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All publications sorted by Thesis
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Jong-Sen Lee and Eric Pottier.
Polarimetric radar imaging: from basics to applications.
CRC Press, Taylor and Francis,
2009.
Keyword(s): SAR Processing,
Polarimetry,
Polarimetric Decomposition.
[bibtex-key = leePottier:PolarimetricRadarImagingBook2009]
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Ingo Walterscheid.
Bistatisches SAR - Signaltheoretische und experimentelle Untersuchung der bistatischen Radarbildgebung,
FHR-Schriftenreihe.
Shaker Verlag,
2008.
ISBN: 978-3-8322-7224-1.
Keyword(s): SAR Processing,
Bistatic SAR,
omega-k,
Range Migration Algorithm,
Wavenumber Domain Algorithm,
Time-Domain Back-Projection,
Back-Projection,
NuSAR,
Airborne SAR,
PAMIR,
Elektrotechnik Radartechnik Signalverarbeitung Radarsignalverarbeitung.
[bibtex-key = walterscheid2008Diss:BistaticSAR]
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Jian Li,
Petre Stoica,
Zhisong Wang,
Robert G. Lorenz,
Stephen P. Boyd,
Alex B. Gershman,
Zhi-Quan Luo,
Shahram Shahbazpanahi,
Xavier Mestre,
Miguel A. Lagunas,
Yonina C. Eldar,
Arye Nehorai,
Alle-Jan van der Veen,
Amir Leshem,
Elio D. Di Claudio,
and Raffaele Parisi.
Robust Adaptive Beamforming.
Wiley-Interscience,
2006.
Keyword(s): SAR Processing,
Beamforming,
Adaptive Beamforming,
Robust Adaptive Beamforming,
MUSIC,
Capon,
Subspace Methods,
SAR Tomography,
Tomography.
[bibtex-key = bookRABLiStoicaEditors2006:Beamforming]
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Ian G. Cumming and Frank H. Wong.
Digital Processing of Synthetic Aperture Radar Data: Algorithms and Implementation.
Artech House Inc.,
Boston, London,
2005.
Keyword(s): SAR Processing,
Range-Doppler Algorithm,
Chirp Scaling Algorithm,
Extended Chirp Scaling Algorithm,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
SPECAN Algorithm,
Comparison of Algorithms,
Demodulation,
Quadrature Demodulation,
Hilbert Transform,
Doppler Centroid Estimation,
Doppler Ambiguity Resolver,
DAR,
Doppler Rate Estimation,
Azimuth FM Rate,
Autofocus Techniques,
ScanSAR,
Range Compression,
Pulse Compression,
Pulse Compression of Linear FM Signals,
Linear FM Signals,
Stolt Mapping,
Quality Assessment,
Quality Measures,
Quality Metrics,
PSLR,
ISLR,
Spaceborne SAR.
Abstract: This cutting-edge resource offers you complete howto guidance on digital processing of synthetic aperture radar (SAR) data. You discover how SAR is used to obtain a high-resolution image from a satellite and learn the mathematical structure and spectral properties of the signal received from a SAR system. Supported with over 600 equations and over 250 figures, the book arms you with state-of-the-art signal processing algorithms and helps you choose the best algorithm for a given SAR system and image quality requirements. This hands-on reference shows you how to process received SAR data into a well-focused image on a digital computer, using the popular range Doppler, chirp scaling, omega-K and SPECAN algorithms. In addition, the book teaches you how to process ScanSAR data using the full-aperture, SPECAN, short IFFT and extended chirp scaling algorithms. You also learn how to estimate the Doppler centroid frequency and azimuth FM rate from a geometry model or from received data. Written from a digital signal processing point of view, this authoritative volume can be fully understood by professionals with a general electrical engineering background. -
Petre Stoica and Randolph L. Moses.
Spectral Analysis of Signals.
Prentice Hall,
Upper Saddle River, NJ,
2005.
Keyword(s): Spectral Estimation,
MUSIC,
Capon,
Beamforming,
Direction-of-arrival estimation,
SAR Processing,
SAR Tomography.
[bibtex-key = stoicaMosesBook2005:SpectralAnalysis]
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Mehrdad Soumekh.
Synthetic Aperture Radar Signal Processing: with MATLAB Algorithms.
John Wiley & Sons,
1999.
Keyword(s): SAR Processing,
Wavefront Reconstruction,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Backprojection,
Time-Domain Backprojection,
Spotlight SAR,
Stripmap SAR,
MATLAB,
Motion Compensation,
Digital Spotlighting,
Monopulse SAR,
Stolt Mapping,
Range Compression,
Pulse Compression,
Pulse Compression of Linear FM Signals,
Linear FM Signals.
Abstract: This book introduces the wavefront reconstruction signal theory that underlies the best SAR imaging methods and provides clear guidelines to system design, implementation, and applications in diverse areas - from airborne reconnaissance to topographic imaging of ocean floors to surveillance and air traffic control to medical imaging techniques, and numerous others. Enabling professionals in radar signal and image processing to use synthetic aperture technology to its fullest potential, this work: includes M-files to supplement this book; provides practical examples and results from real SAR, ISAR, and CSAR databases; outlines unique properties of the SAR signal that cannot be found in other information processing systems; examines spotlight SAR, stripmap SAR, circular SAR, and monopulse SAR modalities; discusses classical SAR processing issues such as motion compensation and radar calibration. - Charles V. Jakowatz, Daniel E. Wahl, Paul H. Eichel, Dennis C. Ghiglia, and Paul A. Thompson. Spotlight-Mode Synthetic Aperture Radar: A Signal Processing Approach. Norwell, MA: Kluwer Academic Publishers, 1996. Keyword(s): SAR Processing, Spotlight SAR, Spotlight mode, Autofocus, Phase Gradient Autofocus, PGA, Motion Compensation, MoComp, Airborne SAR, SAR Tomography, Tomography, InSAR, SAR Interferometry. [bibtex-key = jakowatzWahlEichelGhigliaThompson1996:BookSpotlightSAR]
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Walter G. Carrara,
Ron S. Goodman,
and Ronald M. Majewski.
Spotlight Synthetic Aperture Radar: Signal Processing Algorithms.
Artech House Inc.,
1995.
Keyword(s): SAR Processing,
Spotlight SAR,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Chirp Scaling Algorithm,
Polar Format Algorithm,
Autofocus Techniques,
Demodulation,
Quadrature Demodulation,
Hilbert Transform.
Abstract: The book gives an excellent theoretical and practical background of SAR in general and specifically of spotlight SAR. The rich experience of the authors in spotlight SAR processing is reflected by a very detailed summary of the associated theory as well as a lot of SAR image examples. These images illustrate the techniques described in the book and provide a valuable connection to practice. This book can be highly recommended to all scientists and engineers involved in SAR system design and SAR data evaluation, -- International Journal of Electronics and Communications, January 1996. Contents: Synthetic Aperture Radar Fundamentals. Spotlight SAR and Polar Format Algorithm. Digital Polar Format Processing. Phase Errors. Autofocus Techniques. Processor Design Examples. SAR System Performance. Spotlight Processing Applications. Range Migration Algorithm. Chirp Scaling Algorithm. Comparison of Image Formation Algorithms. Appendices. - Mehrdad Soumekh. Fourier Array Imaging. Englewood Cliffs, NJ: Prentice Hall, 1994. Keyword(s): SAR Processing, Fourier Array Imaging. [bibtex-key = soumekh:FourierArrayImaging1994]
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Gunter Schreier, editor.
SAR Geocoding: Data and Systems.
Wichmann,
1993.
Keyword(s): SAR Processing,
SAR Geocoding,
Geocoding,
Doppler Centroid Estimation.
Abstract: This book gives an overview of the principles of SAR processing, geometric effects of SAR and parametric geocoding of SAR, both ellipsoid and terrain corrected. The new geocoded data sets and the systems and ancillary information to generate these data are described in detail. Basic applications and analysis procedures with the data are described in order to help to understand the content of the geocoded SAR images. Several authors from the German Processing and Archiving Facility (D-PAF) of DLR in Oberpfaffenhofen and other research groups, who actively contributed to algorithms and system aspects of SAR geocoding, contributed chapters of this reference book. An overview of current on-going activities in Europe in this domain concludes the chapters. This volume is intended to introduce new SAR data users as well as those starting with SAR data and Geographic Information Systems (GIS) to the principles of SAR data geocoding and to give experts a detailed overview of used references and algorithms. -
John C. Curlander and Robert N. McDonough.
Synthetic Aperture Radar - Systems and Signal Processing.
John Wiley & Sons,
New York,
1991.
Keyword(s): SAR Processing,
Radar Equation,
Matched Filter,
Pulse Compression,
Range Compression Processing,
Azimuth Processing,
range-Doppler,
Clutterlock,
Doppler Centroid Estimation,
Doppler Centroid,
Autofocus,
Doppler Ambiguity Resolver,
DAR,
Doppler Rate Estimation,
Azimuth FM Rate,
Autofocus Techniques,
Radiometric Calibration,
Geometric Calibration,
Rectangular Algorithm,
Deramp Compression,
Step Transform Processing,
Polar Processing,
Fourier Transform,
Convolution,
Interpolation,
Satellite Orbits.
Abstract: Synthetic Aperture Radar: Systems and Signal Processing specifiecally addresses these items, as applied to the design and implementation of the spaceborne SAR system with a strong emphasis on signal processing techniques. The reader will find that the book has been written with tree key goals. The first is to present a complete picture of SAR from a theoretical perspective by deriving from basic principles the SAR signal processing algorithms. The second goal is to provide some insight into the practical aspects of the sensor and ground system design and implementation. the third is to analyze the system performance given the common error sources and demonstrate their effect on the output image products. This text provieds in a single source the information required both for SAR system design as well as image data analysis. The book serves as an aid for both the radar engineer and the application scientist. The text is generously annotated with figures, plots and images in an effort to make the ideas as accessible as possible. The material is presented such that this text can be used both as an introduction to SAR for new workers in the field and as a reference to the experienced engineer involved in system design and development. Comments: ++ Notes - Merrill I. Skolnik. Radar Handbook (2nd Edition). McGraw-Hill, 1990. [bibtex-key = skolnik90:RadarHandbook]
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Hayden J. Callow.
Signal Processing for Synthetic Aperture Sonar Image Enhancement.
PhD thesis,
University of Canterbury,
2003.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus,
Stripmap,
Stripmap PGA,
Stripmap Phase Gradient Autofocus,
SAS,
Synthetic Aperture Sonar.
Abstract: This thesis contains a description of SAS processing algorithms, offering improvements in Fourier-based reconstruction, motion-compensation, and autofocus. Fourier-based image reconstruction is reviewed and improvements shown as the result of improved system modelling. A number of new algorithms based on the wavenumber algorithm for correcting second order effects are proposed. In addition, a new framework for describing multiple-receiver reconstruction in terms of the bistatic geometry is presented and is a useful aid to understanding. Motion-compensation techniques for allowing Fourier-based reconstruction in widebeam geometries suffering large-motion errors are discussed. A motion-compensation algorithm exploiting multiple receiver geometries is suggested and shown to provide substantial improvement in image quality. New motion compensation techniques for yaw correction using the wavenumber algorithm are discussed. A common framework for describing phase estimation is presented and techniques from a number of fields are reviewed within this framework. In addition a new proof is provided outlining the relationship between eigenvector-based autofocus phase estimation kernels and the phase-closure techniques used astronomical imaging. Micronavigation techniques are reviewed and extensions to the shear average single-receiver micronavigation technique result in a 3-4 fold performance improvement when operating on high-contrast images. The stripmap phase gradient autofocus (SPGA) algorithm is developed and extends spotlight SAR PGA to the wide-beam, wide-band stripmap geometries common in SAS imaging. SPGA supersedes traditional PGA-based stripmap autofocus algorithms such as mPGA and PCA -- the relationships between SPGA and these algorithms is discussed. SPGA's operation is verified on simulated and field-collected data where it provides significant image improvement. SPGA with phase-curvature based estimation is shown and found to perform poorly compared with phase-gradient techniques. The operation of SPGA on data collected from Sydney Harbour is shown with SPGA able to improve resolution to near the diffraction-limit. Additional analysis of practical stripmap autofocus operation in presence of undersampling and space-invariant blurring is presented with significant comment regarding the difficulties inherent in autofocusing field-collected data. Field-collected data from trials in Sydney Harbour is presented along with associated autofocus results from a number of algorithms. -
Oliver Wolfgang Hirsch.
Neue Verarbeitungsverfahren von Along-Track Interferometrie Daten eines Radars mit synthetischer Apertur.
PhD thesis,
Universität-Gesamthochschule Siegen,
2002.
Keyword(s): SAR Processing,
Along Track Interferometry,
Interferometry,
Airborne SAR.
Abstract: The German remote sensing project EURoPAK-B is aimed at the development and the demonstration of a special remote sensing system for the measurement of ocean surface currents and the monitoring of underwater bottom topography in coastal waters on the basis of airborne along- track interferometric (ATI) synthetic aperture radar. In contrast to across-track interferometry ATI is directly sensitive to motions of the scatterers which have a radial velocity component. The ATI phase being directly proportional to the interferometric velocity contains not only contributions resulting from the effective ocean surface currents but also from effects like e. g. orbital motions of longer waves. Thus the actual surface ocean currents differ from the measured interferometric velocities. The processed ATI phase is the starting point for the determination of interferometric velocities and has to be handled accurately. Therefore some concepts concerning a very proper processing of ATI data have to be developed. This includes the correction of phase contributions resulting from the wave guide length at different channel frequencies. Another undesirable contribution to the phase results from the existing across-track component which depends on the squint angle during data acquisition. To minimize that effect the exact positions of the phase centres of both antennas have to be determined in a theoretical way. Also some other effects on the ATI data like the azimuthal displacement of moving targets have to be taken into account for a correct geolocation of the ATI data. This work gives also reasons why the ATI phase has to be unwrapped although the phase resulting from the ocean currents should be within the order of -PI and +PI. It will also been shown how phase unwrapping errors of the ATI phase can be removed. In this work these concepts for accurately processing ATI data are discussed and results are shown. Supplementary it points out the proposed remote sensing technique for accurate measurements of both ocean surface currents and underwater bottom topography in coastal waters generated by the University of Hamburg. -
Andreas Reigber.
Airborne Polarimetric SAR Tomography.
PhD thesis,
University of Stuttgart,
2001.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
Polarimettric SAR,
Pol-InSAR,
L-Band,
E-SAR.
[bibtex-key = reigberDiss2001:Tomo]
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Richard T. Lord.
Aspects of Stepped-Frequency Processing for Low-Frequency SAR Systems.
PhD thesis,
University of Cape Town,
Rondebosch, South Africa,
2000.
Keyword(s): SAR Processing,
Stepped-Frequency Processing,
RFI Suppression,
Low-Frequency SAR,
Wideband SAR.
Abstract: Ultra-wideband synthetic aperture radar (SAR) systems operating in the VHF/UHF region are becoming increasingly popular because of their growing number of applications in the areas of foliage penetration radar (FOPEN) and ground-penetrating radar (GPR). The objective of this thesis is to investigate the following two aspects of low-frequency (VHF/UHF-band) SAR processing: 1. The use of stepped-frequency waveforms to increase the total radar bandwidth, thereby increasing the range resolution, and 2. Radio frequency interference (RFI) suppression. A stepped-frequency system owes its wide bandwidth to the transmission of a group of narrow-bandwidth pulses, which are then combined using a signal processing technique to achieve the wide bandwidth. Apart from providing an economically viable path for the upgrading of an existing single frequency system, stepped-frequency waveforms also offer opportunities for RFI suppression. This thesis describes three methods to process stepped-frequency waveforms, namely an IFFTmethod, a time-domainmethod and a frequency-domainmethod. Both the IFFT method and the time-domain method have been found to be unsuitable for SAR processing applications. The IFFT method produces multiple ghost targets in the high resolution range profile due to the spill-over effect of energy into consecutive coarse range bins, and the time-domain technique is computationally inefficient on account of the upsampling requirement of the narrow-bandwidth pulses prior to the frequency shift. The frequency-domain technique, however, efficiently uses all the information in the narrowband pulses to obtain high-resolution range profiles which do not contain any ghost targets, and is therefore well suited for SAR processing applications. This technique involves the reconstruction of a wider portion of the target\u2019s reflectivity spectrum by combining the individual spectra of the transmitted narrow-bandwidth pulses in the frequency domain. It is shown here how this method may be used to avoid spectral regions that are heavily contaminated with RFI, thereby alleviating the problem of receiver saturation due to RFI. Stepped-frequency waveforms also enable the A/D converter to sample the received narrow-bandwidth waveform with a larger number of bits, which increases the receiver dynamic range, thereby further alleviating the problem of receiver saturation during the presence of RFI. In addition to using stepped-frequency waveforms for RFI suppression, a number of other techniques have been investigated to suppress RFI... Of these, the notch filter and the LMS adaptive filter have been implemented and applied on real P-band data obtained from the E-SAR system of the German Aerospace Center (DLR), Oberpfaffenhofen, and on real VHF-band data obtained from the South African SAR (SASAR) system. Both methods significantly suppressed the RFI in the real images investigated. It was found that the number of range lines upon which the LMS adaptive filter could operate without adaptively changing the filter tap weights was often well above 100. This facilitated the re-writing of the LMS adaptive filter in terms of an equivalent transfer function, which was then integrated with the range-compression stage of the range-Doppler SAR processing algorithm. Since the range-compression and the interference suppression could then be performed simultaneously, large computational savings were achieved. A technique was derived for suppressing the sidelobes which arise as a result of the interference suppression of the LMS adaptive filter. This method was also integrated with the range-compression stage of the range-Doppler processor, leading to a very efficient implementation of the entire RFI suppression routine. Comments: +Frequency/time/IFFT processing of stepped frequencies and applications toward radio frequency interferences (RFI). -
Josef Mittermayer.
Hochauflösende Verarbeitung von Radardaten mit synthetischer Apertur.
PhD thesis,
Universität-Gesamthochschule Siegen,
2000.
Keyword(s): SAR Processing,
Frequency Scaling Algorithm,
Comparison of Algorithms,
Range-Doppler Algorithm,
Wavenumber Domain Algorithm,
omega-k,
Range Migration Algorithm,
Polar Format Algorithm,
SPECAN,
Convolution Back-projection,
Spotlight SAR,
Stripmap SAR,
ScanSAR,
ESAR,
Airborne SAR,
Spaceborne SAR.
Abstract: In this thesis, the novel Frequency Scaling Algorithm for efficient and accurate interpolation-free processing of Spotlight SAR data with Dechirp on Receive has been developed. An accurate analytical model of the Spotlight illumination geometry for a straight flight path of the carrier is introduced. Using this model, a valid and an illuminated target area is defined. A new analytical formulation for SAR raw data with one-dimensional Dechirp on Receive Operation is derived, which expresses the Residual Video Phase Term by a convolution with a chirp signal. Starting with this formulation, an interpolation-free range cell migration correction is developed. This range cell migration correction is called Frequency Scaling. Due to the constant target illumination start and end time in Spotlight SAR data, the SPECAN approach offers a very efficient processing in azimuth but due to the poor accuracy, it has only been used for ScanSAR and not for Spotlight data up to now. Furthermore, a SPECAN approach always requires interpolations. In the frame of this thesis, an azimuth scaling operation has been developed, which allows a highly accurate and interpolation-free processing of Spotlight data by the SPECAN approach. The combination of SPECAN approach and azimuth scaling is first applied to ScanSAR data in order to improve the Extended Chirp Scaling Algorithm. Then it is extended to Spotlight processing. Spotlight raw data with one-dimensional Dechirp on Receive have to be upsampled in azimuth before the data processing. In order to avoid this upsampling, a subaperture approach is introduced, which reduces the required azimuth sampling during the processing down to the pulse repetition frequency of the raw data. The high quality performance of the Frequency Scaling Algorithm is demonstrated by processing simulated and real raw data acquired with the E-SAR-Sensor of DLR. The phase fidelity, which is important for many applications, is proved by point target processing and by the generation of an interferogram of an E-SAR scene. As application example, a spotlight interferogram is generated from E-SAR raw data. Interesting physical properties of the Spotlight mode are demonstrated by the comparison of a Spotlight and a Stripmap interferogram, processed from the same raw data. -
Daoxiang An,
Xiaotao Huang,
Tian Jin,
and Zhimin Zhou.
Extended Nonlinear Chirp Scaling Algorithm for High-Resolution Highly Squint SAR Data Focusing.
Geoscience and Remote Sensing, IEEE Transactions on,
50(9):3595-3609,
Sept. 2012.
ISSN: 0196-2892.
Keyword(s): geophysical image processing,
geophysical techniques,
image registration,
synthetic aperture radar,
2-D frequency domain,
2-D spectrum,
ANLCS operation,
ENLCS algorithm,
SAR data focusing,
applied azimuth frequency modulation rate,
bulk second range compression,
extended nonlinear chirp scaling algorithm,
fast Fourier transform,
highly squint angle,
image misregistration,
modified azimuth NLCS,
radar techniques,
range cell migration,
range-azimuth coupling,
Azimuth,
Chirp,
Couplings,
Focusing,
Frequency domain analysis,
Frequency modulation,
Highly squint angle,
linear range walk correction (LRWC),
nonlinear chirp scaling (NLCS),
synthetic aperture radar (SAR).
[bibtex-key = 6164256]
-
Daoxiang An,
Xiaotao Huang,
Tian Jin,
and Zhimin Zhou.
Extended Two-Step Focusing Approach for Squinted Spotlight SAR Imaging.
Geoscience and Remote Sensing, IEEE Transactions on,
50(7):2889-2900,
July 2012.
ISSN: 0196-2892.
Keyword(s): geophysical image processing,
remote sensing by radar,
synthetic aperture radar,
SAR imaging model,
Stolt-based technique,
azimuth coarse focusing,
extended two-step focusing approach,
nonlinear shift preprocessing method,
preprocessed echo data,
squint angle,
squinted spotlight SAR data,
squinted spotlight SAR imaging,
synthetic aperture radar,
Apertures,
Azimuth,
Bandwidth,
Doppler effect,
Focusing,
Frequency domain analysis,
Wrapping,
Deramping-based technique,
squinted spotlight synthetic aperture radar (SAR),
subscene processing.
[bibtex-key = 6095618]
-
B.J. Doring,
P.R. Looser,
M. Jirousek,
and M. Schwerdt.
Reference Target Correction Based on Point-Target SAR Simulation.
Geoscience and Remote Sensing, IEEE Transactions on,
50(3):951-959,
March 2012.
ISSN: 0196-2892.
Keyword(s): calibration,
geophysical image processing,
geophysical techniques,
interference (signal),
numerical analysis,
radiometry,
synthetic aperture radar,
transponders,
SAR image,
SAR system,
absolute radiometric calibration,
active transponders,
correction coefficients,
design process,
external radiometric calibration process,
frequency response,
imperfect targets,
instrument SAR mode settings,
interference signals,
man-made point targets,
numerical simulation,
passive corner reflectors,
point-target SAR simulation,
point-target SAR simulator,
point-target simulations,
radiometric calibration standard,
radiometric point-target uncertainties,
reference target correction,
synthetic aperture radar calibration,
target backscatter variation,
target properties,
transponder internal calibration strategies,
Bandwidth,
Calibration,
Frequency dependence,
Microwave radiometry,
Transfer functions,
Transponders,
Calibration,
measurement standard,
numerical simulation,
point target,
synthetic aperture radar.
[bibtex-key = 6003773]
-
Fan Feng,
Shiqiang Li,
Weidong Yu,
and Shuo Wang.
Study on the Processing Scheme for Space #x2013;Time Waveform Encoding SAR System Based on Two-Dimensional Digital Beamforming.
Geoscience and Remote Sensing, IEEE Transactions on,
50(3):910-932,
March 2012.
ISSN: 0196-2892.
Keyword(s): array signal processing,
radar imaging,
synthetic aperture radar,
2D DBF,
AASR,
RASR,
SAR system,
azimuth ambiguity-to-signal ratio,
range ASR,
space-time waveform encoding,
synthetic aperture radar,
two-dimensional digital beamforming,
Array signal processing,
Arrays,
Azimuth,
Chirp,
Encoding,
Image resolution,
Synthetic aperture radar,
Ambiguity suppression,
digital beamforming (DBF),
displaced phase center antenna (DPCA),
high-resolution wide-swath (HRWS),
single-input multiple-output (SIMO),
space–time waveform encoding (STWE),
synthetic aperture radar (SAR).
[bibtex-key = Feng_TGRS_2012]
-
Cheng Hu,
Zhipeng Liu,
and Teng Long.
An Improved CS Algorithm Based on the Curved Trajectory in Geosynchronous SAR.
Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal of,
5(3):795-808,
June 2012.
ISSN: 1939-1404.
Keyword(s): geophysical signal processing,
radar imaging,
remote sensing by radar,
series (mathematics),
synthetic aperture radar,
GEO SAR 2D spectrum,
GEO SAR imaging,
azimuth compression function,
chirp frequency rate,
chirp scaling algorithm,
curved trajectory,
geosynchronous SAR,
high order Taylor expansion,
linear trajectory model,
range compression function,
range migration factor,
satellite squint angle,
satellite velocity,
series reversion,
slant histories,
slant range history,
synthetic aperture radar,
vector expression,
Apertures,
Azimuth,
History,
Low earth orbit satellites,
Synthetic aperture radar,
Trajectory,
CS algorithm,
GEO SAR,
curved trajectory,
linear trajectory.
[bibtex-key = 6175967]
-
S.I. Kelly,
C. Du,
G. Rilling,
and M. E. Davies.
Advanced image formation and processing of partial synthetic aperture radar data.
Signal Processing, IET,
6(5):511-520,
July 2012.
ISSN: 1751-9675.
Keyword(s): approximation theory,
image reconstruction,
iterative methods,
least squares approximations,
radar imaging,
synthetic aperture radar,
N2 log2 N complexity,
SAR,
generative model,
image formation framework,
image processing,
image reconstruction,
iterative inversion algorithm,
partial synthetic aperture radar data,
phase errors correction,
polar format algorithm,
reback-projection algorithm,
regularised least square approximation.
[bibtex-key = 6297627]
-
Guangjie Kou,
Zhensong Wang,
and Ping Yao.
Multiple Beams Spaceborne SAR Imaging.
Aerospace and Electronic Systems, IEEE Transactions on,
48(4):3363-3375,
October 2012.
ISSN: 0018-9251.
Keyword(s): image sampling,
radar imaging,
radar resolution,
spaceborne radar,
synthetic aperture radar,
Earth rotation,
MAB SAR,
SAR systems,
azimuth resolution,
conventional spaceborne synthetic aperture radar systems,
differential path error,
displaced phase centers multiple azimuth beams,
multiple beams spaceborne SAR imaging,
nonuniform sampling error,
swath coverage pose contradicting requirements,
Azimuth,
Earth,
Nonuniform sampling,
Receivers,
Space vehicles,
Synthetic aperture radar,
Transmitters.
[bibtex-key = 6324715]
-
Yue Liu,
Yun Kai Deng,
and R. Wang.
Focus Squint FMCW SAR Data Using Inverse Chirp-Z Transform Based on an Analytical Point Target Reference Spectrum.
IEEE Geoscience and Remote Sensing Letters,
9(5):866-870,
Sept. 2012.
ISSN: 1545-598X.
Keyword(s): Azimuth,
Chirp,
Couplings,
Focusing,
Remote sensing,
Signal processing algorithms,
Synthetic aperture radar,
CW radar,
FM radar,
inverse transforms,
radar imaging,
remote sensing by radar,
synthetic aperture radar,
Earth observation,
FMCW imaging mode,
ICZT algorithm,
analytical point target reference spectrum,
computing load reduction,
dechirped signal,
focus squint FMCW SAR data,
frequency-modulated continuous-wave synthetic aperture radar systems,
interpolations,
inverse chirp-Z transform algorithm,
pulsed-mode systems,
range-azimuth coupling term,
receiving operations,
transmitting operations,
Frequency modulated continuous wave (FMCW),
inverse chirp-Z transform (ICZT),
range scaling factor,
synthetic aperture radar (SAR);.
[bibtex-key = Yue:GRSL12]
-
Yan Liu,
Mengdao Xing,
Guangcai Sun,
Xiaolei Lv,
Zheng Bao,
Wen Hong,
and YiRong Wu.
Echo Model Analyses and Imaging Algorithm for High-Resolution SAR on High-Speed Platform.
Geoscience and Remote Sensing, IEEE Transactions on,
50(3):933-950,
March 2012.
ISSN: 0196-2892.
Keyword(s): remote sensing by radar,
synthetic aperture radar,
SAR data,
SAR systems,
SAR working process,
echo model analyses,
high-resolution SAR,
high-resolution imaging,
high-speed platform,
imaging algorithm,
radar motion,
stop-go approximation,
synthetic aperture radar,
Approximation algorithms,
Approximation methods,
Azimuth,
Delay effects,
Imaging,
Spaceborne radar,
“stop–go†approximation,
Echo model,
high-resolution synthetic aperture radar (SAR) on high-speed platform,
two-step.
[bibtex-key = 6018295]
- Stephan Stanko, Winfried Johannes, Rainer Sommer, Alfred Wahlen, Martin Schroder, and Michael Caris. SUMATRA - A UAV based miniaturized SAR System. European Conference on Synthetic Aperture Radar, pp 437-440, Apr. 2012. Keyword(s): Airplanes, Antenna measurements, Radar antennas, Radar imaging, Radar measurements, Synthetic aperture radar;. [bibtex-key = Suma:EUSAR12]
-
G.-C. Sun,
M. Xing,
X.-G. Xia,
J. Yang,
Y. Wu,
and Z. Bao.
A Unified Focusing Algorithm for Several Modes of SAR Based on FrFT.
Geoscience and Remote Sensing, IEEE Transactions on,
PP(99):1-17,
2012.
ISSN: 0196-2892.
Keyword(s): Fractional Fourier transform (FrFT),
sliding spotlight synthetic aperture radar (SAR),
spotlight SAR,
stripmap SAR,
synthetic aperture radar (SAR),
terrain observation by progressive scans (TOPS) SAR,
unified focusing algorithm (UFA).
[bibtex-key = Sun_TGRS_2012]
-
Wen-Qin Wang and Jingye Cai.
MIMO SAR using Chirp Diverse Waveform for Wide-Swath Remote Sensing.
Aerospace and Electronic Systems, IEEE Transactions on,
48(4):3171-3185,
October 2012.
ISSN: 0018-9251.
Keyword(s): MIMO radar,
aperture antennas,
multibeam antennas,
numerical analysis,
radar antennas,
radar imaging,
receiving antennas,
remote sensing by radar,
synthetic aperture radar,
transmitting antennas,
waveform analysis,
MIMO SAR system,
MIMO antenna configuration,
antenna elevation,
chirp diverse waveform design,
chirp-scaling-based image formation algorithm,
multibeam forming algorithm,
multiple-input and multiple-output SAR,
next generation remote sensing technique,
numerical simulation,
range ambiguity performance,
single-antenna SAR system,
subperture antenna,
synthetic aperture radar,
transmit-receive virtual beam,
wide-swath remote sensing,
Arrays,
Azimuth,
Chirp modulation,
MIMO,
Radar antennas,
Remote sensing,
Synthetic aperture radar.
[bibtex-key = 6324689]
-
T. Xiong,
M. Xing,
X.-G. Xia,
and Z. Bao.
New Applications of Omega-K Algorithm for SAR Data Processing Using Effective Wavelength at High Squint.
Geoscience and Remote Sensing, IEEE Transactions on,
PP(99):1-14,
2012.
ISSN: 0196-2892.
Keyword(s): Azimuth,
Data processing,
Geometry,
Imaging,
Receivers,
Synthetic aperture radar,
Transmitters,
Bistatic synthetic aperture radar (BiSAR),
modified Stolt mapping (MSM),
modified omega-K algorithm,
monostatic SAR (MoSAR),
squinted effective wavelength (SEW),
synthetic aperture radar (SAR).
[bibtex-key = 6329425]
-
Lei Zhang,
Zhijun Qiao,
Meng-dao Xing,
Lei Yang,
and Zheng Bao.
A Robust Motion Compensation Approach for UAV SAR Imagery.
Geoscience and Remote Sensing, IEEE Transactions on,
50(8):3202-3218,
Aug. 2012.
ISSN: 0196-2892.
Keyword(s): autonomous aerial vehicles,
geophysical image processing,
geophysical techniques,
maximum likelihood estimation,
motion compensation,
remote sensing by radar,
synthetic aperture radar,
UAV SAR imagery,
atmospheric turbulence,
inertial navigation system,
maximum likelihood WPGA algorithm,
nonsystematic range cell migration function,
range dependent phase error,
range invariant motion error,
remote sensing application,
robust motion compensation approach,
subaperture phase error,
synthetic aperture radar,
unmanned aerial vehicle,
weighted phase gradient autofocus,
Electronics packaging,
Estimation,
Geometry,
Navigation,
Robustness,
Thyristors,
Trajectory,
Local maximum-likelihood (LML),
motion compensation (MOCO),
phase gradient autofocus (PGA),
synthetic aperture radar (SAR),
unmanned aerial vehicle (UAV),
weighted phase gradient autofocus (WPGA).
[bibtex-key = Zhang_MocoUAV_TGRS_2012]
-
Lei Zhang,
Jialian Sheng,
Mengdao Xing,
Zhijun Qiao,
Tao Xiong,
and Zheng Bao.
Wavenumber-Domain Autofocusing for Highly Squinted UAV SAR Imagery.
Sensors Journal, IEEE,
12(5):1574-1588,
May 2012.
ISSN: 1530-437X.
Keyword(s): autonomous aerial vehicles,
gradient methods,
radar imaging,
synthetic aperture radar,
SPGA based motion compensation,
highly squinted UAV SAR imagery,
highly squinted unmanned aerial vehicle SAR imagery,
nonsystematic error,
phase error,
quality phase gradient autofocus,
squinted phase gradient autofocus algorithm,
squinted wavenumber domain imaging,
synthetic aperture radar,
wavenumber domain autofocusing,
weighted phase gradient autofocus,
Algorithm design and analysis,
Approximation algorithms,
Azimuth,
Geometry,
Signal processing algorithms,
Synthetic aperture radar,
Trajectory,
High squinted SAR,
motion compensation (MoCo),
squinted phase gradient autofocus (SPGA),
synthetic aperture radar (SAR),
unmanned aerial vehicle (UAV).
[bibtex-key = Zhang_Sensors_2012]
-
D. Garmatyuk and M. Brenneman.
Adaptive Multicarrier OFDM SAR Signal Processing.
Geoscience and Remote Sensing, IEEE Transactions on,
49(10):3780-3790,
Oct. 2011.
ISSN: 0196-2892.
Keyword(s): OFDM modulation,
frequency-domain analysis,
radar imaging,
search problems,
synthetic aperture radar,
ultra wideband radar,
1-D cross-range profile reconstruction case,
adaptive multicarrier OFDM SAR signal processing,
frequency domain,
grid search algorithm,
range-Doppler algorithm,
synthetic aperture radar signal processing,
ultrawideband orthogonal frequency-division multiplexing,
History,
Image reconstruction,
OFDM,
Radar imaging,
Synthetic aperture radar,
Ultra wideband radar,
orthogonal frequency-division multiplexing (OFDM),
phase history,
radar imaging,
synthetic aperture radar (SAR),
ultrawideband (UWB) radar.
[bibtex-key = 6019043]
-
Cheng Hu,
Teng Long,
Tao Zeng,
Feifeng Liu,
and Zhipeng Liu.
The Accurate Focusing and Resolution Analysis Method in Geosynchronous SAR.
Geoscience and Remote Sensing, IEEE Transactions on,
49(10):3548-3563,
Oct. 2011.
ISSN: 0196-2892.
Keyword(s): artificial satellites,
radar imaging,
satellite communication,
synthetic aperture radar,
Doppler gradient vector,
Doppler parameter,
GEO SAR,
LEO SAR,
accurate focusing,
accurate resolution calculation,
curved synthetic aperture trajectory,
earth rotation,
generalized ambiguity function,
geosynchronous SAR,
low earth orbit SAR,
orbit height,
projection theory,
resolution analysis method,
satellite rotation,
signal propagation delay time,
stop-and-go assumption,
synthetic aperture time,
Apertures,
Azimuth,
Earth,
Focusing,
Orbits,
Satellites,
Geosynchronous SAR (GEO SAR),
gradient vector,
imaging method,
resolution analysis.
[bibtex-key = Cheng_TGRS_2011]
-
A. Ribalta.
Time-Domain Reconstruction Algorithms for FMCW-SAR.
IEEE Geoscience and Remote Sensing Letters,
8(3):396-400,
May 2011.
ISSN: 1545-598X.
Keyword(s): Approximation algorithms,
Approximation methods,
Image resolution,
Reconstruction algorithms,
Synthetic aperture radar,
Time domain analysis,
FM radar,
synthetic aperture radar,
FMCW-SAR,
backprojection algorithm,
frequency-modulated continuous wave synthetic aperture radar,
start-stop approximation,
time-domain correlation algorithm,
time-domain reconstruction,
Backprojection,
FMCW-SAR,
start-stop approximation,
time-domain reconstruction;.
[bibtex-key = Rib:GRSL11]
-
H. Breit,
T. Fritz,
U. Balss,
M. Lachaise,
A. Niedermeier,
and M. Vonavka.
TerraSAR-X SAR Processing and Products.
Geoscience and Remote Sensing, IEEE Transactions on,
48(2):727-740,
Feb. 2010.
ISSN: 0196-2892.
Keyword(s): geophysical signal processing,
radar signal processing,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
AD 2007 06,
AD 2008 01,
SAR data processing,
Spotlight,
TerraSAR multimode SAR processor,
TerraSAR-X,
commissioning phase,
remote sensing,
spaceborne SAR,
synthetic aperture radar,
Spotlight (SL),
TerraSAR multimode SAR processor (TMSP),
TerraSAR-X,
synthetic aperture radar (SAR).
[bibtex-key = 5356148]
-
Michael Jehle,
Othmar Frey,
David Small,
and Erich Meier.
Measurement of Ionospheric TEC in Spaceborne SAR Data.
IEEE Trans. Geosci. Remote Sens.,
48(6):2460-2468,
June 2010.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Total Electron Content Estimation,
TEC Estimation,
Ionospheric TEC,
Faraday Rotation,
Path Delay,
Autofocus,
TEC Autofocus,
Spaceborne SAR,
L-Band,
ALOS,
Phased Array L-band SAR,
PALSAR,
P-Pand,
Simulation,
Calibration.
Abstract: The propagation of spaceborne radar signals operating at L-band frequency or below can be seriously affected by the ionosphere. At high states of solar activity, Faraday rotation (FR) and signal path delays disturb radar polarimetry and reduce resolution in range and azimuth. While these effects are negligible at X-band, FR and the frequency-dependent path delays can become seriously problematic starting at L-band. For quality assurance and calibration purposes, existing L-band or potential spaceborne P-band missions require the estimation of the ionospheric state before or during the data take. This paper introduces two approaches for measuring the ionospheric total electron content (TEC) from single-polarized spaceborne SAR data. The two methods are demonstrated using simulations. Both methods leverage knowledge of the frequency-dependent path delay through the ionosphere: The first estimates TEC from the phase error of the filter mismatch, while the second gauges path-delay differences between up and down chirps. FR, mean (direct current) offsets, and noise contributions are also considered in the simulations. Finally, possibilities for further methodological improvements are discussed. -
G. Krieger,
I. Hajnsek,
K. P. Papathanassiou,
M. Younis,
and A. Moreira.
Interferometric Synthetic Aperture Radar (SAR) Missions Employing Formation Flying.
Proceedings of the IEEE,
98(5):816-843,
May 2010.
ISSN: 0018-9219.
Keyword(s): Tandem-L,
Tandem-X,
Formation Flying,
Spaceborne SAR.
Abstract: This paper presents an overview of single-pass interferometric Synthetic Aperture Radar (SAR) missions employing two or more satellites flying in a close formation. The simultaneous reception of the scattered radar echoes from different viewing directions by multiple spatially distributed antennas enables the acquisition of unique Earth observation products for environmental and climate monitoring. After a short introduction to the basic principles and applications of SAR interferometry, designs for the twin satellite missions TanDEM-X and Tandem-L are presented. The primary objective of TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement) is the generation of a global Digital Elevation Model (DEM) with unprecedented accuracy as the basis for a wide range of scientific research as well as for commercial DEM production. This goal is achieved by enhancing the TerraSAR-X mission with a second TerraSAR-X like satellite that will be launched in spring 2010. Both satellites act then as a large single-pass SAR interferometer with the opportunity for flexible baseline selection. Building upon the experience gathered with the TanDEM-X mission design, the fully polarimetric L-band twin satellite formation Tandem-L is proposed. Important objectives of this highly capable interferometric SAR mission are the global acquisition of three-dimensional forest structure and biomass inventories, large-scale measurements of millimetric displacements due to tectonic shifts, and systematic observations of glacier movements. The sophisticated mission concept and the high data-acquisition capacity of Tandem-L will moreover provide a unique data source to systematically observe, analyze, and quantify the dynamics of a wide range of additional processes in the bio-, litho-, hydro-, and cryosphere. By this, Tandem-L will be an essential step to advance our understanding of the Earth system and its intricate dynamics. Enabling technologies and techniques are described in detail. An ou- tlook on future interferometric and tomographic concepts and developments, including multistatic SAR systems with multiple receivers, is provided. -
P. Lopez-Dekker and J.J. Mallorqui.
Capon- and APES-Based SAR Processing: Performance and Practical Considerations.
Geoscience and Remote Sensing, IEEE Transactions on,
48(5):2388-2402,
May 2010.
ISSN: 0196-2892.
Keyword(s): geophysical techniques,
spectral analysis,
synthetic aperture radar,
2D spectral analysis,
APES-based SAR processing,
Barcelona,
Capon processing chain,
Monte Carlo simulations,
RADARSAT-2 quad-polarization data,
Spain,
adaptive processing,
chip-image size,
diagonal loading,
joint-processing approach,
minimum variance method,
resampling factor,
spectral-estimation algorithms,
synthetic aperture radar,
2-D spectral analysis,
Adaptive processing,
synthetic aperture radar.
[bibtex-key = Lopez_TGRS_2012]
-
Andrea Monti-Guarnieri and Stefano Tebaldini.
ML-Based Fringe-Frequency Estimation for InSAR.
IEEE Geoscience and Remote Sensing Letters,
7(1):136-140,
January 2010.
ISSN: 1545-598X.
Keyword(s): SAR Processing,
InSAR,
SAR Interferometry,
ENVISAR,
ASAR.
Abstract: This letter focuses on estimating the local fringe frequency of the interferometric phase, under the hypothesis of superficial scattering. Starting from the formulation of the maximum-likelihood estimator, a new simplified estimator is derived. Due to computational efficiency and robustness versus model errors, the resulting estimator is suited for large data processing in the presence of model uncertainty. Furthermore, such an estimator can be straightforwardly extended to the multibaseline case, resulting in the possibility to estimate the terrain slope with great accuracy. An application to real data is presented, based on a multibaseline ENVISAT data set. -
P. Prats,
R. Scheiber,
J. Mittermayer,
A. Meta,
and A. Moreira.
Processing of Sliding Spotlight and TOPS SAR Data Using Baseband Azimuth Scaling.
Geoscience and Remote Sensing, IEEE Transactions on,
48(2):770-780,
Feb. 2010.
ISSN: 0196-2892.
Keyword(s): data acquisition,
geophysical image processing,
radar imaging,
synthetic aperture radar,
Doppler centroid,
SAR processing,
ScanSAR mode,
TOPS SAR Data,
TerraSAR-X,
azimuth processing,
baseband azimuth scaling,
data focusing,
phase preserving processor,
sliding spotlight,
synthetic aperture radar,
terrain observation,
Azimuth scaling,
SAR processing,
ScanSAR,
Terrain Observation by Progressive Scans (TOPS),
spotlight,
synthetic aperture radar (SAR).
[bibtex-key = 5272449]
- Angel Ribalta, Ludwig Roessing, Patrick Berens, Manfred Haegelen, and Alfred Wahlen. High Resolution FMCW-SAR Image Generation. European Conference on Synthetic Aperture Radar, pp 1-4, June 2010. Keyword(s): Chirp, Image resolution;. [bibtex-key = Rib:EUSAR2010]
-
M. Rodriguez-Cassola,
S.V. Baumgartner,
G. Krieger,
and A. Moreira.
Bistatic TerraSAR-X/F-SAR Spaceborne-Airborne SAR Experiment: Description, Data Processing, and Results.
IEEE_J_GRS,
48(2):781-794,
February 2010.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Bistatic SAR,
Doppler information,
German Aerospace Center,
TerraSAR-X/F-SAR bistatic data,
backscatter,
bistatic backprojection algorithm,
bistatic synthetic aperture radar,
calibration,
data processing,
first X-band spaceborne-airborne SAR,
nonstationary bistatic acquisitions,
phase-preserving bistatic focusing,
synchronization algorithm,
airborne radar,
backscatter,
calibration,
data acquisition,
geophysical signal processing,
radar signal processing,
remote sensing by radar,
spaceborne radar,
synchronisation,
synthetic aperture radar;.
Abstract: We report about the first X-band spaceborne-airborne bistatic synthetic aperture radar (SAR) experiment, conducted early November 2007, using the German satellite TerraSAR-X as transmitter and the German Aerospace Center's (DLR) new airborne radar system F-SAR as receiver. The importance of the experiment resides in both its pioneering character and its potential to serve as a test bed for the validation of nonstationary bistatic acquisitions, novel calibration and synchronization algorithms, and advanced imaging techniques. Due to the independent operation of the transmitter and receiver, an accurate synchronization procedure was needed during processing to make high-resolution imaging feasible. Precise phase-preserving bistatic focusing can only be achieved if time and phase synchronization exist. The synchronization approach, based on the evaluation of the range histories of several reference targets, was verified through a separate analysis of the range and Doppler contributions. After successful synchronization, nonstationary focusing was performed using a bistatic backprojection algorithm. During the campaign, stand-alone TerraSAR-X monostatic as well as interoperated TerraSAR-X/F-SAR bistatic data sets were recorded. As expected, the bistatic image shows a space-variant behavior in spatial resolution and in signal-to-noise ratio. Due to the selected configuration, the bistatic image outperforms its monostatic counterpart in almost the complete imaged scene. A detailed comparison between monostatic and bistatic images is given, illustrating the complementarity of both measurements in terms of backscatter and Doppler information. The results are of fundamental importance for the development of future nonsynchronized bistatic SAR systems. -
M. Shimada.
Ortho-Rectification and Slope Correction of SAR Data Using DEM and Its Accuracy Evaluation.
Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal of,
3(4):657-671,
Dec. 2010.
ISSN: 1939-1404.
Keyword(s): calibration,
digital elevation models,
radiometry,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
topography (Earth),
ALOS PALSAR data,
Advanced Land Observing Satellite,
DEM-based simulated SAR image,
Phased Array Type L-band SAR,
digital elevation model,
foreshortening,
ground control points,
layover,
ortho-rectification,
radiometric modulation,
radiometric variation,
range and azimuth shift,
shadowing,
slope correction,
synthetic aperture radar,
terrain height variation,
Calibration,
Doppler effect,
Radar imaging,
Radiometry,
Synthetic aperture radar,
ALOS,
PALSAR,
SAR simulation image,
calibration and validation,
ortho-rectification.
[bibtex-key = Shim_STAEORS_2010]
-
I. Walterscheid,
T. Espeter,
A.R. Brenner,
J. Klare,
J. H G Ender,
H. Nies,
R. Wang,
and O. Loffeld.
