},
      title = {Earth system science related imaging spectroscopy--An assessment},
      booktitle = {Imaging Spectroscopy Special Issue},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {Supplement 1},
      pages = {S123--S137},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4W0R3GX-2/2/9a0cd67c55fc314f578851cecd8275a8}
    }
    
    Schaepman-Strub, G., Schaepman, M., Painter, T., Dangel, S. & Martonchik, J. Reflectance quantities in optical remote sensing--definitions and case studies 2006 Remote Sensing of Environment
    Vol. 103(1), pp. 27-42 
    article URL 
    Abstract: The remote sensing community puts major efforts into calibration and validation of sensors, measurements, and derived products to quantify and reduce uncertainties. Given recent advances in instrument design, radiometric calibration, atmospheric correction, algorithm development, product development, validation, and delivery, the lack of standardization of reflectance terminology and products becomes a considerable source of error. This article provides full access to the basic concept and definitions of reflectance quantities, as given by Nicodemus et al. [Nicodemus, F.E., Richmond, J.C., Hsia, J.J., Ginsberg, I.W., and Limperis, T. (1977). Geometrical Considerations and Nomenclature for Reflectance. In: National Bureau of Standards, US Department of Commerce, Washington, D.C. URL: http://physics.nist.gov/Divisions/Div844/facilities/specphoto/pdf/geoConsid.pdf.] and Martonchik et al. [Martonchik, J.V., Bruegge, C.J., and Strahler, A. (2000). A review of reflectance nomenclature used in remote sensing. Remote Sensing Reviews, 19, 9-20.]. Reflectance terms such as BRDF, HDRF, BRF, BHR, DHR, black-sky albedo, white-sky albedo, and blue-sky albedo are defined, explained, and exemplified, while separating conceptual from measurable quantities. We use selected examples from the peer-reviewed literature to demonstrate that very often the current use of reflectance terminology does not fulfill physical standards and can lead to systematic errors. Secondly, the paper highlights the importance of a proper usage of definitions through quantitative comparison of different reflectance products with special emphasis on wavelength dependent effects. Reflectance quantities acquired under hemispherical illumination conditions (i.e., all outdoor measurements) depend not only on the scattering properties of the observed surface, but as well on atmospheric conditions, the object's surroundings, and the topography, with distinct expression of these effects in different wavelengths. We exemplify differences between the hemispherical and directional illumination quantities, based on observations (i.e., MISR), and on reflectance simulations of natural surfaces (i.e., vegetation canopy and snow cover). In order to improve the current situation of frequent ambiguous usage of reflectance terms and quantities, we suggest standardizing the terminology in reflectance product descriptions and that the community carefully utilizes the proposed reflectance terminology in scientific publications.
    BibTeX:
    @article{Schaepman-Strub2006,
      author = {Schaepman-Strub, G. and Schaepman, M.E. and Painter, T.H. and Dangel, S. and Martonchik, J.V.},
      title = {Reflectance quantities in optical remote sensing--definitions and case studies},
      journal = {Remote Sensing of Environment},
      year = {2006},
      volume = {103},
      number = {1},
      pages = {27--42},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4K427VX-1/2/d8f9855bc59ae8233e2ee9b111252701}
    }
    
    Schardt, M., Ziegler, M., Wimmer, A., Wack, R. & Hyyppä, J. Assessment of Forest Parameters by Means of Laser Scanning 2002 ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria, pp. A-302 ff (8 pages)  inproceedings  
    Abstract: This paper deals with forest inventory methods based on laser scanning and satellite remote sensing. It will be demonstrated to what extent forest inventories can benefit from the synergistic use of both sensor types. The forest inventory parameters to be assessed are: tree height, timber volume, tree species, tree age, stand boundary, and basal area. The results presented are derived from the ``HIGHSCAN'' project (Assessing forest stand attributes by integrated use of high-resolution satellite imagery and laser scanner) which is coordinated by the Helsinki University of Technology and financed by the EU, DG XII. Developments have been carried out in close co-operation with forest management authorities, in particular with private forest owners. In this paper the results derived from the Austrian test sites will be presented.
    BibTeX:
    @inproceedings{schardt02,
      author = {Mathias Schardt and Michaela Ziegler and Andreas Wimmer and Roland Wack and Juha Hyyppä},
      title = {Assessment of Forest Parameters by Means of Laser Scanning},
      booktitle = {ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria},
      year = {2002},
      pages = {A-302 ff (8 pages)}
    }
    
    Schenk, T., Seo, S. & Csatho, B. ACCURACY STUDY OF AIRBORNE LASER SCANNING DATA WITH PHOTOGRAMMETRY 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 113-118 
    article  
    Abstract: This paper describes an accuracy study of airborne laser scanning data obtained by the Airborne Topographic Mapper (ATM) laser system over Ocean City, Md. The ATM is a conical scanning laser altimeter developed by NASA for precise measurement of surface elevation changes in polar ice sheets, ocean beaches and drainage systems. First, we determine the internal" accuracy of the system by comparing data from different flight missions. This is followed by a comparison of the merged laser data sets with surface elevations obtained by photogrammetry. Large-scale aerial photographs have been acquired over the test area and an aerial triangulation was performed to determine the exterior orientation parameters. The comparison consists of several experiments that were performed with the digitized photographs and the laser points. First we determine how well the laser points agree with the visible surface as defined by two overlapping images (stereopsis). This is accomplished by backprojecting the laser points to the images based on their exterior orientation parameters. The location of the laser points in the images serve as initial approximations for image matching. We use an adaptive least-squares matching procedure with a variable template size. A non-zero matching vector indicates discrepancies between laser points and photogrammetry. The purpose of the second experiment is to estimate the horizontal accuracy of laser points. One way to accomplish this is to extract linear features and to compare them. Linear features in laser point data sets can only be determined indirectly, e.g. by intersecting planar surface patches. In contrast, linear features in aerial images can be determined directly by an edge operator. We used the Canny operator to extract edges in the images and feature-based matching to find corresponding edges in the stereopair. After describing the procedure, experimental results are reported.
    BibTeX:
    @article{schenk01,
      author = {Toni Schenk and Suyoung Seo and Beata Csatho},
      title = {ACCURACY STUDY OF AIRBORNE LASER SCANNING DATA WITH PHOTOGRAMMETRY},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {113-118}
    }
    
    Schiewe, J. Ein regionen-basiertes Verfahren zur Extraktion der Geländeoberfläche aus Digitalen Oberflächen-Modellen 2001 Photogrammetrie Fernerkundung Geoinformation, pp. 81-90  article  
    BibTeX:
    @article{schiewe01,
      author = {Jochen Schiewe},
      title = {Ein regionen-basiertes Verfahren zur Extraktion der Geländeoberfläche aus Digitalen Oberflächen-Modellen},
      journal = {Photogrammetrie Fernerkundung Geoinformation},
      year = {2001},
      pages = {81-90}
    }
    
    Schlerf, M. & Atzberger, C. Inversion of a forest reflectance model to estimate structural canopy variables from hyperspectral remote sensing data 2006 Remote Sensing of Environment
    Vol. 100(3), pp. 281-294 
    article  
    Abstract: The potential of canopy reflectance modelling to retrieve simultaneously several structural variables in managed Norway spruce stands was investigated using the "Invertible Forest Reflectance Model", INFORM. INFORM is an innovative extension of the FLIM model, with crown transparency, infinite crown reflectance and understory reflectance simulated using physically based sub-models (SAILH, LIBERTY and PROSPECT). The INFORM model was inverted with hyperspectral airborne HyMap data using a neural network approach. INFORM based estimates of forest structural variables were produced using site-specific ranges of stand structural variables. A relatively simple three layer feed-forward backpropagation neural network with two input neurons, one neuron in the hidden layer and three output neurons was employed to map leaf area index (LAI), crown coverage and stem density.To identify the optimum 2-band spectral subset to be used in the inversion process, all 2-band combinations of the HyMap dataset were systematically evaluated for model inversion. Field measurements of structural variables from 39 forest stands were used to validate the maps produced from HyMap imagery. Using two HyMap wavebands at 837 nm and 1148 nm the obtained accuracy of the LAI map amounts to an rmse of 0.58 (relative rmse = 18% of mean, R2 = 0.73). With HyMap data resampled to Landsat TM spectral bands and using two "optimum" bands at 840 nm and 1650 nm, rmse was 0.66 and relative rmse 21%. In contrast to approaches based on empirical relations between spectral vegetation indices and structural variables, the main advantage of the inversion approach is that it does not require previous calibration.
    BibTeX:
    @article{schlerf06,
      author = {Schlerf, Martin and Atzberger, Clement},
      title = {Inversion of a forest reflectance model to estimate structural canopy variables from hyperspectral remote sensing data},
      journal = {Remote Sensing of Environment},
      year = {2006},
      volume = {100},
      number = {3},
      pages = {281--294}
    }
    
    Schlerf, M., Atzberger, C. & Hill, J. Remote sensing of forest biophysical variables using HyMap imaging spectrometer data 2005 Remote Sensing of Environment
    Vol. 95(2), pp. 177-194 
    article  
    Abstract: This study systematically evaluated linear predictive models between vegetation indices (VI) derived from radiometrically corrected airborne imaging spectrometer (HyMap) data and field measurements of biophysical forest stand variables (n=40). Ratio-based and soil-line-related broadband VI were calculated after HyMap reflectance had been spectrally resampled to Landsat TM channels. Hyperspectral VI involved all possible types of two-band combinations of ratio VI (RVI) and perpendicular VI (PVI) and the red edge inflection point (REIP) computed from two techniques, inverted Gaussian Model and Lagrange Interpolation. Cross-validation procedure was used to assess the prediction power of the regression models. Analyses were performed on the entire data set or on subsets stratified according to stand age. A PVI based on wavebands at 1088 nm and 1148 nm was linearly related to leaf area index (LAI) (R2=0.67, RMSE=0.69 m2 m-2 (21% of the mean); after removal of one forest stand subjected to clearing measures: R2=0.77, RMSE=0.54 m2 m-2 (17% of the mean). A PVI based on wavebands at 885 nm and 948 nm was linearly related to the crown volume (VOL) (R2=0.79, RMSE=0.52). VOL was derived from measured biophysical variables through factor analysis (varimax rotation). The study demonstrates that for hyperspectral image data, linear regression models can be applied to quantify LAI and VOL with good accuracy. For broadband multispectral data, the accuracy was generally lower. It can be stated that the hyperspectral data set contains more information relevant to the estimation of the forest stand variables LAI and VOL than multispectral data. When the pooled data set was analysed, soil-line-related VI performed better than ratio-based VI. When age classes were analysed separately, hyperspectral VI performed considerably better than broadband VI. Best hyperspectral VI in relation with LAI were typically based on wavebands related to prominent water absorption features. Such VI are related to the total amount of canopy water; as the leaf water content is considered to be relatively constant in the study area, variations of LAI are retrieved.
    BibTeX:
    @article{schlerf05,
      author = {Schlerf, Martin and Atzberger, Clement and Hill, Joachim},
      title = {Remote sensing of forest biophysical variables using HyMap imaging spectrometer data},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {95},
      number = {2},
      pages = {177--194}
    }
    