Bistatic SAR Experiments With PAMIR and TerraSAR-X #x2014;Setup, Processing, and Image Results.
Geoscience and Remote Sensing, IEEE Transactions on,
48(8):3268-3279,
Aug. 2010.
ISSN: 0196-2892.
Keyword(s): airborne radar,
data acquisition,
geophysical image processing,
geophysical techniques,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
Phased Array Multifunctional Imaging Radar,
TerrasSAR-X satellite,
airborne experiments,
beam steering,
bistatic SAR experiments,
bistatic synthetic aperture radar,
data acquisition,
double sliding spotlight mode,
frequency-domain algorithm,
hybrid experiments,
image processing,
modified backprojection algorithm,
phased-array antennas,
spaceborne experiments,
synchronization system,
Bistatic synthetic aperture radar (bistatic SAR),
SAR,
hybrid experiments,
synchronization.
[bibtex-key = Walterscheid_TGRS_2010]
-
R. Wang,
O. Loffeld,
Y.L. Neo,
H. Nies,
I. Walterscheid,
T. Espeter,
J. Klare,
and J. Ender.
Focusing Bistatic SAR Data in Airborne/Stationary Configuration.
IEEE_J_GRS,
48(1):452-465,
January 2010.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Bistatic SAR,
BiSAR data,
Forschungsgesellschaft fur Angewandte Naturwissenschaften,
PAMIR,
Transall C-160,
airborne SAR system,
azimuth modulation,
bistatic SAR airborne-stationary configuration,
bistatic SAR data,
bistatic point-target reference spectrum,
frequency domain based focusing algorithm,
interpolation free wavenumber domain algorithm,
range offset,
range variant interpolation,
stationary X-band transmitter,
synthetic aperture radar,
target azimuth position,
target range migration trajectory,
airborne radar,
geophysical signal processing,
interpolation,
radar signal processing,
remote sensing by radar,
synthetic aperture radar;.
Abstract: This paper presents a frequency-domain-based focusing algorithm for the bistatic synthetic aperture radar (BiSAR) data in airborne/stationary configuration. In this bistatic configuration, only the moving platform contributes to the azimuth modulation, whereas the stationary platform introduces a range offset (RO) to the range migration trajectories of targets at the same range. The offset is determined by the azimuth position of different targets with respect to the stationary platform. Since the RO is position dependent, monostatic SAR imaging algorithms are not able to focus the bistatic data collected in this configuration. In this paper, an analytical bistatic point-target reference spectrum is derived, and then, a frequency-domain-based algorithm is developed to focus the bistatic data. It uses an interpolation-free wavenumber-domain algorithm as a basis and performs a range-variant interpolation to correct the position-dependent RO in the image domain after coarse focusing. The proposed algorithm is validated by the simulated data and the real BiSAR data acquired by the Forschungsgesellschaft fU¿r Angewandte Naturwissenschaften's airborne SAR system, PAMIR, in December 2007. In this BiSAR experiment, an X-band transmitter was stationary operated on a hill with PAMIR as the receiver mounted on a Transall C-160. -
R. Wang,
O. Loffeld,
H. Nies,
S. Knedlik,
M. Hagelen,
and H. Essen.
Focus FMCW SAR Data Using the Wavenumber Domain Algorithm.
IEEE Transactions on Geoscience and Remote Sensing,
48(4):2109-2118,
Apr. 2010.
ISSN: 0196-2892.
Keyword(s): CW radar,
FM radar,
geophysical signal processing,
geophysical techniques,
remote sensing by radar,
synthetic aperture radar,
FMCW SAR data,
Stolt mapping,
X-band simulation,
frequency-modulation continuous-wave technology,
high-quality imaging sensor,
image quality,
point target reference spectrum,
range cell migration correction,
range-azimuth coupling,
remote sensing,
signal duration time,
signal model,
spotlight modes,
synthetic aperture radar,
wavenumber domain algorithm,
Frequency-modulation continuous wave (FMCW),
point target reference spectrum (PTRS),
range cell migration correction (RCMC),
wavenumber domain algorithm (WDA);.
[bibtex-key = WangLof:TGRS09]
-
C. Bhattacharya and P.R. Mahapatra.
A Generalized Approach to Multiresolution Complex SAR Signal Processing.
Aerospace and Electronic Systems, IEEE Transactions on,
45(3):1089-1103,
July 2009.
ISSN: 0018-9251.
Keyword(s): filtering theory,
radar imaging,
synthetic aperture radar,
wavelet transforms,
biorthogonal shift invariant discrete wavelet transform,
diffuse backscatter,
improved imaging,
multiresolution complex SAR signal processing,
multiresolution synthetic aperture radar image formation,
multiscale complex matched filtering,
speckle reduction,
subband decomposition property,
target detection,
wavelet packet transform,
Azimuth,
Biomedical signal processing,
Discrete wavelet transforms,
Image resolution,
Object detection,
Radar signal processing,
Signal processing,
Signal resolution,
Speckle,
Synthetic aperture radar.
[bibtex-key = 5259185]
-
Antonio De Maio,
Gianfranco Fornaro,
and Antonio Pauciullo.
Detection of Single Scatterers in Multidimensional SAR Imaging.
Geoscience and Remote Sensing, IEEE Transactions on,
47(7):2284-2297,
July 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
radar imaging,
radar interferometry,
synthetic aperture radar,
CFAR detection scheme,
Rao test,
SAR imaging,
SAR interferometry,
Wald test,
constant false alarm rate,
differential interferometry,
generalized likelihood ratio test,
multi-interferogram complex coherence,
multidimensional synthetic aperture radar,
scatterer interferometry,
single scatterers detection,
space deformation-velocity analysis.
Abstract: Multidimensional synthetic aperture radar (SAR) imaging is a technique based on coherent SAR data combination for space (full 3-D) and space deformation-velocity (4-D) analysis. It is an extension of the concepts of SAR interferometry and differential interferometry SAR and offers new options for the analysis and monitoring of ground scenes. In this paper, we consider the problem of detecting single scatterers for localization and monitoring issues. To this end, we resort to a constant false alarm rate (CFAR) detection scheme which can be synthesized according to three different design criteria: generalized likelihood ratio test, Rao test, and Wald test. At the analysis stage, the performance of the aforementioned detector is compared to that of a previously proposed CFAR scheme, based on the multi-interferogram complex coherence and widely used in persistent scatterer interferometry. The analysis is conducted both on simulated and on real SAR data, acquired by ERS-1/2 satellites. Finally, Cramer-Rao lower bounds for the estimation of the scatterer elevation and velocity are provided. -
Esra Erten,
Andreas Reigber,
Olaf Hellwich,
and Pau Prats.
Glacier Velocity Monitoring by Maximum Likelihood Texture Tracking.
IEEE Transactions on Geoscience and Remote Sensing,
47(2):394-405,
Feb. 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
glaciology,
hydrological techniques,
image processing,
maximum likelihood estimation,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
Asia,
ENVISAT-ASAR data acquisition,
Inyltshik glacier,
Kyrgyzstan,
Maximum Likelihood Texture Tracking,
alpine glacier systems,
classical intensity tracking technique,
glacier velocities measurement,
glacier velocity monitoring,
ice flows,
intensity-based matching algorithm,
melting,
multiplicative speckle/noise model,
remotely sensed data,
signal-to-noise ratio,
snowfall,
spatial dynamics,
speckle decorrelation,
statistical description,
synthetic aperture radar data,
temporal dynamics,
temporal speckle structure,
tracking algorithm.
Abstract: The performance of a tracking algorithm considering remotely sensed data strongly depends on a correct statistical description of the data, i.e., its noise model. The objective of this paper is to introduce a new intensity tracking algorithm for synthetic aperture radar (SAR) data, considering its multiplicative speckle/noise model. The proposed tracking algorithm is discussed regarding the measurement of glacier velocities. Glacier monitoring exhibits complex spatial and temporal dynamics including snowfall, melting, and ice flows at a variety of spatial and temporal scales. Due to these complex characteristics, most traditional methods based on SAR suffer from speckle decorrelation that results in a low signal-to-noise ratio. The proposed tracking technique improves the accuracy of the classical intensity tracking technique by making use of the temporal speckle structure. Even though a new intensity-based matching algorithm is proposed, particularly for incoherent data sets, the analysis of the proposed technique was also performed for correlated data sets. As it is demonstrated, the velocity monitoring can be continuously performed by using the maximum likelihood (ML) texture tracking without any assumption concerning the correlation of the data set. The ML texture tracking approach was tested on ENVISAT-ASAR data acquired during summer 2004 over the Inyltshik glacier in Kyrgyzstan, representing one of the largest alpine glacier systems of the world. It will be demonstrated that the proposed technique is capable of robustly and precisely detecting the surface velocity field and velocity changes in time. -
Gianfranco Fornaro and Antonio Pauciullo.
LMMSE 3-D SAR Focusing.
IEEE Transactions on Geoscience and Remote Sensing,
47(1):214-223,
January 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
data acquisition,
remote sensing by radar,
singular value decomposition,
synthetic aperture radar,
LMMSE,
synthetic aperture radar imaging systems,
antenna SAR sensor,
atmospheric phase miscalibration,
atmospheric residual miscalibration,
beamforming,
data correlation properties,
data integration,
linear minimum mean square error method,
multistatic data acquisition,
satellite technology,
singular values decomposition inversion,
stochastic process.
Abstract: Three-dimensional synthetic aperture radar (SAR) imaging, a technique also known as SAR tomography, uses multiple views to extend the capability of SAR systems to 3-D imaging by achieving a profiling of the scattering power at different heights. Multiple views are obtained with the current satellite technology via successive passes of a single antenna SAR sensor over the same scene, but next-generation sensor formations are foreseen to acquire multistatic data. Conventional processing, such as the beamforming, or singular values decomposition inversion is based on geometrical derivations and, hence, assumes the accurate phase calibration and the absence of target decorrelation. This paper analyzes the effects of phase miscalibration due to residual uncompensated atmospheric contribution and temporal decorrelation and proposes a 3-D imaging technique based on a linear minimum mean square error approach. The resulting algorithm extends the possibilities of the conventional processing by carrying out an integration of data that accounts for the a priori data correlation properties. Hence, it allows handling of the presence of additional stochastic contributions such as: temporal coherence losses and atmospheric phase miscalibration. Moreover, with reference to future bistatic and multistatic systems, it permits an improved coherent integration of data acquired by simultaneous antenna in repeated passes. -
G. Fornaro,
D. Reale,
and F. Serafino.
Four-Dimensional SAR Imaging for Height Estimation and Monitoring of Single and Double Scatterers.
IEEE Transactions on Geoscience and Remote Sensing,
47(1):224-237,
Jan. 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
geophysical signal processing,
geophysical techniques,
height measurement,
radar signal processing,
remote sensing by radar,
synthetic aperture radar4D SAR imaging application,
4D space-velocity imaging,
SAR signal postprocessing,
differential SAR tomography,
double scatterer monitoring,
ground scatterers,
height estimation,
interfering target separation,
mean deformation velocity,
multipass SAR interferometry,
nonlinear temporal deformations,
single scatterer monitoring,
slow deformation velocity,
synthetic aperture radar,
target contribution superposition.
Abstract: The superposition of contributions from different stable targets within the same pixel is a phenomenon that may impair the imaging and monitoring of ground scatterers via the multipass synthetic aperture radar (SAR) interferometry technique. Three-dimensional SAR imaging, also known as SAR tomography, uses multiple views to profile the scattering power at different heights. This technique has been shown to be capable of separating interfering target responses on real data. Differential SAR tomography has been recently proposed as a technique that extends the potentialities of SAR tomography to the target deformation monitoring. It performs a 4-D space-velocity imaging that enables not only separating interfering targets in elevation but also distinguishing their single slow deformation velocities. This work addresses for the first time the application of 4-D SAR imaging to real data to determine the height and mean deformation velocity of single scatterers and double-scattering mechanisms interfering at high resolution in the same pixel. It also discusses the postprocessing steps required to identify the presence of stable single and double scatterers after elevation-velocity focusing. Moreover, it proposes a technique for the extraction of time series from interfering targets to measure possible nonlinear temporal deformations. -
Othmar Frey,
Christophe Magnard,
Maurice Rüegg,
and Erich Meier.
Focusing of Airborne Synthetic Aperture Radar Data from Highly Nonlinear Flight Tracks.
IEEE Trans. Geosci. Remote Sens.,
47(6):1844-1858,
June 2009.
Keyword(s): SAR Processing,
Time-Domain Back-Projection,
Back-Projection,
Non-Linear Flight Tracks,
Curvilinear SAR,
Extended Chirp Scaling,
ECS,
Mosaicking,
Geocoding,
Integrated Focusing and Geocoding,
Georeferencing,
mapping,
corridor mapping,
E-SAR,
L-Band,
digital elevation model,
Airborne SAR.
Abstract: Standard focusing of data from synthetic aperture radar (SAR) assumes a straight recording track of the sensor platform. Small non-linearities of airborne platform tracks are corrected for during a motion compensation step while maintaining the assumption of a linear flight path. This paper describes the processing of SAR data acquired from non-linear tracks, typical of sensors mounted on small aircraft or drones flying at low altitude. Such aircraft do not fly along straight tracks, but the trajectory depends on topography, influences of weather and wind, or the shape of areas of interest such as rivers or traffic routes. Two potential approaches for processing SAR data from such highly non-linear flight tracks are proposed: a patchwise frequency-domain processing and mosaicking technique, as well as a time-domain back-projection based technique. Both are evaluated with the help of experimental data featuring tracks with altitude changes, a double bend, a 90-degree curve and a linear flight track. In order to assess the quality of the focused data, close-ups of amplitude images are compared, impulse response functions of a point target are analyzed, and the coherence is evaluated. The experimental data was acquired by the German Aerospace Center's E-SAR L-band system. -
Franck Garestier,
Pascale C. Dubois-Fernandez,
Dominique Guyon,
and Thuy Le Toan.
Forest Biophysical Parameter Estimation Using L- and P-Band Polarimetric SAR Data.
IEEE Transactions on Geoscience and Remote Sensing,
47(10):3379-3388,
October 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Biomass,
Biophysical Parameters,
Forst,
L-Band,
P-Band,
PolSAR,
SAR Polarimetry,
Airborne SAR,
RAMSES,
ONERA.
Abstract: L- and P-band airborne polarimetric synthetic aperture radar (SAR) data acquired by the RAMSES system over different height maritime pine (Pinus Pinaster Ait.) stands of the Nezer forest (Landes, France) have been evaluated for forest biophysical parameter estimation. A pseudolinear correlation has been brought to evidence at P-band between polarimetric anisotropy and mean tree height, which is also linked to other biophysical parameters in the Nezer forest, meaning that SAR polarimetry constitutes a promising tool for forest parameter retrieval at low frequency. The spatial conditions have been evaluated through the quantification of the impact of signal-to-noise ratio diminution and resolution degradation on the forest height inversion. It has been shown that the inversion accuracy remains acceptable for $NEsigma_{0}$, representing the noise level of the SAR image, which is lower than $-$15 dB, and for spatial resolution increasing up to 15 m. -
Scott Goetz,
Alessandro Baccini,
Nadine Laporte,
Tracy Johns,
Wayne Walker,
Josef Kellndorfer,
Richard Houghton,
and Mindy Sun.
Mapping and monitoring carbon stocks with satellite observations: a comparison of methods.
Carbon Balance and Management,
4(1):2,
2009.
ISSN: 1750-0680.
Keyword(s): Carbon Balance,
Carbon stock,
DESDynl mission,
Biomass mission,
biomass,
ecosystem function,
ecosystem structure,
integrated L-band InSAR,
Lidar,
vegetation structure,
optical,
synthetic aperture radar,
vegetation mapping.
Abstract: Mapping and monitoring carbon stocks in forested regions of the world, particularly the tropics, has attracted a great deal of attention in recent years as deforestation and forest degradation account for up to 30 percent of anthropogenic carbon emissions, and are now included in climate change negotiations. We review the potential for satellites to measure carbon stocks, specifically aboveground biomass (AGB), and provide an overview of a range of approaches that have been developed and used to map AGB across a diverse set of conditions and geographic areas. We provide a summary of types of remote sensing measurements relevant to mapping AGB, and assess the relative merits and limitations of each. We then provide an overview of traditional techniques of mapping AGB based on ascribing field measurements to vegetation or land cover type classes, and describe the merits and limitations of those relative to recent data mining algorithms used in the context of an approach based on direct utilization of remote sensing measurements, whether optical or lidar reflectance, or radar backscatter. We conclude that while satellite remote sensing has often been discounted as inadequate for the task, attempts to map AGB without satellite imagery are insufficient. Moreover, the direct remote sensing approach provided more coherent maps of AGB relative to traditional approaches. We demonstrate this with a case study focused on continental Africa and discuss the work in the context of reducing uncertainty for carbon monitoring and markets. -
Irena Hajnsek,
Thomas Jagdhuber,
Helmut Schön,
and Konstantinos P. Papathanassiou.
Potential of Estimating Soil Moisture Under Vegetation Cover by Means of PolSAR.
IEEE Transactions on Geoscience and Remote Sensing,
47(2):442-454,
Feb. 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
agriculture,
crops,
moisture,
radar polarimetry,
remote sensing by radar,
soil,
synthetic aperture radarAgriSAR campaign,
L-band,
PolSAR images,
PolSAR,
agricultural vegetation,
canonical scattering components,
crop types,
dihedral components,
polarimetric SAR acquisitions,
scattering processes,
soil moisture estimation,
synthetic aperture radar,
vegetation cover,
ESAR,
Airborne SAR.
Abstract: In this paper, the potential of using polarimetric SAR (PolSAR) acquisitions for the estimation of volumetric soil moisture under agricultural vegetation is investigated. Soil-moisture estimation by means of SAR is a topic that is intensively investigated but yet not solved satisfactorily. The key problem is the presence of vegetation cover which biases soil-moisture estimates. In this paper, we discuss the problem of soil-moisture estimation in the presence of agricultural vegetation by means of L-band PolSAR images. SAR polarimetry allows the decomposition of the scattering signature into canonical scattering components and their quantification. We discuss simple canonical models for surface, dihedral, and vegetation scattering and use them to model and interpret scattering processes. The performance and modifications of the individual scattering components are discussed. The obtained surface and dihedral components are then used to retrieve surface soil moisture. The investigations cover, for the first time, the whole vegetation-growing period for three crop types using SAR data and ground measurements acquired in the frame of the AgriSAR campaign. -
Michael Jehle,
Maurice Rüegg,
Lukas Zuberbühler,
David Small,
and Erich Meier.
Measurement of Ionospheric Faraday Rotation in Simulated and Real Spaceborne SAR Data.
IEEE Trans. Geosci. Remote Sens.,
47(5):1512-1523,
May 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Ionosphere,
ALOS PALSAR,
Advanced Land Observing Satellite,
Earth's magnetic field,
PALSAR data,
Phased Array L-band Synthetic Aperture Radar,
focused radar images,
frequency-modulated electromagnetic wave traverse,
ionospheric Faraday Rotation measurement,
radar polarimetry,
range-compressed,
signal chirp bandwidth effects,
signal path delays,
spaceborne SAR data,
spaceborne synthetic aperture radar,
total electron content,
TEC,
Faraday effect,
ionospheric electromagnetic wave propagation,
radar polarimetry,
radar signal processing,
remote sensing by radar,
synthetic aperture radar;.
Abstract: The influence of the atmosphere on a frequency-modulated electromagnetic wave traversing the ionosphere is becoming increasingly important for recent and upcoming low-frequency and wide-bandwidth spaceborne synthetic aperture radar (SAR) systems. The ionized ionosphere induces Faraday rotation (FR) at these frequencies that affects radar polarimetry and causes signal path delays resulting in a reduced range resolution. The work at hand introduces a simulation model of SAR signals passing through the atmosphere, including both frequency-dependent FR and path delays. Based on simulation results from this model [proven with real Advanced Land Observing Satellite Phased Array L-band Synthetic Aperture Radar (PALSAR) data], estimation of FR in quad-polarized SAR data using the given approach is shown for raw, range-compressed, and focused radar images. Path delays and signal chirp bandwidth effects are considered. Investigations discuss the suitability of raw and compressed data versus combination of total electron content maps with the Earth's magnetic field for FR estimation and deduced from a large number of analyzed PALSAR data sets. -
Matteo Nannini,
Rolf Scheiber,
and Alberto Moreira.
Estimation of the Minimum Number of Tracks for SAR Tomography.
IEEE Transactions on Geoscience and Remote Sensing,
47(2):531-543,
Feb. 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
SAR Tomography,
Capon,
MUSIC,
image reconstruction,
airboren SAR,
image representation,
radar interferometry,
synthetic aperture radar3D representation,
German Aerospace Center,
DLR,
L-band,
SAR interferometry,
SARTom,
data acquisition,
equivalent targets,
experimental SAR system,
minimum tomographic aperture,
spheroidal wave functions,
subspace superresolution methods,
synthetic aperture radar tomography,
tracks minimum number determination,
volumetric source,
ESAR.
Abstract: Synthetic aperture radar tomography (SARTom) is the natural extension of SAR interferometry to solve for multiple phase centers within a resolution cell and obtain the 3-D representation of a scene. This paper deals with the determination of the minimum number of tracks required to perform SARTom. Through the prolate spheroidal wave functions, the number of equivalent targets of a volumetric source is derived, and from it, the minimum number of observations required to apply subspace superresolution methods is computed. The minimum tomographic aperture length is also investigated. The results are validated on real data acquired in L-band by the experimental SAR system of the German Aerospace Center. -
Pau Prats,
Rolf Scheiber,
Andreas Reigber,
Christian Andres,
and Ralf Horn.
Estimation of the Surface Velocity Field of the Aletsch Glacier Using Multibaseline Airborne SAR Interferometry.
IEEE Transactions on Geoscience and Remote Sensing,
47(2):419-430,
Feb. 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
InSAR,
DInSAR,
airborne SAR,
glaciology,
hydrological techniques,
SAR Interferometry,
Interferometry,
remote sensing by radar,
synthetic aperture radar,
Aletsch Glacier,
Alps,
German Aerospace Center,
L-band,
airborne interferometric synthetic aperture radar,
data acquisition,
differential interferometry,
experimental SAR system,
line-of-sight displacement,
multisquint approach,
navigation system,
residual motion errors,
surface velocity field estimation,
temperate glaciers,
ESAR.
Abstract: This paper presents a methodology to process airborne interferometric synthetic aperture radar (SAR) data to measure surface velocity fields (SVFs) of temperate glaciers, and applies it to data acquired over the Aletsch glacier. The first part of this paper deals with the main limitation in airborne interferometric SAR to retrieve reliable interferometric products, namely, the existence of the so-called residual motion errors - inaccuracies on the order of a few centimeters in the navigation system. An extended multisquint approach is proposed for their estimation in the case of nonstationary scenes. The second part of this paper expounds an efficient methodology to derive SVFs with airborne systems, where the line-of-sight displacement is estimated using differential interferometry and the along-track component by estimating the azimuth coregistration offsets. The necessary steps to finally obtain the 3-D SVF are also presented, as well as the possibility of combining different acquisition geometries. Airborne interferometric SAR data acquired by the Experimental SAR system of the German aerospace center over the Aletsch glacier, located in the Swiss Alps, are used to evaluate the performance of the proposed approach. The motion of the corner reflectors deployed in the scene is retrieved with an accuracy between 1 and 5 cm/day using L-band data. -
S. Sauer,
L. Ferro-Famil,
A. Reigber,
and E. Pottier.
Polarimetric Dual-Baseline InSAR Building Height Estimation at L-Band.
IEEE Geoscience and Remote Sensing Letters,
6(3):408-412,
July 2009.
ISSN: 1545-598X.
Keyword(s): SAR Procerssing,
PolInSAR,
Polarimetry,
InSAR,
SAR Interferometry,
Dual-Baseline,
Multi-baseline SAR,
SAR Tomography,
Tomography,
ESAR,
Airborne SAR,
Building Height.
Abstract: This letter generalizes a multibaseline interferometric synthetic aperture radar (InSAR) signal model to the polarimetric scenario. Based on this formulation, two high-performance spectral analysis techniques are adapted to process multibaseline Pol-InSAR observations. These new methods enhance the height estimation of scatterers by calculating optimal polarization combinations and allow the determination of their physical characteristics. Applying the proposed algorithms to urban environments, the building layover problem is analyzed by means of polarimetric dual-baseline InSAR measurements: the ground and building height are estimated. The techniques are validated using dual-baseline Pol-InSAR data acquired by DLR's Experimental SAR (E-SAR) system over Dresden city. -
Stefano Tebaldini.
Algebraic Synthesis of Forest Scenarios From Multibaseline PolInSAR Data.
IEEE Transactions on Geoscience and Remote Sensing,
47(12):4132-4142,
December 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
E-SAR,
P-Band,
algebra,
geophysical techniques,
radar polarimetry,
remote sensing by radar,
synthetic aperture radar,
vegetationBioSAR,
E-SAR airborne system,
Kronecker products sum,
P-band data set,
Remningstorp,
SAR surveys,
Sweden,
algebraic synthesis,
forest scenarios,
forested areas,
least square solution,
multibaseline PolInSAR data,
multipolarimetric multibaseline synthetic aperture radar,
single-baseline polarimetric SAR interferometry,
statistical uncorrelation,
temporal coherence losses,
volumetric coherence losses.
Abstract: In this paper, a new methodology is proposed for the analysis of forested areas basing on multipolarimetric multibaseline synthetic aperture radar (SAR) surveys. Such a methodology is based on three hypotheses: 1) statistical uncorrelation of the different scattering mechanisms (SMs), such as ground, volume, and ground-trunk scattering; 2) independence of volumetric and temporal coherence losses of each SM on the choice of the polarimetric channel; and 3) invariance (up to a scale factor) of the average polarimetric signature of each SM with respect to the choice of the track. Under these hypotheses, the data covariance matrix can be expressed as a Sum of Kronecker Products, after which it follows that K SMs are uniquely identified by K (K - 1) real numbers. This result provides the basis to perform SM separation by employing not only model-based approaches, generally retained in literature but also model-free and hybrid approaches, while yielding the best Least Square solution given the hypothesis of K SMs. It will be shown that this approach to SM separation is consistent with the inversion procedures usually exploited in single-baseline polarimetric SAR interferometry. Experimental validation of this methodology is provided on the basis of the P-band data set relative to the forest site of Remningstorp, Sweden, acquired by German Aerospace Center's E-SAR airborne system in the framework of the European Space Agency campaign BioSAR. -
R. N. Treuhaft,
B. D. Chapman,
J. R. dos Santos,
F. G. Gonçalves,
L. V. Dutra,
P. M. L. A. Graça,
and J. B. Drake.
Vegetation profiles in tropical forests from multibaseline interferometric synthetic aperture radar, field, and lidar measurements.
J. Geophys. Res.,
114:1-16,
December 2009.
Keyword(s): SAR Processing,
SAR Tomography,
tropical forest structure,
InSAR,
interferometric SAR,
lidar,
Ecosystems,
structure and dynamics,
Remote sensing,
Atmospheric Composition and Structure,
Biosphere atmosphere interactions,
Trace gases.
Abstract: This paper addresses the estimation of vertical vegetation density profiles from multibaseline interferometric synthetic aperture radar (InSAR) data from the AirSAR aircraft at C band over primary, secondary, and abandoned-pasture stands at La Selva Biological Station, Costa Rica in 2004. Profiles were also estimated from field data taken in 2006 and lidar data taken with the LVIS, 25 m spot instrument in 2005. After motivating the study of tropical forest profiles based on their role in the global carbon cycle, ecosystem state, and biodiversity, this paper describes the InSAR, field, and lidar data acquisitions and analyses. Beyond qualitative agreement between profiles from the 3 measurement techniques, results show that InSAR and lidar profile-averaged mean height have RMS scatters about field-measured means of 3.4 m and 3.2 m, 16% and 15% of the average mean height, respectively. InSAR and lidar standard deviations of the vegetation distribution have RMS scatters about the field standard deviations of 1.9 m and 1.5 m, or 27% and 21%, respectively. Dominant errors in the profile-averaged mean height for each measurement technique were modeled. InSAR inaccuracies, dominated by ambiguities in finding the ground altitude and coherence calibration, together account for about 3 m of InSAR error in the mean height. The dominant, modeled error for the field measurements was the inaccuracy in modeling the trees as uniformly filled volumes of leaf area, inducing field errors in mean height of about 3 m. The dominant, modeled lidar error, also due to finding the ground, was 2 m. -
R. Wang,
O. Loffeld,
H. Nies,
and J. Ender.
Focusing Spaceborne/Airborne Hybrid Bistatic SAR Data Using Wavenumber-Domain Algorithm.
IEEE_J_GRS,
47(7):2275-2283,
July 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Bistatic SAR,
SAR data processing,
azimuth time-bandwidth product,
azimuth-dependent range-cell-migration terms,
azimuth-frequency dependence,
bistatic formula,
bistatic point-target reference spectrum,
bistatic synthetic aperture radar,
bistatic-deformation,
hybrid spaceborne/airborne simulation experiment,
inverse scaled Fourier transformation,
inverse sliding-spotlight mode,
sliding-spotlight mode,
spaceborne/airborne hybrid bistatic configuration,
total Doppler spectrum,
wavenumber-domain algorithm,
weighting factor,
Fourier transforms,
airborne radar,
spaceborne radar,
synthetic aperture radar;.
Abstract: This paper focuses on the bistatic synthetic aperture radar (SAR) data processing in a spaceborne/airborne hybrid bistatic configuration. Due to the extreme differences in platform velocities and slant ranges, the airborne system operates in the inverse sliding-spotlight mode, while the spaceborne system works in the sliding-spotlight mode to achieve a tradeoff between azimuth scene size and azimuth resolution. In this extreme bistatic configuration, our original bistatic formula shows a limitation of accurately describing the bistatic point-target reference spectrum, owing to the assumption of equal contributions of transmitter and receiver to the total Doppler spectrum. We extend our previous formula using the weighting operation where the weighting factor is the ratio of the azimuth time-bandwidth product (TBP) of the platform to the total azimuth TBP. In this paper, the bistatic-deformation and azimuth-dependent range-cell-migration terms were removed with phase multiplications performed blockwise in range-azimuth subsections. The remaining quasi-monostatic term shows the characteristic of the conventional monostatic SAR besides an additional azimuth-scaling term. For the monostatic characteristic, any precision monostatic SAR processing algorithms can handle. In this paper, we prefer the wavenumber-domain algorithm (also known as Omega-K), since it can accurately correct the range dependence of the range-azimuth coupling, as well as the azimuth-frequency dependence. For the azimuth-scaling term, an inverse scaled Fourier transformation is performed to correct it. Finally, a hybrid spaceborne/airborne simulation experiment is conducted to validate the proposed processing procedure. -
R. Wang,
O. Loffeld,
H. Nies,
S. Knedlik,
and J. Ender.
Chirp-Scaling Algorithm for Bistatic SAR Data in the Constant-Offset Configuration.
IEEE_J_GRS,
47(3):952-964,
March 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Bistatic SAR,
Chirp Scaling Algorithm,
ECS,
CSA processor,
Doppler phase parameters,
Loffeld bistatic formula,
SAR receiver velocity vector,
SAR transmitter velocity vector,
azimuth invariant configuration,
azimuth stationary configuration,
bistatic SAR data processing method,
bistatic deformation term linearisation,
bistatic motion error model,
bistatic slant range displacement,
chirp scaling algorithm,
constant offset configuration,
monostatic motion compensation technique,
quasimonostatic term linearisation,
trajectory deviation compensattion,
zero Doppler plane,
Doppler radar,
chirp modulation,
geophysical signal processing,
motion compensation,
radar receivers,
radar signal processing,
radar transmitters,
remote sensing by radar,
synthetic aperture radar;.
Abstract: This paper discusses the processing method for bistatic SAR data in the constant-offset configuration. The constant-offset configuration is also known as the azimuth stationary or invariant configuration where transmitter and receiver follow each other, moving on identical velocity vector. In this paper, the proposed processing method for bistatic SAR data is based on Loffeld's bistatic formula that consists of two terms, i.e., the quasi-monostatic (QM) term and bistatic-deformation (BD) term. Our basic idea is to linearize the aforementioned two terms and then incorporate the BD term into the QM term to obtain an analogous monostatic spectrum. Based on the new spectrum, any efficient 2-D frequency or range-Doppler domain processor can easily be employed to process the bistatic data, where the Doppler phase parameters of the processor need to be adjusted. In this paper, we concentrate on the application of chirp-scaling-algorithm (CSA) processor. In addition, a bistatic-motion error model is developed where the position deviations of the two platforms are simplified as the bistatic slant-range displacement in the zero Doppler plane. Using this model, the monostatic motion-compensation technique is applied and integrated into CSA to compensate the trajectory deviations of transmitter and receiver. Finally, real and simulated data are used to validate the proposed processing method. -
Robert Wang,
Otmar Loffeld,
Holger Nies,
Stefan Knedlik,
and Joachim H. G. Ender.
Chirp-Scaling Algorithm for Bistatic SAR Data in the Constant-Offset Configuration.
IEEE Transactions on Geoscience and Remote Sensing,
47(3):952 -964,
March 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Chirp Scaling Algorithm,
CSA,
Bistatic SAR,
Doppler phase parameters,
Loffeld bistatic formula,
SAR receiver velocity vector,
SAR transmitter velocity vector,
azimuth invariant configuration,
azimuth stationary configuration,
bistatic SAR data processing method,
bistatic deformation term linearisation,
bistatic motion error model,
bistatic slant range displacement,
constant offset configuration,
monostatic motion compensation technique,
quasimonostatic term linearisation,
trajectory deviation compensation,
zero Doppler plane,
Doppler radar,
chirp modulation,
geophysical signal processing,
Motion Compensation,
MoComp,
radar receivers,
radar signal processing,
radar transmitters,
remote sensing by radar,
synthetic aperture radar,
Extended Chirp Scaling,
ECS.
Abstract: This paper discusses the processing method for bistatic SAR data in the constant-offset configuration. The constant-offset configuration is also known as the azimuth stationary or invariant configuration where transmitter and receiver follow each other, moving on identical velocity vector. In this paper, the proposed processing method for bistatic SAR data is based on Loffeld's bistatic formula that consists of two terms, i.e., the quasi-monostatic (QM) term and bistatic-deformation (BD) term. Our basic idea is to linearize the aforementioned two terms and then incorporate the BD term into the QM term to obtain an analogous monostatic spectrum. Based on the new spectrum, any efficient 2-D frequency or range-Doppler domain processor can easily be employed to process the bistatic data, where the Doppler phase parameters of the processor need to be adjusted. In this paper, we concentrate on the application of chirp-scaling-algorithm (CSA) processor. In addition, a bistatic-motion error model is developed where the position deviations of the two platforms are simplified as the bistatic slant-range displacement in the zero Doppler plane. Using this model, the monostatic motion-compensation technique is applied and integrated into CSA to compensate the trajectory deviations of transmitter and receiver. Finally, real and simulated data are used to validate the proposed processing method. -
Wen-Qin Wang,
Qicong Peng,
and Jingye Cai.
Waveform-Diversity-Based Millimeter-Wave UAV SAR Remote Sensing.
Geoscience and Remote Sensing, IEEE Transactions on,
47(3):691-700,
March 2009.
ISSN: 0196-2892.
Keyword(s): Doppler radar,
geophysical techniques,
geophysics computing,
millimetre waves,
remote sensing by radar,
remotely operated vehicles,
synthetic aperture radar,
Doppler ambiguity,
FMCW technology,
SAR,
UAV,
adaptive nonlinearity compensation,
frequency-modulated continuous-wave,
imaging algorithm,
power consumption,
remote sensing,
synthetic aperture radar,
unmanned airborne vehicle,
waveform-diversity-based millimeter-wave,
Frequency-modulated continuous-wave (FMCW) radar,
millimeter-wave synthetic aperture radar (SAR),
unmanned airborne vehicle (UAV),
waveform diversity.
[bibtex-key = 4768730]
-
Mengdao Xing,
Xiuwei Jiang,
Renbiao Wu,
Feng Zhou,
and Zheng Bao.
Motion Compensation for UAV SAR Based on Raw Radar Data.
IEEE Transactions on Geoscience and Remote Sensing,
47(8):2870-2883,
August 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Motion Compensation. MoComp,
3D MOCO method,
3D motion error analysis,
Doppler rate estimate,
UAV SAR,
Airborne SAR,
aircraft properties,
atmospheric turbulence,
forward velocity,
inertial navigation system,
line-of-sight direction displacement,
motion parameters extraction,
raw radar data,
synthetic aperture radar systems,
unmanned aerial vehicle,
UAV,
error analysis,
geophysical techniques,
inertial navigation,
radar imaging,
remotely operated vehicles,
synthetic aperture radar.
Abstract: Unmanned aerial vehicle (UAV) synthetic aperture radar (SAR) is very important for battlefield awareness. For SAR systems mounted on a UAV, the motion errors can be considerably high due to atmospheric turbulence and aircraft properties, such as its small size, which makes motion compensation (MOCO) in UAV SAR more urgent than other SAR systems. In this paper, based on 3-D motion error analysis, a novel 3-D MOCO method is proposed. The main idea is to extract necessary motion parameters, i.e., forward velocity and displacement in line-of-sight direction, from radar raw data, based on an instantaneous Doppler rate estimate. Experimental results show that the proposed method is suitable for low- or medium-altitude UAV SAR systems equipped with a low-accuracy inertial navigation system. -
E.C. Zaugg and D.G. Long.
Generalized Frequency-Domain SAR Processing.
Geoscience and Remote Sensing, IEEE Transactions on,
47(11):3761-3773,
Nov. 2009.
ISSN: 0196-2892.
Keyword(s): frequency-domain analysis,
geophysical techniques,
synthetic aperture radar,
2D frequency domain analysis,
SAR processing,
chirp-scaling algorithm,
range-Doppler algorithm,
synthetic aperture radar,
Data processing,
frequency-domain analysis,
synthetic aperture radar (SAR).
[bibtex-key = 5208234]
-
Evan C. Zaugg and David G. Long.
Generalized Frequency-Domain SAR Processing.
IEEE Transactions on Geoscience and Remote Sensing,
47(11):3761-3773,
November 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Azimuth Focusing,
Chirp Scaling Algorithm,
CSA,
Extended Chirp Scaling,
ECS,
range-Doppler algorithm,
omega-k,
wavenumber domain algorithm,
range migration algorithm,
frequency-domain analysis,
geophysical techniques,
synthetic aperture radar,
2D frequency domain analysis.
Abstract: The range-Doppler algorithm and the chirp-scaling algorithm (CSA) process synthetic aperture radar (SAR) data with approximations to ideal SAR processing. These approximations are invalid for data from systems with wide beamwidths, large bandwidths, and/or low center frequencies. While simple and efficient, these frequency-domain methods are thus limited by the SAR parameters. This paper explores these limits and proposes a generalized chirp-scaling approach for extending the utility of frequency-domain processing. We demonstrate how different order approximations of the SAR signal in the 2-D frequency domain affect image focusing for varying SAR parameters. From these results, a guideline is set forth, which suggests the required order of approximation terms for proper focusing. A proposed generalized frequency-domain processing approach is derived. This method is an efficient arbitrary-order CSA that processes the data using the appropriate number of approximation terms. The new method is demonstrated using simulated data. -
Lei Zhang,
Cheng-Wei Qiu,
Mengdao Xing,
and Zheng Bao.
Azimuth preprocessing for monostatic and bistatic spotlight synthetic aperture radar maging based on spectral analysis convolution.
Journal of Applied Remote Sensing,
3(1):1-20,
January 2009.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Bistatic SAR,
SPECAN,
Azimuth Focusing,
Spotlight SAR,
Spotlight-mode data.
Abstract: Dechirping is a technique widely used to reduce sampling rate. It is well suited for the illumination of small scenes. In this paper, we extend this idea to mono/bistatic spotlight synthetic aperture radar (SAR) imaging. An azimuth preprocessor based on the spectral analysis (SPECAN) convolution is presented. The convolution overcomes the Doppler aliasing of echoed signals, while the wavenumber analytic formula keeps unchanged. Since the spatial characteristic of the signal is preserved, the preprocessing is well compatible with conventional focusing approaches, such as chirp scaling algorithm and frequency scaling algorithm. The proposed method is validated by simulations in both monostatic and bistatic cases. -
Lei Zhang,
Meng-dao Xing,
Cheng-Wei Qiu,
and Zheng Bao.
Two-Dimensional Spectrum Matched Filter Banks for High-Speed Spinning-Target Three-Dimensional ISAR Imaging.
IEEE Geoscience and Remote Sensing Letters,
6(3):368-372,
July 2009.
ISSN: 1545-598X.
Keyword(s): SAR Processing,
3D SAR,
ISAR,
Spinning Targets,
Rotating Targets.
Abstract: In this letter, a 3-D inversed synthetic aperture radar imaging algorithm for targets in high-speed spinning is proposed based on 2-D spectrum matched filter (MF) banks. Each spectrum MF bank yields a focused slice for its corresponding scatterers. By extracting the spatial parameters from all slices, the 3-D image of the target can be constructed. Numeric simulation confirms the validity of the algorithm. -
F. Berizzi,
M. Martorella,
A. Cacciamano,
and A. Capria.
A Contrast-Based Algorithm For Synthetic Range-Profile Motion Compensation.
IEEE Transactions on Geoscience and Remote Sensing,
46(10):3053-3062,
October 2008.
ISSN: 0196-2892.
Keyword(s): motion compensation,
radar signal processing,
synthetic aperture radarSAR image reconstruction,
SNR loss,
acceleration distortion effects,
asymmetric smearing,
contrast based algorithm,
contrast optimization,
estimation error analysis,
low PRF radars,
motion compensation technique,
radar pulse repetition frequency,
range shift,
range-profile distortions,
stepped frequency radar,
stepped frequency waveform,
symmetric spreading,
synthetic aperture radar,
synthetic range profile cost function,
synthetic range-profile motion compensation,
target motion,
target radial acceleration,
target radial velocity.
Abstract: In stepped-frequency radar, target motions produce range-profile distortions. Range shift, signal-to-noise ratio loss, and symmetric spreading are produced by target radial velocity, whereas target radial acceleration is mainly responsible for asymmetric smearing. Acceleration-distortion effects are usually negligible when a high Pulse Repetition Frequency (PRF) is used, although this is not the case for low-PRF radars. In this paper, a new motion-compensation technique based on contrast optimization is proposed. The innovative contributions of this paper are as follows: (1) A theoretical analysis of the distortions produced by target motions on the reconstruction of synthetic aperture radar is provided; (2) the proposed technique compensates both phase terms, which are due to target radial velocity and acceleration; therefore, synthetic range profiles can be focused by processing low-PRF radar returns; (3) a new cost function for the synthetic range profiles (namely, contrast) is defined and used for motion compensation; (4) the proposed technique can be applied to any kind of stepped-frequency waveforms; and (5) an estimation error analysis is performed, first theoretically and then by means of both simulations and real data. -
Andreas .R. Brenner and Ludwig Roessing.
Radar Imaging of Urban Areas by Means of Very High-Resolution SAR and Interferometric SAR.
Geoscience and Remote Sensing, IEEE Transactions on,
46(10):2971-2982,
Oct. 2008.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
InSAR,
Interferometry,
SAR Interferometry,
X-Band,
Repeat-Pass Interferometry,
Repeat-Pass,
Single-Pass,
Airborne SAR,
PAMIR,
Autofocus,
Residual Motion Errors,
Motion Compensation,
MoComp,
earthquakes,
radar imaging,
radar interferometry,
remote sensing by radar,
synthetic aperture radar,
topography (Earth),
Forschungsgesellschaft fur Angewandte Naturwissenschaften,
Germany,
PAMIR,
Research Institute for High Frequency Physics and Radar Techniques,
Wachtberg,
X-band demonstrator,
building recognition,
building reconstruction,
earthquake damage mapping,
interferometric SAR sensor,
phased array multifunctional imaging radar,
radar imaging,
radar-based urban analysis,
remote-sensing applications,
structural image analysis,
subdecimeter resolution features,
synthetic aperture radar,
urban area monitoring,
urban elevation models.
Abstract: In remote-sensing applications, the monitoring of urban areas by means of synthetic aperture radar (SAR) sensors has grown into a valuable and indispensable tool. Although SAR imaging with a spatial resolution down to 1 m is widespread, a resolution as fine as 10 cm and below is offered only by very few SAR sensors worldwide. In this paper, the potential of very high-resolution radar imaging of urban areas by means of SAR and interferometric imaging will be demonstrated and discussed. Results of urban SAR imaging down to subdecimeter resolution will be shown. Even though the immanent layover situation in urban areas is an obstacle to simple image understanding, a remedy can be found by using interferometric SAR imaging. Interferometric results based on very high-resolution SAR images acquired over urban areas, partially with a severe layover situation, will be presented. The corresponding data was acquired with the phased array multifunctional imaging radar (PAMIR), the X-band demonstrator of the Research Institute for High Frequency Physics and Radar Techniques (FHR), Forschungsgesellschaft fur Angewandte Naturwissenschaften (FGAN), Wachtberg, Germany. It can be stated that high-resolution interferometric SAR will be an important basis for upcoming radar-based urban analysis. -
A.R. Brenner and L. Roessing.
Radar Imaging of Urban Areas by Means of Very High-Resolution SAR and Interferometric SAR.
Geoscience and Remote Sensing, IEEE Transactions on,
46(10):2971-2982,
Oct. 2008.
ISSN: 0196-2892.
Keyword(s): earthquakes,
radar imaging,
radar interferometry,
remote sensing by radar,
synthetic aperture radar,
topography (Earth),
Forschungsgesellschaft fur Angewandte Naturwissenschaften,
Germany,
PAMIR,
Research Institute for High Frequency Physics and Radar Techniques,
Wachtberg,
X-band demonstrator,
building recognition,
building reconstruction,
earthquake damage mapping,
interferometric SAR sensor,
phased array multifunctional imaging radar,
radar imaging,
radar-based urban analysis,
remote-sensing applications,
structural image analysis,
subdecimeter resolution features,
synthetic aperture radar,
urban area monitoring,
urban elevation models,
High-resolution imaging,
Image resolution,
Image sensors,
Phased arrays,
Radar imaging,
Radar polarimetry,
Remote monitoring,
Spatial resolution,
Synthetic aperture radar,
Urban areas,
Interferometric synthetic aperture radar (IfSAR),
layover,
subdecimeter resolution,
synthetic aperture radar (SAR),
urban areas,
very high-resolution radar imaging.
[bibtex-key = 4637926]
-
D. Cerutti-Maori,
J. Klare,
A.R. Brenner,
and Joachim H. G. Ender.
Wide-Area Traffic Monitoring With the SAR/GMTI System PAMIR.
Geoscience and Remote Sensing, IEEE Transactions on,
46(10):3019-3030,
Oct. 2008.
ISSN: 0196-2892.
Keyword(s): road traffic,
synthetic aperture radar,
target trackingGround Moving Target Indication mode,
SAR-GMTI system,
airborne radar sensor PAMIR,
positioning accuracy,
radial velocity,
scan-MTI mode,
signal-to-noise ratio,
vehicles detection,
wide area traffic monitoring experiment.
Abstract: This paper presents a wide area traffic monitoring experiment under real conditions, using the scan-MTI mode of the airborne radar sensor PAMIR. This flexible GMTI (Ground Moving Target Indication) mode was designed in order to rapidly monitor wide areas for moving targets. The scan operation enables the detection of targets from different aspect angles with a high revisit rate. The parameters (e.g., radial velocity, signal-to-noise ratio, and positioning accuracy) of the detected vehicles are investigated and compared to the expected theoretical GMTI performance. It will be shown that the scan-MTI mode is particularly adapted to perform an efficient wide-area traffic monitoring. -
Karlus A. Câmara de Macedo,
Rolf Scheiber,
and Alberto Moreira.