    Schnadt, K. & Katzenbeisser, R. UNIQUE AIRBORNE FIBER SCANNER TECHNIQUE FOR APPLICATION-ORIENTED LIDAR PRODUCTS 2004 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXVI - 8/W2, pp. 19-23 
    article  
    BibTeX:
    @article{schnadt04,
      author = {K. Schnadt and R. Katzenbeisser},
      title = {UNIQUE AIRBORNE FIBER SCANNER TECHNIQUE FOR APPLICATION-ORIENTED LIDAR PRODUCTS},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2004},
      volume = {XXXVI - 8/W2},
      pages = {19-23}
    }
    
    Schumacher, S., Bugmann, H. & Mladenoff, D.J. Improving the formulation of tree growth and succession in a spatially explicit landscape model 2004 Ecological Modelling
    Vol. 180(1)Modelling disturbance and succession in forest landscapes using LANDIS, pp. 175-194 
    article  
    Abstract: Long-term forest landscape dynamics are determined by a set of driving forces including large-scale natural disturbances, land-use, the physical environment, and stand-scale succession processes. Landscape models have an important role as tools for synthesizing existing information and making projections of possible future vegetation dynamics on large spatial scales. However, current landscape models cannot readily be used to study: (1) the change from weakly to strongly disturbed landscapes; (2) the impact of changing climatic parameters on landscape-scale dynamics; and (3) the effects of such changes on vegetation structure. Using European mountain forests as a case study, this paper focuses on improving the well-established LANDIS landscape model so that it can be applied to study these research questions. We integrated a simple tree succession sub-model in LANDIS, which incorporates quantitative descriptions of forest structure, and included sub-models to capture the influences of competition as well as climatic and edaphic parameters on tree population dynamics. The new model was subjected to a number of quantitative tests against measured data. It accurately predicted the altitudinal distribution of vegetation properties under managed as well as unmanaged conditions in the Dischma valley (Switzerland), and it provided realistic and accurate patterns of vegetation recovery following wind disturbance events, in spite of the very simple model formulations. To demonstrate the utility of the added detail, we applied the model in scenario mode under a range of changes in climatic and disturbance parameters, assuming a continuation of the current management regime. The simulations showed that the various driving forces have quite different effects on different species, and that their combined effect differs from one scenario to the next. Notably, there are few models that integrate forest growth and succession with disturbance dynamics in a semi-mechanistic manner. Our version of LANDIS achieves this integration based on simple concepts and methods that do not require many parameter estimates. We conclude that the new model has the potential to provide an integrated picture of the impacts of both direct and indirect effects of climate change on forest landscape dynamics.
    BibTeX:
    @article{Schumacher2004,
      author = {Schumacher, Sabine and Bugmann, Harald and Mladenoff, David J.},
      title = {Improving the formulation of tree growth and succession in a spatially explicit landscape model},
      booktitle = {Modelling disturbance and succession in forest landscapes using LANDIS},
      journal = {Ecological Modelling},
      year = {2004},
      volume = {180},
      number = {1},
      pages = {175--194}
    }
    
    Schutt, J.B., Kimes, D.S. & Newcomb, W.W. Effect of heliotropism on the bidirectional reflectance of irrigated cotton 1985 Remote Sensing of Environment
    Vol. 17(1), pp. 13-25 
    article  
    Abstract: The dynamic movement of cotton leaves in the presence of sunlight has been described using gyroscopic coordinates. These coordinates were used to calculate the position of leaf normals with respect to the sun on an individual basis. A sensitivity analysis established that the angle between a leaf normal and the sun was most affected by changes in pitch and roll. Averaging leaf normals by quadrant (as established by the direction of the compass) showed the pronounced heliotropic behavior of cotton leaves and the differential behavior of cotton leaves relative to the quadrant of the sun. These results were subsequently applied to the estimation of the phase angle [gamma] between the canopy normals and sun from cross sections of bidirectional reflectance curves obtained for a band spanning 0.57-0.69 [mu]m. From the cross section determined by the principal plane at 6:07 MST, which turned out to be concave and nearly symmetrical, the canopy averaged value for [gamma] was estimated to be about 90?, while the calculated value from the leaf angle data was 85?. At 12:08 MST the same cross section was convex and asymmetrical with respect to rotation about the nadir direction, indicating distinguishable forescattered and backscattered components. For the forescattered component the estimated value for [gamma] was 15?, and the calculated value 20?. For the backscattered component the estimated value for [gamma] was 12?, and the calculated value 21?. These results suggested that bidirectional reflectance information analyzed sequentially using a visible band for which the optical transmission is nearly zero can be used to monitor leaf movement and hence moisture availability.
    BibTeX:
    @article{Schutt1985,
      author = {Schutt, John B. and Kimes, Daniel S. and Newcomb, Wayne W.},
      title = {Effect of heliotropism on the bidirectional reflectance of irrigated cotton},
      journal = {Remote Sensing of Environment},
      year = {1985},
      volume = {17},
      number = {1},
      pages = {13--25}
    }
    
    Sithole, G. & Vosselman, G. Bridge detection in airborne laser scanner data 2006 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 61, pp. 33-46 
    article  
    Abstract: In a landscape bridges are ambiguous features in that they are extensions of the bare earth but they are also man made.

    Therefore, in a Digital Terrain Model (DTM) generation, depending on application it is necessary to keep or remove bridges. For

    this reason they have to be detected explicitly. A geometric bridge detection algorithm is proposed that is based on the idea that

    features can be detected in a landscape based on cross-sections (profiles) in a landscape. The topological information contained in

    the cross-sections are used to identify seed bridge points. The seed bridge points are then used to detect individual bridges. The

    bridge detection algorithm is novel in that the algorithm is blind to the shape of a bridge and is adaptable to different bridge

    designs. Therefore, bridges need not have parallel edges or uniform width. Furthermore, bridges can curve, split into parts, and

    contain holes. The bridge detection algorithm has been tested on various data sets and found to work very well in detecting bridges.

    BibTeX:
    @article{sithole06,
      author = {George Sithole and George Vosselman},
      title = {Bridge detection in airborne laser scanner data},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {2006},
      volume = {61},
      pages = {33-46}
    }
    
    Sithole, G. & Vosselman, G. Experimental comparison of filter algorithms for bare-Earth extraction from airborne laser scanning point cloud 2004 ISPRS Journal of Photogrammetry & Remote Sensing
    Vol. 59, pp. 85-101 
    article  
    Abstract: Over the past years, several filters have been developed to extract bare-Earth points from point clouds. ISPRS Working Group III/3 conducted a test to determine the performance of these filters and the influence of point density thereon, and to identify directions for future research. Twelve selected datasets have been processed by eight participants. In this paper, the test results are presented. The paper describes the characteristics of the provided datasets and the used filter approaches. The filter performance is analysed both qualitatively and quantitatively. All filters perform well in smooth rural landscapes, but all produce errors in complex urban areas and rough terrain with vegetation. In general, filters that estimate local surfaces are found to perform best. The influence of point density could not well be determined in this experiment. Future research should be directed towards the usage of additional data sources, segment-based classification, and self-diagnosis of filter algorithms.
    BibTeX:
    @article{sithole04,
      author = {George Sithole and George Vosselman},
      title = {Experimental comparison of filter algorithms for bare-Earth extraction from airborne laser scanning point cloud},
      journal = {ISPRS Journal of Photogrammetry & Remote Sensing},
      year = {2004},
      volume = {59},
      pages = {85-101}
    }
    
    Skriver, H., Svendsen, M. & Thomsen, A. Multitemporal C- and L-band polarimetric signatures of crops 1999 Geoscience and Remote Sensing, IEEE Transactions on
    Vol. 37(5)Geoscience and Remote Sensing, IEEE Transactions on, pp. 2413-2429 
    article  
    Abstract: Polarimetric synthetic aperture radar (SAR) data of agricultural fields have been acquired by the Danish L- and C-band polarimetric SAR (EMISAR) in March, May, June, and July of 1995, covering the agricultural test site at the Research Centre Foulum located in Central Jutland, Denmark. Polarimetric signatures for a number of agricultural crops, including both spring and winter crops, have been analyzed, both with respect to incidence angle variations, between-field differences, and multitemporal variations for the individual crops. The variation with incidence angle was most pronounced for the early acquisitions (March and May) where the backscatter was dominated by surface scattering. In later acquisitions (June and July), the variation was relatively small except for a few cases. Also, the largest between-field variation was observed for the early acquisitions, probably due to the sensitivity of the polarimetric parameters to differences in plowing and planting direction, soil texture, tillage practice, time of planting, etc. The analysis of the multitemporal signatures revealed significant information about the scattering mechanisms. Especially, the correlation coefficient between HH and VV showed a large difference between spring and winter crops in the beginning of the growing season, because of the dominance of surface scattering for spring crops and volume scattering for winter crops
    BibTeX:
    @article{Skriver1999,
      author = {Skriver, H. and Svendsen, M.T. and Thomsen, A.G.},
      title = {Multitemporal C- and L-band polarimetric signatures of crops},
      booktitle = {Geoscience and Remote Sensing, IEEE Transactions on},
      journal = {Geoscience and Remote Sensing, IEEE Transactions on},
      year = {1999},
      volume = {37},
      number = {5},
      pages = {2413--2429}
    }
    
    Slik, J.W.F. & Van Balen, S. Bird community changes in response to single and repeated fires in a lowland tropical rainforest of eastern Borneo. 2006 Biodiversity and Conservation
    Vol. 15, pp. 4425-4451 
    article  
    BibTeX:
    @article{Slik2006,
      author = {Slik, J. W. F. and Van Balen, S.},
      title = {Bird community changes in response to single and repeated fires in a lowland tropical rainforest of eastern Borneo.},
      journal = {Biodiversity and Conservation},
      year = {2006},
      volume = {15},
      pages = {4425-4451}
    }
    
    Smith, B., Prentice, I. & Sykes, M. Representation of vegetation dynamics in modelling of terrestrial ecosystems: comparing two contrasting approaches within European climate space 2001 Global Ecology and Biogeography
    Vol. 10, pp. 621-637 
    article  
    BibTeX:
    @article{smith01,
      author = {Smith, B. and Prentice, I.C. and Sykes, M.T.},
      title = {Representation of vegetation dynamics in modelling of terrestrial ecosystems: comparing two contrasting approaches within European climate space},
      journal = {Global Ecology and Biogeography},
      year = {2001},
      volume = {10},
      pages = {621-637}
    }
    
    Smolander, S. & Stenberg, P. Simple parameterizations of the radiation budget of uniform broadleaved and coniferous canopies 2005 Remote Sensing of Environment
    Vol. 94(3), pp. 355-363 
    article  
    Abstract: Simulations of the different components of the spectral radiation budget of structurally simple leaf and shoot canopies with varying canopy leaf area index (LAI) were performed. The aims were (1) to test a proposed parameterization of the budget using two spectrally invariant canopy structural parameters (p and pt) governing canopy absorption and transmittance, respectively, and (2) to incorporate the effect of within-shoot scattering in the parameterization for shoot canopies. Results showed that canopy spectral absorption and scattering were well described by a single parameter, the canopy p value or [`]recollision probability', which was closely related to LAI. The relationship between p and LAI was however different in leaf and shoot canopy: e.g., at the same LAI the recollision probability was larger in the shoot canopy. It was shown that the p value of the shoot canopy could be decomposed into the p value of an individual shoot (psh) and the p value of the leaf canopy with the same effective LAI (LAIe). The canopy p value allows calculation of canopy absorption and scattering at any given wavelength from the leaf (or needle) scattering coefficient at the same wavelength. To calculate canopy reflectance, separation of the downward and upward scattered parts is needed in addition. The proposed parameter pt worked rather well in the leaf canopy at moderate values of LAI, but not in the coniferous shoot canopy nor at high values of LAI. However, the simulated fraction of upward scattered radiation increased in a straightforward manner with LAI, and was not particularly sensitive to the leaf (or needle) scattering coefficient. Judged by this [`]smooth' behavior, the existence of another kind of simple parameterization for this separation remains an interesting possibility.
    BibTeX:
    @article{Smolander2005,
      author = {Smolander, Sampo and Stenberg, Pauline},
      title = {Simple parameterizations of the radiation budget of uniform broadleaved and coniferous canopies},
      journal = {Remote Sensing of Environment},
      year = {2005},
      volume = {94},
      number = {3},
      pages = {355--363}
    }
    
    Smolander, S. & Stenberg, P. A method to account for shoot scale clumping in coniferous canopy reflectance models 2003 Remote Sensing of Environment
    Vol. 88(4), pp. 363-373 
    article  
    Abstract: The three-dimensional structure of a coniferous shoot gives rise to multiple scattering of light between the needles of the shoot, causing the shoot spectral reflectance to differ from that of a flat leaf. Forest reflectance models based on the radiative transfer equation handle shoot level clumping by correcting the radiation attenuation coefficient with a clumping index. The clumping index causes a reduction in the interception of radiation by the canopy at a fixed leaf area index (LAI). In this study, we show how within-shoot multiple scattering is related to shoot scale clumping and derive a similar, but wavelength dependent, correction to the scattering coefficient. The results provide a method for integrating shoot structure into current radiative transfer equation based forest reflectance models. The method was applied to explore the effect of shoot scale clumping on canopy spectral reflectance using simple model canopies with a homogeneous higher level structure. The clumping of needles into shoots caused a wavelength dependent reduction in canopy reflectance, as compared to that of a leaf canopy with similar interception. This is proposed to be one reason why coniferous and broad-leaved canopies occupy different regions in the spectral space and exhibit different dependency of spectral vegetation indices on LAI.
    BibTeX:
    @article{Smolander2003,
      author = {Smolander, Sampo and Stenberg, Pauline},
      title = {A method to account for shoot scale clumping in coniferous canopy reflectance models},
      journal = {Remote Sensing of Environment},
      year = {2003},
      volume = {88},
      number = {4},
      pages = {363--373}
    }
    
    Solberg, S., Brunner, A., Hanssen, K.H., Lange, H., Næsset, E., Rautiainen, M. & Stenberg, P. Mapping LAI in a Norway spruce forest using airborne laser scanning 2009 Remote Sensing of Environment
    Vol. In Press, Corrected Proof, pp. -  
    article DOI  
    Abstract: In this study we demonstrate how airborne laser scanning (ALS) can be applied to map effective leaf area index (LAIe) in a spruce forest, after being calibrated with ground based measurements. In 2003 and 2005, ALS data and field estimates of LAIe were acquired in a Norway spruce forest in SE Norway. We used LI-COR's LAI-2000? Plant canopy analyzer (#LAI-2000#) and hemispherical images (#HI#) for field based estimates of LAIe. ALS penetration rate calculated from first echoes and from first and last echoes was strongly related to field estimates of LAIe. We fitted regression models of LAIe against the log-transformed inverse of the ALS penetration rate, and in accordance with the Beer-Lambert law this produced a linear, no-intercept relationship. This was particularly the case for the LAI-2000, having R2 values > 0.9. The strongest relationship was obtained by selecting ALS data from within a circle around each plot with a radius of 0.75 times the tree height. We found a slight difference in the relationship for the two years, which can be attributed to the differences in the ALS acquisition settings. The relationship was valid across four age classes of trees representing different stages of stand development, except in one case with newly regenerated stands which most likely was an artifact. Using LAIe based on HI data produced weaker relationships with the ALS data. This was the case even when we simulated LAI-2000 measurements based on the HI data.
    BibTeX:
    @article{Solberg2009,
      author = {Svein Solberg and Andreas Brunner and Kjersti Holt Hanssen and Holger Lange and Erik Næsset and Miina Rautiainen and Pauline Stenberg},
      title = {Mapping LAI in a Norway spruce forest using airborne laser scanning},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {In Press, Corrected Proof},
      pages = { - },
      doi = {DOI: 10.1016/j.rse.2009.06.010}
    }
    
    Solberg, S., Næsset, E., Hanssen, K.H. & Christiansen, E. Mapping defoliation during a severe insect attack on Scots pine using airborne laser scanning 2006 Remote Sensing of Environment
    Vol. 102(3-4), pp. 364 - 376 
    article DOI  
    Abstract: In a balanced experiment based on 20 field plots located in a 21 km2 Scots pine forest in southeast Norway covering age classes from newly regenerated to old forest, leaf area index (LAI) was determined in field by a LAI-2000 instrument and hemispheric photography. Based on a formalized framework, i.e., the so-called Beer-Lambert law, gap fraction derived from small-footprint airborne laser scanner data was regressed against field-measured LAI. LAI was strongly (R2 = 0.87-0.93), positively, and linearly related to the log-transformed inverse of the gap fraction derived from the laser scanner data. This was as expected according to the Beer-Lambert law, as was the absence of an intercept, producing a directly proportionality of the two variables. We estimated an extinction coefficient for the first return echoes to be 0.7, fortunately fairly stable across age classes, and this is likely to be a parameter specific for the applied laser scanner system under the given flight and system settings, such as flying altitude and laser pulse repetition frequency. It was demonstrated that airborne laser was able to detect defoliation in terms of estimated changes in LAI, by three repeated laser data acquisitions over the area where severe insect attacks were going on in between the acquisitions.
    BibTeX:
    @article{Solberg2006364,
      author = {Svein Solberg and Erik Næsset and Kjersti Holt Hanssen and Erik Christiansen},
      title = {Mapping defoliation during a severe insect attack on Scots pine using airborne laser scanning},
      journal = {Remote Sensing of Environment},
      year = {2006},
      volume = {102},
      number = {3-4},
      pages = {364 - 376},
      doi = {DOI: 10.1016/j.rse.2006.03.001}
    }
    
    Solenthaler, B., Schäfli, J. & Pajarola, R. A Unified Particle Model for Fluid-Solid Interactions 2007 Computer Animation and Virtual Worlds
    Vol. 18(1), pp. 69-82 
    article  
    BibTeX:
    @article{solenthaler07,
      author = {B. Solenthaler and J. Schäfli and R. Pajarola},
      title = {A Unified Particle Model for Fluid-Solid Interactions},
      journal = {Computer Animation and Virtual Worlds},
      year = {2007},
      volume = {18},
      number = {1},
      pages = {69-82}
    }
    
    Sommerfeld, R., Lundquist, J. & Smith, J. Characterizing the canopy gap structure of a disturbed forest using the Fourier transform 2000 Forest Ecology and Managment
    Vol. 128, pp. 101-108 
    article  
    Abstract: Diseases and other small-scale disturbances alter spatial patterns of heterogeneity in forests by killing trees. Canopy gaps caused by tree death are a common feature of forests. Because gaps are caused by different disturbances acting at different times and places, operationally determining the locations of gap edges is often difficult. In this study, digital image analysis using aerial photos was used to formulate an operational definition of gaps and to compare spatial attributes of canopy gap structure in previously unharvested and harvested stands of ponderosa pine forests in the Black Hills of South Dakota. Fourier transforms of monochrome images of the study areas were edited to sequentially remove higher frequency spatial data implementing a type of moving window analysis where window sizes varied over a range of 1????1300 m2. Boolean thresholds were chosen such that the mean gap size approximated the window size for each original image. Plots of mean gap size, mean fractal dimension, double log fractal dimension, and gap size density all versus window size showed distinct differences between treated and untreated plots.
    BibTeX:
    @article{sommerfeld00,
      author = {R.A. Sommerfeld and J.E. Lundquist and J. Smith},
      title = {Characterizing the canopy gap structure of a disturbed forest using the Fourier transform},
      journal = {Forest Ecology and Managment},
      year = {2000},
      volume = {128},
      pages = {101-108}
    }
    