An Autofocus Approach for Residual Motion Errors With Application to Airborne Repeat-Pass SAR Interferometry.
IEEE Transactions on Geoscience and Remote Sensing,
46(10):3151-3162,
October 2008.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Autofocus,
Residual Motion Errors,
WPCA,
Weighted PCA,
Weighted Phase Curvature Autofocus,
Phase Curvature Autofocus,
PCA,
Phase Gradient Autofocus,
PGA,
Repeat-Pass Interferometry,
Interferometry,
InSAR,
D-InSAR,
Differential SAR Interferometry,
E-SAR,
airborne SAR,
Baseline Calibration,
Tomography,
SAR Tomography,
deformation,
geophysical techniques,
synthetic aperture radar,
topography (Earth)E-SAR system,
German Aerospace Center,
airborne repeat-pass SAR Interferometry,
autofocus algorithm,
autofocus techniques,
high-precision navigation system,
image processing,
interferometric-phase accuracy,
phase curvature autofocus,
residual motion errors,
synthetic-aperture-radar,
terrain deformations measurement,
weighted least squares phase estimation.
Abstract: Airborne repeat-pass SAR systems are very sensible to subwavelength deviations from the reference track. To enable repeat-pass interferometry, a high-precision navigation system is needed. Due to the limit of accuracy of such systems, deviations in the order of centimeters remain between the real track and the processed one, causing mainly undesirable phase undulations and misregistration in the interferograms, referred to as residual motion errors. Up to now, only interferometric approaches, as multisquint, are used to compensate for such residual errors. In this paper, we present for the first time the use of the autofocus technique for residual motion errors in the repeat-pass interferometric context. A very robust autofocus technique has to be used to cope with the demands of the repeat-pass applications. We propose a new robust autofocus algorithm based on the weighted least squares phase estimation and the phase curvature autofocus (PCA) extended to the range-dependent case. We call this new algorithm weighted PCA. Different from multisquint, the autofocus approach has the advantage of being able to estimate motion deviations independently, leading to better focused data and correct impulse-response positioning. As a consequence, better coherence and interferometric-phase accuracy are achieved. Repeat-pass interferometry based only on image processing gains in robustness and reliability, since its performance does not deteriorate with time decorrelation and no assumptions need to be made on the interferometric phase. Repeat-pass data of the E-SAR system of the German Aerospace Center (DLR) are used to demonstrate the performance of the proposed approach. -
Othmar Frey,
Felix Morsdorf,
and Erich Meier.
Tomographic Imaging of a Forested Area By Airborne Multi-Baseline P-Band SAR.
Sensors, Special Issue on Synthetic Aperture Radar,
8(9):5884-5896,
September 2008.
Keyword(s): SAR Processing,
SAR Tomography,
Tomographic Processing,
Multi-Baseline SAR,
Time-Domain Back-Projection,
Back-Projection,
E-SAR,
P-Band,
Forestry.
Abstract: In recent years, 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 for airborne L-band data but the quality of the focused tomographic images is limited by several factors. In particular, the common Fourierbased 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. In this paper, a tomographic focusing method based on the time-domain back-projection algorithm is proposed, 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. The tomographic focusing quality is assessed by analysing the impulse response of simulated point targets and an in-scene corner reflector. And, in particular, several tomographic slices of a volume representing a forested area are given. The respective P-band tomographic data set consisting of eleven flight tracks has been acquired by the airborne E-SAR sensor of the German Aerospace Center (DLR). -
José-Tomás González-Partida,
Pablo Almorox-González,
Mateo Burgos-Garcìa,
and Blas-Pablo Dorta-Naranjo.
SAR System for UAV Operation with Motion Error Compensation beyond the Resolution Cell.
Sensors, Special Issue on Synthetic Aperture Radar,
8(5):3384-3405,
2008.
Keyword(s): SAR Processing,
Motion Compensation,
MoComp,
Airborne SAR,
UAV,
Unmanned Airborne Vehicle,
LFM-CW,
Continuous Wave SAR,
Phase Gradient Autofocus,
Autofocus,
PGA,
Range Alignment,
Residual Motion Errors,
mmW SAR,
mmW,
Ka-Band SAR.
Abstract: This paper presents an experimental Synthetic Aperture Radar (SAR) system that is under development in the Universidad Politécnica de Madrid. The system uses Linear Frequency Modulated Continuous Wave (LFM-CW) radar with a two antenna configuration for transmission and reception. The radar operates in the millimeter-wave band with a maximum transmitted bandwidth of 2 GHz. The proposed system is being developed for Unmanned Aerial Vehicle (UAV) operation. Motion errors in UAV operation can be critical. Therefore, this paper proposes a method for focusing SAR images with movement errors larger than the resolution cell. Typically, this problem is solved using two processing steps: first, coarse motion compensation based on the information provided by an Inertial Measuring Unit (IMU); and second, fine motion compensation for the residual errors within the resolution cell based on the received raw data. The proposed technique tries to focus the image without using data of an IMU. The method is based on a combination of the well known Phase Gradient Autofocus (PGA) for SAR imagery and typical algorithms for translational motion compensation on Inverse SAR (ISAR). This paper shows the first real experiments for obtaining high resolution SAR images using a car as a mobile platform for our radar. -
Michael Jehle,
Donat Perler,
David Small,
Adrian Schubert,
and Erich Meier.
Estimation of Atmospheric Path Delays in TerraSAR-X Data using Models vs. Measurements.
Sensors,
8(12):8479-8491,
2008.
ISSN: 1424-8220.
Keyword(s): SAR Processing,
Ionosphere,
TEC,
Total Electron Content,
Troposphere,
Path Delay.
[bibtex-key = jehlePerlerSmallSchubertMeier2008:EstimPathDelay]
-
Shi Jun,
Xiaoling Zhang,
and Jianyu Yang.
Principle and Methods on Bistatic SAR Signal Processing via Time Correlation.
Geoscience and Remote Sensing, IEEE Transactions on,
46(10):3163-3178,
Oct. 2008.
ISSN: 0196-2892.
Keyword(s): fast Fourier transforms,
geophysical signal processing,
radar imaging,
radar signal processing,
remote sensing by radar,
synthetic aperture radar3D scene space ambiguity problem,
AVME,
RVME,
SAR image shifting,
SAR image space bases,
absolute velocity measurement error,
ambiguity region,
bistatic SAR 2D PSF,
bistatic SAR angular velocity direction,
bistatic SAR image space,
bistatic SAR signal processing,
inverse fast Fourier transform,
motion measurement error effects,
perspective line,
perspective operator,
point spread function,
range Doppler algorithm,
relative velocity measurement error,
scaled IFFT,
space truncation error,
synthetic aperture radar,
time correlation radar signal processing,
translational variant bistatic SAR imaging method.
Abstract: In this paper, we discuss the mapping between the 3-D scene space and the bistatic synthetic aperture radar (SAR) image space and show that when the direction of the angular velocity of the bistatic SAR remains constant, the process of bistatic SAR imaging can be approximately modeled as a perspective operator from the 3-D scene space to the 2-D image space, and the perspective line is perpendicular to the plane determined by the composition direction of the T/R line of sight and the composition direction of the angular velocity of the T/R platform. Then, we show that the 2-D point spread function of the bistatic SAR is determined not only by the range and ldquoazimuthrdquo resolutions but also by the geometry of the bistatic SAR and the bases of the SAR image space, and the concept ldquoambiguity regionrdquo is introduced to describe the ambiguity problem in the 3-D scene space. Then, the range-Doppler algorithm is discussed, and a new translational-variant bistatic SAR imaging method is proposed, which uses the scaled inverse fast Fourier transform (IFFT) technique to eliminate the translational-variant feature of the SAR space resolution. The space truncation error of this new algorithm is discussed to analyze the depth of focus of the scaled IFFT bistatic SAR imaging algorithms, and we find that the upper bounce of the space truncation error is proportional to the square of the distance from the scatterer to the T/R platforms. Last, the effects of motion measurement errors are discussed in detail, and, through theoretical analysis and numerical experiments, we show that the absolute position measurement error, the baseline measurement error, the perpendicular (vertical) component of the absolute velocity measurement error (AVME), and the perpendicular component of the relative velocity measurement error (RVME) cause SAR image shifting in the image space mainly, and the parallel component of the AVME and the parallel component of the RVME cause the SAR image to s- - everely defocus. -
Jong-Sen Lee,
T.L. Ainsworth,
J.P. Kelly,
and C. Lopez-Martinez.
Evaluation and Bias Removal of Multilook Effect on Entropy/Alpha/Anisotropy in Polarimetric SAR Decomposition.
Geoscience and Remote Sensing, IEEE Transactions on,
46(10):3039-3052,
Oct. 2008.
ISSN: 0196-2892.
Keyword(s): Monte Carlo methods,
geophysical techniques,
radar interferometry,
radar polarimetry,
remote sensing by radar,
synthetic aperture radar,
vegetationGerman Aerospace Research Center,
JPL,
Jet Propulsion Laboratory,
L-band Advanced Land Observing Satellite,
Monte Carlo simulation,
airborne X-band polarimetric SAR,
airborne interferometric SAR,
alpha estimation,
anisotropy estimation,
bias removal algorithm,
entropy estimation,
forest,
geophysical parameter estimation,
grassland,
multilook processing,
phased array type L-band SAR,
polarimetric SAR decomposition,
scattering mechanisms,
synthetic aperture radar,
urban returns.
Abstract: Entropy, alpha, and anisotropy (H/alpha/A) of the polarimetric target decomposition have been an effective and popular tool for polarimetric synthetic aperture radar (SAR) image analysis and for a geophysical parameter estimation. However, multilook processing can severely affect the values of these parameters. In this paper, a Monte Carlo simulation is used to evaluate and remove the bias generated by the multilook effect on these parameters for various media composed of grassland, forest, and urban returns. Due to insufficient averaging, entropy is underestimated, and anisotropy is overestimated. We also found that the bias in the alpha angle can be either underestimated or overestimated depending on scattering mechanisms. Based on simulation results, efficient bias removal procedures have been developed. In particular, the entropy bias can be precisely corrected, and the amount of correction is independent of the radar frequency and SAR systems. Data from L-band Advanced Land Observing Satellite/phased array type L-band SAR, German Aerospace Research Center (DLR)/enhanced SAR, Jet Propulsion Laboratory (JPL)/airborne SAR, and X-band polarimetric and interferometric SAR are used for demonstration in this paper. -
Lianlin Li and Fang Li.
Ionosphere tomography based on spaceborne SAR.
Advances in Space Research,
42(7):1187-1193,
October 2008.
Keyword(s): SAR Processing,
Ionosphere tomography,
Spaceborne SAR,
Electron density isolines,
Inverse scattering technique for multi-layered random surfaces,
Method of moment,
MoM,
TEC,
Total Electron Content,
CT,
computerized tomography.
Abstract: Two models of ionosphere tomography based on spaceborne SAR (Synthetic Aperture Radar) are proposed. For HF-SAR the signal with sweeping frequency lower than the characteristic frequency of ionosphere will be scatted during the ionosphere propagation and completely reflected at a corresponding height. The ionospheric electron density isolines looked as series of random surfaces can be reconstructed from the HF-SAR echoes by using the inverse scattering technique for layered rough surfaces and the method of moment (MoM). The numerical simulation show that due to the MoM can provide a full wave solution, the ionosphere tomography with high resolution can be obtained as long as enough sampling data of HF-SAR echoes are used. For VHF/UHF/P/L-band SAR the TEC (Total Electron Content) can be obtained from the SAR echoes scattered by some strong point targets (such as the calibrators, etc.) appeared in the SAR imaged ground region, and the ionosphere tomography can be performed by CT technique. -
Fabrizio Lombardini and Matteo Pardini.
3-D SAR Tomography: The Multibaseline Sector Interpolation Approach.
IEEE Geoscience and Remote Sensing Letters,
5(4):630-634,
Oct. 2008.
ISSN: 1545-598X.
Keyword(s): SAR Processing,
Tomography,
SAR Tomography,
Multi-baseline SAR,
Interpolation,
Sector Interpolation,
3-D imaging,
SAR Interferometry,
Interferometry,
InSAR,
Spectral Analysis,
Electromagnetic Tomography,
Signal Sampling.
Abstract: Multibaseline (MB) synthetic aperture radar (SAR) tomography is a promising mode of SAR interferometry, allowing full 3-D imaging of volumetric and layover scatterers in place of a single elevation estimation capability for each SAR cell . However, Fourier-based MB SAR tomography is generally affected by unsatisfactory imaging quality due to a typically low number of baselines with irregular distribution. In this paper, we improve the basic elevation focusing technique by reconstructing a set of uniform baselines data exploiting in the interpolation step the ancillary information about the extension of a height sector which contains all the scatterers. This a priori information can be derived from the knowledge of the kind of the observed scenario (e.g., forest or urban). To demonstrate the concept, an imaging enhancement analysis is carried out by simulation. -
Franz J. Meyer and J.B. Nicoll.
Prediction, Detection, and Correction of Faraday Rotation in Full-Polarimetric L-Band SAR Data.
Geoscience and Remote Sensing, IEEE Transactions on,
46(10):3076-3086,
Oct. 2008.
ISSN: 0196-2892.
Keyword(s): Faraday effect,
electromagnetic wave polarisation,
ionospheric disturbances,
ionospheric electromagnetic wave propagation,
ionospheric techniques,
radar polarimetry,
radiowave propagation,
remote sensing by radar,
spaceborne radar,
synthetic aperture radarAdvanced Land Observing Satellite,
Faraday rotation correction,
Faraday rotation detection,
Faraday rotation estimation,
Faraday rotation prediction,
PALSAR,
SAR data quality degradation,
data continuity,
full polarimetric L-band SAR data,
geophysical parameter recovery accuracy,
kilometer scale ionospheric disturbances,
spaceborne L-band SAR instrument,
synthetic aperture radar.
Abstract: With the synthetic aperture radar (SAR) sensor PALSAR onboard the Advanced Land Observing Satellite, a new full-polarimetric spaceborne L-band SAR instrument has been launched into orbit. At L-band, Faraday rotation (FR) can reach significant values, degrading the quality of the received SAR data. One-way rotations exceeding 25 deg are likely to happen during the lifetime of PALSAR, which will significantly reduce the accuracy of geophysical parameter recovery if uncorrected. Therefore, the estimation and correction of FR effects is a prerequisite for data quality and continuity. In this paper, methods for estimating FR are presented and analyzed. The first unambiguous detection of FR in SAR data is presented. A set of real data examples indicates the quality and sensitivity of FR estimation from PALSAR data, allowing the measurement of FR with high precision in areas where such measurements were previously inaccessible. In examples, we present the detection of kilometer-scale ionospheric disturbances, a spatial scale that is not detectable by ground-based GPS measurements. An FR prediction method is presented and validated. Approaches to correct for the estimated FR effects are applied, and their effectiveness is tested on real data. -
Andrea Monti-Guarnieri and Stefano Tebaldini.
On the Exploitation of Target Statistics for SAR Interferometry Applications.
IEEE Transactions on Geoscience and Remote Sensing,
46(11):3436-3443,
November 2008.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
SAR Tomography,
geophysical techniques,
geophysics computing,
image processing,
radar interferometry,
remote sensing by radar,
synthetic aperture radar,
topography (Earth)ENVISAT images,
Monte Carlo simulations,
SAR interferometry applications,
decorrelation models,
interferometric phases,
line-of-sight displacement,
line-of-sight motion,
multiimage synthetic aperture radar interferometry,
physical parameters,
residual topography,
target statistics.
Abstract: This paper focuses on multiimage synthetic aperture radar interferometry (InSAR) in the presence of distributed scatterers, paying particular attention to the role of target decorrelation in the estimation process. This phenomenon is accounted for by splitting the analysis into two steps. In the first step, we estimate the interferometric phases from the data, whereas in the second step, we use these phases to retrieve the physical parameters of interest, such as line-of-sight (LOS) displacement and residual topography. In both steps, we make the hypothesis that target statistics are at least approximately known. This approach is suited both to derive the performances of InSAR with different decorrelation models and for providing an actual estimate of LOS motion and topography. Results achieved from Monte Carlo simulations and a set of repeated pass ENVISAT images are shown. -
Matteo Pardini,
Fabrizio Lombardini,
and Fabrizio Gini.
The Hybrid Cramér -- Rao Bound on Broadside DOA Estimation of Extended Sources in Presence of Array Errors.
IEEE Transactions on Signal Processing,
56(4):1726-1730,
April 2008.
ISSN: 1053-587X.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
Residual Motion Errors,
InSAR,
SAR Interferometry,
Interferometry,
antenna arrays,
direction-of-arrival estimation,
DOA estimation,
hybrid Cramer-Rao bound,
multibaseline interferometers,
randomly perturbed arrays,
remote sensing systems,
signal direction of arrival,
synthetic aperture radar.
Abstract: In this correspondence we derive explicit expressions for the hybrid Cramer-Rao lower bound (HCRB) on the estimation accuracy of signal direction of arrival (DOA) from data collected by randomly perturbed arrays. The presence of a wavefront spatial decorrelation, which is modeled as a multiplicative correlated noise, has also been taken into account in the data model, since it is typical in those applications involving extended sources. In particular, we consider perturbations in sensor positions. Existing approaches to DOA HCRB calculation do not consider the presence of multiplicative noise and are referred to the assumption of small perturbations only, still not being worked out explicitly. Here, we assume that the impinging wavefronts are coming from broadside or more generally from a narrow DOA sector, allowing the explicit derivation of the HCRB for any variance of the sensor positioning errors in the line-of-sight direction. This scenario corresponds to the typical operative condition of remote sensing systems such as synthetic aperture radar (SAR) multibaseline interferometers, for which a few HCRB sample curves are reported. -
S. Perna,
C. Wimmer,
J. Moreira,
and G. Fornaro.
X-Band Airborne Differential Interferometry: Results of the OrbiSAR Campaign Over the Perugia Area.
Geoscience and Remote Sensing, IEEE Transactions on,
46(2):489-503,
February 2008.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
BFNT,
Backward-Forward to the Nominale Track,
Airborne SAR,
D-InSAR,
differential SAR interferometry,
Interferometry,
OrbiSAR,
X-Band,
Motion Compensation,
Residual Motion Errors,
Autofocus,
Airborne SAR,
airborne radar,
motion compensation,
radar imaging,
synthetic aperture radar airborne SAR images,
digital elevation model inaccuracies,
motion compensation errors,
phase errors.
Abstract: Differential synthetic aperture radar interferometry (DInSAR) is a remote sensing technique that allows monitoring ground deformation with accuracy of the order of fractions of the radiated wavelength, by means of proper combination and processing of repeat-pass data. In contrast to the satellite case, application of such a technique to airborne data is not, today, a well-established task. Several airborne campaigns, involving mainly C/L-band data, have been planned in the last years to exploit the potentialities of these more flexible platforms for deformation monitoring. In this paper, we show the results of an airborne DInSAR X-band experiment carried out over the Perugia area (center of Italy) by using the OrbiSAR system. We discuss the processing chain applied to the acquired data, which allows achieving a satisfactory compromise between accuracy and efficiency. Eleven repeated passes were carried out in two days; two corner reflectors were located on the ground in a hilly region. One corner reflector was vertically moved between the two days to evaluate the system detection capability. Moreover, we carry out an analysis of all possible differential interferograms for a region 2 x 4 km wide. -
Pau Prats,
J.J. Mallorqui,
Andreas Reigber,
Rolf Scheiber,
and Alberto Moreira.
Estimation of the Temporal Evolution of the Deformation Using Airborne Differential SAR Interferometry.
IEEE Transactions on Geoscience and Remote Sensing,
46(4):1065-1078,
April 2008.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
DInSAR,
InSAR,
Interferometry,
digital elevation models,
error analysis,
motion compensation,
MoComp,
radar interferometry,
Multi-Baseline SAR,
synthetic aperture radar,
topography (Earth)DLR,
Experimental SAR system,
E-SAR,
Airborne SAR,
German Aerospace Center,
agricultural fields,
airborne differential synthetic aperture radar interferometry,
baseline error,
corner reflector,
deformation,
differential interferometry processor,
digital elevation model,
image coregistration,
residual motion errors,
temporal evolution,
topography.
Abstract: This paper presents airborne differential synthetic aperture radar (SAR) interferometry results using a stack of 14 images, which were acquired by the Experimental SAR system of the German Aerospace Center (DLR) during a time span of 2.5 h. An advanced differential technique is used to retrieve the error in the digital elevation model and the temporal evolution of the deformation for every coherent pixel in the image. The two main limitations in airborne SAR processing are analyzed, namely, the existence of residual motion errors (RMEs) (inaccuracies in the navigation system on the order of 1-5 cm) and the accommodation of the topography and the aperture dependence on motion errors during the processing. The coupling between them is also addressed, showing that the estimation of the differential RME, i.e., baseline error, can be biased when using techniques based on the coregistration between interferometric looks. The SAR focusing chain to process the data is also presented together with the modifications in the differential interferometry processor to deal with the remaining baseline error. The detected motion of a corner reflector and the measured deformation in several agricultural fields allows one to validate the proposed techniques. -
P. Prats,
J.J. Mallorqui,
A. Reigber,
R. Scheiber,
and A. Moreira.
Estimation of the Temporal Evolution of the Deformation Using Airborne Differential SAR Interferometry.
IEEE Transactions on Geoscience and Remote Sensing,
46(4):1065-1078,
Apr. 2008.
Keyword(s): digital elevation models,
error analysis,
motion compensation,
radar interferometry,
synthetic aperture radar,
topography (Earth),
DLR,
Experimental SAR system,
German Aerospace Center,
agricultural fields,
airborne differential synthetic aperture radar interferometry,
baseline error,
corner reflector,
deformation,
differential interferometry processor,
digital elevation model,
image coregistration,
residual motion errors,
temporal evolution,
topography,
Differential interferometry,
SAR processing,
interferometry,
motion compensation (MoCo),
synthetic aperture radar (SAR);.
[bibtex-key = Prats08:TGRS]
-
Xiaolan Qiu,
Donghui Hu,
and Chibiao Ding.
An Improved NLCS Algorithm With Capability Analysis for One-Stationary BiSAR.
Geoscience and Remote Sensing, IEEE Transactions on,
46(10):3179-3186,
Oct. 2008.
ISSN: 0196-2892.
Keyword(s): geophysical techniques,
synthetic aperture radarBiSAR imaging problem,
NLCS algorithm,
azimuth perturbation,
compensation methods,
differential range cell migration correction,
local fit method,
nonlinear chirp scaling algorithm,
one-stationary bistatic SAR,
range chirp scaling function.
Abstract: This paper deals with the imaging problem of one-stationary bistatic SAR (BiSAR) with large bistatic angle. An improved nonlinear chirp scaling (NLCS) algorithm is proposed for this BiSAR. The main work here includes three aspects. First, a range chirp scaling function for correcting the differential range cell migration correction is derived. Then, the azimuth perturbation is generated by local fit method, which makes the NLCS algorithm suitable for the large bistatic angle case. Furthermore, the negative effects introduced by the perturbation (including phase error and locality error) are discussed, and some compensation methods are proposed to enhance the capability of the algorithm. The simulating results exhibited at the end of this paper validate the correctness of the analysis and the feasibility of the algorithm. -
T.K. Sjogren,
V.T. Vu,
and M.I. Pettersson.
A comparative study of the polar version with the subimage version of Fast Factorized Backprojection in UWB SAR.
International Radar Symposium,
pp 1-4,
May 2008.
Keyword(s): SAR Processing,
Time-Domain Back-Projection,
Backprojection,
Back-Projection,
Fast Factorized Back-Projection,
Comparison of Algorithms,
interpolation,
radar imaging,
synthetic aperture radar,
time-domain analysis,
ultra wideband radar,
UWB SAR,
interpolation method,
phase error,
polar version,
subimage version,
time domain SAR algorithm,
Factorized Backprojection.
Abstract: This paper presents a comparative study of the polar and the subimage based variants of the time domain SAR algorithm Fast Factorized Backprojection. The difference between the two variants with regard to the phase error, which causes defocusing in the image, is investigated. The difference between the algorithms in interpolation between stages is also discussed. To investigate the sidelobes in azimuth, the paper gives simulation results for a low frequency UWB SAR system for both algorithms. How the algorithms differ with regard to amount of beams and length of beams is also discussed. -
Robert Wang,
Otmar Loffeld,
Qurat Ul-Ann,
Holger Nies,
Amaya Medrano Ortiz,
and Ashraf Samarah.
A Bistatic Point Target Reference Spectrum for General Bistatic SAR Processing.
IEEE_J_GRSL,
5(3):517-521,
July 2008.
ISSN: 1545-598X.
Keyword(s): SAR Processing,
Bistatic SAR,
Loffeld bistatic formula,
airborne configuration,
azimuth time-bandwidth products,
bistatic point target reference spectrum,
bistatic synthetic aperture radar,
general bistatic SAR processing,
spaceborne configuration,
total azimuth modulation,
total azimuth phase,
geophysical signal processing,
radar signal processing,
synthetic aperture radar;.
Abstract: A bistatic point target reference spectrum (BPTRS) based on Loffeld's bistatic formula (LBF) is derived in this letter. For LBF, the same contributions of the transmitter and receiver to the total azimuth modulation are assumed. This assumption results in the failure of LBF in the extreme configuration (i.e., spaceborne/airborne configuration). For general bistatic configurations, the azimuth modulations are unequal for the transmitter and receiver due to the different slant ranges and velocities. Therefore, the azimuth time-bandwidth products (TBPs) from the transmitter and receiver are different; in some cases (e.g., spaceborne/airborne case), one of them might be very small, which might even result in a serious error of the principle of stationary phase. This letter uses TBP to weight the azimuth phase modulation contributions of the transmitter and receiver to the common azimuth spectrum to approximately obtain the point of stationary phase of the total azimuth phase history. Simulations show that the proposed BPTRS can work well for spaceborne/airborne configurations. -
Evan C. Zaugg and David G. Long.
Theory and Application of Motion Compensation for LFM-CW SAR.
IEEE Transactions on Geoscience and Remote Sensing,
46(10):2990-2998,
Oct. 2008.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
LFM-CW,
LFM-CW SAR,
MoComp,
motion compensation,
CSA,
ECS,
Chirp Scaling,
Extended Chirp Scaling,
FSA,
Frequency Scaling Algorithm,
Range-Doppler Algorithm,
synthetic aperture radar,
Brigham Young University,
muSAR system,
LFM-CW signal model,
SAR image quality,
aircraft,
atmospheric turbulence,
high-resolution synthetic aperture radar systems,
linear frequency-modulated continuous-wave signal,
motion compensation,
motion correction algorithms,
unmanned aerial vehicle,
Airborne SAR,
geophysical techniques,.
Abstract: Small low-cost high-resolution synthetic aperture radar (SAR) systems are made possible by using a linear frequency-modulated continuous-wave (LFM-CW) signal. SAR processing assumes that the sensor is moving in a straight line at a constant speed, but in actuality, an unmanned aerial vehicle (UAV) or airplane will often significantly deviate from this ideal. This nonideal motion can seriously degrade the SAR image quality. In a continuous-wave system, this motion happens during the radar pulse, which means that existing motion compensation techniques that approximate the position as constant over a pulse are limited for LFM-CW SAR. Small aircraft and UAVs are particularly susceptible to atmospheric turbulence, making the need for motion compensation even greater for SARs operating on these platforms. In this paper, the LFM-CW SAR signal model is presented, and processing algorithms are discussed. The effects of nonideal motion on the SAR signal are derived, and new methods for motion correction are developed, which correct for motion during the pulse. These new motion correction algorithms are verified with simulated data and with actual data collected using the Brigham Young University muSAR system. -
R. Bamler,
F. Meyer,
and W. Liebhart.
Processing of Bistatic SAR Data From Quasi-Stationary Configurations.
IEEE_J_GRS,
45(11):3350-3358,
November 2007.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Bistatic SAR,
Earth surface,
NuSAR approach,
bistatic SAR data processing,
curved orbit,
equivalent velocity approximation,
hyperbolic range function,
quasistationarity restriction,
quasistationary configuration,
radar receiver,
radar transmitter,
range Doppler domain,
synthetic aperture radar,
time-domain post focusing,
time-domain prefocusing,
transfer functions,
velocity vector,
data acquisition,
geophysical signal processing,
geophysical techniques,
radar signal processing,
remote sensing by radar,
synthetic aperture radar,
transfer functions;.
Abstract: Standard synthetic aperture radar (SAR) processing algorithms use analytically derived transfer functions in the 2D frequency and range/Doppler domains. These rely on the assumption of hyperbolic range histories of monostatic SARs with straight flight paths. For bistatic SARs, the range histories are no longer hyperbolic, and simple analytic transforms do not exist. This paper offers two solutions for bistatic SAR data processing under the restriction of quasi-stationarity, i.e., sufficiently equal velocity vectors of transmitter and receiver. 1) Moderately bistatic configurations can be handled satisfactorily by using hyperbolic range functions with a modified velocity parameter, which is a solution already well known for the accommodation of curved orbits in the monostatic case. This "equivalent velocity" approach is shown to be of surprising range of validity even for pronounced bistatic situations. It is not to be confused with the "equivalent monostatic flight path" approximation, which is shown to be inapplicable for any practical case. 2) With increasing separation of transmitter and receiver, the equivalent velocity approximation deteriorates. To cope with extreme bistatic configurations, a general approach named "NuSAR" is proposed, where the involved transfer functions are replaced by numerically computed ones. This paper describes how the transfer functions are computed from the given orbits and the shape of the Earth surface. In any of these two cases, the bistatic SAR data can be processed by standard SAR processors; only the conventional transfer functions need to be replaced. Neither are there time-domain prefocusing or post focusing steps required nor complicated mathematical expansions involved. The presented algorithms are also applicable to very high resolution wide-swath (or squinted) SARs on curved orbits. -
C. Castillo-Rubio,
S. Llorente-Romano,
and M. Burgos-Garcia.
Robust SVA method for every sampling rate condition.
IEEE Transactions on Aerospace and Electronic Systems,
43(2):571 -580,
April 2007.
ISSN: 0018-9251.
Keyword(s): SAR Processing,
Apodization,
Spatially Variant Apodization,
SVA,
SAR system,
finite signal sampling rate condition,
nonlinear filtering,
robust SVA method,
sidelobe levels signal resolution,
synthetic aperture radar,
target detection capability,
two-dimensional generalization,
variant filter,
image resolution.
Abstract: Linear apodization, or data weighting, is the traditional procedure to improve sidelobe levels in a finite sampled signal at the expense of resolution. New apodization methods, such as spatially variant apodization (SVA), apply nonlinear filtering to the signal in order to completely remove sidelobes without any loss of resolution. However, the results are strongly influenced by signal sampling rate. Some variations which improve results have been previously published, but sidelobe cancellation gets worse since sampling frequency is not settled at Nyquist (or a multiple). This paper presents a new and efficient technique based on SVA that drastically reduces sidelobe levels for every sampling rate condition. The algorithm is, essentially, a parameter optimization of a variant filter for each pixel of the image. A one-dimensional case and a two-dimensional generalization are presented, as well as some applications to target detection capability in a synthetic aperture radar (SAR) system. -
C.F. Castillo-Rubio,
S. Llorente-Romano,
and C.M. Burgos-Garcia.
Spatially Variant Apodization for Squinted Synthetic Aperture Radar Images.
IEEE Transactions on Image Processing,
16(8):2023-2027,
August 2007.
ISSN: 1057-7149.
Keyword(s): SAR Processing,
Apodization,
Spatially Variant Apodization,
Nyquist rate,
bidimensional finite impulse response filter,
nonlinear sidelobe reduction technique,
spatially variant apodization,
squinted synthetic aperture radar image,
synthetic aperture radar,
FIR filters,
radar imaging,
synthetic aperture radar,
Algorithms,
Image Enhancement,
Image Interpretation,
Computer-Assisted,
Information Storage and Retrieval,
Radar,
Reproducibility of Results,
Sensitivity and Specificity;.
Abstract: Spatially variant apodization (SVA) is a nonlinear sidelobe reduction technique that improves sidelobe level and preserves resolution at the same time. This method implements a bidimensional finite impulse response filter with adaptive taps depending on image information. Some papers that have been previously published analyze SVA at the Nyquist rate or at higher rates focused on strip synthetic aperture radar (SAR). This paper shows that traditional SVA techniques are useless when the sensor operates with a squint angle. The reasons for this behaviour are analyzed, and a new implementation that largely improves the results is presented. The algorithm is applied to simulated SAR images in order to demonstrate the good quality achieved along with efficient computation. -
Shane R. Cloude.
Dual-Baseline Coherence Tomography.
IEEE Geoscience and Remote Sensing Letters,
4(1):127-131,
January 2007.
ISSN: 1545-598X.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
geophysical techniques,
radar applications,
singular value decomposition,
vegetation,
EMSL,
European Microwave Signature Laboratory,
dual-baseline coherence tomography,
maize plants,
matrix singular value decomposition,
numerical stability,
regularization technique,
scattering mechanisms,
tomograms,
vegetation.
Abstract: In this letter, we consider a dual-baseline formulation of coherence tomography and show how practical application of the method is limited by numerical stability. To help reduce this, we propose a regularization technique based on a matrix singular value decomposition to stabilize the inversion. We then apply the new dual-baseline algorithm to ground-based radar data from the European Microwave Signature Laboratory. We consider a sample of maize plants and employ dual-baseline interferometric data to reconstruct vertical tomograms through the vegetation as a function of frequency. We use these reconstructions to interpret the primary scattering mechanisms and their polarization dependence. -
Ian G. Cumming and S. Li.
Adding Sensitivity to the MLBF Doppler Centroid Estimator.
IEEE Transactions on Geoscience and Remote Sensing,
45(2):279-292,
Feb. 2007.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Multilook Beat Frequency,
MLPF,
Doppler Centroid Estimation,
Doppler Ambiguity Resolver,
DAR,
Doppler radar,
fast Fourier transforms,
frequency estimation,
radar signal processing,
remote sensing by radar,
sensitivity,
synthetic aperture radarDoppler ambiguity,
Doppler centroid estimator,
FFT,
Fourier transform,
MLBF algorithm,
RADARSAT-1,
ScanSAR,
cross beating,
estimation sensitivity,
multilook beat frequency algorithm,
range migration,
target trajectory.
Abstract: The multilook beat frequency (MLBF) algorithm is the Doppler centroid estimator most commonly used in practice to solve the Doppler ambiguity. However, it still makes errors, notably in medium- or low-contrast scenes. In this paper, we present two ways in which the estimation sensitivity of the MLBF algorithm can be improved. First, we give a more thorough frequency-domain explanation of how the MLBF algorithm works and explain how cross beating and range migration cause estimation difficulties. The first improvement to the algorithm replaces the fast Fourier transform (FFT)-based beat frequency estimator with a more accurate one that uses phase increments. It avoids the FFT limitations of resolution and quantization, especially when the signal is discontinuous in one range cell due to range cell migration or burst mode operation (ScanSAR). A second improvement uses range cell migration correction to straighten the target trajectories before the beat frequency estimator is applied. This has the effect of narrowing the bandwidth of the beat signal and reducing the effect of cross beating. Finally, experiments with RADARSAT-1 data are used to illustrate the improved estimation accuracy of the modified algorithm -
K. Huangfu J. Zhihong and W. Jianwei.
A Chirp Transform Algorithm for Processing Squint Mode FMCW SAR Data.
IEEE Geoscience and Remote Sensing Letters,
4(3):377-381,
July 2007.
ISSN: 1545-598X.
Keyword(s): Airborne radar,
Chirp,
Data processing,
Frequency,
High-resolution imaging,
Image reconstruction,
Image sampling,
Radar antennas,
Radar imaging,
Synthetic aperture radar,
fast Fourier transforms,
geophysical techniques,
image processing,
synthetic aperture radar,
chirp transform algorithm,
continous antenna motion,
fast Fourier transforms,
frequency scaling algorithm,
frequency-modulated continuous-wave SAR,
high-resolution airborne imaging radar,
multiplications,
nonchirped raw data,
point target simulation experiments,
range cell migration,
range-Doppler domain,
reconstructed images distortion,
sampling frequency problem,
squint mode FMCW SAR data processing,
Chirp transform algorithm,
frequency-modulated continuous-wave (FMCW) radar,
synthetic aperture radar (SAR);.
[bibtex-key = Zhi:GRSL07]
-
G. Krieger,
A. Moreira,
H. Fiedler,
I. Hajnsek,
M. Werner,
M. Younis,
and M. Zink.
TanDEM-X: A Satellite Formation for High-Resolution SAR Interferometry.
IEEE_J_GRS,
45(11):3317-3341,
November 2007.
ISSN: 0196-2892.
Keyword(s): HRTI-3 specification,
TanDEM-X mission concept,
TerraSAR-X add-on for Digital Elevation Measurement,
TerraSAR-X radar satellites,
bistatic data acquisition,
global digital elevation model,
high-resolution SAR interferometry,
radar applications,
radar imaging techniques,
remote sensing applications,
satellite formation flying concept,
spaceborne radar interferometer,
synchonization,
synthetic aperture radar,
data acquisition,
digital elevation models,
geophysical techniques,
radar imaging,
radar interferometry,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar;.
Abstract: TanDEM-X (TerraSAR-X add-on for digital elevation measurements) is an innovative spaceborne radar interferometer that is based on two TerraSAR-X radar satellites flying in close formation. The primary objective of the TanDEM-X mission is the generation of a consistent global digital elevation model (DEM) with an unprecedented accuracy, which is equaling or surpassing the HRTI-3 specification. Beyond that, TanDEM-X provides a highly reconfigurable platform for the demonstration of new radar imaging techniques and applications. This paper gives a detailed overview of the TanDEM-X mission concept which is based on the systematic combination of several innovative technologies. The key elements are the bistatic data acquisition employing an innovative phase synchronization link, a novel satellite formation flying concept allowing for the collection of bistatic data with short along-track baselines, as well as the use of new interferometric modes for system verification and DEM calibration. The interferometric performance is analyzed in detail, taking into account the peculiarities of the bistatic operation. Based on this analysis, an optimized DEM data acquisition plan is derived which employs the combination of multiple data takes with different baselines. Finally, a collection of instructive examples illustrates the capabilities of TanDEM-X for the development and demonstration of new remote sensing applications. -
Alexander Löw and Wolfram Mauser.
Generation of geometrically and radiometrically terrain corrected SAR image products.
Remote Sensing of Environment,
106(3):337-349,
February 2007.
Keyword(s): SAR Processing,
Radiometric Calibration,
Calibration,
Image enhancement,
Image processing,
Synthetic aperture radar,
Terrain mapping,
SAR geocoding,
Radiometric normalization.
Abstract: Terrain undulations affect the geometric and radiometric quality of synthetic aperture radar images. The correction of these effects becomes indispensable when quantitative image analysis is performed with respect to the derivation of geo- and biophysical parameters. The paper presents a rigorous approach for geometric and radiometric correction of SAR images. Using a digital elevation model, the imaging geometry is reconstructed and is used to perform geometric and radiometric correction of terrain induced distortions. The importance of a stringent radiometric correction based on the integration of the image brightness is emphasized. The approach guarantees that the energy contained in the image data is preserved throughout the geocoding process. The resulting backscattering images are fully terrain corrected and can be used for further quantitative investigations and may also improve qualitative studies as e.g. land cover classifications. The technique is applicable for different sensor types and image products, including already geocoded SAR images. The effect of different resolutions of digital elevation models used for the correction of the backscattering coefficient is investigated. -
Ross F. Nelson,
Peter Hyde,
Patrick Johnson,
Bomono Emessiene,
Marc L. Imhoff,
Robert Campbell,
and Wilson Edwards.
Investigating RaDAR-LiDAR synergy in a North Carolina pine forest.
Remote Sensing of Environment,
110(1):98-108,
September 2007.
ISSN: 0034-4257.
Keyword(s): SAR Processing,
Biomass,
Forest,
VHFRaDAR,
profiling LiDAR,
biomass,
RaDAR-LiDAR synergy,
VHFSAR DATA,
SMALL-FOOTPRINT LIDAR,
AIRBORNE LASER DATA,
STEM VOLUME,
STAND CHARACTERISTICS,
AERIAL-PHOTOGRAPHY,
VEGETATION BIOMASS,
CONIFEROUS FOREST,
BOREAL FORESTS,
SCANNER DATA.
Abstract: A low frequency (80-120 MHz) VHF RaDAR, BioSAR, specifically designed for forest biomass estimation and a profiling LiDAR, PALS, were flown over loblolly pine plantations in the southeastern United States. LiDAR-only, RaDAR-only, and joint LiDAR-RaDAR linear models were developed to determine if returns from two sensors could be used to estimate pine biomass more accurately and precisely than returns from either sensor alone. The best five-variable RaDAR model explained 81.8\% (R (2)) of the stem green biomass variability, with a regression RMSE of 57.5 t/ha. The best one-variable LiDAR model explained 93.3\% of the biomass variation (RMSE=33.9 t/ha). Combining the RaDAR normalized volumetric returns with the profiling LiDAR ranging measurements did little to improve the best LiDAR-only model. The best LiDAR-RaDAR model explained 93.8\% of the biomass variation (RSME=32.7 t/ha). Cross-validation and training/test validation procedures demonstrated (1) that all models are unbiased and (2) the increased precision of the LiDAR-only and LiDAR-RaDAR models. The results of this investigation and a companion study indicate that there is little to be gained combining VHF-RaDAR volumetric returns and profiling LiDAR ranging measurements in pine forests; a LiDAR ranging system is sufficient for accurate, precise biomass estimation. -
Jean-Marie Nicolas,
Gabriel Vasile,
Michel Gay,
Florence Tupin,
and Emmanuel Trouvé.
SAR processing in the temporal domain: application to direct interferogram generation and mountain glacier monitoring.
Canadian Journal of Remote Sensing,
33(1):52-59,
2007.
Keyword(s): SAR Processing,
Time-Domain Back-Projection,
InSAR,
Interferometry,
SAR Interferometry,
Glacier Displacement Measurement,
ERS,
Spaceborne SAR.
Abstract: Synthetic aperture radar (SAR) interferometry has the potential to measure temperate glacier displacement with a large coverage of the surface compared with pointwise terrestrial ground measurements. The significant topographic relief in mountainous areas, however, where most alpine glaciers are located, makes the use of SAR imagery rather difficult. Among the difficulties, when the resolution increases, the focusing of satellite SAR images, usually performed in the frequency domain with a constant-height hypothesis, becomes a critical issue. SAR processing in the temporal domain is a different approach that enables the use of information such as the local topography. In this paper, we present an original method to perform this temporal domain focusing by modeling the relative motion of the satellite and Earth points. The method allows production of SAR single look complex (SLC) images directly in ground geometry and reduces the need for resampling and phase correction to obtain interferograms. A tandem pair of European remote sensing (ERS) SAR images acquired over the Mont-Blanc area is used to illustrate the proposed approach. The results are presented with amplitude images and interferograms measuring glacier 1 day displacements and are compared with the results from the differential interferometric automated process applied to survey of nature (DIAPASON) and repeated orbit interferometry package (ROI-PAC) conventional SAR processors. -
D. Pastina,
F. Colone,
and P. Lombardo.
Effect of Apodization on SAR Image Understanding.
IEEE Transactions on Geoscience and Remote Sensing,
45(11):3533-3551,
November 2007.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Apodization,
Spatially Variant Apodization,
SVA,
SAR images,
apodization effect,
homogeneous regions,
main lobe resolution preservation,
pixel complex amplitude,
probability density function,
radar cross sections,
sidelobe level reduction,
statistical moments,
statistical properties,
supervised classification,
synthetic aperture radar images,
geophysical techniques,
image classification,
radar cross-sections,
synthetic aperture radar.
Abstract: This paper investigates the effect of apodization on the statistical properties of synthetic aperture radar (SAR) images and its impact on the capability of extracting information from homogeneous regions of apodized SAR images. The statistical model for the pixel complex amplitude of the apodized image is derived in terms of both probability density function and statistical moments. Knowledge of the statistical properties is then used to develop appropriate schemes for parameter estimation and supervised classification of homogeneous regions with different radar cross sections in apodized SAR images. The performance analysis shows that the new techniques (properly derived for the apodized case) provide information extraction capabilities only slightly worse than those provided by the conventional techniques applied to the nonapodized case. This allows us to conclude that the use of nonlinear apodization yields sidelobe level reduction and main lobe resolution preservation that can be traded with the small losses above. A full characterization of the estimation and classification performance of these new techniques shows that nonlinear apodization globally introduces a performance degradation comparable to a reduction of the number of looks of a factor of 1.455 for a homogeneous region. -
P. Prats,
K.A. Camara de Macedo,
A. Reigber,
R. Scheiber,
and J.J. Mallorqui.
Comparison of Topography- and Aperture-Dependent Motion Compensation Algorithms for Airborne SAR.
IEEE Geoscience and Remote Sensing Letters,
4(3):349-353,
July 2007.
ISSN: 1545-598X.
Keyword(s): Algorithm design and analysis,
Approximation algorithms,
Azimuth,
Focusing,
Frequency,
Motion compensation,
Performance analysis,
Radar tracking,
Surfaces,
Synthetic aperture radar,
motion compensation,
synthetic aperture radar,
topography (Earth),
DLR,
Fourier-based motion compensation algorithms,
German Aerospace Center,
airborne SAR,
airborne synthetic aperture radar,
angle accommodation,
azimuthal topography accommodation,
beam-center approximation,
computational complexity,
reference height,
track deviations,
Calibration,
image registration,
interferometry,
motion compensation (MoCo),
synthetic aperture radar (SAR);.
[bibtex-key = Prats07:GRSL]
-
P. Prats,
Karlus A. Câmara de Macedo,
A. Reigber,
R. Scheiber,
and J. J. Mallorqui.
Comparison of Topography- and Aperture-Dependent Motion Compensation Algorithms for Airborne SAR.
Geoscience and Remote Sensing Letters, IEEE,
4(3):349-353,
2007.
ISSN: 1545-598X.
Keyword(s): SAR Processing,
Motion Compensation,
PTA-Algorithm,
Precise Topography- and Aperture-Dependent (PTA) Algorithm,
SATA,
Subaperture Topography- and Aperture-dependent (SATA) Algorithm,
Frequency Division (FD) Algorithm,
Topography-Based Motion Compensation,
ESAR,
L-Band Calibration,
image registration,
interferometry,
motion compensation (MoCo),
synthetic aperture radar (SAR),
Comparison,
Comparsion of Motion Compensation Algorithms,
InSAR,
Airborne SAR.
Abstract: This letter presents a comparison between three Fourier-based motion compensation (MoCo) algorithms for airborne synthetic aperture radar (SAR) systems. These algorithms circumvent the limitations of conventional MoCo, namely the assumption of a reference height and the beam-center approximation. All these approaches rely on the inherent time-frequency relation in SAR systems but exploit it differently, with the consequent differences in accuracy and computational burden. After a brief overview of the three approaches, the performance of each algorithm is analyzed with respect to azimuthal topography accommodation, angle accommodation, and maximum frequency of track deviations with which the algorithm can cope. Also, an analysis on the computational complexity is presented. Quantitative results are shown using real data acquired by the Experimental SAR system of the German Aerospace Center (DLR). -
Z. Su,
Y. Peng,
and X. Wang.
Feature-Independent Aperture Evaluator for the Curvilinear SAR.
Geoscience and Remote Sensing Letters, IEEE,
4(2):191-195,
2007.
Keyword(s): SAR Processing,
Non-Linear Flight Path,
SAR Tomography,
3D Feature Extraction,
Feature Extraction,
Curvilinear SAR.