    Spath, H. Cluster Dissection and Analysis: Theory, FORTRAN Programs, Examples 1985   book  
    BibTeX:
    @book{spath,
      author = {H. Spath},
      title = {Cluster Dissection and Analysis: Theory, FORTRAN Programs, Examples},
      publisher = {Halsted Press,New York, 226 pp.},
      year = {1985}
    }
    
    St-Onge, B.A. & Achaichia, N. MEASURING FOREST CANOPY HEIGHT USING A COMBINATION OF LIDAR AND AERIAL PHOTOGRAPHY DATA 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 131-137 
    article  
    Abstract: It has been demonstrated that the height of forest canopies can be measured with a good accuracy using small footprint lidars. This is essentially accomplished by subtracting the last return altitude (ground) from the corresponding first return altitude (canopy surface). The technique is considered superior to photogrammetric methods mainly because the ground level, which is difficult to see on aerial photos of densely forested areas, can be well identified using small footprint lidars. However, lidar cannot be used to characterized past forest states, while these can be assessed, and photogrammetically measured, in the wealth of historical aerial photographs most developed countries possess. Our goal is to replace the first return lidar data by altitude models derived from aerial photos in order to map forest canopy height changes of the past decades. This paper presents the first methodological steps which consist in comparing canopy heights obtained from lidar data only to a combination of lidar and photogrammetry data. The lidar data was acquired over an area of the boreal forest in Quebec, Canada, in 1998, using Optech s ALTM1020 flying at an altitude of 700 m. Two stereo-pairs of aerial black and white photographs were used: 1) a pair of 1:15,000 photos taken in 1994, and 2) a pair of 1:40,000 photos taken in 1998. A lidar canopy height model (CHM) was created by subtracting ground altitudes from canopy altitudes. Aerial photo altitude models were derived using the image correlation methods of Virtuozo 3.2 software. The ground level altitudinal fit between the aerial photo altitude model and the lidar data was checked on rock outcrops. A photo CHM was created by subtracting the lidar ground altitude model from the aerial photo altitude model. The photo CHM and the lidar CHM show a good degree of correlation.
    BibTeX:
    @article{stonge01,
      author = {Benoit A. St-Onge and Nora Achaichia},
      title = {MEASURING FOREST CANOPY HEIGHT USING A COMBINATION OF LIDAR AND AERIAL PHOTOGRAPHY DATA},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {131-137}
    }
    
    St-Onge, B., Hu, Y. & Vega, C. Mapping the height and above-ground biomass of a mixed forest using lidar and stereo Ikonos images 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1277-1294 
    article  
    Abstract: Our objective was to assess the accuracy of the forest height and biomass estimates derived from an Ikonos stereo pair and a lidar digital terrain model (DTM). After the Ikonos scenes were registered to the DTM with submetric accuracy, tree heights were measured individually by subtracting the photogrammetric elevation of the treetop from the lidar ground-level elevation of the tree base. The low residual error (1.66??m) of the measurements confirmed the joint geometric accuracy of the combined models. Matched images of the stereo pair were then used to create a digital surface model. The latter was transformed to a canopy height model (CHM) by subtracting the lidar DTM. Plotwise height percentiles were extracted from the Ikonos-lidar CHM and used to predict the average dominant height and above-ground biomass. The coefficient of determination reached 0.91 and 0.79 for average height and biomass, respectively. In both cases, the accuracy of the Ikonos-lidar CHM predictions was slightly lower than that of the all-lidar reference CHM. Although the CHM heights did not saturate at moderate biomass levels, as do multispectral or radar images, values above 300??Mg??ha-1 could not be predicted accurately by the Ikonos-lidar or by the all-lidar CHM.
    BibTeX:
    @article{St-Onge2008,
      author = {St-Onge, B. and Hu, Y. and Vega, C.},
      title = {Mapping the height and above-ground biomass of a mixed forest using lidar and stereo Ikonos images},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1277--1294}
    }
    
    St-Onge, B., Hu, Y. & Véga, Cé. Reconstruct Forest Canopy Height Using Stereo-Ikonos Panchromatic Images and a LIDAR DTM 2006 International Workshop 3D Remote Sensing in Forestry
    Vol. , Vienna, Feb. 14-15, 2006, pp. 97-102 
    article  
    Abstract: Classifying vegetation points from 3D airborne laser scanner (ALS) point clouds is a challenge and

    focus of current research. In particular, low vegetation points are very difficult to identify. The basic

    problem is that so far the majority of ALS systems have provided only the 3D coordinates of scattering

    objects and most of the criteria used in classifying points had to rely on simple geometric

    characteristics of a point relative to its neighbourhood. Methods for ALS data processing could be

    much improved if ALS systems measure, in addition to the range, further physical observables which

    can be used for vegetation classification. New ALS systems, which record the full echo-waveform,

    may provide crucial information for the classification of vegetation points. In this paper we show that

    the additional features derived from the full-waveform data ? the amplitude, the pulse width and the

    number of pulses - can be used to discriminate between vegetation and non-vegetation points without

    using geometry information. Thus, a truly three dimensional representations of the classified ALS

    points can be obtained. The classification algorithm is based on a decision tree technique. The

    applicability of this method is demonstrated on data collected by the RIEGL LMS-Q560 sensor over

    the Schönbrunn area of Vienna. The performance of the classification algorithm was checked

    manually on 500 points randomly distributed and on several test zones selected over the study area.

    We found an overall accuracy of 88.6% with a kappa coefficient of 0.8.

    BibTeX:
    @article{stonge06,
      author = {Benoit St-Onge and Yong Hu and Cédric Véga},
      title = {Reconstruct Forest Canopy Height Using Stereo-Ikonos Panchromatic Images and a LIDAR DTM},
      journal = {International Workshop 3D Remote Sensing in Forestry},
      year = {2006},
      volume = {, Vienna, Feb. 14-15, 2006},
      pages = {97-102}
    }
    
    Stephens, S.L. Evaluation of the effects of silvicultural and fuels treatments on potential fire behaviour in Sierra Nevada mixed-conifer forests 1998 Forest Ecology and Management
    Vol. 105(1-3), pp. 21-35 
    article  
    Abstract: Fire suppression has increased fuel loads and fuel continuity in mixed-conifer ecosystems, resulting in forest structures that are vulnerable to catastrophic fire. This paper models fire behaviour in a mixed-conifer forest and investigates how silvicultural and fuels treatments affect potential fire behaviour. The computer program FARSITE was used to spatially and temporally model fire growth and behaviour. Fire modelling was performed in the North Crane Creek watershed of Yosemite National Park. Treatments were simulated by adjusting fuel (total load, load-by-size class, depth), height-to-live crown base, tree height, and crown density parameters. Treatments modeled included prescribed burn, pile and burn, cut and scatter, thinning and biomass, thinning and biomass followed by prescribed burn, and salvage or group selection harvest with and without slash and landscape-level fuel treatment. The prescribed burn, thinning and biomassing followed by prescribed burn, and salvage or group selection with slash and landscape fuel treatments resulted in the lowest average fireline intensities, heat per unit area, rate of spread, area burned, and scorch heights. Cut and scatter, salvage or group selection treatments that do not treat slash fuels resulted in fire behaviour that is more extreme than the untreated forest. Restoration of mixed-conifer ecosystems must include an examination of how proposed treatments affect fuel structures. Combinations of prescribed fire and/or mechanical treatments can be used to reduce wildfire hazard.
    BibTeX:
    @article{stephens98,
      author = {Stephens, Scott Lewis},
      title = {Evaluation of the effects of silvicultural and fuels treatments on potential fire behaviour in Sierra Nevada mixed-conifer forests},
      journal = {Forest Ecology and Management},
      year = {1998},
      volume = {105},
      number = {1-3},
      pages = {21--35}
    }
    
    Straatsma, M.W., Warmink, J.J. & Middelkoop, H. Two novel methods for field measurements of hydrodynamic density of floodplain vegetation using terrestrial laser scanning and digital parallel photography 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1595-1617 
    article  
    Abstract: Hydrodynamic vegetation density, the sum of the projected plant area per unit volume, is an important parameter for floodplain flow models. This paper compares two novel techniques to quantify this parameter in the field: terrestrial laser scanning (TLS) and digital parallel photography (PP). Separate field reference data were collected for the two methods, which consisted of (1) a stem map of 650 trees, aggregated into 23 plots in a single forest patch, (2) 17 manually measured forest plots in two floodplains. PP consists of a series of digital photographic images of vegetation against a contrasting background. The centre columns of all images were merged into a single composite parallel image. This mosaic was thresholded to determine the fractional coverage of the vegetation, which is converted to vegetation density using the optical point quadrat method. A sensitivity analysis proved that PP is insensitive to small errors on the selected number of centre columns, photograph spacing should not exceed 20??cm, photograph resolution is important and the plot depth should be measured accurately. TLS was carried out using a Leica HDS3000 time-of-flight laser scanner. Data processing of TLS data consisted of slicing the points around breast height. In a polar grid the vegetation density was predicted using the optical point quadrat method, corrected for missing points. Both methods were compared to the field reference data. PP (EF??=??0.99; bias??=??8.4??10-5??m-1) showed a higher modelling efficiency than the TLS method (EF??=??0.63; bias??=??0.015??m-1). An advantage of the TLS method is the ability to provide a detailed 2-dimensional or even 3-dimensional distribution of vegetation density. PP is cheaper, faster, and data processing is limited. We conclude that TLS and PP are two complementary techniques that show high accuracies for field measurements of vegetation density.
    BibTeX:
    @article{Straatsma2008,
      author = {Straatsma, M. W. and Warmink, J. J. and Middelkoop, H.},
      title = {Two novel methods for field measurements of hydrodynamic density of floodplain vegetation using terrestrial laser scanning and digital parallel photography},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1595--1617}
    }
    