Abstract: Curvilinear synthetic aperture radar (SAR), as a more practicable 3-D SAR imaging system, utilizes parametric target feature estimates extracted from the received data to reconstruct the target image. The reconstructed image quality is then impacted by the estimation accuracy of the features. In this letter, through discussing the correlation between the system parameters and the estimation performance of the curvilinear SAR, a conclusion can be drawn on how the overall location accuracy of a target is determined by the correlation between the azimuth and elevation coordinates of the flight path, compactly characterizing the curvilinear aperture. Consequently, a new index, determined only with the aperture parameters, is proposed as an aperture evaluator, which is referred to as the feature-independent aperture evaluator (FAE). FAE can be used for guiding the operational aperture design. - Jiang Zhihong, Huang Fukan, Wan Jianwei, and Cheng Zhu. Modified frequency scaling algorithm for FMCW SAR data processing. Chinese Journal of Aeronautics, 20:339-345, Jan. 2007. [bibtex-key = Zhi:ChinJournAeron07]
-
Karl-Heinz Bethke,
S. Baumgartner,
M. Gabele,
D. Hounam,
E. Kemptner,
D. Klement,
G. Krieger,
and R. Erxleben.
Air- and spaceborne monitoring of road traffic using SAR moving target indication--Project TRAMRAD.
ISPRS Journal of Photogrammetry and Remote Sensing, Theme Issue: Airborne and Spaceborne Traffic Monitoring,,
61(3-4):243-259,
December 2006.
Keyword(s): SAR Processing,
TRAMRAD,
Traffic Monitoring,
TerraSAR-X,
STAP,
Space-Time Adaptive Processing,
MTI,
Moving Target Indication,
SAR Interferometry,
Interferometry,
ATI,
Along-Track SAR Interferometry.
Abstract: To ensure mobility, future road traffic management urgently needs actual and reliable information about the road traffic over wide areas in order to keep the traffic moving and the travel time short. Nowadays, outside of motorways the actual traffic situation is almost unknown due to the lack of sensor installations. This is the background for the TRAMRAD (TrafficMonitoring with Radar) project. TRAMRAD aims at profiting from research and development in earth observation and advances in radar remote sensing techniques to define realizable future air- or spaceborne sensor systems for the wide area monitoring of road traffic. The project comprises the necessary theoretical and practical investigations, as well as experimental campaigns with airborne instruments. The paper describes the requirements for the systems and the concepts being investigated. In particular, it discusses the complex detection conditions, the requirements on the radar instrument and the methods for processing the data. Possible system concepts are described and their capabilities are discussed. -
Hubert-M.J. Cantalloube and Pascale Dubois-Fernandez.
Airborne X-band SAR imaging with 10 cm resolution: technical challenge and preliminary results.
IEE Proceedings - Radar, Sonar and Navigation,
153(2):163-176,
April 2006.
ISSN: 1350-2395.
Keyword(s): SAR Processing,
Doppler radar,
airborne radar,
antenna radiation patterns,
frequency-domain synthesis,
image resolution,
microwave antennas,
radar antennas,
radar cross-sections,
radar imaging,
radar resolution,
radar tracking,
synthetic aperture radar,
1.2 GHz,
Ku-band,
RAMSES,
bandwidth,
X-band,
Airborne SAR,
antenna pattern compensation,
carrier trajectory,
cross-range resolution,
deterministic motion,
fast-frequency domain synthesis,
isotropic point-like echo,
phase-tracking,
Autofocus,
Residual Motion Errors,
Motion Compensation,
MoComp,
Time-Domain Back-Projection,
TDBP,
temporal-domain back-projection synthesis.
Abstract: The bandwidth of RAMSES, an airborne synthetic aperture radar (SAR) system was recently increased to 1.2 GHz in X- and Ku-bands, yielding (unweighted) 3 dB range resolution of 11 cm. The synthesis of SAR images with matching cross-range resolution requires long integration times, and this disqualifies the temporal-domain back-projection synthesis algorithm as impractically slow. The wider relative bandwidth also disqualifies simplified range/Doppler types of algorithms, as the hypothesis of proportionality between Doppler and squint is no longer valid. Therefore the authors implemented a fast-frequency domain synthesis algorithm (\u03a9-k or range-migration algorithm) and designed a new deterministic motion and antenna pattern compensation method for it. As the required accuracy on carrier trajectory exceeded the performance of the differential GPS-hybridised inertial navigation unit, the authors implemented an autofocus based on the phase-tracking of several isotropic point-like echoes. -
Shane R. Cloude.
Polarization coherence tomography.
Radio Sci.,
41:-,
August 2006.
Keyword(s): SAR Processing,
SAR Tomography,
radar tomography,
polarimetric interferometry,
radar polarimetry,
Remote sensing,
Inverse scattering,
Random media and rough surfaces,
Interferometry,
InSAR,
SAR Interferometry,
PolInSAR.
Abstract: In this paper we introduce a new radar-imaging technique, called polarization coherence tomography (PCT), which employs variation of the interferometric coherence with polarization to reconstruct a vertical profile function in penetrable volume scattering. We first show how this profile function can be efficiently represented as a Fourier-Legendre series, with tomographic reconstruction reducing to estimation of the unknown coefficients of this series from coherence data. We then show that we can linearize this inversion by using a priori knowledge of two parameters, namely, volume depth and topographic phase. We further propose a new algorithm based on polarimetric interferometry to estimate these two from the data itself. To assess stability, we investigate both the single- and dual-baseline conditioning of the associated matrix inversion and then concentrate on the single-baseline case to demonstrate that for sufficient multilooking (around 50), stable retrievals of profiles can be obtained in the presence of coherence noise. Finally, we apply the technique to simulated L band coherent radar data to demonstrate its potential for new applications in radar remote sensing. -
Ian G. Cumming and Shu Li.
Improved slope estimation for SAR Doppler ambiguity resolution.
Geoscience and Remote Sensing, IEEE Transactions on,
44(3):707-718,
2006.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Doppler Centroid Estimation,
Doppler radar,
Radon transforms,
radar resolution,
remote sensing by radar,
synthetic aperture radar,
Doppler Ambiguity Resolver,
DAR,
Radon transform,
SAR,
antenna pointing angle,
look displacement algorithm,
satellite beam pointing angle,
slope estimation.
Abstract: The idea of using the Radon transform to measure the alignment of linear features in synthetic aperture radar (SAR) data has breathed new life into the "look displacement" class of Doppler ambiguity resolution algorithms. In these algorithms, the slope of target energy is estimated to obtain the satellite beam pointing angle accurately enough to resolve the Doppler ambiguity. After explaining the method and adding some minor improvements, it is shown how it can work well on satellite SAR data. Then, an alternate method is developed that combines the ideas of the Radon and look displacement algorithms to obtain a computationally simpler and more accurate algorithm. In addition, the quality checks of the "spatial diversity" approach are used to increase the robustness of the algorithm. Even though the algorithm was conceived for high-contrast scenes, it works remarkably well in low to medium contrast scenes as well. -
G. Fornaro and F. Serafino.
Imaging of Single and Double Scatterers in Urban Areas via SAR Tomography.
Geoscience and Remote Sensing, IEEE Transactions on,
44(12):3497-3505,
2006.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
geophysical techniques,
remote sensing by radar,
synthetic aperture radar,
tomography,
topography (Earth),
3D synthetic aperture radar tomography,
European Remote Sensing 1 satellite,
European Remote Sensing 2 satellite,
Italy,
Naples,
Napoli,
SAR sensors,
data calibration,
microwave scattering,
residual topography,
spatial-differencing technique,
surface deformation,
urban areas,
Multibaseline coherent synthetic aperture radar (SAR) processing,
SAR tomography,
three-dimensional (3-D) SAR focusing.
Abstract: Microwave scattering is a rather complex mechanism, especially in urban areas. Three-dimensional (3-D) synthetic aperture radar (SAR) tomography is a technique that uses multiple views to map the scattering power at different heights, thus extending the capability of SAR sensors to fully image the scene in the 3-D space. This paper presents a first validation of spaceborne long-term SAR tomography by demonstrating the capability to resolve a simple layover case, i.e., to separate single- and double-scattering mechanisms within imaged pixels. Results obtained with real data acquired by the European Remote Sensing 1 and 2 (ERS-1 and ERS-2) satellites over the urban area of Napoli are presented. As an additional contribution, an innovative algorithm estimating residual topography and surface deformation, called the spatial-differencing technique, is also discussed in detail at the data calibration stage -
A. Refice,
F. Bovenga,
and R. Nutricato.
MST-based stepwise connection strategies for multipass Radar data, with application to coregistration and equalization.
Geoscience and Remote Sensing, IEEE Transactions on,
44(8):2029-2040,
2006.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
geophysical signal processing,
image registration,
interferometry,
radar imaging,
remote sensing by radar,
synthetic aperture radar,
European Remote Sensing Satellite,
InSAR coherence,
MST-based stepwise connection strategy,
data processing,
distance function,
geometric shift,
image coregistration,
image equalization,
interferometric SAR,
interferometric coherence,
minimum spanning tree,
multipass radar data,
radar imaging,
radiometric calibration,
radiometric equalization,
synthetic aperture radar,
Data processing,
image registration,
minimum spanning tree (MST),
multipass synthetic aperture radar (SAR) interferometry,
radar imaging,
radiometric calibration.
Abstract: This paper proposes a unified framework for predicting optimized pairing strategies for interferometric processing of multipass synthetic aperture radar data. The approach consists in a minimum spanning tree (MST) structure based on a distance function encoding an a priori model for the interferometric quality of each image pair. Using a distance function modeled after the interferometric coherence allows reproducing many "small baseline" strategies presented in the recent literature. A novel application of the method to the processing steps of image coregistration and equalization is illustrated, using a test European Remote Sensing Satellite dataset. Widespread methods used for these two operations rely on the computation of the amplitude cross correlation over a large number of corresponding tie patches distributed over the scene. Geometric shift and radiometric equalization parameters are estimated over the patches and used, respectively, within a polynomial warp model and a radiometric correction scheme. The number of reliable patches available behaves similarly to the interferometric synthetic aperture radar (InSAR) coherence with respect to the baselines, and can be assimilated to a quality figure for the derivation of the MST. Results show an improvement in the quality of the stepwise (SW)-processed image stack with respect to the classical single-master procedure, confirming that the SW approach is able to provide better conditions for the estimation of correlation-related InSAR parameters. -
Andreas Reigber,
E. Alivizatos,
A. Potsis,
and Alberto Moreira.
Extended wavenumber-domain synthetic aperture radar focusing with integrated motion compensation.
Radar, Sonar and Navigation, IEE Proceedings,
153(3):301-310,
2006.
ISSN: 1350-2395.
Keyword(s): SAR Processing,
omega-k,
Range Migration Algorithm,
Wavenumber Domain Algorithm,
Extended omega-k,
EOK,
Extended Wavenumber Domain Algorithm,
Motion Compensation,
Squinted SAR,
Airborne SAR,
E-SAR,
ECS,
Extended Chirp Scaling.
Abstract: Modern synthetic aperture radar (SAR) systems are continually developing in the direction of higher spatial resolution. This requires the usage of high range bandwidths combined with long azimuth integration intervals. High-quality SAR processing methods, which are able to deal with such sensor parameters, are necessary for focusing the raw data of such sensors. Wavenumber-domain (omegak) processing is commonly accepted as the ideal solution to the SAR focusing problem. However, it is only applicable to spaceborne SAR data where a straight sensor trajectory is given. In the case of airborne data, wavenumber-domain processing is limited because of its inability to perform high-precision motion compensation. Here, the extended chirp scaling (ECS) algorithm has proven to be very powerful, although it has certain limitations concerning long aperture syntheses and highly squinted geometries. In the paper, a new stripmap SAR data-processing algorithm, called extended omega–k (EOK), is analytically derived. The EOK algorithm aims to combine the high focusing accuracy of the wavenumber-domain algorithm with the high-precision motion compensation of the ECS algorithm. The new EOK algorithm integrates a three-step motion compensation correction in the general formulation of the wavenumber-domain algorithm, leading to a new airborne SAR processing scheme, which is also very robust in the cases of long synthetic apertures and high squint angles. As demonstrated, it offers the possibility of processing wide-band, low-frequency airborne SAR data up to nearwavelength resolution. The performance and accuracy of the new EOK SAR data-processing algorithm are demonstrated using simulated data in different data collection scenarios and geometries as well as using interferometric data acquired by the airborne experimental SAR system of DLR at L-band (Horn, 1996; Scheiber, 1999). - A. Reigber, E. Alivizatos, A. Potsis, and A. Moreira. Extended wavenumber-domain synthetic aperture radar focusing with integrated motion compensation. Radar, Sonar and Navigation, IEE Proceedings -, 153(3):301-310, 2006. ISSN: 1350-2395. [bibtex-key = Reigber_EOK_2006]
-
A. Reigber,
P. Prats,
and J.J. Mallorqui.
Refined estimation of time-varying baseline errors in airborne SAR interferometry.
IEEE Geoscience and Remote Sensing Letters,
3(1):145-149,
January 2006.
Keyword(s): SAR Processing,
Airborne SAR,
calibration,
Interferometry,
L-Band,
Baseline refinement,
calibration,
interferometry,
InSAR,
Motion Compensation,
repeat-pass interferometry,
Residual Motion Errors,
RME,
Squinted SAR,
Multi-Squint Processing,
ESAR,
geophysical signal processing,
geophysical techniques,
motion compensation,
remote sensing by radar,
synthetic aperture radar SAR focusing,
airborne SAR data,
airborne SAR interferometry,
digital elevation model,
motion compensation,
multisquint processing approach,
navigation system,
repeat-pass systems,
residual motion errors,
synthetic aperture radar,
time-varying baseline errors.
Abstract: The processing of airborne synthetic aperture radar (SAR) data requires a precise compensation of the deviations of the platform movement from a straight line. This is usually carried out by recording the trajectory with a high-precision navigation system and correcting them during SAR focusing. However, due to the lack of accuracy in current navigation systems, residual motion errors persist in the images. Such residual motion errors are mainly noticeable in repeat-pass systems, where they are causing time-varying baseline errors, visible as artefacts in the derived phase maps. In this letter, a refined method for the estimation of time-varying baseline errors is presented. An improved multisquint processing approach is used for obtaining robust estimates of higher order baseline errors over the entire scene, even if parts of the scene are heavily decorrelated. In a subsequent step, the proposed method incorporates an external digital elevation model for detection of linear and constant components of the baseline error along azimuth. Calibration targets in the scene are not necessary. -
Martin Stangl,
Rolf Werninghaus,
B. Schweizer,
C. Fischer,
Michael Brandfass,
Josef Mittermayer,
and Helko Breit.
TerraSAR-X Technologies and First Results.
Radar, Sonar & Navigation,
153(2):86 - 95,
04 2006.
Keyword(s): SAR Processing,
TerraSAR-X,
Spaceborne SAR,
X-Band,
Instrument Description,
Imaging Modes,
Stripmap,
ScanSAR,
Spotlight SAR,
TerraSAR-X multimode SAR processor,
TMSP,
Chirp Scaling Algorithm,
CSA,
SPECAN Algorithm,
SPECAN.
Abstract: The TerraSAR-X Satellite which is currently being built in the framework of a public private partnership between the German Aerospace Centre DLR and Astrium GmbH Germany carries an X-Band SAR instrument which is equipped with an active phased array antenna. Its operational flexibility allows the use of the instrument for scientific and commercial applications. High amplitude and phase stability of the radar instrument is achieved by a Carbon Fibre Reinforced Plastic (CFRP) slotted waveguide radiator and high precision Transmit/Receive Module. Additionally internal calibration hardware allows for determination of the residual drifts. A precise Central Electronics controls the radar instrument, provides an arbitrary transmit chirp and receives the radar echo with selectable bandwidth and raw data compression ratio. The ground stations multimode SAR processor is supported by a novel satellite steering law to reduce the attitude dependent mean Doppler shift. This article summarises the EUSAR 2004 TerraSAR-X contributions. -
H. C. Stankwitz and S. P. Taylor.
Advances in non-linear apodization.
IEEE Aerospace and Electronic Systems Magazine,
21(1):3-8,
January 2006.
ISSN: 0885-8985.
Keyword(s): SAR Processing,
Apodization,
Spatially Variant Apodization,
SVA,
NonLinear Apodization,
European Soil Moisture and Ocean Salinity system,
GeoSTAR,
Y-type synthetic aperture radiometers,
antenna size,
bandwidth extrapolation,
impulse response performance,
irregularly-shaped apertures,
microwave radar systems,
microwave remote sensing,
nonlinear apodization,
parse coherent apertures,
sidelobe control,
sparse aperture filling property,
superresolution algorithms,
superresolution techniques,
synthetic aperture radar systems,
synthetic multiple aperture radar technology,
microwave measurement,
radar antennas,
radar resolution,
remote sensing by radar,
synthetic aperture radar,.
Abstract: Selected new methods and applications of non-linear apodization for irregularly-shaped and parse coherent apertures and arrays are presented. The benefits include unproved impulse response performance, i.e., reduced peak sidelobes and integrated sidelobe power, along with improved mainlobe resolution, compared to classic windowing techniques. Nonlinear apodization (NLA) techniques can also serve as powerful engines for effective superresolution and bandwidth extrapolation of coherent data for filling sparse apertures. The sparse aperture filling property of superresolution algorithms for radar data forms the basis for a new concept which is introduced here: synthetic multiple aperture radar technology (SMART). Increased swath and/or reduced antenna size are some of the benefits postulated for SMART applied to synthetic aperture radar (SAR) systems. The benefits of these new methods and applications for nonlinear apodization are then demonstrated for two specific applications: 1) sidelobe control for Y-type synthetic aperture radiometers, such as the European Soil Moisture and Ocean Salinity (SMOS) system (Kerr et al.) and JPL's proposed GeoSTAR (Lambrigsten) concept; and, 2) filling of sparse synthetic aperture radar data by exploiting the bandwidth extrapolation properties of nonlinear apodization based superresolution techniques. The methods that have been developed and demonstrated herein have potential application to a wide range of passive and active microwave remote sensing and radar systems. -
Z. Su,
Y. Peng,
and X. Wang.
Evaluation of the Aperture in the Curvilinear SAR.
Radar, 2006. CIE'06. International Conference on,
pp 1-4,
2006.
Keyword(s): SAR Processing,
Non-Linear Flight Path,
SAR Tomography,
Curvilinear SAR.
Abstract: The curvilinear synthetic aperture radar (SAR), as a more practicable three-dimensional (3-D) SAR imaging system, has to utilize the parametric methods to extract the target features from its received data, the sparse data in 3-D frequency space. With the obtained feature estimates, these parametric methods, who can efficiently remove the effects of the sidelobes, reconstruct the target image whose quality is affected by the estimation accuracy of the features. By minimizing the Cramer-Rao bounds (CRBs) of the target features, we show, in this paper, the different effects on the estimation accuracy of different aperture parameters. A feature-independent aperture evaluator is also given for the curvilinear SAR system. -
W. L. Van Rossum,
M. P. G. Otten,
and R. J. P. Van Bree.
Extended PGA for range migration algorithms.
IEEE Transactions on Aerospace and Electronic Systems,
42(2):478-488,
April 2006.
ISSN: 0018-9251.
Keyword(s): SAR Proceedings,
Autofocus,
Phase Gradient Autofocus,
PGA,
gradient methods,
radar imaging,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Spotlight SAR,
synthetic aperture radar.
Abstract: The phase gradient autofocus (PGA) algorithm is extended to work for synthetic aperture radar (SAR) spotlight images processed with range migration (w-k) algorithms. Several pre-processing steps are proposed for aligning the range-compressed phase-history data needed for successful autofocusing of the data. The proposed algorithm gave good results for both data with large point targets and data without point targets. -
I. Walterscheid,
J.H.G. Ender,
A.R. Brenner,
and O. Loffeld.
Bistatic SAR Processing and Experiments.
IEEE_J_GRS,
44(10):2710-2717,
October 2006.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Bistatic SAR,
Airborne Experimental Radar II,
Forschungsgesellschaft fur Angewandte Naturwissenschaften,
Phased Array Multifunctional Imaging Radar,
X-band SAR systems,
antenna pointing,
bistatic SAR,
bistatic reflectivity,
flight coordination,
forward-looking SAR imaging,
motion compensation,
radar cross section,
range migration algorithm,
receive gate timing,
synthetic aperture radar,
transmit pulse,
airborne radar,
geophysical signal processing,
geophysical techniques,
radar imaging,
remote sensing by radar,
synthetic aperture radar;.
Abstract: Bistatic synthetic aperture radar (SAR) uses a separated transmitter and receiver flying on different platforms to achieve benefits like exploitation of additional information contained in the bistatic reflectivity of targets, reduced vulnerability for military applications, forward-looking SAR imaging, or increased radar cross section. Besides technical problems such as synchronization of the oscillators, involved adjustment of transmit pulse versus receive gate timing, antenna pointing, flight coordination, and motion compensation, the development of a bistatic focusing algorithm is still in progress and not sufficiently solved. As a step to a numerically efficient processor, this paper presents a bistatic range migration algorithm for the translationally invariant case, where transmitter and receiver have equal velocity vectors. In this paper, the algorithm was successfully applied to simulated and real bistatic data. The real bistatic data have been acquired with the Forschungsgesellschaft fur Angewandte Naturwissenschaften (FGAN)'s X-band SAR systems, namely the Airborne Experimental Radar II and the Phased Array Multifunctional Imaging Radar, in October 2003 -
L. Xiangle and Y. Ruliang.
Study of Composite Mode Curvilinear SAR.
Radar, 2006. CIE'06. International Conference on,
pp 1-4,
2006.
Keyword(s): SAR Processing,
Non-Linear Flight Path,
SAR Tomography,
Curvilinear SAR.
Abstract: A new mode of curvilinear SAR called "composite mode curvilinear SAR(CCLSAR)" is proposed in this paper. In CCLSAR, the SAR operates in strip mode in azimuth and range dimension but spotlight mode in the height dimension. CCLSAR can synthesize a very large aperture in the direction of height, which cause very high resolution in the height dimension. Compared with the conventional curvilinear SAR, CCLSAR can acquire the imaging of large terrain quickly and immediately. Firstly the CCLSAR scheme was proposed and then the primary three-dimensional imaging in the case of full aperture of CCLSAR was discussed in this paper. -
F. Bordoni,
F. Lombardini,
F. Gini,
and A. Jakobsson.
Multibaseline cross-track SAR interferometry using interpolated arrays.
Aerospace and Electronic Systems, IEEE Transactions on,
41(4):1473-1482,
2005.
ISSN: 0018-9251.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
Layover,
Array Interpolation.
Abstract: This work deals with the problem of interferometric radar phase estimation in the presence of layover. The focus here is on multichannel interferometric synthetic aperture radar (InSAR) systems with a low number of phase centers and nonuniform array geometry. An interpolated array (IA) approach is proposed in order to apply parametric spectral estimation techniques designed for uniform linear arrays (ULAs). In particular, the interpolated MUSIC and weighted subspace fitting (WSF) algorithms are considered and compared with conventional methods. Performance analysis under different InSAR scenarios is carried out based on Monte Carlo simulations. The Cram´er-Rao lower bound (CRLB) for the nonuniform interferometric array is derived and reported as a benchmark on the estimation accuracy. -
Karlus A. Câmara de Macedo and Rolf Scheiber.
Precise topography- and aperture-dependent motion compensation for airborne SAR.
Geoscience and Remote Sensing Letters, IEEE,
2(2):172-176,
2005.
Keyword(s): SAR Processing,
PTA-MoComp,
Postprocessing,
Motion Compensation,
Topography-Based Motion Compensation,
Chirp Scaling Algorithm,
Extended Chirp Scaling Algorithm,
fast Fourier transform-based postprocessing methodology,
FFT,
D-InSAR,
German Aerospace Center,
DLR,
airborne repeat-pass interferometry,
differential interferometry,
geometric fidelity,
motion errors,
phase accuracy,
residual phase errors,
topographic heights,
Topography,
DEM,
Terrain,
wide beamwidth,
Airborne SAR,
ESAR,
P-Band,
differential interferometry,
Interferometry,
motion errors.
Abstract: Efficient synthetic aperture radar (SAR) processing algorithms are unable to exactly implement the aperture- and topography-dependent motion compensation due to the superposition of the synthetic apertures of several targets having different motion errors and potentially different topographic heights. Thus, during motion compensation, a reference level is assumed, resulting in residual phase errors that impact the focusing, geometric fidelity, and phase accuracy of the processed SAR images. This letter proposes a new short fast Fourier transform-based postprocessing methodology capable of efficient and precise compensation of these topography- and aperture-dependent residual phase errors. In addition to wide beamwidth (very high resolution) SAR systems, airborne repeat-pass interferometry especially benefits from this approach, as motion compensation can be significantly improved, especially in areas with high topographic changes. Repeat-pass interferometric data of the E-SAR system of the German Aerospace Center (DLR) are used to demonstrate the performance of the proposed approach. -
G. Fornaro,
G. Franceschetti,
and S. Perna.
Motion compensation errors: effects on the accuracy of airborne SAR images.
IEEE Transactions on Aerospace and Electronic Systems,
41(4):1338-1352,
October 2005.
Keyword(s): SAR Processing,
Motion Compensation,
Residual Motion Errors,
Autofocus,
Airborne SAR,
airborne radar,
interferometry,
motion compensation,
radar imaging,
synthetic aperture radar airborne SAR images,
digital elevation model inaccuracies,
motion compensation errors,
phase errors,
positioning measurement instrument,
repeat pass airborne interferometry,
residual uncompensated motion errors,
synthetic aperture radar.
Abstract: This work addresses the study of the effect of residual uncompensated motion errors due to positioning measurement instrument and digital elevation model inaccuracies on the accuracy of airborne synthetic aperture radar (SAR) images. It is shown that these not only introduce phase errors following pure geometric considerations, but they also cause additional aberrations related to their interaction with the SAR processing procedure. Extension to the repeat pass airborne interferometry is also included to show their impact on the resulting interferograms. -
Gianfranco Fornaro,
Fabrizio Lombardini,
and Francesco Serafino.
Three-dimensional multipass SAR focusing: experiments with long-term spaceborne data.
Geoscience and Remote Sensing, IEEE Transactions on,
43(4):702-714,
2005.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
Interferometry,
airborne SAR,
Spaceborne SAR,
stereo image processing,
three-dimensional multipass SAR focusing,
ERS data,
ERS multipass tomography,
European Remote Sensing satellite,
SAR interferometry,
atmospheric variations,
azimuth-range resolution cell,
critical nonlinear inversion steps,
ground pixel,
height profile reconstruction,
limited spatial-coverage,
limited time-span,
multibaseline 3D SAR focusing,
multiple targets,
radiation penetration,
scattering mechanisms,
scene deformations,
side-looking geometry,
space-varying phase calibration,
tomographic processing,
Multibaseline,
multipass,
three-dimensional focusing.
Abstract: Synthetic aperture radar (SAR) interferometry is a modern efficient technique that allows reconstructing the height profile of the observed scene. However, apart for the presence of critical nonlinear inversion steps, particularly crucial in abrupt topography scenarios, it does not allow one to separate different scattering mechanisms in the elevation (height) direction within the ground pixel. Overlay of scattering at different elevations in the same azimuth-range resolution cell can be due either to the penetration of the radiation below the surface or to perspective ambiguities caused by the side-looking geometry. Multibaseline three-dimensional (3-D) SAR focusing allows overcoming such a limitation and has thus raised great interest in the recent research. First results with real data have been only obtained in the laboratory and with airborne systems, or with limited time-span and spatial-coverage spaceborne data. This work presents a novel approach for the tomographic processing of European Remote Sensing satellite (ERS) real data for extended scenes and long time span. Besides facing problems common to the airborne case, such as the nonuniformly spaced passes, this processing requires tackling additional difficulties specific to the spaceborne case, in particular a space-varying phase calibration of the data due to atmospheric variations and possible scene deformations occurring for years-long temporal spans. First results are presented that confirm the capability of ERS multipass tomography to resolve multiple targets within the same azimuth-range cell and to map the 3-D scattering properties of the illuminated scene. -
F. Gini and F. Lombardini.
Multibaseline Cross-Track SAR Interferometry: A Signal Processing Perspective.
IEEE Aerospace and Electronic Systems Magazine,
20(8):71-93,
2005.
ISSN: 0885-8985.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
AWGN,
array signal processing,
radar signal processing,
speckle,
surface topography measurement,
synthetic aperture radar,
InSAR,
MB SAR tomography,
SAR signal processing,
ULA,
XTI-SAR,
additive white Gaussian noise,
multibaseline cross-track SAR interferometry,
multicomponent signal detection,
multiplicative noise,
natural layover area reflectivity,
nonparametric spectral estimation,
nonperfectly calibrated arrays,
parametric spectral estimation,
radar imaging speckle,
semitransparent volume scattering layers,
surface topography measurement,
synthetic aperture radar interferometry,
uniform linear array.
Abstract: Synthetic aperture radar interferometry (InSAR) is a powerful and increasingly expanding technique for measuring the topography of a surface, its changes over both short- and long-time scale, and other changes in the detailed characteristics of the surface. We provide a tutorial description of recent results on multibaseline (MB) InSAR processing. The main focus is on the problem of retrieving both heights and radar reflectivities of natural layover areas by means of a cross-track InSAR (XTI-SAR) system with a uniform linear array (ULA). It is formulated as the problem of detecting and estimating a multicomponent signal corrupted by multiplicative noise - the speckle in the radar imaging jargon - and by additive white Gaussian noise. Application to the InSAR problem of both nonparametric and parametric modern spectral estimation techniques is described. The problem of estimating the number of signal components in the presence of speckle is also addressed. Finally, a brief mention is given to recent research trends on robust methods for nonperfectly calibrated arrays, on processing for non-ULA configurations, and on MB SAR tomography, which is an extension of MB SAR interferometry for the full 3D mapping of semitransparent volume scattering layers. The state of the art of other advanced multichannel interferometric techniques is also briefly recalled. -
Young-Kyun Kong,
Byung-Lae Cho,
and Young-Soo Kim.
Ambiguity-free Doppler centroid estimation technique for airborne SAR using the Radon transform.
Geoscience and Remote Sensing, IEEE Transactions on,
43(4):715-721,
2005.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Doppler Centroid Estimation,
Doppler effect,
Radon transforms,
airborne radar,
geophysical signal processing,
geophysical techniques,
radar clutter,
synthetic aperture radar,
Doppler Ambiguity Resolver,
DAR,
Radon transform,
SAR image,
SAR signal processing,
airborne SAR,
ambiguity-free Doppler centroid estimation technique,
clutter-lock,
geometric distortion,
geometry-based Doppler estimator,
radiometric error,
signal-to-noise ratio,
squint angle,
synthetic aperture radar,
Clutter-lock.
Abstract: In synthetic aperture radar (SAR) signal processing, the Doppler centroid estimation technique, called the "clutter-lock", is important because it is related to the signal-to-noise ratio, geometric distortion, and radiometric error of the final SAR image. Conventional algorithms have either ambiguity problems or somewhat high computational load. Using the fact that the Doppler centroid and the squint angle are directly related, we propose an ambiguity-free Doppler centroid estimation technique using Radon transform, named geometry-based Doppler estimator. The proposed algorithm is computationally efficient and shows good performance of estimating the absolute Doppler centroid. -
Fabrizio Lombardini.
Differential tomography: a new framework for SAR interferometry.
Geoscience and Remote Sensing, IEEE Transactions on,
43(1):37-44,
2005.
Keyword(s): SAR Processing,
backscatter,
data acquisition,
geophysical signal processing,
geophysical techniques,
multidimensional signal processing,
radiowave interferometry,
remote sensing by radar,
spectral analysis,
synthetic aperture radar,
Tomography,
SAR interferometry,
baseline-time acquisition patterns,
bidimensional baseline-time spectral analysis,
data-dependent bidimensional spectral estimation,
SAR Tomography,
differential SAR tomography,
differential tomography,
electromagnetic tomography,
elevation-velocity resolution,
interferometric technique,
joint baseline-time processing,
layover scatterers,
motion conditions,
multibaseline SAR tomography,
multidimensional signal processing,
multiple scatterers,
sparse sampling,
synthetic aperture radar.
Abstract: A new interferometric mode crossing the differential synthetic aperture radar (SAR) interferometry and multibaseline SAR tomography concepts, that can be termed differential SAR tomography, is proposed. Its potentials, coming from the joint elevation-velocity resolution capability of multiple scatterers, are discussed. Processing is cast in a bidimensional baseline-time spectral analysis framework, with sparse sampling. The use of a modern data-dependent bidimensional spectral estimator is proposed for joint baseline-time processing. Simulated results are reported for different baseline-time acquisition patterns and two motion conditions of layover scatterers, showing that this new challenging interferometric technique is promising. -
Pau Prats,
Andreas Reigber,
and Jordi J. Mallorqui.
Topography-dependent motion compensation for repeat-pass interferometric SAR systems.
Geoscience and Remote Sensing Letters, IEEE,
2(2):206-210,
2005.
Keyword(s): SAR Processing,
Motion Compensation,
Topography-Based Motion Compensation,
ESAR,
L-Band,
Airborne SAR,
radar imaging,
remote sensing by radar,
synthetic aperture radar,
Topography,
German Aerospace Center E-SAR,
DLR,
SAR data processing,
airborne L-band repeat-pass interferometric data,
Interferometry,
Chirp Scaling Algorithm,
Extended Chirp Scaling Algorithm,
azimuth compression,
azimuth coregistration errors,
external digital elevation model,
DEM,
image enhancement,
image registration,
impulse response degradation,
phase artifacts,
repeat-pass interferometric SAR systems,
Calibration,
image registration,
repeat-pass interferometry.
Abstract: This letter presents a new motion compensation algorithm to process airborne interferometric repeat-pass synthetic aperture radar (SAR) data. It accommodates topography variations during SAR data processing, using an external digital elevation model. The proposed approach avoids phase artifacts, azimuth coregistration errors, and impulse response degradation, which usually appear due to the assumption of a constant reference height during motion compensation. It accurately modifies phase history of all targets before azimuth compression, resulting in an enhanced image quality. Airborne L-band repeat-pass interferometric data of the German Aerospace Center experimental airborne SAR (E-SAR) is used to validate the algorithm. -
A. Reigber and L. Ferro-Famil.
Interference suppression in synthesized SAR images.
Geoscience and Remote Sensing Letters, IEEE,
2(1):45-49,
2005.
Keyword(s): SAR Processsing,
filtering theory,
interference suppression,
radar imaging,
radar interference,
synthetic aperture radar,
German Aerospace Agency,
L-Band,
ESAR,
SAR imaging,
data processing,
experimental SAR system,
filtering theory,
focused SAR images,
SLC,
image degradation,
interferometric coherence,
interferometric repeat-pass data,
polarimetric descriptors,
RFI Suppression,
sensitive parameters estimation,
synthetic aperture radar imaging.
Abstract: Radio interferences are becoming more and more an important source for image degradation in synthetic aperture radar (SAR) imaging. Especially at longer wavelengths, interferences are often very strong, and their suppression is required during data processing. However, at shorter wavelengths, interferences are often not obvious in the image amplitude, and filtering is not performed in an operational way. Nevertheless, interferences might significantly degrade the image phase, and the estimation of sensitive parameters like interferometric coherence or polarimetric descriptors becomes imprecise. Interference suppression is usually performed on the raw data, which are in most cases not available to the end-user. In this letter, a new interference suppression method for focused SAR images is proposed. Its performance is tested on interferometric repeat-pass data acquired by the German Aerospace Agency's experimental SAR system (E-SAR) at L-band. -
Brian D. Rigling and Randolph L. Moses.
Taylor expansion of the differential range for monostatic SAR.
Aerospace and Electronic Systems, IEEE Transactions on,
41(1):60-64,
2005.
Keyword(s): SAR Processing,
polynomial approximation,
radar imaging,
synthetic aperture radar,
Taylor expansion,
differential range,
linear approximation,
monostatic SAR,
Polar Format Algorithm,
second-order Taylor series approximation,
Spotlight SAR.
Abstract: The polar format algorithm (PFA) for spotlight synthetic aperture radar (SAR) is based on a linear approximation for the differential range to a scatterer. We derive a second-order Taylor series approximation of the differential range. We provide a simple and concise derivation of both the far-field linear approximation of the differential range, which forms the basis of the PFA, and the corresponding approximation limits based on the second-order terms of the approximation. -
Petre Stoica,
Zhisong Wang,
and Jian Li.
Extended derivations of MUSIC in the presence of steering vector errors.
IEEE Transactions on Signal Processing,
53(3):1209-1211,
March 2005.
ISSN: 1053-587X.
Keyword(s): SAR Processing,
MUSIC,
MUltiple SIgnal Classifier,
direction-of-arrival estimation,
DOA,
robustness to steering vector errors,
extended derivation,
steering vector error,
SAR Tomography,
Tomography,
multi-baseline SAR,
InSAR.
Abstract: We present two extensions of MUSIC to the case in which the steering vector is imprecisely known and show that the extended methods lead to the same direction-of-arrival (DOA) estimates as MUSIC. This somewhat surprising result provides a more general motivation of MUSIC than those currently available and shows that MUSIC possesses a certain degree of inherent robustness to steering vector errors. -
K.A.C. de Macedo and R. Scheiber.
Precise topography- and aperture-dependent motion compensation for airborne SAR.
IEEE Geoscience and Remote Sensing Letters,
2(2):172-176,
Apr. 2005.
ISSN: 1545-598X.
Keyword(s): Azimuth,
Data processing,
Focusing,
Interferometry,
Layout,
Motion compensation,
Radar tracking,
Sensor phenomena and characterization,
Surfaces,
Synthetic aperture radar,
fast Fourier transforms,
motion compensation,
radar imaging,
radiowave interferometry,
remote sensing by radar,
synthetic aperture radar,
D-InSAR,
German Aerospace Center,
SAR images,
SAR processing algorithms,
airborne SAR,
airborne repeat-pass interferometry,
differential interferometry,
fast Fourier transform-based postprocessing methodology,
geometric fidelity,
motion compensation,
motion errors,
phase accuracy,
residual phase errors,
synthetic aperture radar,
topographic heights,
topography,
wide beamwidth,
Airborne,
differential interferomertry (D-InSAR),
interferometry,
motion errors,
synthetic aperture radar (SAR),
topography,
wide beamwidth;.
[bibtex-key = DeMacedo05:GRSL]
-
Sune R.J. Axelsson.
Beam characteristics of three-dimensional SAR in curved or random paths.
Geoscience and Remote Sensing, IEEE Transactions on,
42(10):2324-2334,
Oct. 2004.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
Non-Linear Flight Path,
Non-linear SAR.
Abstract: Interferometric synthetic aperture radar (InSAR) provides average height information by combining data from two parallel paths. True three-dimensional (3-D) SAR also detects the height distribution, which is of significant interest in airborne reconnaissance, forest inventory, and subsurface or wall-penetrating sensing applications as examples. In this paper, the beam performance of 3-D SAR is studied and compared for different curved line paths, such as circles, ellipses, and spirals ending up with random sampling. Curved path geometry reduces the ambiguity in height angle of traditional multipass SAR, and random path variation further improves the sidelobe suppression. The poor sidelobe suppression of a single circle path is significantly improved in near-range geometry in combination with high range resolution. By introducing a window function dependent on focus point and path position, high sidelobe suppression was achieved in an extended ground area below the circle path. -
Ciro Cafforio,
Pietro Guccione,
and Andrea Monti-Guarnieri.
Doppler Centroid Estimation for ScanSAR Data.
IEEE Transactions on Geoscience and Remote Sensing,
42(1):14-23,
January 2004.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Doppler Ambiguity Resolver,
DAR,
Clutterlock,
Satellite SAR,
RADARSAT 1,
ENVISAT,
ScanSAR.
Abstract: We introduce a novel accurate technique to estimate the Doppler centroid (DC) in ScanSAR missions. The technique starts from the ambiguous DC measures in the subswaths and uses a method alternative to standard unwrapping to undo the jumps in estimates induced by modulo pulse repetition frequency (PRF) measures. The proposed alternative is less error prone than the usual unwrapping techniques. Doppler Ambiguity is then solved by implementing a maximum-likelihood estimate that exploits the different PRFs used in different subswaths. An azimuth pointing of the antenna that does not change with subswaths, or that changes in a known way, is assumed. However, if the PRF diversity is strong enough, unknown small changes in azimuth pointing are tolerated and accurately estimated. This estimator is much simpler and more efficient, than those in the literature. Results achieved with both RADARSAT 1 and ENVISAT ScanSAR data are reported. -
Ian G. Cumming.
A Spatially Selective Approach to Doppler Estimation for Frame-Based Satellite SAR Processing.
IEEE Transactions on Geoscience and Remote Sensing,
42(6):1135-1148,
June 2004.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Clutterlock,
Satellite SAR,
Geometry Models,
Quality Metrics,
Global Surface Fit.
Abstract: When Doppler centroid estimators are applied to satellite SAR data, biased estimates are often obtained because of anomalies in the received data. Typical anomalies include areas of low SNR, strong discrete targets and radiometric discontinuities. In this paper, a new method of Doppler centroid estimation is presented that takes advantage of principles such as spatial diversity, estimator quality checks, geometric models, and the fitting of a "global" estimate over a wide area of a SAR scene. In the proposed scheme, Doppler estimates are made over small blocks of data covering a whole frame, so that all parts of the scene are potentially represented. The quality of each block estimate is examined using data statistics or estimator quality measures. Poor estimates are rejected, and the remaining estimates are used to fit a surface model of the Doppler centroid versus the range and azimuth extent of the scene. A physical model that relates the satellite's orbit, attitude and beam-pointing-direction to the Doppler centroid is used to get realistic surface fits and to reduce the complexity (dimensionality) of the estimation problem. The method is tested with RADARSAT-1 and Shuttle Radar Topography Mission X-band SAR (SRTM/X-SAR) spaceborne data and is found to work well with scenes that do have radiometric anomalies, and in scenes where attitude adjustments cause the Doppler to change rapidly. -
Knut Eldhuset.
Ultra high resolution spaceborne SAR processing.
Aerospace and Electronic Systems, IEEE Transactions on,
40(1):370-378,
2004.
Keyword(s): SAR Processing,
radar signal processing,
spaceborne radar,
synthetic aperture radar,
transfer functions,
EETF4,
SAR geometry,
X-band radar,
azimuth signal accuracy requirements,
erroneous Doppler parameters,
fourth-order extended exact transfer function,
spaceborne SAR processing,
squint,
synthetic aperture radar,
ultra high resolution SAR.
Abstract: The accuracy requirements of the azimuth signal for spaceborne synthetic aperture radar (SAR) processing is analysed. Degradations of simulated extended scenes and point targets are studied at high squint or if erroneous Doppler parameters are used. At a resolution less than 1 m for X-band it is shown that the azimuth signal for spaceborne SAR geometry should be used. It is found that the fourth-order extended exact transfer function (EETF4) is a good candidate for demanding SAR processing. -
Andrew S. Milman.
The Hyperbolic Geometry of SAR Imaging.
Submitted to RADIO SCIENCE,
0(0):0-0,
unknown 2004.
Keyword(s): SAR Processing,
Hyperbolic Functions,
Fourier-Hankel Inversion,
Hankel Transform,
Abel Transform,
Wavenumber Domain Algorithm,
omega-k,
Range Migration Algorithm,
Stolt Mapping.
Abstract: This paper shows how we can use hyperbolic functions to write an exact mathematical representation of SAR imaging. This problem is primarily a geometric one, that of accounting for curved wavefronts: the spirit of this paper is to emphasize these geometrical properties over electromagnetic ones. This gives us a new and fruitful way to think about SAR imaging. Within this framework, I show how to correct for deviations of a radar from a straight flight path. This method will work even in situations where the curvature of the wavefronts is very large, where traditional methods do not. The image-formation algorithm, called omega-k migration, that results from this analysis of SAR imaging is simpler and faster than polar formatting, especially for radars with very large beamwidths as they will at very low frequencies. As an added benefit, omega-k migration is surprisingly simple to derive. -
Mats I. Pettersson.
Detection of Moving Targets in Wideband SAR.
IEEE Transactions on Aerospace and Electronic Systems,
40(3):780-796,
July 2004.
Keyword(s): SAR Processing,
Fast Backprojection,
Factorized Backprojection,
Time Domain Backprojection,
Backprojection,
Moving Target Indication,
Ultra-Wideband SAR,
Wideband SAR,
VHF SAR,
UHF SAR,
CARABAS,
LORA,
Airborne SAR,
C-Band.
Abstract: A likelihood ratio is proposed for moving target detection in a wideband (WB) synthetic aperture radar (SAR) system. WB is defined here as any systems having a large fractional bandwidth, i.e., an ultra wide frequency band combined with a wide antenna beam. The developed method combines time-domain fast backprojection SAR processing methods with moving target detection using space-time processing. The proposed method reduces computational load when sets of relative speeds can be tested using the same clutter-suppressed subaperture beams. The proposed method is tested on narrowband radar data. -
Pau Prats,
Andreas Reigber,
and Jordi J. Mallorqui.
Interpolation-free coregistration and phase-correction of airborne SAR interferograms.
Geoscience and Remote Sensing Letters, IEEE,
1(3):188-191,
2004.
Keyword(s): SAR Processing,
Airborne SAR,
calibration,
Interferometry,
L-Band,
synthetic aperture radar,
airborne L-band repeat-pass interferometry,
airborne SAR interferograms,
azimuth registration errors,
interpolation-free coregistration,
navigation system,
phase azimuth undulations,
residual motion error correction,
spectral diversity technique,
synthetic aperture radar,
Calibration,
SAR,
image registration,
interferometry,
Motion Compensation,
repeat-pass interferometry,
synthetic aperture radar.
Abstract: This letter discusses the detection and correction of residual motion errors that appear in airborne synthetic aperture radar (SAR) interferograms due to the lack of precision in the navigation system. As it is shown, the effect of this lack of precision is twofold: azimuth registration errors and phase azimuth undulations. Up to now, the correction of the former was carried out by estimating the registration error and interpolating, while the latter was based on the estimation of the phase azimuth undulations to compensate the phase of the computed interferogram. In this letter, a new correction method is proposed, which avoids the interpolation step and corrects at the same time the azimuth phase undulations. Additionally, the spectral diversity technique, used to estimate registration errors, is critically analyzed. Airborne L-band repeat-pass interferometric data of the German Aerospace Center (DLR) experimental airborne SAR is used to validate the method. -
B.D. Rigling and R.L. Moses.
Flight path strategies for 3-D scene reconstruction from bistatic SAR.
Radar, Sonar and Navigation, IEE Proceedings -,
151(3):149-157,
2004.
ISSN: 1350-2395.
Keyword(s): SAR Processing,
Non-linear Flight Path,
SAR Tomography,
Curvilinear SAR,
Bistatic SAR,
airborne radar,
image reconstruction,
parameter estimation,
radar imaging,
synthetic aperture radar,
3-D scene reconstruction,
bistatic SAR,
data collection strategy,
flight path strategies,
nonlinear receiver trajectory,
nonparametric scene reconstructions,
phase history,
receiver flight paths,
three-dimensional information,
three-dimensional scattering centre location parameter estimates,
three-dimensional scene information.
Abstract: Proper design of receiver flight paths allows three-dimensional information to be encoded in sensed bistatic SAR phase history data. The authors show how the flight path taken by the receiving platform determines the resolution of nonparametric scene reconstructions and determines the variance of three-dimensional scattering centre location parameter estimates. Based on these relationships, a bistatic SAR data collection strategy can be designed, involving a nonlinear receiver trajectory that allows preservation of three-dimensional scene information. -
B.D. Rigling and R.L. Moses.