    Sun, G. & Ranson, K. Modeling lidar returns from forest canopies 2000 IEEE Transactions on Geoscience and Remote Sensing
    Vol. 38(6), pp. 2617-2626 
    article  
    Abstract: Remote sensing techniques that utilize light detection and ranging (lidar) provide unique data on canopy geometry and subcanopy topography. This type of information will lead to improved understanding of important structures and processes of Earth's vegetation cover. To understand the relation between canopy structure and the lidar return waveform, a three-dimensional (3D) model was developed and implemented. Detailed field measurements and forest growth model simulations of forest stands were used to parameterize this vegetation lidar waveform model. In the model, the crown shape of trees determines the vertical distribution of plant material and the corresponding lidar waveforms. Preliminary comparisons of averaged waveforms from an airborne lidar and model simulations shows that the shape of the measured waveform was more similar to simulations using an ellipsoid or hemi-ellipsoid shape. The observed slower decay of the airborne lidar waveforms than the simulated waveforms may indicate the existence of the understories and may also suggest that higher order scattering from the upper canopy may contribute to the lidar signals. The lidar waveforms from stands simulated from a forest growth model show the dependence of the waveform on stand structure.
    BibTeX:
    @article{sun00,
      author = {G. Sun and K.J. Ranson},
      title = {Modeling lidar returns from forest canopies},
      journal = {IEEE Transactions on Geoscience and Remote Sensing},
      year = {2000},
      volume = {38},
      number = {6},
      pages = {2617-2626}
    }
    
    Sun, G., Ranson, K., Kimes, D., Blair, J. & Kovacs, K. Forest vertical structure from GLAS: An evaluation using LVIS and SRTM data 2008 Remote Sensing of Environment
    Vol. 112(1), pp. 107-117 
    article  
    Abstract: The Geoscience Laser Altimeter System (GLAS) on the Ice, Cloud and land Elevation Satellite (ICESat) is the first spaceborne lidar instrument for continuous global observation of the Earth. GLAS records a vertical profile of the returned laser energy from its footprint. To help understand the application of the data for forest spatial structure studies in our regional projects, an evaluation of the GLAS data was conducted using NASA's Laser Vegetation Imaging Sensor (LVIS) data in an area near NASA's Goddard Space Flight Center in Greenbelt, Maryland, USA. The tree height indices from airborne large-footprint lidars such as LVIS have been successfully used for estimation of forest structural parameters in many previous studies and served as truth in this study. The location accuracy of the GLAS footprints was evaluated by matching the elevation profile from GLAS with the Shuttle Radar Topography Mission (SRTM) DEM. The results confirmed the location accuracy of the GLAS geolocation, and showed a high correlation between the height of the scattering phase center from SRTM and the top tree height from GLAS data. The comparisons between LVIS and GLAS data showed that the GLAS waveform is similar to the aggregation of the LVIS waveforms within the GLAS footprint, and the tree height indices derived from the GLAS and LVIS waveforms were highly correlated. The best correlations were found between the 75% waveform energy quartiles of LVIS and GLAS (r2?=?0.82 for October 2003 GLAS data, and r2?=?0.65 for June 2005 GLAS data). The correlations between the 50% waveform energy quartiles of LVIS and GLAS were also high (0.77 and 0.66 respectively). The comparisons of the top tree height and total length of waveform of the GLAS data acquired in fall of 2003 and early summer of 2005 showed a several meter bias. Because the GLAS footprints from these two orbits did not exactly overlap, several other factors may have caused this observed difference, including difference of forest structures, seasonal difference of canopy structures and errors in identifying the ground peak of waveforms.
    BibTeX:
    @article{Sun2008,
      author = {Sun, G. and Ranson, K.J. and Kimes, D.S. and Blair, J.B. and Kovacs, K.},
      title = {Forest vertical structure from GLAS: An evaluation using LVIS and SRTM data},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {1},
      pages = {107--117}
    }
    
    Séro-Guillaume, O. & Margerit, J. Modeling forest fires. Part I: a complete set of equations derived by extended irreversible thermodynamics 2002 International Journal of Heat and Mass Transfer
    Vol. 45, pp. 1705-1722 
    article  
    BibTeX:
    @article{sero02a,
      author = {O. Séro-Guillaume and J. Margerit},
      title = {Modeling forest fires. Part I: a complete set of equations derived by extended irreversible thermodynamics},
      journal = {International Journal of Heat and Mass Transfer},
      year = {2002},
      volume = {45},
      pages = {1705-1722}
    }
    
    Tan, S. & Narayanan, R.M. Design and performance of a multiwavelength airborne polarimetric lidar for vegetation remote sensing 2004 Applied Optics
    Vol. 43(11), pp. 2360-2368 
    article  
    BibTeX:
    @article{tan04,
      author = {Songxin Tan and Ram M. Narayanan},
      title = {Design and performance of a multiwavelength airborne polarimetric lidar for vegetation remote sensing},
      journal = {Applied Optics},
      year = {2004},
      volume = {43},
      number = {11},
      pages = {2360-2368}
    }
    
    Tanaka, T., Park, H. & Hattoria, S. Measurement of forest canopy structure by a laser plane range-finding method Improvement of radiative resolution and examples of its application 2004 Agricultural and Forest Meteorology
    Vol. 125, pp. 129-142 
    article  
    Abstract: In studies of flux in forests, the measurement and description of forest canopy characteristics are important but difficult tasks. In 1998, we assessed a laser plane range-finding method as a new, non-destructive way of measuring the three-dimensional (3-D) structure of forest canopies. Our ultimate goal is to develop the method and the instrument in such a way that we can accurately measure the 3-D architecture of forest canopies and automatically distinguish foliage and stems. In the current study we improved the system concerning the radiative resolution. This improvement was conducted by introducing a highly sensitive digital charge-coupled device (CCD) camera whose exposure time could be controlled by a personal computer and a proposed algorithm of plural exposure time. We expect the principle of using two wavelengths of laser light to be valid for distinguishing foliage from stems. Distinguishing each element of the canopy was conducted successfully by the regional segmentation method. With this system, we could acquire a hemispherical range-finding image in which each pixel had its own range-finding information. As an example of the application of this system, we proposed a new method to calibrate Leaf Area Index (LAI) value using the hemispherical range-finding image as follows: (1) normalizing the canopy into a horizontal unit thickness (1 m), (2) compensating radiative intensity for normalized canopy by using Beer?s Equations, (3) calculating LAI of the normalized canopy, and (4) reconstructing ?Real canopy? and estimating ?Real LAI? by multiplying by the canopy thickness. Practical examples executed in a real forest have proved that this new method is efficient.
    BibTeX:
    @article{tanaka04,
      author = {Takafumi Tanaka and Hotaek Park and Shigeaki Hattoria},
      title = {Measurement of forest canopy structure by a laser plane range-finding method Improvement of radiative resolution and examples of its application},
      journal = {Agricultural and Forest Meteorology},
      year = {2004},
      volume = {125},
      pages = {129-142}
    }
    
    Tian, Y., Wang, Y., Zhang, Y., Knyazikhin, Y., Bogaert, J. & Myneni, R.B. Radiative transfer based scaling of LAI retrievals from reflectance data of different resolutions 2003 Remote Sensing of Environment
    Vol. 84(1), pp. 143-159 
    article  
    Abstract: The problem of how the scale, or spatial resolution, of reflectance data impacts retrievals of vegetation leaf area index (LAI) is addressed in this article. We define the goal of scaling as the process by which it is established that LAI values derived from coarse resolution sensor data equal the arithmetic average of values derived independently from fine resolution sensor data. The increasing probability of land cover mixtures with decreasing resolution is defined as heterogeneity, which is a key concept in scaling studies. The effect of pixel heterogeneity on spectral reflectances and LAI retrievals is investigated with 1-km Advanced Very High Resolution Radiometer (AVHRR) data aggregated to different coarse spatial resolutions. It is shown that LAI retrieval errors at coarse resolution are inversely related to the proportion of the dominant land cover in such pixel. Further, large errors in LAI retrievals are incurred when forests are minority biomes in non-forest pixels compared to when forest biomes are mixed with one another, and vice versa. A physically based scaling with explicit spatial resolution-dependent radiative transfer formulation is developed. The successful application of this theory to scaling LAI retrievals from AVHRR data of different resolutions is demonstrated. These principles underlie our approach to the production and validation of LAI product from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multi-angle Imaging Spectroradiometer (MISR) aboard the TERRA platform.
    BibTeX:
    @article{tian03,
      author = {Tian, Yuhong and Wang, Yujie and Zhang, Yu and Knyazikhin, Yuri and Bogaert, Jan and Myneni, Ranga B.},
      title = {Radiative transfer based scaling of LAI retrievals from reflectance data of different resolutions},
      journal = {Remote Sensing of Environment},
      year = {2003},
      volume = {84},
      number = {1},
      pages = {143--159}
    }
    
    Todd, K.W., Csillag, F. & Atkinson, P.M. Three-dimensional mapping of light transmittance and foliage distribution using lidar 2003 Canadian Journal of Remote Sensing
    Vol. 29(5), pp. 544-555 
    article  
    Abstract: The horizontal and vertical distributions of light transmittance were evaluated as a function of foliage distribution using lidar (light detection and ranging) observations for a sugar maple (Acer saccharum) stand in the Turkey Lakes Watershed. Along the vertical profile of vegetation, horizontal slices of probability of light transmittance were derived from an Optech ALTM 1225 instrument?s return pulses (two discrete, 15-cm diameter returns) using indicator kriging. These predictions were compared with (i) below canopy (1-cm spatial resolution) transect measurements of the fraction of photosynthetically active radiation (FPAR) and (ii) measurements of tree height. A first-order trend was initally removed from the lidar returns. The vertical distribution of vegetation height was then sliced into nine percentiles and indicator variograms were fitted to them. Variogram parameters were found to vary as a function of foliage height above ground. In this paper, we show that the relationship between ground measurements of FPAR and kriged estimates of vegetation cover becomes stronger and tighter at coarser spatial resolutions. Three-dimensional maps of foliage distribution were computed as stacks of the percentile probability surfaces. These probability surfaces showed correspondence with individual treebased observations and provided a much more detailed characterization of quasi-continuous foliage distribution. These results suggest that discrete-return lidar provides a promising technology to capture variations of foliage characteristics in forests to support the development of functional linkages between biophysical and ecologicalstudies.
    BibTeX:
    @article{todd03,
      author = {Kenton W. Todd and Ferenc Csillag and Peter M. Atkinson},
      title = {Three-dimensional mapping of light transmittance and foliage distribution using lidar},
      journal = {Canadian Journal of Remote Sensing},
      year = {2003},
      volume = {29},
      number = {5},
      pages = {544-555}
    }
    