Polar format algorithm for bistatic SAR.
IEEE_J_AES,
40(4):1147-1159,
October 2004.
ISSN: 0018-9251.
Keyword(s): SAR Processing,
Bistatic SAR,
backprojection algorithms,
bistatic far-field assumption,
matched filtering,
monostatic SAR image formation,
phase history data,
polar format algorithm,
synthetic aperture radar,
backpropagation,
computational complexity,
matched filters,
radar imaging,
synthetic aperture radar;.
Abstract: Matched filtering (MF) of phase history data is a mathematically ideal but computationally expensive approach to bistatic synthetic aperture radar (SAR) image formation. Fast backprojection algorithms (BPAs) for image formation have recently been shown to give improved O(N2 log2N) performance. An O(N2 log2N) bistatic polar format algorithm (PFA) based on a bistatic far-field assumption is derived. This algorithm is a generalization of the popular PFA for monostatic SAR image formation and is highly amenable to implementation with existing monostatic image formation processors. Limits on the size of an imaged scene, analogous to those in monostatic systems, are derived for the bistatic PFA. -
Brian D. Rigling and Randolph L. Moses.
Polar format algorithm for bistatic SAR.
Aerospace and Electronic Systems, IEEE Transactions on,
40(4):1147-1159,
2004.
Keyword(s): SAR Processing,
backpropagation,
computational complexity,
matched filters,
radar imaging,
synthetic aperture radar,
Backprojection,
Time-Domain Backprojection,
Fast Backprojection,
Bistatic SAR,
bistatic far-field assumption,
matched filtering,
monostatic SAR image formation,
phase history data,
Polar Format Algorithm,
synthetic aperture radar.
Abstract: Matched filtering (MF) of phase history data is a mathematically ideal but computationally expensive approach to bistatic synthetic aperture radar (SAR) image formation. Fast backprojection algorithms (BPAs) for image formation have recently been shown to give improved O(N/sup 2/ log/sub 2/N) performance. An O(N/sup 2/ log/sub 2/N) bistatic polar format algorithm (PFA) based on a bistatic far-field assumption is derived. This algorithm is a generalization of the popular PFA for monostatic SAR image formation and is highly amenable to implementation with existing monostatic image formation processors. Limits on the size of an imaged scene, analogous to those in monostatic systems, are derived for the bistatic PFA. -
Z. Su,
Y. Peng,
and X. Wang.
Efficient algorithm for three-dimensional target feature extraction via CLSAR.
Electronics Letters,
40(15):965-966,
2004.
ISSN: 0013-5194.
Keyword(s): SAR Processing,
Non-Linear Flight Path,
SAR Tomography,
Curvilinear SAR,
fast Fourier transforms,
feature extraction,
radar imaging,
synthetic aperture radar,
Cramer-Rao bounds,
LODIPS algorithm,
RELAX algorithm,
SNR,
computational load,
curvilinear synthetic aperture radar system,
lower dimensional FFT,
lower dimensional position searching,
three dimensional target feature extraction.
Abstract: A lower dimensional position searching (LODIPS) algorithm is proposed for three-dimensional (3-D) target feature extraction via the curvilinear synthetic aperture radar (CLSAR) system. Compared with another similarly structured algorithm RELAX, the LODIPS algorithm dramatically reduces the computational load through the utilisation of lower dimensional FFTs. Simulation results show that the new algorithm can reach CRB at low SNR. -
Robert N. Treuhaft,
Beverly E. Law,
and Gregory P. Asner.
Forest Attributes from Radar Interferometric Structure and Its Fusion with Optical Remote Sensing.
BioScience,
54(6):561-571,
2004.
Keyword(s): SAR Processing,
InSAR,
SAR Interferometry,
Forest,
remote sensing,
carbon cycle,
LiDAR,
optical remote sensing,
forest ecology,
SAR Tomography.
Abstract: The possibility of global, three-dimensional remote sensing of forest structure with interferometric synthetic aperture radar (InSAR) bears on important forest ecological processes, particularly the carbon cycle. InSAR supplements two-dimensional remote sensing with information in the vertical dimension. Its strengths in potential for global coverage complement those of lidar (light detecting and ranging), which has the potential for high-accuracy vertical profiles over small areas. InSAR derives its sensitivity to forest vertical structure from the differences in signals received by two, spatially separate radar receivers. Estimation of parameters describing vertical structure requires multiple-polarization, multiple-frequency, or multiple-baseline InSAR. Combining InSAR with complementary remote sensing techniques, such as hyperspectral optical imaging and lidar, can enhance vertical-structure estimates and consequent biophysical quantities of importance to ecologists, such as biomass. Future InSAR experiments will supplement recent airborne and spaceborne demonstrations, and together with inputs from ecologists regarding structure, they will suggest designs for future spaceborne strategies for measuring global vegetation structure. -
Silvia Cimmino,
Giorgio Franceschetti,
Antonio Iodice,
Daniele Riccio,
and Giuseppe Ruello.
Efficient Spotlight SAR Raw Signal Simulation of Extended Scenes.
IEEE Transactions on Geoscience and Remote Sensing,
41(10):2329-2337,
October 2003.
Keyword(s): SAR Processing,
Simulation,
SAR Simulator,
Raw Data Simulator,
Spotlight SAR.
Abstract: Synthetic aperture radar (SAR) raw signal simulation is a powerful tool for designing new sensors, testing processing algorithms, planning missions, and devising inversion algorithms. In this paper, a spotlight SAR raw signal simulator for distributed targets is presented. The proposed procedure is based on a Fourier domain analysis: a proper analytical reformulation of the spotlight SAR raw signal expression is presented. It is shown that this reformulation allows us to design a very efficient simulation scheme that employs fast Fourier transform codes. Accordingly, the computational load is dramatically reduced with respect to a time-domain simulation and this, for the first time, makes spotlight simulation of extended scenes feasible. -
F.M. Dickey,
L.A. Romero,
J.M. DeLaurentis,
and A.W. Doerry.
Super-resolution, degrees of freedom and synthetic aperture radar.
Radar, Sonar and Navigation, IEE Proceedings -,
150(6):419-429,
2003.
ISSN: 1350-2395.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
Fourier transforms,
eigenvalues and eigenfunctions,
extrapolation,
inverse problems,
mathematical operators,
radar imaging,
radar resolution,
synthetic aperture radar,
Fourier transform extrapolation,
SAR images,
degrees of freedom,
eigenvalue spectrum,
ill posed problem,
operator inversion problem,
super-resolution,
synthetic aperture radar.
Abstract: Super-resolution concepts offer the potential of resolution beyond the classical limit. This great promise has not generally been realised. The potential application of super-resolution concepts to synthetic aperture radar is investigated. The analytical basis for super-resolution theory is discussed. The application of the concept to synthetic aperture radar is investigated as an operator inversion problem. Generally, the operator inversion problem is ill posed. However, it is shown that it is the particular form of the eigenvalue spectrum of the associated operator that precludes any significant resolution enhancement of synthetic aperture radar images. A criterion for judging super-resolution processing of an image is presented. -
Fred M. Dickey,
Louis A. Romero,
and Armin W. Doerry.
Window functions for imaging radar: a maximum energy approach to contiguous and notched spectrums.
Optical Engineering,
42(7):2113-2128,
2003.
Keyword(s): SAR Processing,
radar imaging,
synthetic aperture radar,
sidelobes,
window functions,
filtering,
notched spectrum.
Abstract: Imaging systems such as synthetic aperture radar collect band-limited data from which an image of a target scene is rendered. The band-limited nature of the data generates sidelobes, or spilled energy, most evident in the neighborhood of bright point-like objects. It is generally considered desirable to minimize these sidelobes, even at the expense of some generally small increase in system bandwidth. This is accomplished by shaping the spectrum with window functions prior to inversion or transformation into an image. A window function that minimizes sidelobe energy can be constructed based on prolate spheroidal wave functions. A parametric design procedure allows doing so, even with constraints on allowable increases in system bandwidth. This approach is extended to accommodate spectral notches or holes, although the guaranteed minimum sidelobe energy can be quite high in this case. Interestingly, for a fixed bandwidth, the minimum mean-squared-error image rendering of a target scene is achieved with no windowing at all (rectangular or boxcar window). -
G. Fornaro,
F. Serafino,
and F. Soldovieri.
Three-dimensional focusing with multipass SAR data.
Geoscience and Remote Sensing, IEEE Transactions on,
41(3):507-517,
2003.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
focusing,
synthetic aperture radar,
3D tomography reconstruction,
linear inverse problem,
multipass SAR data,
multipass synthetic aperture radar data,
nonuniform orbit separation,
processing technique,
scattering mechanism,
singular value decomposition,
volumetric scattering.
Abstract: Deals with the use of multipass synthetic aperture radar (SAR) data in order to achieve three-dimensional tomography reconstruction in presence of volumetric scattering. Starting from azimuth- and range-focused SAR data relative to the same area, neglecting any mutual interaction between the targets, and assuming the propagation in homogeneous media, we investigate the possibility to focus the data also in the elevation direction. The problem is formulated in the framework of linear inverse problem and the solution makes use of the singular value decomposition of the relevant operator. This allows us to properly take into account nonuniform orbit separation and to exploit a priori knowledge regarding the size of the volume interested by the scattering mechanism, thus leading to superresolution in the elevation direction. Results obtained on simulated data demonstrate the feasibility of the proposed processing technique. -
Jong-Sen Lee,
S. R. Cloude,
K. P. Papathanassiou,
M. R. Grunes,
and I. H. Woodhouse.
Speckle filtering and coherence estimation of polarimetric SAR interferometry data for forest applications.
IEEE_J_GRS,
41(10):2254-2263,
October 2003.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Forest,
Forest parameters,
biomass,
averaging,
boxcar filter,
coherence estimation,
forest applications,
forest heights,
ground topography,
interferometric coherence,
neighboring pixels,
polarimetric SAR interferometry data,
polarimetric interferometry matrix,
polarimetric synthetic aperture radar interferometry,
random volume,
scattering characteristics,
speckle filtering,
adaptive filters,
forestry,
radar imaging,
radar polarimetry,
radiowave interferometry,
remote sensing by radar,
speckle,
synthetic aperture radar;.
Abstract: Recently, polarimetric synthetic aperture radar (SAR) interferometry has generated much interest for forest applications. Forest heights and ground topography can be extracted based on interferometric coherence using a random volume over ground coherent mixture model. The coherence estimation is of paramount importance for the accuracy of forest height estimation. The coherence (or correlation coefficient) is a statistical average of neighboring pixels of similar scattering characteristics. The commonly used algorithm is the boxcar filter, which has the deficiency of indiscriminate averaging of neighboring pixels. The result is that coherence values are lower than they should be. In this paper, we propose a new algorithm to improve the accuracy in the coherence estimation based on speckle filtering of the 6 times;6 polarimetric interferometry matrix. Simulated images are used to verify the effectiveness of this adaptive algorithm. German Aerospace Center (DLR) L-Band E-SAR data are applied to demonstrate the improved accuracy in coherence and in forest height estimation. -
Jian Li,
Petre Stoica,
and Zhisong Wang.
On robust Capon beamforming and diagonal loading.
Signal Processing, IEEE Transactions on [see also Acoustics, Speech, and Signal Processing, IEEE Transactions on],
51(7):1702-1715,
2003.
ISSN: 1053-587X.
Keyword(s): SAR Processing,
Capon,
Spectral Estimation,
Beamforming,
array signal processing,
interference suppression,
parameter estimation,
signal resolution,
SOI power estimation,
SOI steering vector,
adaptive arrays,
array steering vector,
data-independent beamformer,
diagonal loading,
interference rejection,
robust Capon beamforming,
signal of interest,
signal resolution,
standard Capon beamformer,
uncertain steering vectors,
uncertainty set.
Abstract: The Capon (1969) beamformer has better resolution and much better interference rejection capability than the standard (data-independent) beamformer, provided that the array steering vector corresponding to the signal of interest (SOI) is accurately known. However, whenever the knowledge of the SOI steering vector is imprecise (as is often the case in practice), the performance of the Capon beamformer may become worse than that of the standard beamformer. Diagonal loading (including its extended versions) has been a popular approach to improve the robustness of the Capon beamformer. We show that a natural extension of the Capon beamformer to the case of uncertain steering vectors also belongs to the class of diagonal loading approaches, but the amount of diagonal loading can be precisely calculated based on the uncertainty set of the steering vector. The proposed robust Capon beamformer can be efficiently computed at a comparable cost with that of the standard Capon beamformer. Its excellent performance for SOI power estimation is demonstrated via a number of numerical examples. -
F. Lombardini,
M. Montanari,
and F. Gini.
Reflectivity estimation for multibaseline interferometric radar imaging of layover extended sources.
IEEE Transactions on Signal Processing,
51(6):1508-1519,
June 2003.
ISSN: 1053-587X.
Keyword(s): SAR Processing,
Tomography,
SAR Tomography,
Multi-baseline SAR,
Interferometry,
SAR Interferometry,
AWGN,
Monte Carlo methods,
amplitude estimation,
radar imaging,
radiowave interferometry,
synthetic aperture radar APES,
Capon's approach,
InSAR,
Monte Carlo simulation,
RELAX,
SAR,
additive white Gaussian noise,
amplitude estimation,
complex orography,
component sinusoidal signal,
hybrid spectral estimators,
layover extended sources,
multibaseline interferometric radar imaging,
multibaseline operation,
multiplicative complex correlated noise,
nonparametric estimators,
parametric estimators,
reflectivity estimation,
spatial frequency estimation,
synthetic aperture radar interferometry,
terrain height,
undistorted multibaseline image formation.
Abstract: In recent years, there has been great interest in exploiting the advanced multibaseline operation of synthetic aperture radar interferometry (InSAR) for solving layover effects from complex orography, which can degrade both SAR and InSAR imagery of terrain radar reflectivity and height. In this work, the problem of retrieving radar reflectivity of layover areas is addressed. It is formulated as the problem of estimating a multicomponent sinusoidal signal corrupted by multiplicative complex correlated noise and additive white Gaussian noise. Application of nonparametric [e.g., Capon, amplitude and phase estimation filter (APES)], parametric [least squares, modern parametric RELAXation spectral estimator (RELAX)], and hybrid spectral estimators for amplitude estimation is investigated for a multilook scenario. In particular, the multilook extensions of RELAX and APES are applied to the interferometric problem. Performance analysis is investigated through a Cramer-Rao lower bound calculation and Monte Carlo simulation. The method of least squares, coupled with Capon's approach to spatial frequency estimation, multilook APES, and multilook RELAX turn out to provide accurate reflectivity estimates for undistorted multibaseline image formation of layover areas. -
Clifford J. Nolan and Margaret Cheney.
Synthetic Aperture Inversion for Arbitrary Flight Paths and Nonflat Topography.
IEEE Transactions on Image Processing,
12(9):1035-1043,
Sept 2003.
Keyword(s): SAR Processing,
Back-Projection,
Backprojection,
FOPEN,
Non-Flat Topography,
Non-Linear Flight Path.
Abstract: This paper considers synthetic aperture radar (SAR) and other synthetic aperture imaging systems in which a backscattered wave is measured from positions along an arbitrary (known) flight path.We assume a single-scattering model for the radar data, and we assume that the ground topography is known but not necessarily flat. We focus on cases in which the antenna footprint is so large that the standard narrow-beam algorithms are not useful.We showthat certain artifacts can be avoided if the antenna and antenna footprint avoid particular relationships with the ground topography. In this case, we give an explicit backprojection imaging algorithm that corrects for the ground topography, flight path, antenna beam pattern, source waveform, and other geometrical factors. For the case of a nondirectional antenna, the image produced by the above algorithm contains artifacts. For this case, we analyze the strength of the artifacts relative to the strength of the true image. The analysis shows that the artifacts can be somewhat suppressed by increasing the frequency, integration time, and the curvature of the flight path. -
Pau Prats and Jordi J. Mallorqui.
Estimation of azimuth phase undulations with multisquint processing in airborne interferometric SAR images.
Geoscience and Remote Sensing, IEEE Transactions on,
41(6):1530-1533,
2003.
Keyword(s): SAR Processing,
Squinted SAR,
airborne radar,
radar imaging,
synthetic aperture radar,
ESAR,
DLR experimental airborne SAR,
Germany,
Oberpfaffenhofen test site,
azimuth phase undulations,
calibration,
image pairs,
interferometric airborne synthetic aperture radar systems,
multisquint processing,
phase error correction,
phase error detection,
single-pass interferometrie data,
squint angles,
technique,
InSAR,
Interferometry.
Abstract: Presents a technique to detect and correct phase errors appearing in interferometric airborne synthetic aperture radar (SAR) systems due to the lack of precision in the navigation system. The technique is based on a multisquint processing approach, i.e. by processing the same image pairs with different squint angles we can combine the information of different interferograms to obtain the desired phase correction. Airborne single-pass interferometric data from the Deutsches Zentrum fuer Luft- und Raumfahrt (DLR) experimental airborne SAR is used to validate the method. -
A. Reigber and R. Scheiber.
Airborne differential SAR interferometry: first results at L-band.
Geoscience and Remote Sensing, IEEE Transactions on,
41(6):1516-1520,
2003.
Keyword(s): SAR Processing,
airborne radar,
radiowave interferometry,
remote sensing by radar,
synthetic aperture radar,
vegetation mapping,
Earth surface,
Germany,
L-Band,
Oberpfaffenhofen test site,
agricultural areas,
airborne differential SAR interferometry,
airborne sensors,
atmospheric effects,
centimetre-scale deformations,
critical region monitoring,
data acquisition intervals,
forested areas,
glacier flows,
interferometric repeat-pass mode,
landslides,
long-term decorrelation,
motion compensation,
motion errors,
phase artifacts,
synthetic aperture radar,
ESAR,
Motion Compensation,
Interferometric SAR,
Interferometry,
D-InSAR.
Abstract: In recent years, differential interferometry using spaceborne synthetic aperture radar (SAR) sensors has become an established technique for detecting and monitoring centimetre-scale deformations of the Earth's surface, as well as glacier flows and landslides. Although often very efficient, the use of spaceborne SAR data has several drawbacks, namely phase artifacts caused by atmospheric effects and very low coherence due to long data acquisition intervals and the short radar wavelength of the sensor. Most important, current spaceborne sensors are not able to ensure flexible monitoring of critical regions. Airborne sensors may overcome most of the problems mentioned above, but up to now, the operational use of airborne differential SAR interferometry has been prevented by insufficiently accurate motion compensation of the platform. In this letter, first results of airborne differential interferometry using the German Aerospace Center (DLR) experimental SAR system (E-SAR) in the interferometric repeat-pass mode are addressed. This includes an analysis of long-term decorrelation behavior in L-band and, particularly, the correction of residual motion errors in heavily decorrelated interferograms. A first differential interferogram of agricultural and forested areas is presented and analyzed. -
Petre Stoica,
Zhisong Wang,
and Jian Li.
Robust Capon beamforming.
IEEE Signal Processing Letters,
10(6):172-175,
June 2003.
ISSN: 1558-2361.
Keyword(s): SAR Processing,
Capon,
Capon Beamforming,
Robust Capon beamforming,
Beamforming,
Spectral Estimation,
array signal processing,
interference suppression,
signal resolution adaptive arrays,
adaptive beamforming,
array steering vector,
interference rejection capability,
resolution,
signal of interest,
uncertain steering vectors.
Abstract: The Capon beamformer has better resolution and much better interference rejection capability than the standard (data-independent) beamformer, provided that the array steering vector corresponding to the signal of interest (SOI) is accurately known. However, whenever the knowledge of the SOI steering vector is imprecise (as is often the case in practice), the performance of the Capon beamformer may become worse than that of the standard beamformer. We present a natural extension of the Capon beamformer to the case of uncertain steering vectors. The proposed robust Capon beamformer can no longer be expressed in a closed form, but it can be efficiently computed. Its excellent performance is demonstrated via a number of numerical examples. -
G. Tavernier,
J. P. Granier,
C. Jayles,
P. Sengenes,
and F. Rozo.
The current evolutions of the DORIS system.
Advances in Space Research,
31(8):1947-1952,
2003.
Keyword(s): DORIS,
Orbit,
Precise Orbit,
Accuracy,
ENVISAT,
ASAR,.
Abstract: DORIS was developed for precise orbit determination and precise positioning on Earth. Three new satellites fitted out with dual-channel second-generation receivers have been recently launched. Jason-1, ENVISAT and SPOT-5 acquired a real autonomy thanks to DIODE real time on-board orbit determination software. Today the DORIS system has built up a global network of 55 stations. In order to reach new accuracy goals for Jason-1 and ENVISAT, it was decided to improve the long-term stability of the antennas when necessary. Third-generation beacons deployed from the end of 2001 offer new features and greater reliability. The satellites relay acquired and stored data at regular intervals to SSALTO, the new DORIS mission control center. DORIS data from the different satellites are currently available in the two Data Centers and used by the International DORIS Service Analysis groups. -
Lars M. H. Ulander,
Hans Hellsten,
and Gunnar Stenström.
Synthetic-Aperture Radar Processing Using Fast Factorized Back-Projection.
IEEE Transactions on Aerospace and Electronic Systems,
39(3):760-776,
July 2003.
Keyword(s): SAR Processing,
Fast Factorized Back-Projection,
Time-Domain Back-Projection,
Backprojection,
Fast Back-Projection,
Factorized Back-Projection,
Ultra-Wideband SAR,
VHF SAR,
CARABAS,
Airborne SAR.
Abstract: Exact synthetic aperture radar (SAR) inversion for a linear aperture may be obtained using fast transform techniques. Alternatively, back-projection integration in time domain can also be used. This technique has the benefit of handling a general aperture geometry. In the past, however, back-projection has seldom been used due to heavy computational burden. We show that the back-projection integral can be recursively partitioned and an effective algorithm constructed based on aperture factorization. By representing images in local polar coordinates it is shown that the number of operations is drastically reduced and can be made to approach that of fast transform algorithms. The algorithm is applied to data from the airborne ultra-wideband CARABAS SAR and shown to give a reduction in processing time of two to three orders of magnitude. -
H.L. Chan and T.S. Yeo.
Comments on Non-iterative quality phase-gradient autofocus (QPGA) algorithm for spotlight SAR imagery.
Geoscience and Remote Sensing, IEEE Transactions on,
40(11):2517,
Nov. 2002.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus,
Quality Phase Gradient Autofocus,
QPGA.
Abstract: The quality phase-gradient autofocus (QPGA) technique was proposed to speed up the estimation convergence of phase-gradient autofocus by selectively increasing the pool of quality synchronization sources instead of selecting the “brightest†pixels within the image. It is now found that the QPGA, with its inherent scatter “growing†concept and target-filtering procedure, is also able to focus in environments with stationary and moving targets. -
Per-Olov Frölind and Lars M. H. Ulander.
Digital Elevation Map Generation Using VHF-Band SAR Data in Forested Areas.
IEEE Transactions on Geoscience and Remote Sensing,
40(8):1769-1776,
August 2002.
Keyword(s): SAR Processing,
Interferometry,
DEM Generation,
Time Domain Backprojection,
Backprojection,
Ultra-Wideband SAR,
VHF SAR,
CARABAS,
Airborne SAR.
Abstract: The paper investigates digital elevation model (DEM) generation based on data from the ultra wideband coherent all radio band sensing (CARABAS) very high frequency (VRF)-band synthetic aperture radar (SAR). The results show excellent capability to penetrate forest areas, i.e., the generated DEMs are found to be close to the true ground height. A conventional DEM, based on stereo photography and surveying, and additional phase differential Global Positioning System (GPS) measurements have been used for comparison. The results in heavily vegetated areas (stem volume up to 600 m^3/ha) show a mean height difference of less than 1.5 m and a root-mean-square (rms) error of less than 1.0 in compared to the conventional DEM. Stable backscattering properties allows us to use large baselines in order to obtain high height sensitivity. However, the amount of poor data due to low coherence increases with the increase of the baseline. The optimum baseline which balances these two effects is found to correspond to an incidence angle difference of 4 deg - 8 deg. -
Dirk Geudtner,
Manfred Zink,
Christoph Gierull,
and Scott Shaffer.
Interferometric Alignment of the X-SAR Antenna System on the Space Shuttle Radar Topography Mission.
IEEE Transactions on Geoscience and Remote Sensing,
40(5):995-1006,
May 2002.
Keyword(s): SAR Processing,
Antenna Beam Alignment,
Interferometry,
SRTM,
X-SAR.
Abstract: The on-orbit alignment of the antenna beams of both the X-band and C-band radar systems during operations of the shuttle radar topography mission/X-band synthetic aperture radar (SRTM/X-SAR) was a key requirement for achieving best interferometric performance. In this paper, we consider the X-SAR antenna beam alignment in azimuth. For a single-pass cross-track SAR interferometer, we establish the relation between yaw and pitch misalignment of the antenna beams and the resulting relative shift of the Doppler frequency bands. This relation is used to provide solutions for the mechanical adjustments of the outboard antenna and electronic beam steering to correct for azimuth misalignment. Furthermore, the effects of the X-SAR effective outboard antenna pattern on the azimuth beam alignment are analyzed. As a result, a so-called relaxing factor is derived, which increases the limit for the difference in antenna azimuth angle with respect to the requirement on spectral overlap, and hence spatial interferogram resolution. However, we also show that the alignment requirement is driven by the constraint on decreasing the azimuth ambiguity-to-signal ratio (AASR) for the effective outboard antenna pattern to reduce the resulting additional height error. The strategy for misalignment determination and correction is presented, and results of the analysis of the in-flight X-SAR antenna beam alignment are discussed. -
F. Gini,
F. Lombardini,
and M. Montanari.
Layover solution in multibaseline SAR interferometry.
Aerospace and Electronic Systems, IEEE Transactions on,
38(4):1344-1356,
2002.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
Monte Carlo methods,
airborne radar,
radiowave interferometry,
remote sensing by radar,
synthetic aperture radar,
MUSIC,
Cramer-Rao lower bounds,
Interferometry,
InSAR,
M-RELAX,
Monte Carlo simulations,
RELAX algorithm,
baseline diversity,
discontinuities,
height contributions,
layover solution,
multibaseline SAR interferometry,
multichannel interferometric synthetic aperture radar,
multiplicative noise,
natural targets,
nonparametric techniques,
parametric techniques,
range-azimuth resolution cell,
spectral estimation techniques,
terrain slopes.
Abstract: In this work, spectral estimation techniques are used to exploit baseline diversity of a multichannel interferometric synthetic aperture radar (SAR) system and overcome the layover problem. This problem arises when different height contributions collapse in the same range-azimuth resolution cell, due to the presence of strong terrain slopes or discontinuities in the sensed scene. We propose a multilook approach to counteract the presence of multiplicative noise, which is due to the extended nature of natural targets; to this purpose we extend the RELAX algorithm to the multilook data scenario (M-RELAX). A thorough performance analysis of nonparametric (beamforming and Capon) and parametric (root MUSIC and M-RELAX) techniques is carried out based on Monte Carlo simulations and Cramer-Rao lower bounds (CRLB) calculation. The results suggest the superiority of parametric methods over nonparametric ones. -
Jürgen Holzner and Richard Bamler.
Burst-Mode and ScanSAR Interferometry.
IEEE Transactions on Geoscience and Remote Sensing,
40(9):1917-1934,
Sept 2002.
Keyword(s): SAR Processing,
Burst-mode,
ScanSAR,
Interferometry,
pack-and-go algorithm,
ENVISAT,
RADARSAT,
SRTM.
Abstract: ScanSAR interferometry is an attractive option for efficient topographic mapping of large areas and for monitoring of large-scale motions. Only ScanSAR interferometry made it possible to map almost the entire landmass of the earth in the 11-day Shuttle Radar Topography Mission. Also the operational satellites RADARSAT and ENVISAT offer ScanSAR imaging modes and thus allow for repeat-pass ScanSAR interferometry. This paper gives a complete description of ScanSAR and burst-mode interferometric signal properties and compares different processing algorithms. The problems addressed are azimuth scanning pattern synchronization, spectral shift filtering in the presence of high squint, Doppler centroid estimation, different phase-preserving ScanSAR processing algorithms, ScanSAR interferogram formation, coregistration, and beam alignment. Interferograms and digital elevation models from RADARSAT ScanSAR Narrow modes are presented. The novel pack-and-go algorithm for efficient burst-mode range processing and a new time-variant fast interpolator for interferometric coregistration are introduced. -
Lance M. Kaplan,
James H. McClellan,
and Seung-Mok Oh.
Prescreening During Image Formation for Ultrawideband Radar.
IEEE Transactions on Aerospace and Electronic Systems,
38(1):74-88,
January 2002.
Keyword(s): SAR Processing,
Backprojection,
Ultra-Wideband SAR,
Prescreening,
Quadtree Processing,
Divide and Conquer Methods.
Abstract: Standard radar image formation techniques waste computational resources by full resolving all areas of the scene, even regions of benign clutter. We introduce a multiscale prescreener algorithm that runs as part of the image formation processing step for ultrawideband (UWB) synthetic aperture radar (SAR) systems. The prescreener processes intermediate radar data generated by a quadtree backprojection image former. As the quadtree algorithm iterates, it is resolving increasingly finer subpatches of the scene. After each quadtree stage, the prescreener makes an estimate of the signal-to-background ratio of each subpatch and applies a constant false alarm rate (CFAR) detector to decide which ones might contain a target of interest. Whenever the prescreener determines that a subpatch is not near a detection, it cues the image former to terminate further processing of that subpatch. Using a small database of UWB radar field data, we demonstrate that the prescreener is able to decrease the overall computational load of the image formation process. We also show that the new multiscale prescreener method produces fewer false alarms than the conventional two-parameter CFAR prescreener applied to the completely formed image. -
A. Ferretti and F. Prati, C.and Rocca.
Permanent scatterers in SAR interferometry.
Geoscience and Remote Sensing, IEEE Transactions on,
39(1):8-20,
2001.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Interferometry,
Permanent scatterers,
geodesy,
geophysical techniques,
remote sensing by radar,
synthetic aperture radar,
terrain mapping,
topography (Earth)InSAR,
SAR interferometry,
atmospheric disturbance,
atmospheric phase screen,
differential interferometry,
geodesy,
geometrical decorrelation,
geophysical measurement technique,
land surface topography,
permanent scatterer,
radar remote sensing,
stable natural reflector,
surface deformation monitoring,
synthetic aperture radar,
terrain mapping,
topographic profile reconstruction.
Abstract: Temporal and geometrical decorrelation often prevents SAR interferometry from being an operational tool for surface deformation monitoring and topographic profile reconstruction. Moreover, atmospheric disturbances can strongly compromise the accuracy of the results. The authors present a complete procedure for the identification and exploitation of stable natural reflectors or permanent scatterers (PSs) starting from long temporal series of interferometric SAR images. When, as it often happens, the dimension of the PS is smaller than the resolution cell, the coherence is good even for interferograms with baselines larger than the decorrelation one, and all the available images of the ESA ERS data set can be successfully exploited. On these pixels, submeter DEM accuracy and millimetric terrain motion detection can be achieved, since atmospheric phase screen (APS) contributions can be estimated and removed. Examples are then shown of small motion measurements, DEM refinement, and APS estimation and removal in the case of a sliding area in Ancona, Italy. ERS data have been used -
Fabrizio Lombardini and Hugh D. Griffiths.
Optimum and Suboptimum Estimator Performance for Multibaseline InSAR.
EUSAR 2000 Special Issue, Frequenz, Zeitschrift für Telekommunikation (Journal of Telecommunications),
55:114-118,
March/April 2001.
Keyword(s): SAR Processing,
Interferometry,
Multibaseline InSAR,
Model-Based Interferometric Processing.
Abstract: Multibaseline methods have been recently proposed to reduce problems of phase ambiguity and data noise in SAR interferometry for topographic mapping. Both phase-only interferometry and direct processing of the complex multibaseline data have been considered. In this paper, two non-model based multibaseline estimators and two recently proposed model based algorithms are discussed and compared in terms of statistical accuracy of the reduced-ambiguity phase estimate. lt is shown that model-based processing of the complex multibaseline data can be significantly more efficient than the other methods. -
X. Luo,
Lars M. H. Ulander,
J. Askne,
G. Smith,
and Per-Olov Frölind.
RFI Suppression in Ultra-Wideband SAR Systems Using LMS Filters in Frequency Domain.
Electronics Letters,
37(4):241-243,
February 2001.
Keyword(s): SAR Processing,
RFI Suppression,
Backprojection,
Ultra-Wideband SAR,
VHF SAR,
CARABAS,
Airborne SAR.
Abstract: A least-mean-square algorithm in the frequency domain, with amplitude normalisation, is proposed to remove narrowband radio frequency interference in low-frequency ultra-wideband synthetic aperture radar systems. The performance of the algorithm was tested on experimental data acquired with the CARABAS system -
Andrea Monti-Guarnieri and Pietro Guccione.
Optimal Focusing for Low Resolution ScanSAR.
IEEE Transactions on Geoscience and Remote Sensing,
39(3):479-491,
March 2001.
Keyword(s): SAR Processing,
ScanSAR,
Focusing.
Abstract: This paper deals with the focusing of low resolution ScanSAR data, for both detected amplitude images and interferometric applications. The SAR reference is exploited to achieve ScanSAR focusing in conventional techniques. Such techniques provide quite effective compensation of the azimuth antenna pattern (AAP) (e.g., no scalloping) when the azimuth time-bandwidth product (TBP ) of the ScanSAR echo is large, but fail to do so as the burst shortens, being reduced to an ineffective weighting of the output. The result is an azimuth varying distortion of the focused impulse responses, a distortion that is partly compensated for in the multilook average (not available for interferometric applications) at the price of a reduction in the processed Doppler bandwidth. This paper proposes quite a different approach. A set of short kernels, each suitable for focusing at a specific azimuth bin, has been optimized to reconstruct source reflectivity in the minimum mean square error (MMSE) sense. That pseudoinversion converges to the conventional focusing when the burst extent is large and for short bursts, edge effects are accounted for. These azimuth-varying kernels can be suitably tuned to meet constraints in the resolution/sidelobes trade-off and have proved capable of providingfairly undistorted output and fine resolution. They better exploit the available Doppler bandwidth, maximizing the number of looks and the interferometric quality. A decomposition is suggested that implements the inverse operator as a fast preprocessing to be followed by a conventional ScanSAR processor. -
A. Potsis,
A. Reigber,
J. Mittermayer,
A. Moreira,
and N. Uzunoglou.
Sub-aperture algorithm for motion compensation improvement in wide-beam SAR data processing.
Electronics Letters,
37(23):1405-1407,
2001.
Keyword(s): SAR Processing,
error compensation,
Motion Compensation,
radar imaging,
Airborne SAR,
synthetic aperture radar,
motion compensation improvement,
residual motion error compensation,
strong motion errors,
sub-aperture algorithm,
synthetic aperture radar processing,
wide-beam SAR data processing,
wide-beam azimuth processing,
ESAR,
P-Band.
Abstract: The effects of strong motion errors in wide-beam azimuth synthetic aperture radar (SAR) processing are analysed and discussed, using simulated data, as well as data collected by the airborne experimental SAR system of the Deutsches Zentrum fur Luft- und Raumfahrt e.V. (DLR) (E-SAR). A new sub-aperture approach for residual motion error compensation in wide-beam azimuth processing is proposed. -
A. Reigber.
Correction of residual motion errors in airborne SAR interferometry.
Electronics Letters,
37(17):1083-1084,
2001.
Keyword(s): SAR Processing,
airborne radar,
error correction,
motion compensation,
radar interference,
radiowave interferometry,
synthetic aperture radar,
airborne SAR interferometry,
airborne repeat pass interferometric SAR data,
interferometric phase,
residual motion compensation errors,
residual motion error correction,
uncompensated motion errors,
Motion Compensation,
Interferometry,
interferometric SAR.
Abstract: The main limitation for a wider applicability of airborne repeat pass interferometric SAR data is the presence of small uncompensated motion errors. The effect of residual motion compensation errors is addressed and a new technique to minimise their influence on the interferometric phase is proposed. -
Andreas Reigber,
Konstantinos P. Papathanassiou,
Shane R. Cloude,
and Alberto Moreira.
SAR Tomography and Interferometry for the Remote Sensing of Forested Terrain.
EUSAR 2000 Special Issue, Frequenz, Zeitschrift für Telekommunikation (Journal of Telecommunications),
55:119-122,
March/April 2001.
Keyword(s): SAR Processing,
Tomography,
SAR Tomography,
Interferometry,
Multi-Antenna Interferometry,
Multi-Baseline Interferometry,
3D imaging,
Airborne SAR,
L-Band,
E-SAR.
Abstract: SAR interferometry and tomography are two potential techniques for resolving the scattering behaviour of volume scatterers. Therefore, they can be used to investigate the vertical structure of forested terrain. ln this paper we contrast the principles and the performance of the two approaches and show experimental results achieved using airborne SAR data acquired by the experimental SAR systemof DLR (E-SAR). -
Ludwig Rössing and Joachim H.G. Ender.
Multi-Antenna SAR Tomography Using Superresolution Techniques.
EUSAR 2000 Special Issue, Frequenz, Zeitschrift für Telekommunikation (Journal of Telecommunications),
55:123-128,
March/April 2001.
Keyword(s): SAR Processing,
Tomography,
SAR Tomography,
Interferometry,
Multi-Antenna Interferometry,
3D imaging,
superresolution,
a posteriori probability density function,
Airborne SAR,
X-Band,
Multi-Channel X-Band,
AER-II,
FGAN.
Abstract: Classical SAR interferometry provides a two-dimensional image of the surface together with a pixel-to-pixel measurement of the elevation angle of that pixel with respect to the radar antenna. The elevation angle can be transformed to a height estimate for each pixel yielding a digital elevation map. This assumes that the scattering points are distributed over a two dimensional surface and that for each azimuth-range resolution cell there is only one elevation angle. In this paper, we look for solutions for those cases, in which this assumption is invalid, i.e. where there are multiple point-like scatterers with distinct elevation angles in a single resolution cell. Using a parametric approach these distinct elevation angles can be estimated simultaneously. Since for single-pass interferometry the height resolution is mostly poor because of the limited baseline, we want to apply superresolution to get an appropriate height resolution. To achieve imaging also along the third dimension we propose a calculation of an a posteriori marginal distribution of the elevation angle. This approach is illustrated by simulation results and with airborne SAR data from the multi-channel X-band system 'AER-II'. -
Mehrdad Soumekh.
Wavefront-Based Synthetic Aperture Radar Signal Processing.
EUSAR 2000 Special Issue, Frequenz, Zeitschrift für Telekommunikation (Journal of Telecommunications),
55:99-113,
March/April 2001.
Keyword(s): SAR Processing,
Time Domain Backprojection,
Backprojection,
Moving Target Indication,
Range Stacking Algorithm,
Wavefront Reconstruction,
Range Migration Algorithm,
Wavenumber Domain Algorithm,
omega-k,
Comparison of Algorithms,
Wideband SAR,
Squinted SAR,
FOPEN,
Motion Compensation.
Abstract: This paper is concerned with the processing of Synthetic Aperture Radar (SAR) data, using Gabor's theory of wavefront reconstruction [9]. In the framework of this theory, multidimensional digital signal processing algorithms have been developed for accurate and computationally-efficient analysis of SAR data via a single or multi processor computer. This paper exhibits the utility of the SAR wavefront signal theory and its associated digital algorithms in addressing the practical information processing issues that are encountered in high-resolution and/or specialized SAR systems. We present results from two modern SAR systems. One system is the United States Navy P-3 ultra wideband UHF stripmap SAR that is intended for imaging man-made targets hidden under foliage (FOliage PENetrating, FOPEN, SAR). The other system is a high-resolution X-band spotlight SAR that is operated in an along-track monopulse, mode (single transmitter and dual receivers) for Ground Moving Target Indication (GMTI). -
Mehrdad Soumekh,
David A. Nobles,
Michael C. Wicks,
and Gerard J. Genello.
Signal Processing of Wide Bandwidth and Wide Beamwidth P-3 SAR data.
IEEE Transactions on Aerospace and Electronic Systems,
37(4):1122-1141,
October 2001.
Keyword(s): SAR Processing,
P-Band,
Ultra-Wideband SAR,
Backprojection,
RFI Suppression.
Abstract: This research is concerned with multidimensional signal processing and image formation with FOliage PENetrating (FOPEN) airborne radar data which were collected by a Navy P-3 ultra wideband (UWB) radar in 1995. The digital signal processors that were developed for the P-3 data commonly used a radar beamwidth angle that was limited to 35 deg. Provided that the P-3 radar beamwidth angle (after slow-time FIR filtering and 6:1 decimation) was 35 deg, the P-3 signal aperture radar (SAR) system would approximately yield alias-free data in the slow-time Doppler domain. We provide an analysis here of the slow-time Doppler properties of the P-3 SAR system. This study indicates that the P-3 database possesses a 50 deg beamwidth angle within the entire [215, 730] MHz band of the P-3 radar. We show that the 50-degree beamwidth limit is imposed by the radar (radial) range swath gate; a larger beamwidth measurements would be possible with a larger range swath gate. The 50-degree beamwidth of the P-3 system results in slow-time Doppler aliasing within the frequency band of [444, 730] MHz. We outline a slow-time processing of the P-3 data to minimize the Doppler aliasing. The images which are formed via this method are shown to be superior in quality to the images which are formed via the conventional P-3 processor. In the presentation, we also introduce a method for converting the P-3 deramped (range-compressed) data into its alias-free baseband echoed data; the utility of this conversion for suppressing radio frequency interference signals is shown -
Marc Bara,
Rolf Scheiber,
Antoni Broquetas,
and Alberto Moreira.
Interferometric SAR signal analysis in the presence of squint.
IEEE Transactions on Geoscience and Remote Sensing,
38(5):2164-2178,
September 2000.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
InSAR,
Interferometry,
SAR Interferometry,
Airborne SAR,
Phase Ramp,
Impulse Response Function,
IRF Analysis,
Phase Plots,
E-SAR,
geophysical techniques,
radar imaging,
remote sensing by radar,
synthetic aperture radar,
terrain mapping,
topography (Earth),
geophysical measurement technique,
high squint angle,
impulse response function,
interferometric SAR,
land surface,
misregistration,
phase bias,
phase ramp,
radar imaging,
radar remote sensing,
squint,
synthetic aperture radar,
terrain mapping,
topography.
Abstract: This paper develops an analysis of the SAR impulse response function from the interferometric point of view, with the intention of studying its phase behavior in the presence of high squint angle values. It will be pointed out that in this case, a phase ramp is present in the range direction, which, in combination with a certain degree of misregistration between the two images induces an offset in the generated interferometric phase. This behavior, if not compensated, imposes strong limits on the performance of the interferometric techniques in a squinted case, especially for airborne SAR systems. The article proposes two new techniques, which are appropriate to correct the phase bias coming from this source. The first one is based on a modification of the azimuth compression filter, which cancels the phase ramp of the range impulse response function for one specific squint value. In case the SAR processing is performed with variable squint over range, the authors propose a second method oriented to estimating the expected misregistration and thus, the phase bias by means of an iterative approach. Simulated data as well as real corner reflector responses are used to show that the correct topography can be recovered precisely even in the presence of phase bias coming from the squinted geometry. -
Marina Dragosevic and Burkhard Plache.
Doppler Tracker for a Spaceborne ScanSAR System.
IEEE Transactions on Aerospace and Electronic Systems,
36(3):907-924,
2000.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Clutterlock,
Doppler Tracker,
Attitude Angles,
Doppler Ambiguity Resolver,
DAR,
Satellite SAR.
Abstract: This paper presents a methodology for tracking the Doppler parameters in long swaths of ScanSAR signals. The approach is entirely developed around the physical model of the Doppler effect, parameterized in terms of the spacecraft attitude angles. A new, combined algorithm is designed to estimate yaw and pitch and resolve the PRF (pulse repetition frequency) ambiguity using all available, current, and past, return samples. It is shown that the variance of the Doppler centroid (DC) estimates can be brought down to the low single-digit Hz level with computationally simple estimation algorithms -
Jong-Sen Lee,
D.L. Schuler,
and T.L. Ainsworth.
Polarimetric SAR data compensation for terrain azimuth slope.
IEEE Transactions on Geoscience and Remote Sensing,
38(5):2153-2163,
2000.
Keyword(s): geophysical techniques,
radar imaging,
radar polarimetry,
remote sensing by radar,
synthetic aperture radar,
terrain mapping,
POLSAR,
azimuth slope variation,
data compensation,
effective scattering pixel area,
geophysical measurement technique,
land surface,
polarimetric SAR,
polarization,
radar cross section,
radar imaging,
radar polarimetry,
radar remote sensing,
radiometric slope correction,
synthetic aperture radar,
terrain mapping.
Abstract: This paper addresses the problem of polarimetric SAR (POLSAR) data -
Juan M. Lopez-Sanchez and Joaquim Fortuny-Guasch.
3-D Radar Imaging Using Range Migration Techniques.
IEEE Transactions on Antennas and Propagation,
48(5):728-737,
May 2000.
Keyword(s): SAR Processing,
Near Field,
Radar Imaging,
Range Migration Algorithm,
Wavenumber Domain Algorithm,
omega-k,
3D imaging algorithm,
Stationary Phase Method.
Abstract: An imaging system with three-dimensional (3-D) capability can be implemented by using a stepped frequency radar which synthesizes a two-dimensional (2-D) planar aperture. A 3-D image can be formed by coherently integrating the backscatter data over the measured frequency band and the two spatial coordinates of the 2-D synthetic aperture. This paper presents a near-field 3-D synthetic aperture radar (SAR) imaging algorithm. This algorithm is an extension of the 2-D range migration algorithm (RMA). The presented formulation is justified by using the method of the stationary phase (MSP). Implementation aspects including the sampling criteria, resolutions, and computational complexity are assessed. The high computational efficiency and accurate image reconstruction of the algorithm are demonstrated both with numerical simulations and measurements using an outdoor linear SAR system. -
Richard Rau and James H. McClellan.
Analytic Models and Postprocessing Techniques for UWB SAR.
IEEE Transactions on Aerospace and Electronic Systems,
36(4):1058-1074,
October 2000.
Keyword(s): SAR Processing,
Backprojection,
Ultra-Wideband SAR.
Abstract: The latest generation of fully polarimetric, ultra wideband (UWB), wide angle, low frequency, foliage and ground-penetrating synthetic aperture radars (SARs) record huge amounts of data that must be processed to focus high quality images. At the same time only a few small subimages contain important information. We investigate the relationship between the focused image and the reflectivity profile and show that a linear shift-invariant model adequately represents the overall process when the focusing is done with a backprojection algorithm over a constant integration angle. The derived signal model can be used to replace many computationally expensive processing techniques, previously performed on the raw data, with equivalent postprocessing algorithms which can be applied selectively to subimages. -
A. Reigber and A. Moreira.
First Demonstration of Airborne SAR Tomography Using Multibaseline L-Band Data.
IEEE Transactions on Geoscience and Remote Sensing,
38(5):2142-2152,
2000.
Keyword(s): SAR Processing,
airborne radar,
geophysical techniques,
radar imaging,
radar polarimetry,
remote sensing by radar,
synthetic aperture radar,
terrain mapping,
topography (Earth),
InSAR,
L-Band,
SAR interferometry,
SAR Tomography,
Tomography,
UHF,
airborne radar,
aperture synthesis,
geophysical measurement technique,
height ambiguity,
land surface,
multibaseline imaging geometry,
multibaseline method,
phase difference,
radar imaging,
radar polarimetry,
radar remote sensing,
synthetic aperture radar,
terrain mapping,
tomographic imaging,
topography,
undersampled spatial distribution,
ESAR.