    Trabaud, L. & Lepart, J. Changes in the floristic composition of a Quercus coccifera L. garrigue in relation to different fire regimes. 1981 Vegetatio
    Vol. 46, pp. 105-116 
    article  
    BibTeX:
    @article{Trabaud1981,
      author = {Trabaud, L. and Lepart, J.},
      title = {Changes in the floristic composition of a Quercus coccifera L. garrigue in relation to different fire regimes.},
      journal = {Vegetatio},
      year = {1981},
      volume = {46},
      pages = {105-116}
    }
    
    Turner, D.P., Cohen, W.B., Kennedy, R.E., Fassnacht, K.S. & Briggs, J.M. Relationships between Leaf Area Index and Landsat TM Spectral Vegetation Indices across Three Temperate Zone Sites 1999 Remote Sensing of Environment
    Vol. 70(1), pp. 52-68 
    article  
    Abstract: Mapping and monitoring of leaf area index (LAI) is important for spatially distributed modeling of vegetation productivity, evapotranspiration, and surface energy balance. Global LAI surfaces will be an early product of the MODIS Land Science Team, and the requirements for LAI validation at selected sites have prompted interest in accurate LAI mapping at a more local scale. While spectral vegetation indices (SVIs) derived from satellite remote sensing have been used to map LAI, vegetation type, and related optical properties, and effects of Sun-surface-sensor geometry, background reflectance, and atmospheric quality can limit the strength and generality of empirical LAI-SVI relationships. In the interest of a preliminary assessment of the variability in LAI-SVI relationships across vegetation types, we compared Landsat 5 Thematic Mapper imagery from three temperate zone sites with on-site LAI measurements. The sites differed widely in location, vegetation physiognomy (grass, shrubs, hardwood forest, and conifer forest), and topographic complexity. Comparisons were made using three different red and near-infrared-based SVIs (NDVI, SR, SAVI). Several derivations of the SVIs were examined, including those based on raw digital numbers (DN), radiance, top of the atmosphere reflectance, and atmospherically corrected reflectance. For one of the sites, which had extreme topographic complexity, additional corrections were made for Sun-surface-sensor geometry. Across all sites, a strong general relationship was preserved, with SVIs increasing up to LAI values of 3 to 5. For all but the coniferous forest site, sensitivity of the SVIs was low at LAI values above 5. In coniferous forests, the SVIs decreased at the highest LAI values because of decreasing near-infrared reflectance associated with the complex canopy in these mature to old-growth stands. The cross-site LAI-SVI relationships based on atmospherically corrected imagery were stronger than those based on DN, radiance, or top of atmosphere reflectance. Topographic corrections at the conifer site altered the SVIs in some cases but had little effect on the LAI-SVI relationships. Significant effects of vegetation properties on SVIs, which were independent of LAI, were evident. The variability between and around the best fit LAI-SVI relationships for this dataset suggests that for local accuracy in development of LAI surfaces it will be desirable to stratify by land cover classes (e.g., physiognomic type and successional stage) and to vary the SVI.
    BibTeX:
    @article{turner99,
      author = {Turner, David P. and Cohen, Warren B. and Kennedy, Robert E. and Fassnacht, Karin S. and Briggs, John M.},
      title = {Relationships between Leaf Area Index and Landsat TM Spectral Vegetation Indices across Three Temperate Zone Sites},
      journal = {Remote Sensing of Environment},
      year = {1999},
      volume = {70},
      number = {1},
      pages = {52--68}
    }
    
    Turner, W., Spector, S., Gardiner, N., Fladeland, M., Sterling, E. & Steininger, M. Remote sensing for biodiversity science and conservation. 2003 Trends in Ecology & Evolution
    Vol. 18, pp. 306-314 
    article  
    BibTeX:
    @article{Turner2003,
      author = {Turner, W. and Spector, S. and Gardiner, N. and Fladeland, M. and Sterling, E. and Steininger, M.},
      title = {Remote sensing for biodiversity science and conservation.},
      journal = {Trends in Ecology & Evolution},
      year = {2003},
      volume = {18},
      pages = {306-314}
    }
    
    Ustin, S.L., Gitelson, A., Jacquemoud, S., Schaepman, M., Asner, G.P., Gamon, J.A. & Zarco-Tejada, P. Retrieval of foliar information about plant pigment systems from high resolution spectroscopy 2009 Remote Sensing of Environment
    Vol. 113(Supplement 1)Imaging Spectroscopy Special Issue, pp. S67-S77 
    article URL 
    Abstract: Life on Earth depends on photosynthesis. Photosynthetic systems evolved early in Earth history and have been stable for 2.5?billion years, providing prima facie evidence for the significance of pigments in plant functions. Photosynthetic pigments fill multiple roles from increasing the range of energy captured for photosynthesis to protective functions. Given the importance of pigments to leaf functioning, greater effort is needed to determine whether individual pigments can be identified and quantified in vivo using high fidelity spectroscopy. We review recent advances in detecting plant pigments at the leaf level and discuss successes and reasons why challenges remain for robust remote observation and quantification. New methods to identify and quantify individual pigments in the presence of overlapping absorption features would provide a major advance in understanding their biological functions, quantifying net carbon exchange, and identifying plant stresses.
    BibTeX:
    @article{Ustin2009a,
      author = {Ustin, Susan L. and Gitelson, A.A. and Jacquemoud, St?phane and Schaepman, Michael and Asner, Gregory P. and Gamon, John A. and Zarco-Tejada, Pablo},
      title = {Retrieval of foliar information about plant pigment systems from high resolution spectroscopy},
      booktitle = {Imaging Spectroscopy Special Issue},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {Supplement 1},
      pages = {S67--S77},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4W7RJYR-1/2/58a4cb652674c7aea4caed7df189aacc}
    }
    
    Ustin, S.L. & Schaepman, M.E. Imaging spectroscopy special issue 2009 Remote Sensing of Environment
    Vol. 113(Supplement 1)Imaging Spectroscopy Special Issue, pp. S1-S1 
    article URL 
    BibTeX:
    @article{Ustin2009,
      author = {Ustin, Susan L. and Schaepman, Michael E.},
      title = {Imaging spectroscopy special issue},
      booktitle = {Imaging Spectroscopy Special Issue},
      journal = {Remote Sensing of Environment},
      year = {2009},
      volume = {113},
      number = {Supplement 1},
      pages = {S1--S1},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4W4BMMJ-1/2/acb7082bca6f1db317c08c9949ff27cc}
    }
    
    Van Wagner, C.E. Conditions for the start and spread of crown fire. 1977 Canadian Journal of Forest Research
    Vol. 7, pp. 23-44 
    article  
    BibTeX:
    @article{vanwagner77,
      author = {Van Wagner, C. E.},
      title = {Conditions for the start and spread of crown fire.},
      journal = {Canadian Journal of Forest Research},
      year = {1977},
      volume = {7},
      pages = {23-44}
    }
    
    Verbree, E. & van Oosterom, P. Scanline forced Delaunay TENs for surface representation 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 45-51 
    article  
    Abstract: The general idea that a Delaunay TIN (DT) is more appropriate than non-Delaunay TINs, due to better shaped triangles, might be true for many applications, but not for height dependent analytical queries. This is because the distribution of the triangle tessellation is defined in the two-dimensional XY-plane, by ignoring the Z-value in the Delaunay empty circum circle criterion. Alternatively, Data Dependent Triangulations (DDT) aim to identify which triangulation of a given function z=f(x,y) over a given set of points will optimize some quality, i.e. the minimal spatial area of the surface or the volume below the resulting surface. This might be a good approach, but still there is no certainty the TIN represents the actual surface. Besides that, a 2D-TIN (Delaunay or not) is only capable to solve 2D (or 2.5D) data distributions. The reconstruction of the surface given by a set of surface points alone is therefore not unambiguous. This paper describes a surface reconstruction method based on the scanlines, the lines-of-sight or measurements between the observer (or the measurement platform) and the target (the measured point). As the scanlines do not belong to the surface, we have to use a real 3D triangulation construction method, resulting in a Tetrahedronized Irregular Network. This TEN is capable to store all kinds of surfacefeatures (as the target-points) and the scanlines as well. The scanlines are forced to split by adding Steiner points until they are part of the Delaunay TEN. This procedure gives us the additional information needed to use the TEN to reconstruct the surface. The method is demonstrated by the non-trivial case of a set of measured points in a regular square distribution showing the improved surface reconstruction technique.
    BibTeX:
    @article{verbree01,
      author = {Edward Verbree and Peter van Oosterom},
      title = {Scanline forced Delaunay TENs for surface representation},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {45-51}
    }
    
    Verrelst, J., Schaepman, M., Koetz, B. & Kneub?hler, M. Angular sensitivity analysis of vegetation indices derived from CHRIS/PROBA data 2008 Remote Sensing of Environment
    Vol. 112(5)Earth Observations for Terrestrial Biodiversity and Ecosystems Special Issue, pp. 2341-2353 
    article URL 
    Abstract: View angle effects present in spectral vegetation indices can either be regarded as an added source of uncertainty for variable retrieval or as a source of additional information, enhancing the variable retrieval; however, the magnitude of these angular effects remains for most indices unknown or unquantified. We use the ESA-mission CHRIS-PROBA (Compact High Resolution Imaging Spectrometer onboard the Project for On-board Autonomy) providing spaceborne imaging spectrometer and multiangular data to assess the reflectance anisotropy of broadband as well as recently developed narrowband indices. Multiangular variability of Hemispherical Directional Reflectance Factor (HDRF) is a prime factor determining the indices? angular response. Two contrasting structural vegetation types, pine forest and meadow, were selected to study the effect of reflectance anisotropy on the angular response. Calculated indices were standardized and statistically evaluated for their varying HDRF. Additionally we employ a coupled radiative transfer model (PROSPECT/FLIGHT) to quantify and substantiate the findings beyond an incidental case study. Nearly all tested indices manifested a prominent anisotropic behaviour. Apart from the conventional broadband greenness indices [e.g. Simple Ratio Index (SRI), Normalized Difference Vegetation Index (NDVI)], light use efficiency and leaf pigment indices [e.g. Structure Insensitive Pigment Index (SIPI), Photochemical Reflectance Index (PRI) and Anthocyanin Reflectance Index (ARI)] did express significant different angular responses depending on the vegetation type. Following the quantification of the impact, we conclude that the angular-dependent fraction of non-photosynthetic material is of critical importance shaping the angular signature of these VIs. This work highlights the influence of viewing geometry and surface reflectance anisotropy, particularly when using light use efficiency and leaf pigment indices.
    BibTeX:
    @article{Verrelst2008,
      author = {Verrelst, J. and Schaepman, M.E. and Koetz, B. and Kneub?hler, M.},
      title = {Angular sensitivity analysis of vegetation indices derived from CHRIS/PROBA data},
      booktitle = {Earth Observations for Terrestrial Biodiversity and Ecosystems Special Issue},
      journal = {Remote Sensing of Environment},
      year = {2008},
      volume = {112},
      number = {5},
      pages = {2341--2353},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4RWJVYW-1/2/1c15086a554b93350fe2e5eb91845d99}
    }
    
    Verrelst, J., Schaepman, M.E., Malenovsk?, Z. & Clevers, J.G. Effects of woody elements on simulated canopy reflectance: Implications for forest chlorophyll content retrieval 2010 Remote Sensing of Environment
    Vol. 114(3), pp. 647-656 
    article URL 
    Abstract: An important bio-indicator of actual plant health status, the foliar content of chlorophyll a and b (Cab), can be estimated using imaging spectroscopy. For forest canopies, however, the relationship between the spectral response and leaf chemistry is confounded by factors such as background (e.g. understory), canopy structure, and the presence of non-photosynthetic vegetation (NPV, e.g. woody elements)--particularly the appreciable amounts of standing and fallen dead wood found in older forests. We present a sensitivity analysis for the estimation of chlorophyll content in woody coniferous canopies using radiative transfer modeling, and use the modeled top-of-canopy reflectance data to analyze the contribution of woody elements, leaf area index (LAI), and crown cover (CC) to the retrieval of foliar Cab content. The radiative transfer model used comprises two linked submodels: one at leaf level (PROSPECT) and one at canopy level (FLIGHT). This generated bidirectional reflectance data according to the band settings of the Compact High Resolution Imaging Spectrometer (CHRIS) from which chlorophyll indices were calculated. Most of the chlorophyll indices outperformed single wavelengths in predicting Cab content at canopy level, with best results obtained by the Maccioni index ([R780?-?R710]?/?[R780?-?R680]). We demonstrate the performance of this index with respect to structural information on three distinct coniferous forest types (young, early mature and old-growth stands). The modeling results suggest that the spectral variation due to variation in canopy chlorophyll content is best captured for stands with medium dense canopies. However, the strength of the up-scaled Cab signal weakens with increasing crown NPV scattering elements, especially when crown cover exceeds 30%. LAI exerts the least perturbations. We conclude that the spectral influence of woody elements is an important variable that should be considered in radiative transfer approaches when retrieving foliar pigment estimates in heterogeneous stands, particularly if the stands are partly defoliated or long-lived.
    BibTeX:
    @article{Verrelst2010,
      author = {Verrelst, Jochem and Schaepman, Michael E. and Malenovsk?, Zbynek and Clevers, Jan G.P.W.},
      title = {Effects of woody elements on simulated canopy reflectance: Implications for forest chlorophyll content retrieval},
      journal = {Remote Sensing of Environment},
      year = {2010},
      volume = {114},
      number = {3},
      pages = {647--656},
      url = {http://www.sciencedirect.com/science/article/B6V6V-4XY3KDM-2/2/cd7754583a3324a537b80a84cfb906e1}
    }
    
    Vospernik, S. & Reimoser, S. Modelling changes in roe deer habitat in response to forest management. 2008 Forest Ecology and Management
    Vol. 255, pp. 530-545 
    article  
    BibTeX:
    @article{Vospernik2008,
      author = {Vospernik, S. and Reimoser, S.},
      title = {Modelling changes in roe deer habitat in response to forest management.},
      journal = {Forest Ecology and Management},
      year = {2008},
      volume = {255},
      pages = {530-545}
    }
    
    Vosselman, G. On the Estimation of Planimetric Offsets in Laser Altimetry Data 2002 ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria, pp. A-375 ff (6 pages)  inproceedings  
    Abstract: Offsets between overlapping strips of laser altimetry data serve as the input for strip adjustment procedures that estimate and eliminate systematic errors in laser altimetry datasets. For a three-dimensional strip adjustment offsets are to be measured in three dimensions. Height offsets can be determined straightforward by comparing the heights of horizontal planes. Planimetric offsets are more difficult to determine. This paper shows that the usage of standard least squares matching algorithms on height data as well as on reflectance data may lead to significant biases in the estimation of planimetric offsets. For height data, a model based estimation of linear features is proposed since the number of locations in strip overlaps that are suitable for the estimation of offsets in three dimensions may not be sufficient to estimate all error parameters of a strip adjustment. To improve both the offset estimation and the offset variance estimation using reflectance data an edge response function is introduced. This function takes into account the difference in size of a laser beam's footprint and the distance between successive laser points.
    BibTeX:
    @inproceedings{vosselman02b,
      author = {George Vosselman},
      title = {On the Estimation of Planimetric Offsets in Laser Altimetry Data},
      booktitle = {ISPRS Commission III, Symposium 2002 September 9 - 13, 2002, Graz, Austria},
      year = {2002},
      pages = {A-375 ff (6 pages)}
    }
    
    Vosselman, G. & Dijkman, S. 3D BUILDING MODEL RECONSTRUCTION FROM POINT CLOUDS AND GROUND PLANS 2001 International Archives of Photogrammetry and Remote Sensing
    Vol. XXXIV-3/W4, pp. 37-43 
    article  
    Abstract: Airborne laser altimetry has become a very popular technique for the acquisition of digital elevation models. The high point density that can be achieved with this technique enables applications of laser data for many other purposes. This paper deals with the construction of 3D models of the urban environment. A three-dimensional version of the well-known Hough transform is used for the extraction of planar faces from the irregularly distributed point clouds. To support the 3D reconstruction usage is made of available ground plans of the buildings. Two different strategies are explored to reconstruct building models from the detected planar faces and segmented ground plans. Whereas the first strategy tries to detect intersection lines and height jump edges, the second one assumes that all detected planar faces should model some part of the building. Experiments show that the second strategy is able to reconstruct more buildings and more details of this buildings, but that it sometimes leads to additional parts of the model that do not exist. When restricted to buildings with rectangular segments of the ground plan, the second strategy was able to reconstruct 83 buildings out of a dataset with 94 buildings.
    BibTeX:
    @article{vosselman01,
      author = {George Vosselman and Sander Dijkman},
      title = {3D BUILDING MODEL RECONSTRUCTION FROM POINT CLOUDS AND GROUND PLANS},
      journal = {International Archives of Photogrammetry and Remote Sensing},
      year = {2001},
      volume = {XXXIV-3/W4},
      pages = {37-43}
    }
    
    Vu, T. & Tokunaga, M. Wavelet and Scale-Space Theory in Segmentation of Airborne Laser Scanner Data 2001 Proc. ACRS 2001 - 22nd Asian Conference on Remote Sensing
    Vol. 1, pp. 176-180 
    article  
    BibTeX:
    @article{vu01,
      author = {T.Thuy Vu and Mitsuharu Tokunaga},
      title = {Wavelet and Scale-Space Theory in Segmentation of Airborne Laser Scanner Data},
      journal = {Proc. ACRS 2001 - 22nd Asian Conference on Remote Sensing},
      year = {2001},
      volume = {1},
      pages = {176-180}
    }
    
    Wack, R. & Stelzl, H. Laser DTM generation for south-tyrol and 3D-visualization 2005 ISPRS WG III/3, III/4, V/3 Workshop "Laser scanning 2005", Enschede, the Netherlands, September 12-14,  inproceedings  
    BibTeX:
    @inproceedings{wack05,
      author = {R. Wack and H. Stelzl},
      title = {Laser DTM generation for south-tyrol and 3D-visualization},
      booktitle = {ISPRS WG III/3, III/4, V/3 Workshop "Laser scanning 2005", Enschede, the Netherlands, September 12-14,},
      year = {2005}
    }
    
    Wagner, W., Hollaus, M., Briese, C. & Ducic, V. 3D vegetation mapping using small-footprint full-waveform airborne laser scanners 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1433-1452 
    article  
    Abstract: Small-footprint full-waveform airborne laser scanning (ALS) is a remote sensing technique capable of mapping vegetation in three dimensions with a spatial sampling of about 0.5???2??m in all directions. This is achieved by scanning the laser beam across the Earth's surface and by emitting nanosecond-long infrared pulses with a high frequency of typically 50???150??kHz. The echo signals are digitized during data acquisition for subsequent off-line waveform analysis. In addition to delivering the three-dimensional (3D) coordinates of scattering objects such as leaves or branches, full-waveform laser scanners can be calibrated for measuring the scattering properties of vegetation and terrain surfaces in a quantitative way. As a result, a number of physical observables are obtained, such as the width of the echo pulse and the backscatter cross-section, which is a measure of the electromagnetic energy intercepted and re-radiated by objects. The main aim of this study was to build up an understanding of the scattering characteristics of vegetation and the underlying terrain. It was found that vegetation typically causes a broadening of the backscattered pulse, while the backscatter cross-section is usually smaller for canopy echoes than for terrain echoes. These scattering properties allowed classification of the 3D point cloud into vegetation and non-vegetation echoes with an overall accuracy of 89.9% for a dense natural forest and 93.7% for a baroque garden area. In addition, by removing the vegetation echoes before the filtering process, the quality of the digital terrain model could be improved.
    BibTeX:
    @article{Wagner2008,
      author = {Wagner, W. and Hollaus, M. and Briese, C. and Ducic, V.},
      title = {3D vegetation mapping using small-footprint full-waveform airborne laser scanners},
      journal = {International Journal of Remote Sensing},
      publisher = {Taylor & Francis},
      year = {2008},
      volume = {29},
      number = {5},
      pages = {1433--1452}
    }
    