Abstract: In synthetic aperture radar (SAR) interferometry, the phase differences between two different sensor positions are used to estimate the terrain topography. Although it is possible in this way to find a three-dimensional (3D) surface representation, the distribution of the different scatterers in the height direction at a fixed range and azimuth position remains unknown. Contrary to this, tomographic techniques enable a real geometric resolution capability in the height direction and introduce new possibilities for many applications and inversion problems. Even misinterpretations in SAR images caused by layover and foreshortening effects can be solved by the tomographic processing. In this paper, the successful experimental realization of polarimetric airborne SAR tomography is demonstrated for the first time. The authors present the concept of aperture synthesis for tomographic imaging for the case of a multibaseline imaging geometry and discuss the constraints arising from the limited number of flight tracks. They propose a method for reduction of the height ambiguities associated to the irregular and undersampled spatial distribution of the imaging positions. Finally, they address the experimental requirements for polarimetric airborne SAR tomography and show experimental results using a multibaseline data set acquired in L-band by DLR's experimental SAR (E-SAR) of a test-site near Oberpfaffenhofen, Germany. -
Rolf Scheiber and Alberto Moreira.
Coregistration of interferometric SAR images using spectral diversity.
IEEE Transactions on Geoscience and Remote Sensing,
38(5):2179-2191,
September 2000.
Keyword(s): SAR Processing,
Spectral Diversity,
Coregistration,
Image Coregistration,
InSAR,
SAR Interferometry,
Airborne SAR,
Spaceborne SAR,
geophysical signal processing,
geophysical techniques,
image registration,
radar imaging,
remote sensing by radar,
synthetic aperture radar,
terrain mappingInSAR,
complex SAR signal,
geophysical measurement technique,
image registration,
land surface,
radar imaging,
radar remote sensing,
relative misregistration,
synthetic aperture radar,
terrain mapping.
Abstract: This article presents a technique for the determination of the relative misregistration between two interferometric SAR images. The proposed technique is based on the spectral properties of the complex SAR signal. Unlike conventional coregistration methods, the proposed technique does not need any interpolation nor cross-correlation procedures and also no coherence or fringe optimization must be performed. Instead, the phase information of different spectral looks is evaluated giving misregistration information on a pixel by pixel basis. The proposed technique is at least as accurate as the conventional algorithms and its implementation is very simple. Airborne repeat-pass interferometric data and simulated ScanSAR data are used to illustrate the operation of the proposed technique -
Robert N. Treuhaft and Paul R. Siqueira.
Vertical structure of vegetated land surfaces from interferometric and polarimetric radar.
Radio Science,
35:141-178,
2000.
Keyword(s): SAR Processing,
InSAR,
Interferometry,
Pol-InSAR,
Multi-Baseline SAR,
Vegetation Parameters,
Parameter Extraction,
Topography,
SAR Tomography.
Abstract: This paper describes the estimation of parameters characterizing the vertical structure of vegetated land surfaces, from combined interferometric and polarimetric radar data. Physical models expressing radar observations in terms of parameters describing vegetated land surfaces are the foundation for parameter estimation techniques. Defining a general complex cross correlation enables the unified development of models for interferometry and polarimetry, including polarimetric interferometry. Three simple physical models in this paper express this complex cross correlation in terms of vegetation parameters: (1) a randomly oriented volume, (2) a randomly oriented volume with a ground return, and (3) an oriented volume. For the first two models the parameters include vegetation height, extinction coefficient, underlying topography, and another parameter depending on ground electrical properties and roughness. For the oriented volume, additional parameters depend on the refractivity, extinction coefficients, and backscattering characteristics of waves propagating along eigenpolarizations of the vegetation volume. The above models show that the interferometric cross-correlation amplitude and the polarimetric {HHHH/VVVV} ratio both change by about 1% per meter of vegetation height change, for experimental conditions typical of airborne and spaceborne interferometric radars. These vertical-structure sensitivities prompt a parameter estimation demonstration with two-baseline TOPSAR interferometric and zero-baseline polarimetric data from the Boreal Ecosystem-Atmosphere Study (BOREAS) Southern Study Area in Prince Albert National Park, Saskatchewan, Canada. The demonstrations show the feasibility of measuring vegetation height to better than 4.2 m, underlying topography to better than 6.5 m, and the ratio of ground-to-volume power to better than 10%, using interferometry and polarimetry, coupled with parameter-constraining assumptions, concerning the degree of surface roughness. This paper suggests that single-baseline and multibaseline fully polarimetric interferometry have the potential to obviate the need for such assumptions, thereby making parameter estimation more robust, accurate, and realistic. -
C. Wimmer,
R. Siegmund,
M. Schwabisch,
and João Moreira.
Generation of high precision DEMs of the Wadden Sea with airborneinterferometric SAR.
Geoscience and Remote Sensing, IEEE Transactions on,
38(5):2234-2245,
2000.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
InSAR,
Interferometry,
airborne radar,
bathymetry,
geodesy,
geophysical techniques,
oceanographic regions,
remote sensing by radar,
seafloor phenomena,
synthetic aperture radar,
terrain mapping,
topography (Earth),
AeS-1,
Bremerhaven,
DEM,
German Bight,
Germany,
InSAR,
North Sea,
Wadden Sea,
airborne interferometric radar,
airborne radar,
coast,
digital elevation model,
geophysical measurement technique,
interferometric SAR,
intertidal zone,
land surface topography,
ocean,
radar remote sensing,
seafloor,
synthetic aperture radar,
terrain mapping,
verification,
Airborne SAR,
Doppler Centroid Estimation.
Abstract: This paper describes how high-precision digital elevation models(DEMs) are obtained over the Wadden Sea using the AeS-1 airborneinterferometric radar. The Wadden Sea is an intertidal zone along thecoast having height variations less than 5 m over 30 km and is free ofvegetation. The resulting DEM has a grid spacing of 2.5 m and anabsolute height accuracy of 5 cm root mean square (rms), as verified bytheodolite measurements. This paper describes the radar system, theprocessing techniques, the test area, the results, and the verificationprocedure -
S. Albrecht and I. Cumming.
Application of momentary Fourier transform to SAR processing.
IEE Proceedings - Radar, Sonar and Navigation,
146(6):285-297,
December 1999.
ISSN: 1350-2395.
Keyword(s): SAR Processing,
SPECAN,
Modified SPECAN,
discrete Fourier transforms,
fast Fourier transforms,
inverse problems,
radar signal processing,
synthetic aperture radar,
DFT,
FFT/IFFT algorithms,
IDFT,
SAR processing,
SIFFT method,
general matrix transforms,
image processing,
inverse momentary Fourier transform,
momentary Fourier transform,
MFT,
recursive momentary Fourier transform,
signal processing,
synthetic aperture radar,
windowing.
Abstract: A common technique in signal and image processing is to extract a portion of the signal by windowing, and then perform the DFT on the window contents. The momentary Fourier transform (MFT) applies to the particular case where the window is moved one data sample along the signal between successive transforms. An alternative derivation of the recursive form of the MFT using general matrix transforms is given. How DFTs and IDFTs are used in the SPECAN (spectral analysis) and SIFFT (short IFFT) methods of synthetic aperture radar (SAR) processing is described. The MFT and inverse MFT are applied to those methods and the advantages and disadvantages they have compared to the FFT/IFFT algorithms are shown -
S.R. Cloude,
J. Fortuny,
J.M. Lopez-Sanchez,
and A.J. Sieber.
Wide-band polarimetric radar inversion studies for vegetation layers.
IEEE Transactions on Geoscience and Remote Sensing,
37(5):2430-2441,
September 1999.
ISSN: 0196-2892.
Keyword(s): backscatter,
forestry,
geophysical techniques,
image classification,
radar cross-sections,
radar polarimetry,
remote sensing by radar,
synthetic aperture radar,
vegetation mappingbackscatter,
canopy,
complex volume scattering,
entropy-alpha target decomposition scheme,
ficus tree,
fig,
fir tree,
forest,
forestry,
geophysical measurement technique,
image classification scheme,
inversion algorithm,
parametric inversion,
polarimetric radar inversion,
radar polarimetry,
radar scattering,
radar theory,
random particle cloud model,
small anisotropic particles,
two-parameter model,
vegetation layer,
vegetation mapping,
wide band method.
Abstract: The authors show how the entropy-alpha target decomposition scheme may be used for parametric inversion studies on random particle cloud models for vegetation layers. The decomposition is detailed first and then applied to a two-parameter model for backscatter from a random cloud of small anisotropic particles. The two main parameters used are the mean particle shape and the mean orientation angle of the cloud. An inversion algorithm is presented and applied to broad-band polarimetric radar data from the European Microwave Signature Laboratory (EMSL), Joint Research Center, Ispra, Italy. The results have been obtained from measurements of a fir tree and a ficus tree. They show a wavelength scale dependence of the shape and distribution of scatterers, which reflects the complex volume scattering nature of such problems. Moreover, the values and trends from these two trees as a function of the frequency are different, as expected from their physical structures. Consequently, this algorithm has the potential to be useful in the construction of classification schemes for vegetation -
Gianfranco Fornaro.
Trajectory Deviations in Airborne SAR: Analysis and Compensation.
IEEE Transactions on Aerospace and Electronic Systems,
35(3):997-1009,
July 1999.
Keyword(s): SAR Processing,
Motion Compensation,
Airborne SAR,
Residual Motion Errors,
Non-Linear Flight Path,
Non-linear SAR.
Abstract: This paper concerns the analysis and compensation of trajectory deviations in airborne synthetic aperture radar (SAR) systems. Analysis of the received data spectrum is carried out with respect to the system geometry in the presence of linear, sinusoidal, and general aircraft displacements. This shows trajectory deviations generally produce spectral replicas along the azimuth frequency that strongly impair the quality of the focused image. Based on the derived model, we explain the rationale of the motion compensation (MOCO) strategy that must be applied at the SAR processing stage in order to limit the resolution loss. To this end aberration terms are separated into range space invariant and variant components. The former can be accounted for either in a preprocessing step or efficiently at range compression stage. The latter needs a prior accommodation of range migration effect. We design the procedure for efficient inclusion of the MOCO within a high precision Scaled FT based SAR processing algorithm. Finally, we present results on simulated data aimed at validating the whole analysis and the proposed procedure. -
Xiaotao Huang and Diannong Liang.
Gradual RELAX Algorithm for RFI Suppression in UWB-SAR.
Electronics Letters,
35(22):1916-1917,
October 1999.
Keyword(s): SAR Processing,
RFI Suppression,
Ultra-Wideband SAR,
Gradual RELAX Algorithm.
Abstract: Parametric methods of radio frequency interference (RFI) suppression in ultra-wideband synthetic aperture radar (UWB-SAR) often outperform their non-parametric counterparts at the expense of computational complexity. The authors present a parametric algorithm that gradually applies the RELAX algorithm and results in greatly improved computational efficiency and stability -
Jong-Sen Lee,
M.R. Grunes,
T.L. Ainsworth,
Li-Jen Du,
D.L. Schuler,
and Shane R. Cloude.
Unsupervised classification using polarimetric decomposition and the complex Wishart classifier.
IEEE Transactions on Geoscience and Remote Sensing,
37(5):2249-2258,
September 1999.
ISSN: 0196-2892.
Keyword(s): geophysical signal processing,
geophysical techniques,
image classification,
radar imaging,
radar polarimetry,
remote sensing by radar,
synthetic aperture radar,
terrain mappingSAR,
complex Wishart classifier,
complex Wishart distribution,
covariance matrix,
entropy-alpha plane,
geophysical measurement technique,
image classification,
initial classification map,
iteration,
land surface,
man-made object,
maximum likelihood classifier,
polarimetric decomposition,
polarimetric target decomposition,
polarization,
radar imaging,
radar polarimetry,
radar remote sensing,
synthetic aperture radar,
terrain mapping,
terrain type,
training,
unsupervised classification.
Abstract: The authors propose a new method for unsupervised classification of terrain types and man-made objects using polarimetric synthetic aperture radar (SAR) data. This technique is a combination of the unsupervised classification based on polarimetric target decomposition, S.R. Cloude et al. (1997), and the maximum likelihood classifier based on the complex Wishart distribution for the polarimetric covariance matrix, J.S. Lee et al. (1994). The authors use Cloude and Pottier's method to initially classify the polarimetric SAR image. The initial classification map defines training sets for classification based on the Wishart distribution. The classified results are then used to define training sets for the next iteration. Significant improvement has been observed in iteration. The iteration ends when the number of pixels switching classes becomes smaller than a predetermined number or when other criteria are met. The authors observed that the class centers in the entropy-alpha plane are shifted by each iteration. The final class centers in the entropy-alpha plane are useful for class identification by the scattering mechanism associated with each zone. The advantages of this method are the automated classification, and the interpretation of each class based on scattering mechanism. The effectiveness of this algorithm is demonstrated using a JPL/AIRSAR polarimetric SAR image -
J. Li,
Z. Bi,
and Z.-S. Liu.
Autofocus and feature extraction in curvilinear SAR via a relaxation-based algorithm.
Radar, Sonar and Navigation, IEE Proceedings -,
146(4):201-207,
1999.
ISSN: 1350-2395.
Keyword(s): SAR Processing,
Non-Linear Flight Path,
SAR Tomography,
Curvilinear SAR,
error analysis,
feature extraction,
focusing,
radar imaging,
synthetic aperture radar,
3D target features,
AUTORELAX,
CLSAR,
SAR imaging,
aperture errors compensation,
curvilinear SAR,
curvilinear synthetic aperture radar,
data model,
estimation accuracy,
experimental results,
feature extraction,
relaxation-based algorithm,
relaxation-based autofocus algorithm,
simulation results,
target parameters.
Abstract: The paper presents a relaxation-based autofocus (AUTORELAX) algorithm that can be used to compensate for the aperture errors in curvilinear synthetic aperture radar (CLSAR) and to extract three-dimensional target features. A self-contained detailed derivation of the data model for the autofocus problem in CLSAR is presented. Experimental and simulation results show that AUTORELAX can be used to significantly improve the estimation accuracy of the target parameters. -
Richard T. Lord and Michael R. Inggs.
Efficient RFI suppression in SAR using LMS adaptive filter integrated with range/Doppler algorithm.
Electronics Letters,
35(8):629-630,
1999.
Keyword(s): SAR Processing,
Doppler radar,
adaptive filters,
interference suppression,
least mean squares methods,
radar imaging,
radar interference,
synthetic aperture radar,
Doppler algorithm,
LMS adaptive filter,
RFI Suppression,
SAR image processing,
radiofrequency interference,
range compression.
Abstract: Radio frequency interference (RFI) suppression in SAR images often requires a great amount of computation. The authors describe how significant computational savings can be achieved by integrating the RFI suppression stage, implemented with a least-mean-squared (LMS) adaptive filter, with the range compression stage of the range/Doppler SAR processing algorithm -
Josef Mittermayer,
Alberto Moreira,
and Otmar Loffeld.
Spotlight SAR data processing using the frequency scaling algorithm.
Geoscience and Remote Sensing, IEEE Transactions on,
37(5):2198-2214,
September 1999.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Spotlight SAR,
dechirp,
dechirp-on-receive,
Doppler radar,
geophysical signal processing,
radar imaging,
remote sensing by radar,
spectral analysis,
synthetic aperture radarazimuth processing,
azimuth scaling,
chirp convolution,
frequency scaling algorithm,
Chirp Scaling Algorithm,
nonchirped SAR signals,
nonchirped raw data,
range Doppler domain,
range cell migration correction,
residual video phase,
RVP,
spectral analysis approach,
spotlight SAR data processing,
stripmap raw data,
subaperture approach.
Abstract: This paper presents a new processing algorithm for spotlight SAR data processing. The algorithm performs the range cell migration correction for non-chirped raw data without interpolation by using a novel frequency scaling operation. The azimuth processing is based on a spectral analysis approach which is made highly accurate by azimuth scaling. In almost all processing stages, a subaperture approach is introduced for efficient azimuth processing. In this paper, the complete derivation of the algorithm is presented. A very useful formulation for non-chirped SAR signals in the range Doppler domain is also proposed where the residual video phase is expressed by a chirp convolution. The algorithm performance is shown by several simulations. A spotlight image, which has been extracted from stripmap raw data of the experimental SAR system of DLR, shows the validity of the frequency scaling algorithm -
Andreas Reigber.
Range dependent spectral filtering to minimize the baseline decorrelation in airborne SAR interferometry.
3:1721-1723,
1999.
Keyword(s): SAR Processing,
SAR Interferometry,
Interferometry,
InSAR,
Range Spectral Filter,
Spectral Filter,
adaptive signal processing,
airborne radar,
geophysical signal processing,
geophysical techniques,
radar imaging,
radar theory,
remote sensing by radar,
synthetic aperture radar,
terrain mapping,
E-SAR,
InSAR,
L-band,
SAR,
Airborne SAR interferometry,
Airborne SAR,
Baseline Decorrelation,
fixed bandwidth filtering,
geometric resolution,
geophysical measurement technique,
interferogram coherence,
interferometric SAR,
land surface,
radar imaging,
radar remote sensing,
range dependent spectral filtering,
repeat-pass,
spectral misalignment,
synthetic aperture radar,
terrain mapping.
Abstract: This paper discusses two methods to solve the problem of a range-dependent baseline decorrelation occurring especially in airborne repeat-pass SAR interferometry. The first approach allows a fixed bandwidth filtering for the whole range avoiding the spectral misalignment of the standard method. The second approach enables a real adaptive filtering of the range-dependent baseline decorrelation and allows one also to obtain the best geometric resolution for each range position without decreasing the interferogram coherence. The efficiency of the two methods is demonstrated by using interferograms obtained from DLR's E-SAR in the L-band repeat-pass-mode -
R. N. Treuhaft and S. R. Cloude.
The structure of oriented vegetation from polarimetric interferometry.
IEEE_J_GRS,
37(5):2620-2624,
September 1999.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Forest,
Forest parameters,
biomass,
forest canopy,
forestry,
geophysical measurement technique,
height,
oriented object,
oriented vegetation,
oriented-vegetation volume,
polarimetric interferometry,
radar polarimetry,
radar remote sensing,
randomly oriented volume,
single-baseline polarimetric interferometry,
underlying topography,
vegetated land surface,
vegetation mapping,
geophysical techniques,
radar polarimetry,
remote sensing by radar,
vegetation mapping;.
Abstract: Polarimetric radar interferometry is much more sensitive to the distribution of oriented objects in a vegetated land surface than either polarimetry or interferometry alone. This paper shows that single-baseline polarimetric interferometry can be used to estimate the heights of oriented-vegetation volumes and underlying topography, while at least two baselines are needed for randomly oriented volumes. Single-baseline, calculated vegetation-height accuracies are in the range of 2-8 m for reasonable levels of vegetation orientation in forest canopies -
Wei Ye,
Tat Soon Yeo,
and Zheng Bao.
Weighted least-squares estimation of phase errors for SAR/ISAR autofocus.
IEEE Transactions on Geoscience and Remote Sensing,
37(5):2487-2494,
September 1999.
Keyword(s): SAR Processsing,
Autofocus,
Weighted Least-Squares Estimation,
WLS,
Residual Motion Errors,
geophysical techniques,
measurement errors,
remote sensing by radar,
synthetic aperture radar,
terrain mapping,
ISAR,
SAR,
geophysical measurement technique,
inverse SAR,
land surface,
phase error,
phase error estimation,
phase errors,
radar remote sensing,
synthetic aperture radar,
terrain mapping.
Abstract: A new method of phase error estimation that utilizes the weighted least-squares (WLS) algorithm is presented for synthetic aperture radar (SAR)/inverse SAR (ISAR) autofocus applications. The method does not require that the signal in each range bin be of a certain distribution model, and thus it is robust for many kinds of scene content. The most attractive attribute of the new method is that it can be used to estimate all kinds of phase errors, no matter whether they are of low order, high order, or random. Compared with other methods, the WLS estimation is optimal in the sense that it has the minimum variance of the estimation error. Excellent results have been obtained in autofocusing and imaging experiments on real SAR and ISAR data -
Richard Bamler and Philipp Hartl.
Synthetic Aperture Radar Interferometry.
Inverse Problems,
14:1-54,
August 1998.
Keyword(s): SAR Processing,
Interferometry.
Abstract: Synthetic aperture radar (SAR) is a coherent active microwave imaging method. In remote sensing it is used for mapping the scattering properties of the Earth's surface in the respective wavelength domain. Many physical and geometric parameters of the imaged scene contribute to the grey value of a SAR image pixel. Scene inversion suffers from this high ambiguity and requires SAR data taken at different wavelength, polarization, time, incidence angle, etc. Interferometric SAR (InSAR) exploits the phase differences of at least two complex-valued SAR images acquired from different orbit positions and/or at different times. The information derived from these interferometric data sets can be used to measure several geophysical quantities, such as topography, deformations (volcanoes, earthquakes, ice fields), glacier flows, ocean currents, vegetation properties, etc. This paper reviews the technology and the signal theoretical aspects of InSAR. Emphasis is given to mathematical imaging models and the statistical properties of the involved quantities. Coherence is shown to be a useful concept for system description and for interferogram quality assessment. As a key step in InSAR signal processing two-dimensional phase unwrapping is discussed in detail. Several interferometric configurations are described and illustrated by real-world examples. A compilation of past, current and future InSAR systems concludes the paper. -
Hian Lim Chan and Tat Soon Yeo.
Noniterative quality phase-gradient autofocus (QPGA) algorithm for spotlight SAR imagery.
Geoscience and Remote Sensing, IEEE Transactions on,
36(5):1531-1539,
Sept. 1998.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus.
Abstract: The phase-gradient autofocus (PGA) technique is robust over a wide range of imagery and phase error functions, but the convergence usually requires four–six iterations. It is necessarily iterative in an attempt to converge on a dominant target against clutter interference, while sufficiently capturing the blur function. In this paper, we propose to speed the estimation convergence by selectively increasing the pool of quality synchronization sources and not be limited by the range pixels of the SAR map. This is highly probable since each range bin contains more than one prominent scatterer across the integration aperture. It is also highly probable that the least-brightest selected scatterer in a range gate may turn out to be of higher energy as compared to the maximum brightest scatterer of another gate. With appropriate target filtering to final select the quality scatterers out of the large pool and with higher order phase error measurement tool, the new algorithm achieves near-convergence focusing quality without iteration. We named this solution the quality PGA (QPGA) algorithm. -
Hyeokho Choi and David C. Munson, Jr..
Direct-Fourier Reconstruction in Tomography and Synthetic Aperture Radar.
International Journal of Imaging Systems and Technology,
9(1):1-13,
1998.
Keyword(s): SAR Processing,
Tomography,
Computed Tomography,
CT,
Convolution Backprojection,
CBP,
Direct-Fourier Image Reconstruction,
DF,
Interpolator,
Fourier-Domain Interpolator.
Abstract: We investigate the use of direct-Fourier (DF) image reconstruction in computed tomography and synthetic aperture radar (SAR). One of our aims is to determine why the convolution-backprojection (CBP) method is favored over DF methods in tomography, while DF methods are virtually always used in SAR. We show that the CBP algorithm is equivalent to DF reconstruction using a Jacobian-weighted two-dimensional periodic sinc-kernel interpolator. This interpolation is not optimal in any sense, which suggests that DF algorithms using optimal interpolators may surpass CBP in image quality. We consider use of two types of DF interpolation: a windowed sinc kernel, and the least-squares optimal Yen interpolator. Simulations show that reconstructions using the Yen interpolator do not possess the expected visual quality, because of regularization needed to preserve numerical stability. Next, we show that with a concentric-squares sampling scheme, DF interpolation can be performed accurately and efficiently, producing imagery that is superior to that obtainable by other algorithms. In the case of SAR, we show that the DF method performs very well with interpolators of low complexity. We also study DF reconstruction in SAR for trapezoidal grids. We conclude that the success of the DF method in SAR imaging is due to the nearly Cartesian shape of the sampling grid. -
S.R. Cloude and Konstantinos P. Papathanassiou.
Polarimetric SAR interferometry.
IEEE Transactions on Geoscience and Remote Sensing,
36(5):1551-1565,
September 1998.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
PolInSAR,
geophysical techniques,
radar imaging,
radar polarimetry,
radar theory,
remote sensing by radar,
synthetic aperture radarInSAR,
coherence optimization problem,
elevated forest canopy,
general formulation,
geophysical measurement technique,
interferogram,
interferometric SAR,
interferometric coherence,
land surface,
linear combinations,
maximization,
polarimetric SAR interferometry,
polarimetric basis transformation,
radar polarimetry,
radar remote sensing,
scalar interferometry,
stochastic scattering model,
strong polarization dependency,
synthetic aperture radar,
terrain mapping,
vector wave interferometry,
SAR Tomography.
Abstract: The authors examine the role of polarimetry in synthetic aperture radar (SAR) interferometry. They first propose a general formulation for vector wave interferometry that includes conventional scalar interferometry as a special case. Then, they show how polarimetric basis transformations can be introduced into SAR interferometry and applied to form interferograms between all possible linear combinations of polarization states. This allows them to reveal the strong polarization dependency of the interferometric coherence. They then solve the coherence optimization problem involving maximization of interferometric coherence and formulate a new coherent decomposition for polarimetric SAR interferometry that allows the separation of the effective phase centers of different scattering mechanisms. A simplified stochastic scattering model for an elevated forest canopy is introduced to demonstrate the effectiveness of the proposed algorithms. In this way, they demonstrate the importance of wave polarization for the physical interpretation of SAR interferograms. They investigate the potential of polarimetric SAR interferometry using results from the evaluation of fully polarimetric interferometric shuttle imaging radar (SIR)-C/X-SAR data collected during October 8-9, 1994, over the SE Baikal Lake Selenga delta region of Buriatia, Southeast Siberia, Russia -
Stuart R. DeGraaf.
SAR imaging via modern 2-D spectral estimation methods.
Image Processing, IEEE Transactions on,
7(5):729-761,
1998.
ISSN: 1057-7149.
Keyword(s): SAR Processing,
Spectral Estimation,
adaptive estimation,
adaptive signal processing,
estimation theory,
image resolution,
interference suppression,
radar imaging,
radar interference,
radiowave interferometry,
speckle,
spectral analysis,
synthetic aperture radar,
2-D spectral estimation methods,
ASR,
MVM,
RRMVM,
SVA,
adaptive SAR imaging,
adaptive nulling,
adaptive sidelobe reduction,
adaptive spectral estimation,
averaging,
height estimates,
interferometric height,
minimum variance method,
multichannel variants,
polarimetric displaced-aperture interferometric data,
power spectrum estimation methods,
reduced-rank MVM,
reflectivity intensity,
resolution,
scattering intensity,
sidelobe artifacts,
space variant apodization,
speckle,
synthetic aperture radar imaging,
MUSIC.
Abstract: Discusses the use of modern 2D spectral estimation algorithms forsynthetic aperture radar (SAR) imaging. The motivation for applyingpower spectrum estimation methods to SAR imaging is to improveresolution, remove sidelobe artifacts, and reduce speckle compared towhat is possible with conventional Fourier transform SAR imagingtechniques. This paper makes two principal contributions to the field ofadaptive SAR imaging. First, it is a comprehensive comparison of 2Dspectral estimation methods for SAR imaging. It provides a synopsis ofthe algorithms available, discusses their relative merits for SARimaging, and illustrates their performance on simulated and collectedSAR imagery. Some of the algorithms presented or their derivations arenew, as are some of the insights into or analyses of the algorithms.Second, this work develops multichannel variants of four relatedalgorithms, minimum variance method (MVM), reduced-rank MVM (RRMVM),adaptive sidelobe reduction (ASR) and space variant apodization (SVA) toestimate both reflectivity intensity and interferometric height frompolarimetric displaced-aperture interferometric data. All of theseinterferometric variants are new. In the interferometric contest,adaptive spectral estimation can improve the height estimates through acombination of adaptive nulling and averaging. Examples illustrate thatMVM, ASR, and SVA offer significant advantages over Fourier methods forestimating both scattering intensity and interferometric height, andallow empirical comparison of the accuracies of Fourier, MVM, ASR, andSVA interferometric height estimates -
Knut Eldhuset.
A new fourth-order processing algorithm for spaceborne SAR.
Aerospace and Electronic Systems, IEEE Transactions on,
34(3):824-835,
1998.
Keyword(s): SAR Processing,
digital simulation,
radar theory,
signal processing,
spaceborne radar,
synthetic aperture radar,
transfer functions,
azimuth lines,
extended ETF,
fourth-order EETF,
fourth-order processing algorithm,
fourth-order signal aperture radar,
high quality images,
integration times,
phase corrections,
phase preservation,
range-variant phase corrections,
satellite-Earth relative motion,
spaceborne SAR,
spatial resolution,
synthetic aperture radar,
two-dimensional exact transfer function.
Abstract: A new fourth-order signal aperture radar (SAR) processingalgorithm has been developed for a general satellite-Earth relativemotion. The two-dimensional exact transfer function (ETF) is calculatedand range-variant phase corrections have been calculated in order toprocess many azimuth lines per block. The ETF together with the phasecorrections has been called the fourth-order EETF (extended ETF). It isalso shown that a fourth-order EETF is necessary to process high qualityimages from spaceborne SAR with long integration times with spatialresolution around 1 m. The algorithm is fast and is anticipated to havegood phase preservation properties -
Giorgio Franceschetti,
Antonio Iodice,
Maurizio Migliaccio,
and Daniele Riccio.
A Novel Across-Track SAR Interferometry Simulator.
IEEE Transactions on Geoscience and Remote Sensing,
36(3):950-962,
May 1998.
Keyword(s): SAR Processing,
Simulation,
SAR Simulator,
Raw Data Simulator,
Interferometry,
Interferometry Simulator.
Abstract: A novel across-track interferometric synthetic aperture radar (SAR) raw signal simulator is presented. It is based on an electromagnetic backscattering model of the scene and an accurate description of the SAR system impulse response function. A set of meaningful examples are also presented. They show that the proposed simulator is structurally consistent and correctly simulates the decorrelation effect, both in the mean and in the distribution sense. -
Aruna Gunawardena and Dennis Longstaff.
Wave Equation Formulation of Synthetic Aperture Radar (SAR) Algorithms in the Time-Space Domain.
IEEE Transactions on Geoscience and Remote Sensing,
36(6):1995-1999,
November 1998.
Keyword(s): SAR Processing,
Time-Space Domain Algorithm,
Wavenumber Domain Algorithm,
omega-k,
Range Migration Algorithm,
Comparison of Algorithms.
Abstract: In this paper, we propose an alternative wave equationbased time-space domain synthetic aperture radar (SAR) algorithm. The proposed algorithm can be interpreted as the exact time-space domain counterpart of the wave equation-based omega-k domain SAR algorithms proposed in recent years. Links to conventional SAR and seismic migration algorithm are also established. -
R. Lanari,
S. Hensley,
and P.A. Rosen.
Chirp z-transform based SPECAN approach for phase-preserving ScanSAR image generation.
Radar, Sonar and Navigation, IEE Proceedings -,
145(5):254-261,
October 1998.
ISSN: 1350-2395.
Keyword(s): SAR Processing,
Modified SPECAN,
SPECAN,
Spectral Analysis,
Z transforms,
airborne radar,
image resolution,
radar imaging,
radar resolution,
InSAR,
SAR Interferometry,
radiowave interferometry,
spaceborne radar,
synthetic aperture radar,
time-domain analysis,
transient response,
ScanSAR,
airborne platform,
algorithm,
azimuth focusing,
chirp z-transform,
chirp-z,
experiments,
high resolution microwave images,
image impulse response,
interferometric ScanSAR systems,
modified SPECAN algorithm,
phase analysis,
phase-preserving ScanSAR image generation,
real data,
scan mode synthetic aperture radar,
simulated data,
spaceborne platform,
standard range-Doppler approach,
time domain.
Abstract: The scan mode synthetic aperture radar (ScanSAR) image impulse response is derived in the time domain, and particular attention is given to the analysis of the phase, which is important for several applications, and especially in interferometric ScanSAR systems. A new algorithm for phase-preserving azimuth focusing of ScanSAR data, that extends the basic SPECAN procedure, is presented. The proposed algorithm avoids the interpolation step needed to achieve a constant azimuth pixel spacing by replacing the standard Fourier transform used in the SPECAN procedure with an appropriate chirp z-transform. The relationship between the modified SPECAN algorithm and the standard range-Doppler approach is also discussed. Experiments on real and simulated data are carried out to validate the theory -
Zheng-She Liu and Jian Li.
Synthetic-aperture-radar motion compensation and feature extraction by means of a relaxation-based algorithm.
J. Opt. Soc. Am. A,
15(3):599-610,
1998.
Keyword(s): SAR Processing,
Autofocus,
Motion Compensation,
MoComp,
Residual Motion Errors,
Airborne SAR,
Phase Gradient Autofocus,
PGA,
RELAX,
MCRELAX,
Cramer-Rao Bound,
Parametric Estimation.
[bibtex-key = liuLi98:Autofocus]
-
Lars M. H. Ulander and Per-Olov Frölind.
Ultra-Wideband SAR Interferometry.
IEEE Transactions on Geoscience and Remote Sensing,
36(5):1540-1550,
Sept 1998.
Keyword(s): SAR Processing,
Interferometry,
DEM Generation,
Fourier-Hankel Inversion,
Hankel Transform,
Abel Transform,
Ultra-Wideband SAR,
VHF SAR,
CARABAS,
Airborne SAR.
Abstract: We introduce ultra-wideband synthetic aperture radar (SAR) interferometry as a new technique for topographic height retrieval. It is based on using a SAR system with large relative bandwidth that acquires data along two parallel tracks with a separation of the same order of magnitude as the flight altitude. The complex SAR image data are resampled onto a common reference surface, filtered, and followed by a Hermitian multiplication. The resulting interferogram is shown to have a finite depth-of-focus (DOF) in terms of phase coherence. The achieved height precision is controlled by the ambiguity height, which is shown to scale to the DOF as the relative bandwidth. This means that only one fringe is within the DOF as the resolution approaches the fundamental wavelength limit; i.e., the phase is unambiguously related to topographic height. The topography may thus be determined by changing the reference surface and retrieving the height at each step. The technique is successfully demonstrated to generate fringes based on VHF-band data acquired by the CARABAS airborne SAR system. Temporal decorrelation is not a problem due to the long wavelengths nor is the effect of tropospheric delay on the retrieved height. -
Shane R. Cloude and Eric Pottier.
An entropy based classification scheme for land applications of polarimetric SAR.
IEEE Transactions on Geoscience and Remote Sensing,
35(1):68-78,
January 1997.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Polarimetry,
PolSAR,
Entropy,
Anisotropy,
Alpha,
H-A-alpha,
S-matrix theory,
geophysical signal processing,
geophysical techniques,
image classification,
radar imaging,
radar polarimetry,
radar theory,
remote sensing by radar,
synthetic aperture radar,
S-matrix theory,
average target scattering matrix parameters,
coherency matrix,
eigenvalue analysis,
entropy based classification,
geophysical measurement technique,
image classification,
land surface,
land use,
parameterization,
polarimetric SAR,
polarimetric scattering problem,
quantitative analysis,
radar polarimetry,
radar remote sensing,
scattering entropy,
terrain mapping,
three-level Bernoulli statistical model,
unsupervised classifier.
Abstract: The authors outline a new scheme for parameterizing polarimetric scattering problems, which has application in the quantitative analysis of polarimetric SAR data. The method relies on an eigenvalue analysis of the coherency matrix and employs a three-level Bernoulli statistical model to generate estimates of the average target scattering matrix parameters from the data. The scattering entropy is a key parameter is determining the randomness in this model and is seen as a fundamental parameter in assessing the importance of polarimetry in remote sensing problems. The authors show application of the method to some important classical random media scattering problems and apply it to POLSAR data from the NASA/JPL AIRSAR data base -
H. Israelsson,
L. M. H. Ulander,
J. L. H. Askne,
J. E. S. Fransson,
P.-O. Frölind,
A. Gustavsson,
and H. Hellsten.
Retrieval of forest stem volume using VHF SAR.
IEEE_J_GRS,
35(1):36-40,
January 1997.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Forest,
Forest parameters,
biomass,
28 to 60 MHz,
CARABAS,
HF radar,
Oland,
SAR,
Sweden,
VHF radar,
airborne radar,
backscattering coefficient,
biomass,
coherent all radio band sensing,
deciduous mixed forest,
dense forest,
discrimination,
forest stem volume,
forestry,
geophysical measurement technique,
horizontal dipole array,
radar imaging,
radar remote sensing,
radar scattering,
tree trunk,
vegetation mapping,
wood,
airborne radar,
forestry,
geophysical techniques,
radar cross-sections,
radar imaging,
remote sensing by radar,
synthetic aperture radar;.
Abstract: The ability to retrieve forest stem volume using CARABAS (coherent all radio band sensing) SAR images (28-60 MHz) has been investigated. The test site is a deciduous mixed forest on the island of Oland in southern Sweden. The images have been radiometrically calibrated using an array of horizontal dipoles. The images exhibit a clear discrimination between the forest and open fields. The results show that the dynamic range of the backscattering coefficient among the forest stands is higher than what has been found with conventional SAR using microwave frequencies. The backscatter increases with increasing radar frequency. This work shows an advantage compared to higher frequencies for stem volume estimation in dense forests -
Riccardo Lanari and Gianfranco Fornaro.
A short discussion on the exact compensation of the SAR range-dependent range cell migration effect.
IEEE Transactions on Geoscience and Remote Sensing,
35(6):1446-1452,
November 1997.
Keyword(s): SAR Processing,
Motion Compensation,
Comparison of Algorithms,
Chirp Scaling Algorithm,
Range Cell Migration,
Range Migration,
FM radar,
geophysical signal processing,
geophysical techniques,
radar imaging,
remote sensing by radar,
synthetic aperture radar,
RCM,
RDRCM,
SAR,
chirp z-transform,
exact compensation,
geophysical measurement technique,
land surface,
radar imaging,
radar remote sensing,
range-dependent range cell migration effect,
synthetic aperture radar,
terrain mapping.
Abstract: Efficient and precise compensation of the range cell migration (RCM) effect is a key point for a fast and accurate synthetic aperture radar (SAR) data processor. In particular the range-dependent nature of the range cell migration effect complicates the compensation operation. It has been recently shown that an exact compensation of the range-dependent RCM (RDRCM) phenomenon can be carried out either by applying the chirp scaling algorithm or the chirp z-transform procedure. This paper investigates the relationship between the two methods. In particular, it is shown that the chirp z-transform based approach represents a particular implementation of the chirp scaling algorithm. A final discussion is dedicated to show how the chirp z-transform and the chirp scaling procedure can be applied within a SAR data processing algorithm. -
J. Li,
Z. Bi,
Z.S. Liu,
and K. Knaell.
Use of curvilinear SAR for three-dimensional target feature extraction.
Radar, Sonar and Navigation, IEE Proceedings-,
144(5):275-283,
1997.
Keyword(s): SAR Processing,
Non-Linear Flight Path,
SAR Tomography,
Feature Extraction,
Target Feature Extraction,
Curvilinear SAR.
[bibtex-key = liBiLiuKnaell1997:NonLinearSARTomo]
-
J. Li,
Z.-S. Liu,
and Petre Stoica.
3-D target feature extraction via interferometric SAR.
Radar, Sonar and Navigation, IEE Proceedings -,
144(2):71-80,
1997.
ISSN: 1350-2395.
Keyword(s): SAR Processing,
Tomography,
SAR Tomography,
InSAR,
fast Fourier transforms,
feature extraction,
least squares approximations,
parameter estimation,
radar cross-sections,
radar signal processing,
radiowave interferometry,
signal resolution,
synthetic aperture radar,
3D target feature extraction,
Capon,
Cramer-Rao bounds,
FTF,
IFRELAX,
IFSAR,
MUSIC,
data model,
interferometric SAR,
interferometric synthetic aperture radar,
nonlinear least squares parameter estimation method,
nonparametric methods,
parameter estimates,
parameter identifiability conditions,
performance,
point scatterers,
two-dimensional feature extraction methods,
windowed FFT.
Abstract: The authors consider 3-D (three-dimensional) target feature extraction via an interferometric synthetic aperture radar (IFSAR). The targets of interest are relatively small and consist of a small number of distinct point scatterers. Since using IFSAR to extract the features of such targets has not been addressed before, a self-contained detailed derivation of the data model is presented. A set of sufficient parameter identifiability conditions on the data model and the Cramer-Rao bounds (CRBs) on the parameter estimates are also derived. Four existing two-dimensional feature extraction methods (FFT, windowed FFT, Capon and MUSIC) are extended to estimate the 3-D parameters of the target scatterers. A new nonlinear least squares parameter estimation method, referred to as IFRELAX, is also derived to extract the target features. Finally, numerical examples are presented to compare the performances of the presented methods with each other and with the corresponding CRBs.The authors show by means of numerical examples that, among the three nonparametric methods (FFT, windowed FFT, and Capon), Capon has the best resolution. The parametric methods MUSIC and IFRELAX can have much better resolution and provide much more accurate parameter estimates than the nonparametric methods. It is shown IFRELAX can be faster and provide much better parameter estimates than MUSIC. -
T. Miller,
L. Potter,
and John W. McCorkle.
RFI suppression for ultra wideband radar.
Aerospace and Electronic Systems, IEEE Transactions on,
33(4):1142-1156,
1997.
Keyword(s): SAR Processing,
interference suppression,
least squares approximations,
radar imaging,
radar interference,
radiofrequency interference,
synthetic aperture radar,
Army Research Laboratory,
RFI Suppression,
SAR imagery,
UWB rail SAR,
bias,
estimate-and-subtract algorithm,
estimated targets,
foliage-penetrating imaging,
ground-penetrating imaging,
radio frequency interference,
real-time digital suppression,
sidelobe levels,
signal model,
target energy loss,
ultra wideband radar,
ultrawideband synthetic aperture radar.
Abstract: An estimate-and-subtract algorithm is presented for the real-time -
Andrea Monti-Guarnieri and C. Prati.
SAR interferometry: A ``Quick and dirty'' coherence estimator for data browsing.
IEEE Transactions on Geoscience and Remote Sensing,
35(3):660-669,
May 1997.
Keyword(s): SAR Processing,
Coherence,
Coherence Estimation,
geophysical signal processing,
geophysical techniques,
radar imaging,
remote sensing by radar,
spaceborne radar,
speckle,
synthetic aperture radarERS,
SAR interferometry,
coherence estimator,
coherence map,
data browsing,
fast algorithm,
geophysical measurement technique,
land surface,
quick method,
radar imaging,
radar remote sensing,
spaceborne radar,
speckle similarity,
synthetic aperture radar,
terrain mapping.
Abstract: Usual coherence estimation in SAR interferometry is a time consuming task since an accurate estimation of the local frequency of the interferometric fringes is required. This paper presents a fast algorithm for generating coherence maps, mainly intended for data browsing. The proposed estimator is based on the speckle similarity of coherent SAR data, and is thus independent of fringe frequency. The following advantages, with respect to the usual estimates, are achieved: (a) The estimator is more than 100 times faster, achieved at the cost of a reduced statistical confidence. (b) The estimator is not affected by possible local frequency estimation errors. (c) The estimator can be directly applied to single look detected images. The theoretical derivation of the statistical properties of the frequency independent estimator is carried out in the stationary case. The nonstationary case is then analyzed on real ERS SAR images -
Regine Bolter,
Margrit Gelautz,
and Franz Leberl.
SAR Speckle Simulation.
International Archives of Photogrammetry and Remote Sensing,
21:20-25,
1996.
Keyword(s): SAR Processing,
Simulation,
Speckle,
Speckle Simulation.
Abstract: After a short introduction to the principles of SAR speckle generation and its statistical properties, we give a review of different speckle simulation methods described in literature. Then, the implementation of some selected algorithms is described, and their performance is tested on simulated ERS-1 images. Special attention is paid to the modeling of multiple looks, and the differences between image pixel size and original radar ground resolution. A chi-square distribution and a Rayleigh distribution with multiple file averaging were found to produce the most realistic results. -
Shane R. Cloude and Eric Pottier.
A review of target decomposition theorems in radar polarimetry.
IEEE Transactions on Geoscience and Remote Sensing,
34(2):498-518,
March 1996.
ISSN: 0196-2892.
Keyword(s): S-matrix theory,
backscatter,
covariance matrices,
eigenvalues and eigenfunctions,
geophysical signal processing,
matrix decomposition,
radar cross-sections,
radar imaging,
radar polarimetry,
remote sensing by radar,
reviews,
Mueller matrix,
Stokes vector,
backscatter,
coherency matrix,
coherent decomposition,
covariance matrix,
eigenvector analysis,
radar polarimetry,
scattering matrix,
target decomposition theorems,
terrain,
transformation theory.
Abstract: In this paper, we provide a review of the different approaches used for target decomposition theory in radar polarimetry. We classify three main types of theorem; those based on the Mueller matrix and Stokes vector, those using an eigenvector analysis of the covariance or coherency matrix, and those employing coherent decomposition of the scattering matrix. We unify the formulation of these different approaches using transformation theory and an eigenvector analysis. We show how special forms of these decompositions apply for the important case of backscatter from terrain with generic symmetries -
G.W. Davidson,
Ian G. Cumming,
and M.R. Ito.
A chirp scaling approach for processing squint mode SAR data.
IEEE_J_AES,
32(1):121-133,
January 1996.
ISSN: 0018-9251.
Keyword(s): SAR Processing,
C-band,
L-band,
chirp scaling algorithm,
image degradations,
image formation,
nonlinear FM chirp scaling,
phase modulation,
range-variant filtering,
resolution width,
secondary range compression,
sidelobe level,
squint mode SAR data,
FM radar,
data compression,
filtering theory,
image resolution,
phase modulation,
radar imaging,
synthetic aperture radar;.
Abstract: Image formation from squint mode synthetic aperture radar (SAR) is limited by image degradations caused by neglecting the range-variant filtering required by secondary range compression (SRC). Introduced here is a nonlinear FM chirp scaling, an extension of the chirp scaling algorithm, as an efficient and accurate approach to range variant SRC. Two methods of implementing the approach are described. The nonlinear FM filtering method is more accurate but adds a filtering step to the chirp scaling algorithm, although the extra computation is less than that of a time domain residual compression filter. The nonlinear FM pulse method consists of changing the phase modulation of the transmitted pulse, thus avoiding an increase in computation. Simulations show both methods significantly improve resolution width and sidelobe level, compared with existing SAR processors for squint angles above 10 deg for L-band and 20 deg for C-band. -
Michael Y. Jin.
Optimal Range and Doppler Centroid Estimation for a ScanSAR System.
IEEE Transactions on Geoscience and Remote Sensing,
34(2):479-488,
March 1996.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Clutterlock,
ScanSAR,
SIR-C,
ERS.
Abstract: This paper presents a new range and Doppler centroid estimation algorithm for a ScanSAR system. This algorithm is based on processing the image data in the overlapped region of two bursts of the same beam or adjacent beams. It leads to highly accurate radar pointing angles that are paramount to achieving good radiometric performance in ScanSAR imagery. The achievable accuracy is derived theoretically and verified by tests performed using SIR-C ScanSAR data and ERS data. This algorithm is computationally efficient and easy to implement. The proposed Doppler centroid estimation algorithm is also an excellent candidate for a strip mode SAR system. -
Andrea Monti-Guarnieri.
Residual SAR Focusing: An Application to Coherence Improvement.
IEEE Transactions on Geoscience and Remote Sensing,
34(1):201-211,
January 1996.
Keyword(s): SAR Processing,
Interferometry,
Residual Azimuth Compression,
Coherence Improvement.