    Wagner, W., Ullrich, A. & Briese, C. Der Laserstrahl und seine Interaktion mit der Erdoberfläche 2003 Österreichische Zeitschrift für Vermessung & Geoinformation
    Vol. 4, pp. 223-235 
    article  
    BibTeX:
    @article{wagner03,
      author = {Wolfgang Wagner and Andreas Ullrich and Christian Briese},
      title = {Der Laserstrahl und seine Interaktion mit der Erdoberfläche},
      journal = {Österreichische Zeitschrift für Vermessung & Geoinformation},
      year = {2003},
      volume = {4},
      pages = {223-235}
    }
    
    Wagner, W., Ullrich, A., Ducic, V., Melzer, T. & Studnicka, N. Gaussian decomposition and calibration of a novel small-footprint full-waveform digitising airborne laser scanner 2006 ISPRS Journal of Photogrammetry and Remote Sensing
    Vol. 60(2), pp. 100-112 
    article  
    Abstract: In this study we use a technique referred to as Gaussian decomposition for processing and calibrating data acquired with a novel small-footprint airborne laser scanner that digitises the complete waveform of the laser pulses scattered back from the Earth's surface. This paper presents the theoretical basis for modelling the waveform as a series of Gaussian pulses. In this way the range, amplitude, and width are provided for each pulse. Using external reference targets it is also possible to calibrate the data. The calibration equation takes into account the range, the amplitude, and pulse width and provides estimates of the backscatter cross-section of each target. The applicability of this technique is demonstrated based on RIEGL LMS-Q560 data acquired over the city of Vienna.
    BibTeX:
    @article{wagner06,
      author = {Wagner, Wolfgang and Ullrich, Andreas and Ducic, Vesna and Melzer, Thomas and Studnicka, Nick},
      title = {Gaussian decomposition and calibration of a novel small-footprint full-waveform digitising airborne laser scanner},
      journal = {ISPRS Journal of Photogrammetry and Remote Sensing},
      year = {2006},
      volume = {60},
      number = {2},
      pages = {100--112}
    }
    
    Wang, Y., Buermann, W., Stenberg, P., Smolander, H., Hame, T., Tian, Y., Hu, J., Knyazikhin, Y. & Myneni, R.B. A new parameterization of canopy spectral response to incident solar radiation: case study with hyperspectral data from pine dominant forest 2003 Remote Sensing of Environment
    Vol. 85(3), pp. 304-315 
    article  
    Abstract: A small set of independent variables generally seems to suffice when attempting to describe the spectral response of a vegetation canopy to incident solar radiation. This set includes the soil reflectance, the single-scattering albedo, canopy transmittance, reflectance and interception, the portion of uncollided radiation in the total incident radiation, and portions of collided canopy transmittance and interception. All of these are measurable; they satisfy a simple system of equations and constitute a set that fully describes the law of energy conservation in vegetation canopies at any wavelength in the visible and near-infrared part of the solar spectrum. Further, the system of equations specifies the relationship between the optical properties at the leaf and the canopy scales. Thus, the information content of hyperspectral data can be fully exploited if these variables can be retrieved, for they can be more directly related to some of the physical properties of the canopy (e.g. leaf area index). This paper demonstrates this concept through retrievals of single-scattering albedo, canopy absorptance, portions of uncollided and collided canopy transmittance, and interception from hyperspectral data collected during a field campaign in Ruokolahti, Finland, June 14-21, 2000. The retrieved variables are then used to estimate canopy leaf area index, vegetation ground cover, and also the ratio of direct to total incident solar radiation at blue, green, red, and near-infrared spectral intervals.
    BibTeX:
    @article{wang03,
      author = {Wang, Yujie and Buermann, Wolfgang and Stenberg, Pauline and Smolander, Heikki and Hame, Tuomas and Tian, Yuhong and Hu, Jiannan and Knyazikhin, Yuri and Myneni, Ranga B.},
      title = {A new parameterization of canopy spectral response to incident solar radiation: case study with hyperspectral data from pine dominant forest},
      journal = {Remote Sensing of Environment},
      year = {2003},
      volume = {85},
      number = {3},
      pages = {304--315}
    }
    
    Wang, Y., Weinacker, H. & Koch, B. A Lidar Point Cloud Based Procedure for Vertical Canopy Structure Analysis And 3D Single Tree Modelling in Forest 2008 Sensors
    Vol. 8(6), pp. 3938-3951 
    article DOI URL 
    Abstract: A procedure for both vertical canopy structure analysis and 3D single tree modelling based on Lidar point cloud is presented in this paper. The whole area of research is segmented into small study cells by a raster net. For each cell, a normalized point cloud whose point heights represent the absolute heights of the ground objects is generated from the original Lidar raw point cloud. The main tree canopy layers and the height ranges of the layers are detected according to a statistical analysis of the height distribution probability of the normalized raw points. For the 3D modelling of individual trees, individual trees are detected and delineated not only from the top canopy layer but also from the sub canopy layer. The normalized points are resampled into a local voxel space. A series of horizontal 2D projection images at the different height levels are then generated respect to the voxel space. Tree crown regions are detected from the projection images. Individual trees are then extracted by means of a pre-order forest traversal process through all the tree crown regions at the different height levels. Finally, 3D tree crown models of the extracted individual trees are reconstructed. With further analyses on the 3D models of individual tree crowns, important parameters such as crown height range, crown volume and crown contours at the different height levels can be derived.
    BibTeX:
    @article{s8063938,
      author = {Wang, Yunsheng and Weinacker, Holger and Koch, Barbara},
      title = {A Lidar Point Cloud Based Procedure for Vertical Canopy Structure Analysis And 3D Single Tree Modelling in Forest},
      journal = {Sensors},
      year = {2008},
      volume = {8},
      number = {6},
      pages = {3938--3951},
      url = {http://www.mdpi.com/1424-8220/8/6/3938/},
      doi = {http://dx.doi.org/10.3390/s8063938}
    }
    
    Wang, Y., Woodcock, C.E., Buermann, W., Stenberg, P., Voipio, P., Smolander, H., Hame, T., Tian, Y., Hu, J., Knyazikhin, Y. & Myneni, R.B. Evaluation of the MODIS LAI algorithm at a coniferous forest site in Finland 2004 Remote Sensing of Environment
    Vol. 91(1), pp. 114-127 
    article  
    Abstract: Leaf area index (LAI) collected in a needle-leaf forest site near Ruokolahti, Finland, during a field campaign in June 14-21, 2000, was used to validate Moderate Resolution Imaging Spectroradiometer (MODIS) LAI algorithm. The field LAI data was first related to 30-m resolution Enhanced Thermal Mapper Plus (ETM+) images using empirical methods to create a high-resolution LAI map. The analysis of empirical approaches indicates that preliminary segmentation of the image followed by empirical modeling with the resulting patches, was an effective approach to developing an LAI validation surface. Comparison of the aggregated high-resolution LAI map and corresponding MODIS LAI retrievals suggests satisfactory behavior of the MODIS LAI algorithm although variation in MODIS LAI product is higher than expected. The MODIS algorithm, adjusted to high resolution, generally overestimates the LAI due to the influence of the understory vegetation. This indicates the need for improvements in the algorithm. An improved correlation between field measurements and the reduced simple ratio (RSR) suggests that the shortwave infrared (SWIR) band may provide valuable information for needle-leaf forests.
    BibTeX:
    @article{wang04,
      author = {Wang, Yujie and Woodcock, Curtis E. and Buermann, Wolfgang and Stenberg, Pauline and Voipio, Pekka and Smolander, Heikki and Hame, Tuomas and Tian, Yuhong and Hu, Jiannan and Knyazikhin, Yuri and Myneni, Ranga B.},
      title = {Evaluation of the MODIS LAI algorithm at a coniferous forest site in Finland},
      journal = {Remote Sensing of Environment},
      year = {2004},
      volume = {91},
      number = {1},
      pages = {114--127}
    }
    
    Waser, L.T., Baltsavias, E., Ecker, K., Eisenbeiss, H., Ginzler, C., K??chler, M., Thee, P. & Zhang, L. High-resolution digital surface models (DSMs) for modelling fractional shrub/tree cover in a mire environment 2008 International Journal of Remote Sensing
    Vol. 29(5), pp. 1261-1276 
    article  
    Abstract: This paper describes the development of a fractional shrub/tree cover in open mire land using logistic regression and airborne remote sensing data (the DSM is derived from colour infrared images). The present study was carried out in the framework of the Swiss Mire Protection Program, where shrub encroachment is a key issue. An example of the use of this modelling approach in a mire biotope in the Pre-alpine zone of central Switzerland is presented. As a first step, a DSM was automatically generated using an image matching approach from 12 colour infrared (CIR) aerial images. Two discrete forest masks with different levels of detail were then generated combining a canopy cover derived from the DSM with a multi-resolution segmentation and a fuzzy classification. Then, fractional shrub/tree covers for open mire land were calculated using six explanatory variables derived from the DSM only and the forest masks as the response variable. Validation with field samples revealed highest accuracies for the cover stratum 30???100%. An advantage of this approach for future mire protection work is that small shrubs and single trees of open mire land can be modelled with high accuracy and the estimated cover is not restricted to a simple forest/non-forest decision. The optimal, most reliable cover stratum can be achieved by individually tuning the probability threshold of the fractional shrub/tree covers according to the individual vegetation characteristics of a mire ecosystem. This study clearly revealed that 3-dimensional information, as obtained by digital photogrammetry, is indispensable for modelling tree and shrub occurrence.