Abstract: The focusing quality of a SAR processor greatly depends on the accuracy of the system geometry estimate. Sometimes ancillary data do not provide enough accuracy, therefore autofocusing has to be performed to get the finest quality possible. A residual azimuth compression is introduced to show how a defocused image can be compensated by means of a monodimensional local operator. The residual transfer function that generates defocusing is then derived. The effects of the defocusing are shown on both a complex single SAR image and a SAR interferogram. SAR interferograms, however, are much more sensitive to defocusing than the single SAR image. Two algorithms have been developed to estimate, and compensate for, the defocusing in both the single SAR image and SAR interferometric cases. The processors select data suitable for estimating focusing parameters from the whole images by exploring Kurtosis (for single image focusing) or coherence (for interferometric autofocusing). The residual, short time-domain operator is then exploited to retrieve the focusing parameter values and, finally, to get the focused image. The limitations and accuracy of the algorithm in terms of parameter estimation are investigated. Experimental results, obtained from different SAR missions, are presented -
Alberto Moreira,
Josef Mittermayer,
and Rolf Scheiber.
Extended Chirp Scaling Algorithm for Air- and Spaceborne SAR Data Processing in Stripmap and ScanSAR Imaging Modes.
IEEE Transactions on Geoscience and Remote Sensing,
34(5):1123-1136,
Sept. 1996.
Keyword(s): SAR Processing,
Chirp Scaling Algorithm,
Extended Chirp Scaling Algorithm,
Spaceborne SAR,
Airborne SAR,
ScanSAR,
Automatic Azimuth Coregistration,
Azimuth Scaling,
Squinted SAR,
Interferometry,
Phase-Preserving Processing,
Range Scaling Formulation,
Stripmap SAR,
Subaperture Processing,
Terrain Mapping.
Abstract: This paper resents a generalized formulation of the extended chirp scaling (ECS) approach for high precision processing of air- and spaceborne SAR data. Based on the original chirp scaling function, the ECS algorithm incorporates a new azimuth scaling function and a subaperture approach, which allow an effective phase-preserving processing of ScanSAR data without interpolation for azimuth geometric correction. The azimuth scaling can also be used for automatic azimuth coregistration of interferometric image pairs which are acquired with different sampling distances. Additionally, a novel range scaling formulation is proposed for automatic range coregistration of interferometric image pairs or for improved robustness for the processing of highly squinted data. Several simulation and processing results of air- and spaceborne SAR data are presented to demonstrate the validity of the proposed algorithms -
M. Soumekh.
Reconnaissance with slant plane circular SAR imaging.
Image Processing, IEEE Transactions on,
5(8):1252-1265,
1996.
ISSN: 1057-7149.
Keyword(s): SAR Processing,
Non-Linear Flight Path,
Fourier analysis,
Fourier transforms,
Green's function methods,
image reconstruction,
image resolution,
inverse problems,
radar imaging,
synthetic aperture radar,
Fourier analysis,
Green's function,
SAR data inversion,
SAR system,
aspect angle,
circular flight path,
full rotation,
ground penetrating UHF radar signature,
image resolution,
imaging system,
partial segment,
reconnaissance,
reconstruction algorithm,
simulated target,
slant plane circular SAR imaging,
slant plane data,
slant plane linear SAR,
synthetic aperture radar,
target scene,
three-dimensional imaging,
ultrawideband foliage penetrating radar signature.
Abstract: This paper presents a method for imaging from the slant plane data collected by a synthetic aperture radar (SAR) over the full rotation or a partial segment of a circular flight path. A Fourier analysis for the Green's function of the imaging system is provided. This analysis is the basis of an inversion for slant plane circular SAR data. The reconstruction algorithm and resolution for this SAR system are outlined. It is shown that the slant plane circular SAR, unlike the slant plane linear SAR, has the capability to extract three-dimensional imaging information of a target scene. The merits of the algorithm are demonstrated via a simulated target whose ultra wideband foliage penetrating (FOPEN) or ground penetrating (GPEN) ultrahigh frequency (UHF) radar signature varies with the radar's aspect angle -
Robert N. Treuhaft,
Soren N. Madsen,
Mahta Moghaddam,
and Jakob J. van Zyl.
Vegetation characteristics and underlying topography from interferometric radar.
Radio Science,
31(6):1449-1485,
1996.
Keyword(s): SAR Processing,
InSAR,
Interferometry,
Vegetation Parameters,
Parameter Extraction,
Topography,
SAR Tomography.
Abstract: This paper formulates and demonstrates methods for extracting vegetation characteristics and underlying ground surface topography from interferometric synthetic aperture radar (INSAR) data. The electromagnetic scattering and radar processing, which produce the INSAR observations, are modeled, vegetation and topographic parameters are identified for estimation, the parameter errors are assessed in terms of INSAR instrumental performance, and the parameter estimation is demonstrated on INSAR data and compared to ground truth. The fundamental observations from which vegetation and surface topographic parameters are estimated are (1) the cross-correlation amplitude, (2) the cross-correlation phase, and (3) the synthetic aperture radar (SAR) backscattered power. A calculation based on scattering from vegetation treated as a random medium, including the effects of refractivity and absorption in the vegetation, yields expressions for the complex cross correlation and backscattered power in terms of vegetation characteristics. These expressions lead to the identification of a minimal set of four parameters describing the vegetation and surface topography: (1) the vegetation layer depth, (2) the vegetation extinction coefficient (power loss per unit length), (3) a parameter involving the product of the average backscattering amplitude and scatterer number density, and (4) the height of the underlying ground surface. The accuracy of vegetation and ground surface parameters, as a function of INSAR observation accuracy, is evaluated for aircraft INSAR, which is characterized by a 2.5 m baseline, an altitude of about 8 km, and a wavelength of 5.6 cm. It is found that for ~0.5% accuracy in the INSAR normalized cross-correlation amplitude and ~5° accuracy in the interferometric phase, few-meter vegetation layer depths and ground surface heights can be determined from INSAR for many types of vegetation layers. With the same observational accuracies, extinction coefficients can be estimated at the 0.1-dB/m level. Because the number of parameters exceeds the number of observations for current INSAR data sets, external extinction coefficient data are used to demonstrate the estimation of the vegetation layer depth and ground surface height from INSAR data taken at the Bonanza Creek Experimental Forest in Alaska. This demonstration shows approximately 5 m average ground truth agreement for vegetation layer depths and ground-surface heights, with a clear dependence of error on stand height. These errors suggest refinements in INSAR data acquisition and analysis techniques which will potentially yield few-meter accuracies. The information in the INSAR parameters is applicable to a variety of ecological modeling issues including the successional modeling of forested ecosystems. -
Lars M. H. Ulander.
Radiometric slope correction of synthetic-aperture radar images.
IEEE Transactions on Geoscience and Remote Sensing,
34(5):1115-1122,
1996.
Keyword(s): SAR Processing,
Radiometric Correction,
Topography,
geophysical techniques,
radar imaging,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
SAR,
algorithm,
calibration equation,
fringe frequencies,
geophysical measurement technique,
land surface,
maximum-likelihood estimator,
radar imaging,
radar remote sensing,
radiometric slope correction,
spaceborne radar,
synthetic aperture radar image,
terrain mapping,
topographic height variation.
Abstract: The brightness in a SAR image is affected by topographic height -
Frank Wong and Ian G. Cumming.
A Combined SAR Doppler Centroid Estimation Scheme Based Upon Signal Phase.
IEEE Transactions on Geoscience and Remote Sensing,
34(3):696-707,
May 1996.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Multilook Cross Correlation,
MLCC,
Multilook Beat Frequency,
MLBF,
Clutterlock,
Doppler Ambiguity Resolver,
DAR.
Abstract: This paper describes a complete end-to-end Doppler centroid estimation scheme, which determines the fractional PRF part of the Doppler centroid. It also resolves the Doppler ambiguity. Experiments show that the scheme works successfully over various terrain types, including land, water, and ice, and that it requires only a modest amount of SAR data to perform reliably. The proposed scheme has an added advantage that it is directly applicable to RADARSAT and ENVISAT ScanSAR data. The scheme uses two complementary Doppler estimation algorithms, both utilizing the phase information embedded in the radar signal. In each algorithm, upper and lower parts of the available bandwidth of the received signal are extracted to form two range looks. The first algorithm, called multilook cross correlation (MLCC), computes the average cross correlation coefficient between adjacent azimuth samples for each of the two looks and then takes the difference between the angles of the two coefficients. The Doppler ambiguity is determined from the angle difference. The fractional pulse repetition frequency (PRF) part is also determined from the cross correlation coefficients. In the second algorithm, called multilook beat frequency (MLBF), the two looks are multiplied together to generate a beat signal. The beat frequency is then estimated and the Doppler ambiguity determined from the beat frequency. The MLCC algorithm performs better with low contrast scenes while the MLBF works better with high contrast ones. Although each algorithm works well on its own with sufficient averaging, it is also possible to use quality measures to select the best result from either algorithm. In this way, scenes of different content or contrast can be handled reliably. This paper presents the analysis of the two algorithms, explaining why their performance is affected by scene contrast, which is confirmed by experimental results with ERS-1 and JERS-1 data. -
Giorgio Franceschetti,
Riccardo Lanari,
and E. S. Marzouk.
Efficient and High Precision Space-Variant Processing of SAR Data.
IEEE Transactions on Aerospace and Electronic Systems,
31(1):227-237,
January 1995.
Keyword(s): SAR Processing,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Range-Doppler Algorithm,
Space-Variance Compensation,
Space-Variant Processing,
Earth Rotation Effect,
Nonstandard Fourier Transform.
Abstract: We investigate the space-variance of the synthetic aperture radar (SAR) transfer function due to focus depth variation and Earth rotation effect. We introduce a procedure for efficient space-variance compensation which is based on the use of a nonstandard Fourier transform (FT). A number of experiments confirming theoretical results are presented -
J.O. Hagberg,
L. M. H. Ulander,
and J. Askne.
Repeat-pass SAR interferometry over forested terrain.
IEEE_J_GRS,
33(2):331-340,
March 1995.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
SAR interferometry,
forest,
forested terrain,
forestry,
general system model,
geophysical method,
interferometry,
land surface topography,
measurement technique,
radar remote sensing,
repeat pass method,
scene scattering,
synthetic aperture radar,
topographic map,
vegetation mapping,
forestry,
geophysical techniques,
radar applications,
radar imaging,
remote sensing,
remote sensing by radar,
synthetic aperture radar,
topography (Earth);.
Abstract: Repeat-pass synthetic aperture radar (SAR) interferometry provides the possibility of producing topographic maps and geocoded as well as radiometrically calibrated radar images. However, the usefulness of such maps and images depends on our understanding of how different types of terrain affect the radar measurements. It is essential that the scene coherence between passes is sufficient. In this paper, the authors derive a general system model including both radar system and scene scattering properties. The model is used to interpret measurements over a forested area where the scene coherence varies between 0.2 and 0.5. The coherence is found to be sensitive to temperature changes around 0 deg Celsius but surprisingly insensitive to wind speed. The interferometric height discontinuity at the forest to open-field boundary shows good agreement with in situ tree height measurements. For a dense boreal forest, but is observed to decrease for a less dense forest. This suggests the possibility of estimating bole volume from the interferometric tree height and a ground DEM. The decrease of scene coherence over a dense forest with increasing baseline is also used to estimate the effective scattering layer thickness -
Marc L. Imhoff.
Radar backscatter and biomass saturation: ramifications for global biomass inventory.
IEEE Transactions on Geoscience and Remote Sensing,
33(2):511-518,
March 1995.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
backscatter,
forestry,
geophysical techniques,
radar applications,
radar cross-sections,
radar imaging,
remote sensing by radar,
synthetic aperture radar,
0.44 to 5.3 GHz,
C-band,
Hawaii,
L-band,
P-band,
SAR,
UHF SHF microwave,
biomass saturation,
biome,
broadleaf evergreen forest,
canopy,
coniferous forest,
forestry,
geophysical measurement technique,
global biomass inventory,
land surface,
phytomass,
radar backscatter,
radar remote sensing,
synthetic aperture radar,
vegetated surface,
vegetation mapping,
Space-borne SAR,
SAR Tomography,
Tomography.
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° and 50° 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 ≈100 tons/ha for P-band (0.44 GHz), ≈40 tons/ha for L-band (1.25 GHz), and ≈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 (>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 -
C.V. Jakowatz and P.A. Thompson.
A new look at spotlight mode synthetic aperture radar as tomography: imaging 3-D targets.
Image Processing, IEEE Transactions on,
4(5):699-703,
1995.
ISSN: 1057-7149.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
Fourier transforms,
image reconstruction,
radar imaging,
synthetic aperture radar,
tomography,
3D Fourier transform,
3D tomographic formulation,
demodulated radar return data,
layover,
projection effect,
radar target reflectivities,
reconstructed 2D SAR image,
spotlight mode synthetic aperture radar,
tomography.
Abstract: A new 3D tomographic formulation of spotlight mode synthetic aperture radar (SAR) is developed. This extends the pioneering work of Munson et al. (1983), who first formally described SAR in terms of tomography but who made the simplifying assumption that the target scene was 2D. The present authors treat the more general and practical case in which the radar target reflectivities comprise a 3D function. The main goal is to demonstrate that the demodulated radar return data from a spotlight mode collection represent a certain set of samples of the 3D Fourier transform of the target reflectivity function and to do so using a tomographic paradigm instead of traditional range-Doppler analysis. They also show that the tomographic approach is useful in interpreting the reconstructed 2D SAR image corresponding to a 3D scene. Specifically, the well-known SAR phenomenon of layover is easily explained in terms of tomographic projections and is shown to be analogous to the projection effect in conventional optical imaging -
Nick Marechal.
Tomographic formulation of interferometric SAR for terrain elevation mapping.
IEEE Transactions on Geoscience and Remote Sensing,
33(3):726-739,
May 1995.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
SAR Interferometry,
Interferometry,
InSAR,
Spotlight SAR,
SAR Tomography,
geophysical signal processing,
geophysical techniques,
radar applications,
radar imaging,
remote sensing by radar,
synthetic aperture radar,
topography (Earth)SAR image,
SAR image model,
baseline separation,
correlation,
equations,
geophysical measurement technique,
image pair decorrelation,
interferometric SAR,
phase difference,
radar remote sensing,
spotlight synthetic aperture radar,
terrain elevation mapping,
terrain mapping,
tomographic formulation,
tomography,
topographic height error variance model.
Abstract: Topographic mapping with spotlight synthetic aperture radar (SAR) using an interferometric technique is studied. Included is a review of the equations for determination of terrain elevation from the phase difference between a pair of SAR images formed from data collected at two differing imaging geometries. This paper builds upon the systems analysis of Li and Goldstein in which image pair decorrelation as a function of the \u201cbaseline\u201d separation between the receiving antennas was first analyzed. In this paper correlation and topographic height error variance models are developed based on a SAR image model derived from a tomographic image formation perspective. The models are general in the sense that they are constructed to analyze the case of single antenna, two-pass interferometry with arbitrary antenna line of sight, and velocity vector directions. Correlation and height error variance sensitivity to SAR system parameters and terrain gradients are studied -
H. C. Stankwitz,
R. J. Dallaire,
and J. R. Fienup.
Nonlinear apodization for sidelobe control in SAR imagery.
IEEE Transactions on Aerospace and Electronic Systems,
31(1):267-279,
January 1995.
ISSN: 0018-9251.
Keyword(s): SAR Processing,
Apodization,
Nonlinear Apodization,
Dual Apodization,
Complex Dual Apodization,
Multiapodization,
Spatially Variant Apodization,
DA,
CDA,
SVA,
Fourier transform,
SAR imagery,
antenna design,
complex-valued SAR imagery,
digital filtering,
mainlobe resolution,
nonlinear apodization techniques,
sequential nonlinear operations,
ships. sidelobe control,
sonar,
spectral weighting,
synthetic aperture radar imagery,
Nyquist diagrams,
fast Fourier transforms,
frequency-domain analysis,
synthetic aperture radars.
Abstract: Synthetic aperture radar (SAR) imagery often requires sidelobe control, or apodization, via weighting of the frequency domain aperture. This is of particular importance when imaging scenes containing objects such as ships or buildings having very large radar cross sections. Sidelobe improvement using spectral weighting is invariably at the expense of mainlobe resolution presented here is a class of nonlinear operators which significantly reduce sidelobe levels without degrading mainlobe resolution implementation is via sequential nonlinear operations applied to complex-valued (undetected) SAR imagery. SAR imaging is used to motivate the concepts developed in this work. However, these nonlinear apodization techniques have potentially broad and far-ranging applications in antenna design, sonar, digital filtering etc., i.e., whenever data can be represented as the Fourier transform of a finite-aperture signal.<> -
Petre Stoica and M. Cedervall.
On LP-MUSIC.
IEEE Transactions on Signal Processing,
43(2):552-555,
February 1995.
ISSN: 1053-587X.
Keyword(s): SAR Processing,
MUSIC,
SAR Tomography,
frequency estimation,
noise,
prediction theory,
signal processing,
LP-MUSIC,
consistency properties,
frequency estimates,
linear prediction algorithm,
linear prediction-MUSIC,
noisy data,
signal subspace,
spatial frequency estimation,
temporal frequency estimation.
Abstract: Studies the consistency properties of a method recently proposed for temporal or spatial frequency estimation from noisy data. The method in question is a MUSIC technique that makes use of a linear prediction algorithm to determine the signal subspace. It is shown that the signal subspace determined by the subject linear prediction-MUSIC (LP-MUSIC) algorithm can collapse in certain scenarios and. Hence, that the LP-MUSIC frequency estimates are not always consistent. The difficulties LP-MUSIC may encounter in some cases are illustrated by means of numerical examples -
Giorgio Franceschetti,
Maurizio Migliaccio,
and Daniele Riccio.
SAR Raw Signal Simulation of Actual Ground Sites Described in Terms of Sparse Input Data.
IEEE Transactions on Geoscience and Remote Sensing,
32(6):1160-1169,
November 1994.
Keyword(s): SAR Processing,
Simulation,
SAR Simulator,
Raw Data Simulator,
Fractals,
Sparse Input Data,
SARAS.
Abstract: Deals with the simulation of synthetic aperture radar (SAR) raw signal of actual ground sites described in terms of sparse input data. Since in most cases the input data reference system does not match SAR requirements, it is necessary to adopt appropriate interpolation schemes. The authors focus their attention on elevation input data, noting that natural surfaces exhibit fractal properties. Fractal and nonfractal interpolation schemes are discussed and applied. Simulated images are shown and compared to actual examples. Subjective and objective tests validate the simulation and support the fractal-based elevation interpolation. -
Fabio Gatelli,
Andrea Monti-Guarnieri,
Francesco Parizzi,
Paolo Pasquali,
Claudio Prati,
and Fabio Rocca.
The wavenumber shift in SAR interferometry.
IEEE Transactions on Geoscience and Remote Sensing,
32(4):855-865,
July 1994.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
SAR Interferometry,
Interferometry,
InSAR,
Range Spectral Filter,
geophysical techniques,
remote sensing by radar,
synthetic aperture radar,
TINSAR,
decorrelation reduction,
Baseline Decorrelation,
geophysical measurement technique,
ground wavenumber spectra,
land surface,
local slope,
low noise interferogram,
off-nadir angle,
phase unwrapping,
quick-look interferogram,
radar imaging,
range resolution enhancement,
relative shift,
remote sensing,
spectral shift,
terrain mapping,
wavenumber shift.
Abstract: SAR surveys from separate passes show relative shifts of the ground wavenumber spectra that depend on the local slope and the off-nadir angle. The authors discuss the exploitation of this spectral shift for different applications: 1) generation of \u201clow noise\u201d interferograms benefiting phase unwrapping, 2) generation of quick-look interferograms, 3) decorrelation reduction by means of tunable SAR systems (TINSAR), 4) range resolution enhancement, and 5) the combination of SAR data gathered by different platforms (airborne and satellite) for a \u201clong-time coherence\u201d study -
Dieter Just and Richard Bamler.
Phase Statistics of Interferograms with Applications to Synthetic Aperture Radar.
Applied Optics,
33(20):4361-4368,
July 1994.
Keyword(s): SAR Processing,
InSAR,
Interferometry,
SAR Interferometry,
Phase Statistics,
Decorrelation,
Aberrations,
Wavenumber Shift,
Coregistration.
Abstract: Interferometric methods are well established in optics and radio astronomy. In recent years, interferometric concepts have been applied successfully to synthetic aperture radar (SAR) and have opened up new possibilities in the area of earth remote sensing. However interferometric SAR applications require thorough phase control through the imaging process. The phase accuracy of SAR images is affected by decorrelation effects between the individual surveys. We analyze quantitatively the influence of decorrelation on the phase statistics of SAR interferograms. In particular, phase aberrations as they occur in typical SAR processors are studied in detail. The dependence of the resulting phase bias and variance on processor parameters is presented in several diagrams. -
D. Massonnet,
F. Adragna,
and M. Rossi.
CNES general-purpose SAR correlator.
Geoscience and Remote Sensing, IEEE Transactions on,
32(3):636-643,
1994.
Keyword(s): SAR Processing,
Presumming,
geophysical techniques,
geophysics computing,
image processing,
remote sensing,
remote sensing by radar,
synthetic aperture radar,
CNES general-purpose SAR correlator,
constant phase reference,
contrast seeker,
data presumming,
fast Fourier transform,
frequency azimuth frequency domain,
geophysical measurement technique,
interferometry,
land surface,
migration compensation,
multilooking,
polynomial law generator,
quick look,
radar remote sensing,
radiometric equalization map,
signal processing,
software,
standard single look complex product,
synthetic aperture radar,
terrain mapping.
Abstract: CNES has designed a new SAR correlator to process both airborne -
Alberto Moreira and Yonghong Huang.
Airborne SAR Processing of Highly Squinted Data Using a Chirp Scaling Approach with Integrated Motion Compensation.
IEEE Transactions on Geoscience and Remote Sensing,
32(5):1029-1040,
Sept. 1994.
Keyword(s): SAR Processing,
Chirp Scaling Algorithm,
Extended Chirp Scaling Algorithm,
Motion Compensation,
Motion Estimation,
Squinted SAR,
Cubic Phase Term,
Airborne SAR,
Automatic Azimuth Coregistration,
Azimuth Scaling,
Squinted SAR,
Interferometry,
Phase-Preserving Processing,
Range Scaling Formulation,
Stripmap SAR,
Subaperture Processing,
Terrain Mapping.
Abstract: Proposes a new approach for high-resolution airborne SAR data processing, which uses a modified chirp scaling algorithm to accommodate the correction of motion errors, as well as the variations of the Doppler centroid in range and azimuth. By introducing a cubic phase term in the chirp scaling phase, data acquired with a squint angle up to 30? can be processed with no degradation of the impulse response function. The proposed approach is computationally very efficient, since it accommodates the variations of Doppler centroid without using block processing. Furthermore, a motion error extraction algorithm can be incorporated into the proposed approach by means of subaperture processing in azimuth. The new approach, denoted as extended chirp scaling, is considered to be a generalized algorithm suitable for the high-resolution processing of most airborne SAR systems. -
R. Keith Raney,
Hartmut Runge,
Richard Bamler,
Ian G. Cumming,
and Frank Wong.
Precision SAR Processing Using Chirp Scaling.
IEEE Transactions on Geoscience and Remote Sensing,
32(4):786-799,
July 1994.
Keyword(s): SAR Processing,
Chirp Scaling Algorithm,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Phase Preserving,
Range-Doppler Algorithm,
Comparison of Algorithms.
Abstract: A space-variant interpolation is required to compensate for the migration of signal energy through range resolution cells when processing synthetic aperture radar (SAR) data, using either the classical range/Doppler (R/D) algorithm or related frequency domain techniques. In general, interpolation requires significant computation time, and leads to loss of image quality, especially in the complex image. The new chirp scaling algorithm avoids interpolation, yet performs range cell migration correction accurately. The algorithm requires only complex multiplies and Fourier transforms to implement, is inherently phase preserving, and is suitable for wide-swath, large-beamwidth, and large-squint applications. This paper describes the chirp scaling algorithm, summarizes simulation results, presents imagery processed with the algorithm, and reviews quantitative measures of its performance. Based on quantitative comparison, the chirp scaling algorithm provides image quality equal to or better than the precision range/Doppler processor. Over the range of parameters tested, image quality results approach the theoretical limit, as defined by the system bandwidth. -
Andrew Reilly,
Gordon Frazer,
and Boualem Boashash.
Analytic Signal Generation-Tips and Traps.
Signal Processing, IEEE Transactions on [see also Acoustics, Speech, and Signal Processing, IEEE Transactions on],
42(11):3241-3245,
1994.
Keyword(s): Analytic Signal,
Hilbert Transform,
filtering theory,
frequency estimation,
parameter estimation,
signal processing,
signal synthesis,
time-frequency analysis,
Hilbert transform filters,
analytic signal generation,
discrete analytic signal,
discrete real-valued signal,
instantaneous-frequency estimation,
modem designs,
negative frequencies,
positive frequencies,
quadrature filters,
time-frequency signal analysis.
Abstract: In this correspondence we discuss methods to produce the discreteanalytic signal from a discrete real-valued signal. Such an analyticsignal is complex and contains only positive frequencies. Its projectiononto the real axis is the same as the original signal. Our use stemsfrom instantaneous-frequency estimation and time-frequency signalanalysis problems. For these problems the negative frequency componentof real signals causes unwanted interference. The task of designing afilter to produce an approximation to the ideal analytic signal is notas simple as its formulation might suggest. Our result is that thedirect methods of zeroing the negative frequencies, or using Hilberttransform filters, have undesirable defects. We present an alternative which is similar to the quadrature filters used in modemdesigns -
D.E. Wahl,
P.H. Eichel,
D.C. Ghiglia,
and C.V. Jakowatz.
Phase gradient autofocus-a robust tool for high resolution SAR phase correction.
IEEE Transactions on Aerospace and Electronic Systems,
30(3):827-835,
July 1994.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus.
Abstract: The phase gradient autofocus (PGA) technique for phase error correction of spotlight mde synthetic aperture radar (SAR) imagery is examined carefully in the context of four fundamental signal processing steps that constitute the algorithm We demnstrate that excellent results over a wide variety of scene content, and phase error function structure are obtained if and only if all of these steps are included in the processing. Finally, we show that the computational demands of the full PGA algorithm do not represent a large fraction of the total image formation problem, when mid to large size images are involved. -
Charles V. Jakowatz and Daniel E. Wahl.
Eigenvector method for maximum-likelihood estimation of phase errors in synthetic-aperture-radar imagery.
J. Opt. Soc. Am. A,
10(12):2539-2546,
1993.
Keyword(s): SAR Processing,
Autofocus,
Motion Compensation,
MoComp,
Residual Motion Errors,
Airborne SAR,
Phase Gradient Autofocus,
PGA,
Eigenvector Method,
Maximum Likelihood Estimation.
[bibtex-key = JakowatzJrWahl1993:Autofocus]
-
M. D. Macleod.
Fast Interpolation by FFT with Greatly Increased Accuracy.
Electronics Letters,
29(13):1200-1201,
June 1993.
Keyword(s): Interpolation,
Interpolation by FFT,
Fast Fourier Transforms,
FFT,
Nyquist limit,
RMS error,
Sampling Rate Conversion,
Upsampling,
Error Analysis,
Block Edges.
Abstract: When the FFT (or DCT or DST) is used for fast interpolation, errors arise due to the assumed periodicity in the data, and the resulting implied discontinuities of the function and its derivatives at the block edges. By adding simple functions before interpolation and subtracting them again afterwards, these interpolation errors can be removed. -
S.N. Madsen,
H.A. Zebker,
and J. Martin.
Topographic mapping using radar interferometry: processing techniques.
IEEE Transactions on Geoscience and Remote Sensing,
31(1):246-256,
January 1993.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
InSAR,
Interferometry,
Interferometric SAR,
Airborne SAR,
cartography,
geophysical techniques,
remote sensing by radar,
topography (Earth),
NASA,
JPL,
TOPSAR,
SAR,
height maps,
land surface,
mapping,
measurement,
motion compensation,
phase ambiguity,
processing algorithm,
radar interferometry,
technique,
terrain,
three-dimensional target location algorithm,
topographic radar mapper,
topography.
Abstract: A new processing algorithm for the NASA JPL TOPSAR topographic radar mapper is described. It incorporates extensive motion compensation features as well as accurate three-dimensional target location algorithm. The processor applies an algorithm to resolving the absolute phase ambiguity. This allows rectified height maps to be generated without any use of ground reference points. The processor was tested using data acquired with extreme aircraft motion so that performance could be evaluated under adverse conditions. The topographic maps generated by the radar were compared to digital elevation models (DEMs) derived using conventional optical stereo techniques. In one region, the RMS elevation deviations measured were less than the specified DEM accuracy, and, in the region covered by the more accurate DEM, errors varied from 2.2 m RMS in relatively flat terrain up to 5.0 m in mountainous area. The RMS difference between radar and DEM elevation over the 6.5-km by 22-km area covered by the more accurate DEM was 3.6 m -
Andrew S. Milman.
SAR Imaging by Omega-K Migration.
International Journal of Remote Sensing,
14(10):1965-1979,
1993.
Keyword(s): SAR Processing,
Wavenumber Domain Algorithm,
omega-k,
Range Migration Algorithm,
Stolt Mapping,
Stationary Phase Method.
Abstract: A new method of processing synthetic aperture radar (SAR) data was originally developed by a group of geophysicists, who use seismic migration to generate seismic images of the Earth. Called here omega-k migration, it has several advantages over more traditional methods of forming SAR images; they all arise because this method provides a mathematically exact solution to the imaging problem, in that the emitted waves are not being treated as plane waves. This paper discusses how migration processing can be applied to chirped radars; how it applies to spotlight data; and how to correct for non-uniform motions of the SAR platform. -
Harish Subbaram and Ken Abend.
Interference suppression via orthogonal projections: a performance analysis.
Antennas and Propagation, IEEE Transactions on,
41(9):1187-1194,
1993.
Keyword(s): SAR Processsing,
RFI Suppression,
orthogonal projections,
subspace separation,
principle component analysis,
antenna phased arrays,
antenna radiation patterns,
array signal processing,
interference suppression,
jamming,
adaptive jammer suppression,
additive noise,
average residual interference,
computer simulations,
interference suppression,
jammer plus noise power,
jammer snapshots,
mainbeam,
performance analysis,
performance parameters,
performance predictions,
phased array antennas,
sample matrix inversion algorithm,
sidelobe levels,
vector spaces,
weight vector.
Abstract: Several recent studies indicate the promise of subspace separation principles when applied to adaptive jammer suppression in phased arrayantennas. This paper theoretically analyzes the performance of a subspace separation technique based on orthogonal projections (OP) foradaptively suppressing interference in phased arrays; the theoretical performance predictions are validated using computer simulations. Thisanalysis holds for the case when it is possible to differentiate between the vector spaces spanned by jammers and additive noise. The performance parameters used are (a) the average residual interference (jammer plusnoise) power at the output of the adapted array as a function of the number of jammer snapshots used for calculating the weight vector, and (b) the similarity of the adapted array pattern to the design pattern away from the jammer locations. The performance of the OP-based subspace separation technique is compared with the sample matrix inversion (SMI) algorithm. It is shown that the weight vector calculated using OP converges more quickly to the optimal solution (infinite number of interference snapshots) than the SMI weight vector. Further, in contrast to the SMI adapted pattern, which exhibits large sidelobe levels away from the jammer locations, the OP adapted pattern closely follows the design pattern both in the main beam and in the sidelobe region away from the jammer locations. -
Richard Bamler.
A Comparison of Range-Doppler and Wavenumber Domain SAR Focusing Algorithms.
IEEE Transactions on Geoscience and Remote Sensing,
30(4):706-713,
July 1992.
Keyword(s): SAR Processing,
Range-Doppler Algorithm,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Secondary Range Compression,
Comparison of Algorithms.
Abstract: Focusing of SAR data requires a space-variant two-dimensional correlation. Different algorithms are compared with each other in terms of their focusing quality and their ability to handle the space-variance of the correlation kernel: the range-Doppler approach with and without secondary range compression, modified range-Doppler algorithms, and four versions of the wavenumber domain processor. The phase aberrations of the different algorithms are given in analytic form. Numerical examples are presented for Seasat and ERS-1. A novel systems theoretical derivation of the wavenumber domain algorithm is presented. -
C. Y. Chang and John C. Curlander.
Application of the Multiple PRF Technique to Resolve Doppler Centroid Estimation Ambiguity for Spaceborne SAR.
IEEE Transactions on Geoscience and Remote Sensing,
30(5):941-949,
Sept 1992.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Multiple PRF Technique,
Range Cross-Correlation Technique,
Clutterlock,
SIR-C.
Abstract: Estimation of the Doppler centroid ambiguity is a necessary element of the signal processing for synthetic aperture radar (SAR) systems with large antenna pointing errors. Without proper resolution of the Doppler centroid estimation (DCE) ambiguity, the image quality will be degraded in the system impulse response function and the geometric fidelity. Two techniques for resolution of DCE ambiguity for the spaceborne SAR are presented in this paper. They include a brief review of the range cross-correlation technique and presentation of a new technique using multiple pulse repetition frequencies (PRFs). We formulate an algorithm employing simple integer arithmetic for radar systems, such as moving target indicator radar (MTIR) systems, where the PRFs contain a large common divisor. For SAR systems, where other performance factors control selection of the PRFs, an algorithm is devised to resolve the ambiguity that uses PRFs of arbitrary numerical values. The performance of this multiple PRF technique is analyzed based on a statistical error model. An example is presented that demonstrates for the Shuttle Imaging Radar-C (SIR-C) C-band SAR, the probability of correct ambiguity resolution is higher than 95 percent for antenna attitude errors as large as 3?. -
C. Y. Chang,
M. Jin,
and John C. Curlander.
SAR Processing Based on the Exact Two-Dimensional Transfer Function.
IGARSS '92, International Geoscience and Remote Sensing Symposium,
pp 355-359,
May 1992.
Keyword(s): SAR Processing,
Azimuth Processing,
Range-Doppler Algorithm,
Range Migration Algorithm,
Wavenumber Domain Algorithm,
omega-k,
Point Target Transfer Funtion,
Two-Dimensional Fourier Transform,
Doppler Centroid,
Doppler Rate Estimation,
Autofocus.
Abstract: The two-dimensional transfer funtions of several synthetic aperture radar (SAR) focussing algorithms are derived considering the spaceborne SAR environments. The formulation includes the factors of the earth rotation and the antenna squint angles. The resultant functions are explicitly expressed in terms of Doppler centroid frequency and Doppler frequency rate, which can be conveniently and accurately estimated from the SAR data. Point target simulation results show that the algorithm based on the two-dimensional Fourier transformation out-performs the one-dimensional one for processing data acquired from high squint angles. The two-dimensional Fourier transformation approach appears to be a viable and simple solution for the processor design of future spceborne SAR systems. -
Jorgen Dall.
A Fast Autofocus Algorithm for Synthetic Aperture Radar Processing.
IEEE International Conference on Acoustics, Speech, and Signal Processing ICASSP,
3:5-8,
September 1992.
Keyword(s): SAR Processing,
Doppler Rate Estimation,
Autofocus,
Airborne SAR.
Abstract: High-resolution synthetic aperture radar (SAR) imaging requires the motion of the radar platform to be known very accurately. Otherwise, phase errors are induced in the processing of the raw SAR data, and bad focusing results. In particular, a constant error in the measured along-track velocity or the cross-track acceleration leads to a phase error that varies quadratically over the synthetic aperture. The process of estimating this quadratic phase error directly from the radar data is termed autofocus. A novel autofocus algorithm with a computational complexity which is at least an order of magnitude lower than that of other algorithms providing comparable accuracies is presented. The algorithm has been tested on data from the Danish Airborne SAR, and the performance is compared with that of the traditional map drift algorithm. -
Mita D. Desai and W. Kenneth Jenkins.
Convolution Backprojection Image Reconstruction for Spotlight Mode Synthetic Aperture Radar.
IEEE Transactions on Image Processing,
1(4):505 - 517,
October 1992.
Keyword(s): SAR Processing,
Spotlight SAR,
Backprojection,
Convolution Backprojection.
Abstract: Synthetic aperture radar (SAR) image reconstruction falls into the class of inverse (deconvolution) problems. A spotlight mode SAR system obtains line integrals (projections) of the ground reflectivity at various look angles as the radar platform progresses along the flight trajectory. The image of the ground area is then reconstructed from this set of projections. Conventionally, the SAR image has been produced by a direct Fourier reconstruction algorithm referred to here as the 2-D inverse FFT method. This method has two major problems: 1) due to the batch processing nature of the FFT, all returns must be recorded before the image processing can begin, and 2) a polar-to-cartesian interpolation, which is computationally intensive and error prone due to interpolation inaccuracies, is necessary before a 2-D inverse FFT can be performed. In this paper, a method based on a convolution backprojection (CBP) algorithm is presented. CBP is a widely used technique in computer-aided tomography (CAT). The CBP algorithm has been modified and applied to image reconstruction from SAR data. A quantitative evaluation using computer simulation of the CBP algorithm for spotlight mode SAR is presented. Its performance is then compared with the 2-D inverse FFT method with respect to the multiplicative noise ratio (MNR). Conclusions are supported by a reconstruction example on real SAR data collected by the Lincoln Laboratory's high resolution (0.3 m) radar. -
M. C. Dobson,
F. T. Ulaby,
T. LeToan,
A. Beaudoin,
E. S. Kasischke,
and N. Christensen.
Dependence of radar backscatter on coniferous forest biomass.
IEEE_J_GRS,
30(2):412-415,
March 1992.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Forest,
Forest parameters,
biomass,
C-band,
Duke,
France,
L-band,
Landes,
North Carolina,
P-band,
SAR data,
United States,
age,
coniferous forest biomass,
maritime pines,
plantations,
radar backscatter,
remote sensing,
backscatter,
ecology,
forestry,
remote sensing by radar;.
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 -
Giorgio Franceschetti,
Maurizio Migliaccio,
Daniele Riccio,
and Gilda Schirinzi.
SARAS: A Synthetic Aperture Radar (SAR) Raw Signal Simulator.
IEEE Transactions on Geoscience and Remote Sensing,
30(1):110-123,
January 1992.
Keyword(s): SAR Processing,
Simulation,
SAR Simulator,
Raw Data Simulator.
Abstract: A SAR simulator of an extended three-dimensional scene is presented. It is based on a facet model for the scene, asymptotic evaluation of SAR unit response, and a two-dimensional fast Fourier transform code for the data processing. Prescribed statistics of the model account for a realistic speckle of the image. The simulator is implemented in Synthetic Aperture Radar Advance Simulators (SARAS), whose performance is described and illustrated by a number of examples. -
Claudio Prati and Fabio Rocca.
Focusing SAR Data With Time-Varying Doppler Centroid.
IEEE Transactions on Geoscience and Remote Sensing,
30(3):550-559,
May 1992.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Clutterlock.
Abstract: SAR data spatially sampled at the Nyquist limit can be correctly processed if the Doppler centroid is precisely known. Whenever the Doppler centroid shows rapid variations either with range or azimuth, more care is required in order to take advantage of the computational efficiency of frequency domain techniques. In this paper it is shown that such focusing techniques can still be exploited, provided that SAR raw data are previously modified and a space-varying nondimensional filter is applied to the focused image. The computational cost increases, but it is still smaller than time-space domain processing. Results obtained with simulated SIR-C/X-SAR data and SPOTlight geometries are presented. -
R. Keith Raney.
An exact wide field digital imaging algorithm.
International Journal of Remote Sensing,
13:991-998,
March 1992.
Keyword(s): SAR Processing,
Chirp Scaling,
Extended Chirp Scaling,
ECS.
Abstract: A new imaging algorithm is presented for Synthetic Aperture Radar (SAR) that is exact in the sense that it is capable of producing a complex image with excellent geometrical, radiometrical and phase fidelity. No interpolations or significant approximations are required, yet the method accomplishes range curvature correction over the complete range swath. The key to the approach is a quadratic phase perturbation of the range linearly frequency modulated signals while in the range signal, azimuth frequency transform (Doppler) domain. Range curvature correction is completed by a phase multiply in the two-dimensional frequency domain. Other operations required are relatively conventional. The method is generalizable to imaging geometries encountered in squint and spotlight SAR, inverse SAR, seismics, sonar, and tomography. -
Mehrdad Soumekh.
A System Model and Inversion for Synthetic Aperture Radar Imaging.
IEEE Transactions on Image Processing,
1(1):64-76,
January 1992.
Keyword(s): SAR Processing,
Wavenumber Domain Algorithm,
omega-k,
Range Migration Algorithm.
Abstract: A system model and its corresponding inversion for synthetic aperture radar (SAR) imaging are presented. The system model incorporates the spherical nature of a radar's radiation pattern at far field. The inverse method based on this model performs a spatial Fourier transform (Doppler processing) on the recorded signals with respect to the available coordinates of a translational radar (SAR) or target (inverse SAR). It is shown that the transformed data provide samples of the spatial Fourier transform of the target's reflectivity function. The inverse method can be modified to incorporate deviations of the radar's motion from its prescribed straight line path. The effects of finite aperture on resolution, reconstruction, and sampling constraints for the imaging problem are discussed. -
Richard Bamler.
Doppler Frequency Estimation and the Cramer-Rao Bound.
IEEE Transactions on Geoscience and Remote Sensing,
29(3):385-390,
May 1991.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Cramer-Rao Bound,
Correlation-Based Estimator,
Maximum-Likelihood Estimator,
Accuracy Comparison,
Clutterlock.
Abstract: This paper addresses the problem of Doppler frequency estimation in the presence of speckle and receiver noise. An ultimate accuracy bound for Doppler frequency estimation is derived from the Cramer-Rao inequality. It is shown that estimates based on the correlation of the signal power spectra with an arbitrary weighting function are approximately Gaussian-distributed. Their variance is derived in terms of the weighting function. It is shown that a special case of a correlation-based estimator is a maximum-likelihood estimator that reaches the Cramer-Rao bound. These general results are applied to the problem of Doppler centroid estimation from SAR data. Different estimators known from the literature are investigated with respect to their accuracy. Numerical examples are presented and compared with experimental results. -
Richard Bamler and Hartmut Runge.
PRF-Ambiguity Resolving by Wavelength Diversity.
IEEE Transactions on Geoscience and Remote Sensing,
29(6):997-1003,
November 1991.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Doppler Ambiguity Resolver,
DAR,
Wavelength Diversity,
Clutterlock.
Abstract: For high-precision synthetic aperture radar (SAR) processing, the determination of the Doppler centroid is indispensable. The Doppler frequency estimated from azimuth spectra, however, suffers from the fact that the data are sampled with the pulse repetition frequency (PRF) and an ambiguity about the correct PRF band remains. A new algorithm to resolve this ambiguity is proposed. It uses the fact that the Doppler centroid depends linearly on the transmitted radar frequency for a given antenna squint angle. This dependence is not subject to PRF ambiguities. It can be measured by Fourier transforming the SAR data in the range direction and estimating the Doppler centroid at each range frequency. The achievable accuracy is derived theoretically and verified with Seasat data of different scene content. The algorithm works best with low contrast scenes, where the conventional look correlation technique fails. It needs no iterative processing of the SAR data and causes only low computational load. -
Ciro Cafforio,
Claudio Prati,
and Fabio Rocca.
SAR Data Focusing Using Seismic Migration Techniques.
IEEE Transactions on Aerospace and Electronic Systems,
27(2):194-207,
March 1991.
Keyword(s): SAR Processing,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Stationary Phase Method.
Abstract: The focusing of synthetic-aperture-radar (SAR) data using migration techniques quite similar to those used in geophysics is treated. The algorithm presented works in the omega-kx domain. Because time delays can be easily accommodated with phase shifts that increase linearly with omega, range migration poses no problem. The algorithm is described in plane geometry first, where range migration and phase history can be exactly matched. The effects of the sphericity of the Earth, of the Earth's rotation, and of the satellite trajectory curvature are taken into account, showing that the theoretically achievable spatial resolution is well within the requirements of present day and near future SAR missions. Terrestrial swaths as wide as 100 km can be focused simultaneously with no serious degradation. The algorithm has been tested with synthetic data, with Seasat-A data, and with airplane data (NASA-AIR). The experimental results fully support the theoretical analysis. -
Claudio Prati,
Fabio Rocca,
Yuval Kost,
and Elvio Damonti.
Blind Deconvolution for Doppler Centroid Estimation in High Frequency SAR.
IEEE Transactions on Geoscience and Remote Sensing,
29(6):934-941,
November 1991.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Doppler Ambiguity Resolver,
DAR,
Clutterlock.
Abstract: For high quality SAR processing, the Doppler centroid frequency is needed. However, SAR data are sampled along the azimuth direction at the Pulse Repetition Frequency (PRF); the estimation of the Doppler centroid frequency by means of spectral analysis techniques may produce ambiguous results due to aliases. The mathematical expression of the residual error that occurs when SAR data are focused with an incorrect alias of the PRF is thus derived. Then, a blind deconvolution technique is used to estimate the actual PRF replica from the focused image. Squinted X-band data, corresponding to those that will be generated by the SIR-C mission, have benn generated from the JPL-AirSAR L and C band data by means of an inversion of the focusing process. Even if the real data may show differences with respect to the simulated data, the blind deconvolution method appears to be more precise and robust than the other conventional techniques tested. -
Lars M. H. Ulander.
Accuracy of Using Point Targets for SAR Calibration.
IEEE Transactions on Aerospace and Electronic Systems,
27(1):139-148,
January 1991.
ISSN: 0018-9251.
Keyword(s): SAR Processing,
Radiometric Calibration,
calibration,
measurement errors,
radar,
radiometry,
remote sensing by radar,
RMS errors,
SAR calibration,
equivalent rectangle system resolution,
impulse response,
integral method,
nonlinear phase errors,
reference point targets,
synthetic aperture radar,
system focus.
Abstract: The peak and integral methods for radiometric calibration of a synthetic aperture radar (SAR) using reference point targets are analyzed. Both calibration methods are shown to be unbiased, but the peak method requires knowledge of the equivalent rectangle system resolution which is sensitive to system focus. Exact expressions for the RMS errors of both methods are derived. It is shown that the RMS error resulting from the peak method is always smaller than or equal to that from the integral method for a well-focused system. However, for robust radiometric calibration of SAR, or when nonlinear phase errors are present, the integral method is recommended, because it does not require detailed knowledge of the impulse response and the resulting RMS error is not dependent on system focus. -
Fuk K. Li and R. M. Goldstein.
Studies of Multibaseline Spaceborne Interferometric Synthetic Aperture Radars.
IEEE Transactions on Geoscience and Remote Sensing,
28(1):88-97,
January 1990.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
SAR Interferometry,
Interferometry,
InSAR,
Multi-Baseline SAR,
SAR Tomography,
geophysical techniques,
radar applications,
radar measurement,
radiowave interferometry,
remote sensing,
topography (Earth)INSAR design,
Seasat,
baseline separations,
geophysical technique,
multibaseline spaceborne interferometric synthetic aperture radars,
performance,
phase measurement error model,
remote sensing,
signal-to-noise ratios,
topography measurement capability.
Abstract: The authors have utilized a set of Seasat synthetic aperture radar (SAR) data that were obtained in nearly repeat ground-track orbits to demonstrate the performance of spaceborne interferometric SAR (INSAR) systems. An assessment of the topography measurement capability is presented. A phase measurement error model is described and compared with the data obtained at various baseline separations and signal-to-noise ratios. Finally, the implications of these results on future spaceborne INSAR design are discussed -
João Moreira.
A New Method Of Aircraft Motion Error Extraction From Radar Raw Data For Real Time Motion Compensation.
IEEE Transactions on Geoscience and Remote Sensing,
28(4):620-626,
July 1990.
ISSN: 0196-2892.
Keyword(s): SAR Processing,
Autofocus,
Motion Compensation,
MoComp,
Residual Motion Errors,
Airborne SAR,
ESAR.
Abstract: Presented is a new solution for real-time motion compensation. The main idea is to extract all the necessary motions of the aircraft from the radar backscatter signal using a new radar configuration and new methods for evaluating the azimuth spectra of the radar signal. Hence an inertial navigation system becomes unnecessary for many applications. The motion compensation parameters for realtime motion error correction are the range delay, the range dependent phaseshift, and the pulse repetition frequency. The motions of the aircraft to be extracted are the displacement in line-of-sight (LOS) direction, the aircraft\u2019s yaw and drift angle, and the forward velocity. Results show that a three-look image with an azimuth resolution of 3 m in L-band using a small aircraft is achievable, and the implementation of this method in real time using an array processor is feasible. -
Claudio Prati,
Fabio Rocca,
Andrea Monti-Guarnieri,
and Elvio Damonti.
Seismic Migration For Sar Focusing: Interferometrical Applications.
IEEE Transactions on Geoscience and Remote Sensing,
28(4):627-640,
July 1990.
Keyword(s): SAR Processing,
Wavenumber Domain Algorithm,
omega-k,
Range Migration Algorithm,
Interferometry.
Abstract: Conventional techniques for Synthetic Aperture Radar (SAR) image focusing use the matched filter concept and convolve the data with a reference phase signal which changes with range. The resulting algorithm is space-variant and its frequency-domain implementation is cumbersome. SAR data, however, can be focused using migration techniques identical to those used in seismic signal processing for oil prospecting. The implications of the higher precision achieved with migration as regards the phases of the synthesized radar returns is discussed. Two interferometrical applications where the phases of the returns are essential for the recovery of interesting parameters of the observed scene are presented: the determination from a satellite of the altitude map of the terrain and the determination from an airplane of the attitude of the sensor. In both cases the precision achieved is satisfactory. -
Petre Stoica and A. Nehorai.
MUSIC, maximum likelihood, and Cramer-Rao bound: further results and comparisons.
IEEE Transactions on Acoustics, Speech and Signal Processing,
38(12):2140-2150,
December 1990.
ISSN: 0096-3518.
Keyword(s): SAR Processing,
MUSIC,
SAR Tomography,
parameter estimation,
signal detection,
signal processing,
statistical analysisCramer-Rao bound,
covariance matrix,
direction-of-arrival,
maximum likelihood estimator,
multiple signal characterization,
narrowband plane waves,
noisy measurements,
parameter estimation,
performance comparisons,
statistical performance,
superimposed signals,
uniform linear sensor arrays,
unweighted MUSIC estimator,
weighted MUSIC estimators.
Abstract: The problem of determining the direction-of-arrival of narrowband plane waves using sensor arrays and the related problem of estimating the parameters of superimposed signals from noisy measurements are studied. A number of results have been recently presented by the authors on the statistical performance of the multiple signal characterization (MUSIC) and the maximum likelihood (ML) estimators for the above problems. This work extends those results in several directions. First, it establishes that in the class of weighted MUSIC estimators, the unweighted MUSIC achieves the best performance (i.e. the minimum variance of estimation errors), in large samples. Next, it derives the covariance matrix of the ML estimator and presents detailed analytic studies of the statistical efficiency of MUSIC and ML estimators. These studies include performance comparisons of MUSIC and MLE with each other, as well as with the ultimate performance corresponding to the Cramer-Rao bound. Finally, some numerical examples are given which provide a more quantitative study of performance for the problem of finding two directions with uniform linear sensor arrays -
D. Blacknell,
A. Freeman,
S. Quegan,
I.A. Ward,
I.P. Finley,
C.J. Oliver,
R.G. White,
and J.W. Wood.
Geometric accuracy in airborne SAR images.
Aerospace and Electronic Systems, IEEE Transactions on,
25(2):241-258,
March 1989.
ISSN: 0018-9251.
Keyword(s): SAR Processing,
Airborne SAR,
Motion Compensation,
Motion Errors,
Residual Motion Errors,
aircraft instrumentation,
microwave imaging,
position measurement,
radar,
X-band,
airborne SAR images,
autofocus,
azimuth processing,
azimuthal positioning accuracy,
defocusing,
geometric accuracy,
microwave imaging,
range positioning accuracy,
synthetic aperture radar.
Abstract: Uncorrected across-track motions of a synthetic aperture radar (SAR) platform can cause both a severe loss of azimuthal positioning accuracy in, and defocusing of, the resultant SAR image. It is shown how the results of an autofocus procedure can be incorporated in the azimuth processing to produce a fully focused image that is geometrically accurate in azimuth. Range positioning accuracy is also discussed, leading to a comprehensive treatment of all aspects of geometric accuracy. The system considered is an X-band SAR -
P. H. Eichel,
D. C. Ghiglia,
and C. V. Jakowatz.
Speckle processing method for synthetic-aperture-radar phase correction.
Opt. Lett.,
14(1):1,
1989.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus,
PGA.
Abstract: Uncompensated phase errors present in synthetic-aperture-radar data can have a disastrous effect on reconstructed image quality. We present a new iterative algorithm that holds promise of being a robust estimator and corrector for arbitrary phase errors. Our algorithm is similar in many respects to speckle processing methods currently used in optical astronomy. We demonstrate its ability to focus scenes containing large amounts of phase error regardless of the phase-error structure or its source. The algorithm works extremely well in both high and low signal-to-clutter conditions without human intervention. -
P. H. Eichel and C. V. Jakowatz.
Phase-gradient algorithm as an optimal estimator of the phase derivative.
Opt. Lett.,
14(20):1101,
1989.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus,
PGA.
Abstract: The phase-gradient algorithm represents a powerful new signal-processing technique with applications to aperturesynthesis imaging. These include, for example, synthetic-aperture-radar phase correction and stellar-image reconstruction. The algorithm combines redundant information present in the data to arrive at an estimate of the phase derivative. We show that the estimator is in fact a linear, minimum-variance estimator of the phase derivative. -
Donald Fraser.
Interpolation by the FFT Revisited - an Experimental Investigation.
IEEE Transactions on Acoustics, Speech, and Signal Processing,
37(5):665-675,
May 1989.
Keyword(s): Interpolation,
Interpolation by FFT,
Fast Fourier Transforms,
FFT,
Nyquist limit,
RMS error,
Sampling Rate Conversion,
Upsampling,
Sinusoidal Test Signal.
Abstract: Interpolation by the FFT has become a practial proposition in many new areas, such as image resampling, with the recent emergence of extremly fast FFT and microcircuits. This paper desctibes a numerical investigation into the accuracy of interpolation by fast Fourier transform (FFT) using a sinusoidal test signal. The method is precisely defined, including a previously unnoticed detail which makes a significant difference to the accuracy of the result. The experiments show that, with no input windowing, the accuracy of interpolation is almost independent of sinusoidal wavelength very close to the Nyquist limit. The resulting RMS error is inversely proportional to input sequence length and is very low for sequence lengths likely to be encountered in practice. As wavelength passes through the Nyquist limit, there is a sudden increase in error, as is expected from sampling theory. If the sequence ends are windowed by short, cosine half-bells, accuracy is further improved at longer wavelengths. In comparison, small-kernel convolution methods, such as linear interpolation and cubic convolution, perform badly at wavelengths anywhere near the Nyquist limit -
Soren N. Madsen.
Estimating the Doppler Centroid of SAR Data.
IEEE Transactions on Aerospace and Electronic Systems,
25(2):134-140,
1989.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Clutterlock,
Sign Doppler Estimator,
SDE,
Correlation Doppler Estimator,
CDE,
delta E Estimator,
Satellite SAR,
SEASAT.
Abstract: After reviewing frequency-domain techniques for estimating the Doppler centroid of synthetic-aperture radar (SAR) data, the author describes a time-domain method and highlights its advantages. In particular, a nonlinear time-domain algorithm called the sign-Doppler estimator (SDE) is shown to have attractive properties. An evaluation based on an existing SEASAT processor is reported. The time-domain algorithms are shown to be extremely efficient with respect to requirements on calculations and memory, and hence they are well suited to real-time systems where the Doppler estimation is based on raw SAR data. For offline processors where the Doppler estimation is performed on processed data, which removes the problem of partial coverage of bright targets, the delta_E estimator and the CDE (correlation Doppler estimator) algorithm give similar performance. However, for nonhomogeneous scenes it is found that the nonlinear SDE algorithm, which estimates the Doppler-shift on the basis of data signs alone, gives superior performance. -
R.L. Mitchell.
Creating complex signal samples from a band-limited real signal.
Aerospace and Electronic Systems, IEEE Transactions on,
25(3):425-427,
1989.
Keyword(s): quadrature demodulation,
demodulation,
digital filters,
filtering and prediction theory,
radar theory,
signal processing,
FIR filter,
band-limited real signal,
filter,
finite-duration impulse response,
image band rejection,
radar theory,
signal processing.
Abstract: A very efficient method of creating complex signal samples from a band-limited real signal is presented. Because the method employs a simple mixer followed by one analog-to-digital (A/D) converter, plus a finite-duration impulse response (FIR) filter for image band rejection, there is no phase distortion in the resulting sampled signal. The method is more efficient than competing methods based on infinite-duration impulse response (IIR) filters. -
Petre Stoica,
Randolph L. Moses,
Benjamin Friedlander,
and Torsten Söderström.
Maximum likelihood estimation of the parameters of multiple sinusoids from noisy measurements.
Acoustics, Speech, and Signal Processing [see also IEEE Transactions on Signal Processing], IEEE Transactions on,
37(3):378-392,
1989.
ISSN: 0096-3518.
Keyword(s): RFI Suppression,
filtering and prediction theory,
spectral analysis,
Cramer-Rao bound covariance matrix,
initial estimates,
maximum-likelihood,
maximum-likelihood estimator,
MLE,
multiple sinusoids,
noisy measurements,
spectral analysis.
Abstract: The problem of estimating the frequencies, phases, and amplitudesof sinusoidal signals is considered. A simplified maximum-likelihoodGauss-Newton algorithm which provides asymptotically efficient estimatesof these parameters is proposed. Initial estimates for this algorithmare obtained by a variation of the overdetermined Yule-Walker method andperiodogram-based procedure. Use of the maximum-likelihood Gauss-Newtonalgorithm is not, however, limited to this particular initializationmethod. Some other possibilities to get suitable initial estimates arebriefly discussed. An analytical and numerical study of the shape of thelikelihood function associated with the sinusoids-in-noise processreveals its multimodal structure and clearly sets the importance of theinitialization procedure. Some numerical examples are presented toillustrate the performance of the proposed estimation procedure.Comparison to the performance corresponding to the Cramer-Rao lowerbound is also presented, using a simple expression for the asymptoticCramer-Rao bound covariance matrix derived in the paper -
P. Stoica and Arye Nehorai.
MUSIC, maximum likelihood, and Cramer-Rao bound.
IEEE Transactions on Acoustics, Speech and Signal Processing,
37(5):720-741,
May 1989.
ISSN: 0096-3518.
Keyword(s): SAR Processing,
MUSIC,
SAR Tomography,
radio direction-finding,
signal processing,
Cramer-Rao bound,
MUSIC estimator,
covariance matrix,
direction finding,
maximum likelihood method,
plane waves,
signal processing,
statistical efficiency,
uniform linear array.
Abstract: The performance of the MUSIC and ML methods is studied, and their statistical efficiency is analyzed. The Cramer-Rao bound (CRB) for the estimation problems is derived, and some useful properties of the CRB covariance matrix are established. The relationship between the MUSIC and ML estimators is investigated as well. A numerical study is reported of the statistical efficiency of the MUSIC estimator for the problem of finding the directions of two plane waves using a uniform linear array. An exact description of the results is included -
B.D. Carlson.
Covariance matrix estimation errors and diagonal loading in adaptive arrays.
IEEE Transactions on Aerospace and Electronic Systems,
24(4):397-401,
July 1988.
ISSN: 0018-9251.
Keyword(s): SAR Processing,
Beamforming,
array processing,
antenna phased arrays,
antenna theory,
digital simulation,
eigenvalues and eigenfunctions,
estimation theory,
matrix algebraadapted antenna patterns,
adaptive arrays,
covariance matrix sample size,
diagonal loading,
distorted mainbeams,
eigenvector decomposition,
estimation errors,
low-level interference,
nulling,
sample matrix inversion,
sidelobes.
Abstract: Simulations were used to investigate the effect of covariance matrix sample size on the system performance of adaptive arrays using the sample matrix inversion (SMI) algorithm. Inadequate estimation of the covariance matrix results in adapted antenna patterns with high sidelobes and distorted mainbeams. A technique to reduce these effects by modifying the covariance matrix estimate is described from the point of view of eigenvector decomposition. This diagonal loading technique reduces the system nulling capability against low-level interference, but parametric studies show that it is an effective approach in many situations -
Mehrdad Soumekh.
Band-Limited Interpolation from Unevenly Spaced Sampled Data.
IEEE Transactions on Acoustics, Speech, and Signal Processing,
36(1):110-122,
January 1988.
Keyword(s): Interpolation,
Band-Limited,
Reconstruction,
Unevenly Spaced Data.
Abstract: This paper adresses the problem of reconstructing a band-limited signal from a finite number of unevenly spaced sampled data. A Fourier analysis of the available unevenly spaced sampled data is presented. The result is utilized to develop an interpolation scheme from the available data. Conditions for accurate reconstruction are examined. Algorithms to implement the reconstruction scheme are discussed. The method's application in one-dimensional and two-dimensional reconstruction problems are shown. -
Alan di Cenzo.
A New Look at Nonseparable Synthetic Aperture Radar Processing.
IEEE Transactions on Aerospace and Electronic Systems,
24(3):218-223,
May 1988.
Keyword(s): SAR Processing,
Template Correlation,
2D Filter,
Nonseparable SAR Processing,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm.
Abstract: The author examines the nonseparable, template correlation approach to digital-strip-mode synthetic-aperture radar (SAR) phase history processing and concludes that it can now outperform the traditional separable approaches in the areas of speed, image quality, control simplicity, and flexibility. A working nonseparable frequency-domain SAR processor is described and evaluated. The image quality is seen to be superior to that resulting from the separable approaches. Based on the working intermediate hardware implementation, the author strongly suggests that future VHSIC and other advanced implementation will provide extremely fast (real time), high-quality, small, flexible SAR processors. -
Hans Hellsten and Lars E. Andersson.
An inverse method for the processing of synthetic aperture radar data.
Inverse Problems,
3(1):111-124,
1987.
Keyword(s): SAR Processing,
Backprojection,
Hankel Transform,
Fourier-Hankel Inversion,
Abel Transform.
Abstract: An inverse method for the processing of synthetic aperture radar signals is presented. The method is independent of the relative bandwidth of the radar signal and should thus work when, for instance, the frequency of the emitted radiation is of the same order as the bandwidth, i.e. in low frequency, high resolution applications. It is shown that the obtained relations reduce to the correlation integrals of conventional SAR image processing in the case that the relative bandwidth of the signal is small. Range attenuation and antenna illumination effects may be fully compensated for. -
Fabio Rocca.
Synthetic Aperture Radar: a New Application for Wave Equation Techniques.
Stanford Exploration Project SEP-56,
pp 167-189,
1987.
Keyword(s): SAR Processing,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Seismic Migration Techniques.
Abstract: The techniques of downward continuation and imaging invented for seismic waves can be applied to other types of waves. In this paper, we see how this application can be made in the case of electromagnetic surveys conducted with Synthetic Aperture Radar (SAR). The algorithms used closely follow those used for seismic waves. Differences are induced by alternate wavelengths, wave velocities, distances between sources and reflectors etc. In the case that we analyze in detail, a survey carried out using a satellite, difficulties arise from the fact that the orbit of the satellite cannot be approximated with a simple straight line if the spatial resolution of the survey is high. We determine appropriate techniques for the correction of the distortion induced by the latter and we delimit the resolution of the observed data, as seen from a satellite. Finally we show examples of the application of the technique of seismic migration to satellite data that were irradiated to earth during the short but productive life of SEASAT. -
Michael Y. Jin.
Optimal Doppler Centroid Estimation for SAR Data from a Quasi-Homogeneous Source.
IEEE Transactions on Geoscience and Remote Sensing,
24(6):1022-1025,
1986.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Clutterlock,
Satellite SAR.
Abstract: In synthetic aperture radar (SAR) signal processing, an accurate Doppler centroid is required for most applications involving target motion estimation and antenna pointing direction estimation. In some cases the Doppler centroid can be sufficiently determined using available information regarding the terrain topography, the relative motion between the sensor and the terrain, and the antenna pointing direction. But most often, a highly accurate Doppler centroid value has to be derived by analyzing the received SAR signal itself. This kind of signal processing is referred to as Doppler centroid estimation (DCE). This correspondence briefly describes two DCE algorithms, provides a performance summary for these algorithms, and presents the experimental results. These algorithms include a previously reported one and a newly developed one that is optimized for quasi-homogeneous sources. The performance enhancement achieved by the optimal DCE algorithm is clearly demonstrated by the experimental results. -
Ralph O. Schmidt.
Multiple emitter location and signal parameter estimation.
IEEE Transactions on Antennas and Propagation,
34(3):276-280,
March 1986.
ISSN: 0018-926X.
Keyword(s): MUSIC,
Multiple Signal Classification,
null Adaptive arrays,
DOA estimation,
Direction-of-arrival estimation,
Parameter estimation,
Signal processing antennas.
Abstract: Processing the signals received on an array of sensors for the location of the emitter is of great enough interest to have been treated under many special case assumptions. The general problem considers sensors with arbitrary locations and arbitrary directional characteristics (gain/phase/polarization) in a noise/interference environment of arbitrary covariance matrix. This report is concerned first with the multiple emitter aspect of this problem and second with the generality of solution. A description is given of the multiple signal classification (MUSIC) algorithm, which provides asymptotically unbiased estimates of 1) number of incident wavefronts present; 2) directions of arrival (DOA) (or emitter locations); 3) strengths and cross correlations among the incident waveforms; 4) noise/interference strength. Examples and comparisons with methods based on maximum likelihood (ML) and maximum entropy (ME), as well as conventional beamforming are included. An example of its use as a multiple frequency estimator operating on time series is included. -
Alan di Cenzo.
A Comparison of Resolution for Spotlight Synthetic-Aperture Radar and Computer-Aided Tomography.
Proceedings of the IEEE,
74:1165-1166,
August 1986.
Keyword(s): SAR Processing,
Tomography,
Resolution,
Comparison of Algorithms,
Spotlight SAR.
Abstract: It is shown that the difference between computer-aided tomographic (CAT) resolution and spotlight synthetic-aperture radar (SAR) resolution for narrow apertures is a consequence of the magnification in Fourier bandwidth induced by the SAR offset carrier frequency. Implications for CAT are discussed. -
B. C. Barber.
Theory of Digital Imaging from Orbital Synthetic-Aperture Radar.
International Journal of Remote Sensing,
6(7):1009-1057,
1985.
Keyword(s): SAR Processing,
Range Migration,
Range Compression,
Range Polynomial,
Azimuth Processing,
Upsampling,
2D Filter,
Time Domain Correlation,
Satellite SAR.
Abstract: Digital synthetic-aperture radar (SAR) imaging techniques have previously only been reported in the literature in a fragmentary manner. This article presents a comprehensive review of the theory of digital SAR imaging from Earth-orbiting satellites. The digital SAR imaging process is explained, including a discussion of various aspects which are specific to satellite-borne SAR. A number of relevant digital-processing techniques are reviewed and it is shown how these techniques may be applied to the processing of digital SAR data. The range migration problem is discussed and various techniques for overcoming it are presented. The paper should be useful not only to the designer of SAR processors, but also to the user of digital SAR data and images. -
John C. Curlander,
Benjamin Holt,
and Kevin J. Hussey.
Determination of sea ice motion using digital SAR imagery.
Oceanic Engineering, IEEE Journal of,
10(4):358-367,
1985.
Keyword(s): SAR Processing,
Image analysis,
motion,
Image motion analysis,
Sea ice,
Sea surface electromagnetic scattering,
Synthetic-aperture radar.
Abstract: Using digital SEASAT synthetic aperture radar (SAR) imagery, high-precision densely sampled maps of ice motion have been derived by tracking ice features to determine the small-scale spatial variability of ice deformation. The digital SAR imagery was processed to remove geometric distortions and located on the Earth to an accuracy of about 100 m utilizing an algorithm based on the spacecraft orbital data and the characteristics of the SAR data collection system, independent of attitude information or ground reference points. Radiometric enhancement of the imagery using a variable linear stretch algorithm was performed to remove a system-related gradient and improve the identification of sea ice features. Using ice features common to an overlapping pair of images, vector plots of ice motion were then produced. Examples of ice motion are shown in the marginal ice zone and in the central ice pack where mean displacements of 15.3 km/day and 5.0 km/day were measured, respectively. Considering errors in Earth location with those in feature identification an overall error of 150-200 m in displacement measurements was estimated. The ice motion vector plots indicate a high degree of spatial deformation, demonstrating the potential value of spaceborne SAR data for production of precision large-scale maps of ice displacement with a spatial resolution of ice deformation on scales much less than 100 km. -
Fuk-Kwok Li,
Daniel N. Held,
John C. Curlander,
and Chialin Wu.
Doppler Parameter Estimation for Spaceborne Synthetic-Aperture Radars.
IEEE Transactions on Geoscience and Remote Sensing,
23(1):47-56,
1985.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Doppler Ambiguity Resolver,
DAR,
Clutterlock,
Satellite SAR,
SEASAT,
Doppler Rate Estimation,
Autofocus.
Abstract: Problems in the determination of Doppler parameters for spaceborne synthetic-aperture radar (SAR) data processing are examined. The degradations in image quality due to errors in these parameters are summarized. We show that these parameters can be estimated using accurate spacecraft ancillary data. In cases where such data are not available, we propose two techniques to estimate these parameters using the coherent radar return. These techniques were tested with the Seasat SAR data and the test results demonstrate that the accuracies achieved exceed the system performance requirements. Possible applications of these techniques in other areas of SAR data utilization are briefly discussed. -
David C. Munson, Jr.,
James Dennis O'Brien,
and W. Kenneth Jenkins.
A tomographic formulation of spotslight-mode synthetic aperture radar.
Proceedings of the IEEE,
71(8):917-925,
August 1983.
ISSN: 0018-9219.
Keyword(s): SAR Processing,
Polar Format Algorithm,
Convolution Back-Projection,
Spotlight SAR,
Spotlight mode,
Tomographic formulation.
Abstract: Spotlight-mode synthetic aperture radar (spotlight-mode SAR) synthesizes high-resolution terrain maps using data gathered from multiple observation angles. This paper shows that spotlight-mode SAR can be interpreted as a tomographic reeonstrution problem and analyzed using the projection-slice theorem from computer-aided tomograpy (CAT). The signal recorded at each SAR transmission point is modeled as a portion of the Fourier transform of a central projection of the imaged ground area. Reconstruction of a SAR image may then be accomplished using algorithms from CAT. This model permits a simple understanding of SAR imaging, not based on Doppler shifts. Resolution, sampling rates, waveform curvature, the Doppler effect, and other issues are also discussed within the context of this interpretation of SAR. -
Chialin Wu,
K.Y. Liu,
and M. Jin.
Modeling and a Correlation Algorithm for Spaceborne SAR Signals.
IEEE_J_AES,
18(5):563-575,
September 1982.
ISSN: 0018-9251.
Keyword(s): SAR Processing,
Range-Doppler Algorithm,
RDA,
Spaceborne SAR.
Abstract: A mathematical model of a spaceborne synthetic aperture radar (SAR) response is presented. The associated SAR system performance, in terms of the resolution capability, is also discussed. The analysis of spaceborne SAR target response indicates that the SAR correlation problem is a two-dimensional one with a linear shift-variant response function. A new digital processing algorithm is proposed here in order to realize an economical digital SAR correlation system. The proposed algorithm treats the two-dimensional correlation by a combination of frequency domain fast correlation in the azimuth dimension and a time-domain convolver type of operation in the range dimension. Finally, digitally correlated SEASAT satellite SAR imagery is used in an exemplary sense to validate the SAR response model and the new digital processing technique developed. -
Jack L. Walker.
Range-Doppler Imaging of Rotating Objects.
IEEE Transactions on Aerospace and Electronic Systems,
AES-16(1):23-52,
January 1980.
ISSN: 0018-9251.
Keyword(s): SAR Processing,
Polar Format Algorithm,
PFA.
Abstract: During the integration time required to obtain fine Dopplerfrequency resolution in a range-Doppler imaging radar, a point on a rotating object may move through several range and Doppler resolution cells and produce a smeared image. This motion can be compensated by storing the appropriately processed return pulse, and the angular coordinates are determined by the angular coordinates of the radar antenna. The resulting stored data represents the three-dimensional Fourier transform of the object reflectivity density, and hence can be processed by an inverse Fourier transformation. Also included is an analysis of the three-dimensional radar/object geometry with separate source and receiver locations. The effects of various system aberrations are investigated and experimental results from a microwave test range which demonstrate the image improvement are presented. -
R. H. Stolt.
Migration by Fourier Transform.
Geophysics,
43(1):23-48,
February 1978.
Keyword(s): SAR Processing,
Migration,
Wavenumber Domain Algorithm,
omega-k,
Range Migration Algorithm,
Stolt Mapping.
Abstract: Wave equation migration is known to be simpler in principle when the horizontal coordinates are replaced by their Fourier conjugates. Two practical migration schemes utilization this concept are developed in this paper. One scheme extends the Claerbout finite difference method, greatly reducing dispersion problems usually associated with this method at higher dips and frequencies. The second scheme effects a Fourier transform in both space and time; by using the full scalar wave equation in the conjugate space, the method eliminates (up to the aliasing frequency) dispersion altogether. The second method in particular appears adaptable to three-dimensional migration and migration before stack. -
John C. Kirk.
Motion Compensation for Synthetic Aperture Radar.
IEEE Transactions on Aerospace and Electronic Systems,
AES-11(3):338-348,
May 1975.
ISSN: 0018-9251.
Keyword(s): SAR Processing,
Airborne SAR,
Motion Compensation,
MoComp,
Stripmap SAR,
Spotlight SAR,.
Abstract: A generalized motion compensation approach applicable to all SAR modes, i.e., strip mapping (side-looking or squint), spotlight (or telescope) mapping, and Doppler beam sharpened mapping (DBS), is described. The basic concept is the formation for unit vector ¿ and the slaving of the real illuminating antenna and the processed synthetic antenna to this unit vector. The amount of motion compensation which is required is developed in terms of transfer curves for the main motion reduction paths, i.e., translational, rotational (lever arm), and real antenna stabilization. The transfer curves are obtained by dividing the expected motion spectrum by the required sensitivity spectrum. The most critical motion reduction path for typical parameters is shown to be the translational path. The lever arm and real antenna stabilization paths are less critical, but must also be implemented. -
W. M. Brown,
G. G. Houser,
and R. G. Jenkins.
Synthetic aperture processing with limited storage and presumming.
IEEE Transactions on Aerospace and Electronic Systems,
9:166-176,
1973.
Keyword(s): SAR Processing,
Presumming,
Limited Storage.
Abstract: Presumming of data prior to correlation is considered as a means for achieving the desired performance in a side-looking radar with a minimum amount of digital storage. A presummer with optimal resolution is derived for this purpose, and the optimal apportionment of the available storage capacity between the presumming and correlation operations is determined. The optimal presumming coefficients are given for the condition that the illumination pattern of the antenna illuminates uniformly a Doppler bandwidth equal to the PRF of the radar. The obtainable optimum resolution is given as a function of total storage and of the number of transmitted pulses in the received Doppler history. Expressions are also given for responses with presumming for linearly frequency-modulated signals and their matched filters. -
Jack Capon.
High-resolution frequency-wavenumber spectrum analysis.
Proceedings of the IEEE,
57(8):1408-1418,
August 1969.
ISSN: 0018-9219.
Keyword(s): SAR Processing,
Capon,
Capon beamforming,
SAR Tomography,
Tomography,
super-resolution.
Abstract: The output of an array of sansors is considered to be a homogeneous random field. In this case there is a spectral representation for this field, similar to that for stationary random processes, which consists of a superposition of traveling waves. The frequency-wavenumber power spectral density provides the mean-square value for the amplitudes of these waves and is of considerable importance in the analysis of propagating waves by means of an array of sensors. The conventional method of frequency-wavenumber power spectral density estimation uses a fixed-wavenumber window and its resolution is determined essentially by the beam pattern of the array of sensors. A high-resolution method of estimation is introduced which employs a wavenumber window whose shape changes and is a function of the wavenumber at which an estimate is obtained. It is shown that the wavenumber resolution of this method is considerably better than that of the conventional method. Application of these results is given to seismic data obtained from the large aperture seismic array located in eastern Montana. In addition, the application of the high-resolution method to other areas, such as radar, sonar, and radio astronomy, is indicated. - Yunkai Deng, Yue Liu, Robert Wang, and Xiaoxue Jia. FMCW SAR raw signal simulator for extended scenes. In European Conference on Synthetic Aperture Radar, Nuremberg, Apr. 2012. [bibtex-key = DYWX:EUSAR12]
-
Yunhua Luo,
Hongjun Song,
Yang Gao,
Yunkai Deng,
and R. Wang.
Modified frequency scaling processing for FMCW SAR.
In IEEE International Geoscience and Remote Sensing Symposium,
pages 2129-2132,
July 2012.
ISSN: 2153-6996.
Keyword(s): Algorithm design and analysis,
Analytical models,
Approximation algorithms,
Azimuth,
Frequency domain analysis,
Signal processing algorithms,
Synthetic aperture radar,
CW radar,
FM radar,
synthetic aperture radar,
FMCW SAR data,
analytical slant model,
modified frequency scaling processing method,
FMCW,
Frequency scaling,
SAR;.
[bibtex-key = Yunhua:IGARSS12]
- Christophe Magnard, Thorsten Brehm, Helmut Essen, and Erich Meier. High Resolution MEMPHIS SAR Data Processing and Applications. In PIERS Proceedings, Kuala Lumpur, pages 328-332, Mar. 2012. [bibtex-key = CM:PIERS12]
-
D.M. Vavriv and O.O. Bezvesilniy.
Multi-look SAR processing: Novel benefits.
In Radar Symposium (IRS), 2012 13th International,
pages 382-386,
May 2012.
ISSN: 2155-5754.
Keyword(s): airborne radar,
radar imaging,
synthetic aperture radar,
Ku-band airborne SAR systems,
X-band airborne SAR system,
aircraft flight conditions,
geometric image distortions,
light-weight aircrafts,
multilook SAR processing,
radiometric image distortions,
speckle noise,
Aircraft,
Radar antennas,
Radiometry,
Real time systems,
Synthetic aperture radar,
Airborne radar,
multi-look processing,
radar applications,
radar imaging,
synthetic aperture radar.
[bibtex-key = 6233351]
-
V.-T. Vu,
T.K. Sjogren,
and M.I. Pettersson.
SAR imaging in ground plane using Fast Backprojection for mono- and bistatic cases.
In Radar Conference (RADAR), 2012 IEEE,
pages 0184-0189,
May 2012.
ISSN: 1097-5659.
Keyword(s): radar imaging,
synthetic aperture radar,
FBP,
SAR imaging,
SAR scene,
bistatic cases,
fast back-projection algorithm,
fast backprojection,
ground plane,
illuminated synthetic aperture radar,
monostatic cases,
simulated SAR data,
slant-range plane,
Apertures,
Image reconstruction,
Proposals,
Radar imaging,
Synthetic aperture radar,
Transmitters.
[bibtex-key = 6212134]
-
V. Zamparelli,
S. Perna,
and G. Fornaro.
An improved topography and aperture dependent motion compensation algorithm.
In IEEE International Geoscience and Remote Sensing Symposium,
pages 5805-5808,
July 2012.
ISSN: 2153-6996.
Keyword(s): Algorithm design and analysis,
Approximation algorithms,
Approximation methods,
Focusing,
Motion compensation,
Remote sensing,
Synthetic aperture radar,
airborne radar,
geophysical image processing,
motion compensation,
radar imaging,
synthetic aperture radar,
MOCO algorithms,
PTA algorithm,
SAR image,
airborne SAR focusing,
motion compensation,
motion error,
precise topography and aperture,
Airborne SAR focusing,
SAR,
SAR Motion Compensation;.
[bibtex-key = Zampa12:IGARSS]
- A. Haderer, P. Scherz, J. Schrattenecker, and A. Stelzer. Real-time implementation of an FMCW backprojection algorithm for 1D and 2D apertures. In European Radar Conference, pages 53-56, Oct. 2011. Keyword(s): Antenna measurements, Apertures, Image reconstruction, Interpolation, Radar imaging, Signal processing algorithms, CW radar, FM radar, field programmable gate arrays, image reconstruction, interpolation, radar imaging, synthetic aperture radar, 1D apertures, 2D apertures, FMCW backprojection algorithm, FPGA, SAR, field programmable gate array, frequency-modulated continuous-wave radar, image reconstruction algorithm, instantaneous measurement, nearest-neighbor interpolation method, real-time implementation, synthetic aperture radar systems;. [bibtex-key = Haderer:ERC11]
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D.M. Vavriv and O.O. Bezvesilniy.
Potential of multi-look SAR processing.
In Recent Advances in Space Technologies (RAST), 2011 5th International Conference on,
pages 365-369,
June 2011.
Keyword(s): airborne radar,
radar imaging,
stereo image processing,
synthetic aperture radar,
topography (Earth),
3D topography,
Ku-band airborne SAR,
built-in geometric correction algorithm,
conventional strip-map SAR,
high-quality multilook SAR images,
multilook SAR processing,
multilooks SAR images,
radar data,
radiometric correction approach,
unstable aircraft flight conditions,
Accuracy,
Antennas,
Doppler effect,
Radar imaging,
Radiometry,
Synthetic aperture radar,
Airborne radar,
multi-look processing,
radar applications,
radar imaging,
synthetic aperture radar.
[bibtex-key = 5966857]
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D.M. Vavriv,
O.O. Bezvesilniy,
R. V. Kozhyn,
V.V. Vynogradov,
V. A. Volkov,
and S. S. Sekretarov.
SAR systems for light-weight aircrafts.
In Microwaves, Radar and Remote Sensing Symposium (MRRS), 2011,
pages 15-19,
Aug. 2011.
Keyword(s): airborne radar,
aircraft,
radar imaging,
synthetic aperture radar,
SAR images,
airborne synthetic aperture radar,
light-weight aircrafts,
Aircraft,
Radar antennas,
Radar imaging,
Real time systems,
Signal processing algorithms,
Synthetic aperture radar,
airborne radar,
radar applications,
synthetic aperture radar.
[bibtex-key = 6053592]
- Li Yueli, Yan Shaoshi, Zhu Guofu, Li Jiangyang, and Zhou Zhimin. Ultra wide band synthetic aperture radar real time processing with a subaperture nonlinear chirp scaling algorithm. In International Asia-Pacific Conference on Synthetic Aperture Radar, pages 1-4, Sept. 2011. [bibtex-key = LYZLZ:APSAR11]
- O.O. Bezvesilniy, I.M. Gorovyi, S.V. Sosnytskiy, V.V. Vynogradov, and D.M. Vavriv. Improving SAR images: Built-in geometric and multi-look radiometric corrections. In Radar Conference (EuRAD), 2010 European, pages 256-259, 2010. Keyword(s): aircraft antennas, geometry, radar imaging, radiometry, synthetic aperture radar, SAR systems, antenna orientation, azimuth reference functions, built-in geometric corrections, light-weight aircraft, multilook radiometric corrections, range migration curves, time-domain multilook stripmap SAR processing algorithm, Aircraft, Antennas, Azimuth, Doppler effect, Radiometry, Synthetic aperture radar, Time domain analysis. [bibtex-key = 5614898]
-
LeRoy A. Gorham and Brian D. Rigling.
Dual format algorithm for monostatic SAR.
In Edmund G. Zelnio and Frederick D. Garber, editors,
,
volume 7699,
pages 769905,
2010.
SPIE.
Keyword(s): SAR Processing,
Dual Format Algorithm,
DFA,
Polar Format Algorithm,
PFA,
Spotlight SAR,
Spotlight-mode data.
[bibtex-key = gorhamRiglingDualFormatAlgorithm2010]
-
Charles V. Jakowatz,
Daniel E. Wahl,
and David A. Yocky.
A beamforming algorithm for bistatic SAR image formation.
In Edmund G. Zelnio and Frederick D. Garber, editors,
,
volume 7699,
pages 769902,
2010.
SPIE.
Keyword(s): SAR Processing,
Bistatic SAR,
Bistatic Spotlight-mode SAR,
Autofocus,
Autofocus in the TDBP Framework,
Back-projection,
Time-Domain Back-Projection,
TDBP,
Fast Back-projection,
Fast-Factorized Back-Projection,
FFBP,
Spotlight SAR,
Spotlight-mode data,
Beamforming.
[bibtex-key = jakowatzWahlYockyBeamformingBistatic2010]
- H. Essen, M. Bräutigam, R. Sommer, A. Wahlen, W. Johannes, J. Wilcke, M. Schlechtweg, and A. Tessmann. SUMATRA, a W-band SAR for UAV application. In International Radar Conference, pages 1-4, Oct. 2009. [bibtex-key = Suma:IRC09]
-
Hai-ping Hou,
Chang-wen Qu,
Han-bing Sun,
and Ru-gang Song.
Research on FMCW SAR signal characteristic and improved azimuth matched filtering algorithm.
In Asia-Pacific Conference on Synthetic Aperture Radar,
pages 290-293,
Oct. 2009.
Keyword(s): Azimuth,
Bandwidth,
Filtering algorithms,
Frequency conversion,
Interpolation,
Layout,
Matched filters,
Radar polarimetry,
Signal analysis,
Signal processing,
CW radar,
FM radar,
radar signal processing,
FMCW SAR signal characteristic,
frequency modulated continuous wave SAR,
improved azimuth matched filtering algorithm,
range Doppler algorithm,
scene range cell covering algorithm,
FMCW SAR,
RDA,
azimuth matched filtering,
signal characteristic analysis;.
[bibtex-key = HAI:APSAR09]
-
F. Hélière,
C.C. Lin,
F. Fois,
M. Davidson,
A. Thompson,
and P. Bensi.
BIOMASS: A P-band SAR Earth explorer core mission candidate.
In Proc. IEEE Radar Conf.,
pages 1-6,
May 2009.
ISSN: 1097-5659.
Keyword(s): BIOMASS mission,
Earth explorer core mission candidate,
P-band,
forest area,
forest biomass,
forest disturbances,
frequency 425 MHz,
global maps,
synthetic aperture radar,
terrestrial carbon cycle,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar;.
Abstract: The greatest uncertainties in the global carbon cycle involve estimating how carbon dioxide is taken up by land. The BIOMASS mission aims to improve the present assessment and future projection of the terrestrial carbon cycle by providing consistent global maps of forest biomass and forest area, forest disturbances and recovery with time, and the extent and evolution of the forest flooding. The BIOMASS primary objectives can be achieved through P-band (435 MHz) synthetic aperture radar (SAR) observations of global forest cover. Two parallel industrial studies at phase 0 level were awarded respectively to Astrium GmbH and Thales Alenia Space Italy. This paper presents the resulting system concepts as elaborated by the industrial teams. The result of the phase 0 was presented to the user community in January 2009 in Lisbon together with other Earth Explorer candidates for further down-selection. If successfully selected after phase 0 and phase A, BIOMASS will be launched during 2016. -
Charles V. Jakowatz and Daniel E. Wahl.
Considerations for autofocus of spotlight-mode SAR imagery created using a beamforming algorithm.
In Edmund G. Zelnio and Frederick D. Garber, editors,
,
volume 7337,
pages 73370A,
2009.
SPIE.
Keyword(s): SAR Processing,
Autofocus,
Autofocus in the TDBP Framework,
Back-projection,
Time-Domain Back-Projection,
TDBP,
Fast Back-projection,
Fast-Factorized Back-Projection,
FFBP,
Spotlight SAR,
Spotlight-mode data,
Beamforming.
[bibtex-key = jakowatzWahlAutofocusBeamformingSpotlight2009]
-
W.T.K. Johnson,
P.A. Rosen,
S. Hensley,
and A. Freeman.
Radar designs for the DESDynI mission.
In IEEE Radar Conference,
pages 1-3,
May 2009.
ISSN: 1097-5659.
Keyword(s): DESDynI mission,
InSAR,
Lidar,
SweepSAR,
dual polarization,
ecosystem structure,
ice dynamics,
interferometric radar design,
near-polar orbit,
quadpolarization,
solid Earth,
spacecraft,
vegetation,
electromagnetic wave polarisation,
geophysical techniques,
ice,
optical radar,
radar interferometry,
synthetic aperture radar;.
Abstract: The interferometric radar (InSAR) design has undergone several iterations in the years that this mission has been under consideration. In the most recent proposal the InSAR is combined with a Lidar and the mission is called deformation, ecosystem structure, and dynamics of ice (DESDynI). This spacecraft would be in a near-polar orbit around the Earth and repeatedly collect data to monitor changes in the solid Earth, vegetation, and ice. The radar is a repeat pass interferometric SAR with dual and quad polarization capability. This paper examines the state of the configuration of the radar including a ldquoSweepSARrdquo method that has been incorporated as the present baseline. -
G. Krieger,
I. Hajnsek,
K. P. Papathanassiou,
M. Eineder,
M. Younis,
F. De Zan,
P. Prats,
S. Huber,
M. Werner,
H. Fiedler,
A. Freeman,
P. Rosen,
S. Hensley,
W. Johnson,
L. Veilleux,
B. Grafmueller,
R. Werninghaus,
R. Bamler,
and A. Moreira.
The Tandem-L mission proposal: Monitoring Earth's dynamics with high resolution SAR interferometry.
In Proc. IEEE Radar Conf.,
pages 1-6,
May 2009.
ISSN: 1097-5659.
Keyword(s): Earth's Dynamics Monitoring,
Tandem-L mission,
advanced digital beamforming techniques,
biomass inventories,
glacier movement observations,
global forest height,
high data acquisition,
high resolution SAR interferometry,
innovative interferometric radar mission,
millimetric displacements measurements,
polarimetric radar mission,
synthetic aperture radar,
tectonic shifts,
data acquisition,
glaciology,
radar interferometry,
radar polarimetry,
remote sensing by radar,
synthetic aperture radar,
tectonics,
vegetation;.
Abstract: Tandem-L is a proposal for an innovative interferometric and polarimetric radar mission that enables the systematic monitoring of dynamic processes on the Earth surface. Important mission objectives are global forest height and biomass inventories, large scale measurements of millimetric displacements due to tectonic shifts, and systematic observations of glacier movements. The innovative mission concept and the high data acquisition capacity of Tandem-L provide a unique data source to observe, analyze and quantify the dynamics of a wide range of mutually interacting processes in the bio-, litho-, hydro- and cryosphere. By this, Tandem-L will be an essential step to advance our understanding of the Earth system and its intricate dynamics. This paper provides an overview of the Tandem-L mission concept and its main application areas. Performance predictions show the great potential of Tandem-L to acquire a wide range of bio- and geophysical parameters with high accuracy on a global scale. Innovative aspects like the employment of advanced digital beamforming techniques to improve performance and coverage are discussed in detail. - Jianyang Li, Wenge Chang, and Yueli Li. An on-board real-time UWB SAR processor. In Radar Conference, 2009 IET International, pages 1-4, April 2009. ISSN: 0537-9989. Keyword(s): DSP, azimuth pre-processing, real-time UWB SAR processor, sub-aperture NCS. [bibtex-key = 5367304]
-
F. Lombardini and M. Pardini.
Detection of scatterer multiplicity in spaceborne SAR tomography with array errors.
In Radar Conference, 2009 IEEE,
pages 1-6,
4-8 May 2009.
[bibtex-key = Lombardini2009]
-
Antonio Moccia and Alfredo Renga.
Hybrid space-airborne bistatic SAR geometric resolutions.
In Lorenzo Bruzzone,
Claudia Notarnicola,
and Francesco Posa, editors,
,
volume 7477,
pages 74771Y,
2009.
SPIE.
Keyword(s): SAR Processing,
Bistatic SAR,
Geometric Resolution,
Geometric Bistatic Resolution,
Bistatic Resolution,
Resolution,
Airborne SAR,
Spaceborne SAR.
[bibtex-key = mocciaRengaBistaticResolutions2010]
-
Alberto Moreira,
Gerhard Krieger,
Irena Hajnsek,
Kostas Papathanassiou,
Michael Eineder,
Francesco De Zan,
Marwan Younis,
and Marian Werner.
Tandem-L: Monitoring the Earth's Dynamics with InSAR and Pol-InSAR.
In Proc. PolInSAR,
Frascati, Italy (ESA SP-668),
January 2009.
Keyword(s): Earth's Dynamics Monitoring,
Tandem-L mission,
advanced digital beamforming techniques,
biomass inventories,
glacier movement observations,
global forest height,
high data acquisition,
high resolution SAR interferometry,
innovative interferometric radar mission,
millimetric displacements measurements,
polarimetric radar mission,
synthetic aperture radar,
tectonic shifts,
data acquisition,
glaciology,
radar interferometry,
radar polarimetry,
remote sensing by radar,
synthetic aperture radar,
tectonics,
vegetation;.
Abstract: Tandem-L is a proposal for an innovative interferometric radar mission that enables the systematic monitoring of dynamic processes on the Earth surface. Important application examples are global forest height and biomass inventories, measurements of Earth deformations due to tectonic processes, observations of 3-D structure changes in ice, and the monitoring of ocean surface currents. The innovative mission concept and the high data acquisition capacity of Tandem-L provide a unique data source to observe, analyze and quantify a wide range of mutually interacting processes in the bio-, litho-, hydro- and cryosphere. By this, Tandem-L will be an essential step to advance our understanding of the Earth system and its climate dynamics. The Tandem-L mission concept relies on a systematic data acquisition strategy using a pair of cooperating L-band SAR satellites flying in close formation. The satellite system is operated in two basic data acquisition modes: 1) The 3-D structure mode employs fully-polarimetric single-pass SAR interferometry (Pol-InSAR) to acquire structural parameters and quasi-tomographic images of volume scatterers like vegetation, sand, and ice. 2) The deformation mode employs repeat-pass interferometry (InSAR) in an ultra-wide swath mode to measure small shifts on the Earth surface with millimetric accuracy and short repetition intervals. This paper provides an overview of the Tandem-L mission concept and its main application areas. Performance predictions show the great potential of Tandem-L to acquire a wide range of bio- and geophysical products with high accuracy on a global scale. Furthermore, innovative technical aspects like for example the use of digital beamforming to improve performance and coverage will be presented. -
R.K. Raney.
DESDynI adopts hybrid polarity SAR architecture.
In Radar Conference, 2009 IEEE,
pages 1-4,
May 2009.
ISSN: 1097-5659.
Keyword(s): DESDynI mission,
L-band synthetic aperture radar,
The National Research Council's Earth Science 2007 Decadal Survey,
circular polarization,
forest biomass,
hybrid-polarity dual-polarised SAR,
quadrature-polarimetric SAR mode,
terrain surface deformation,
polarisation,
synthetic aperture radar;.
Abstract: DESDynl-Deformation, Ecosystem Structure, and Dynamics of Ice-is one of the first-tier missions recommended in The National Research Council's Earth Science 2007 Decadal Survey. DESDynI's L-band synthetic aperture radar (SAR) is designed to measure terrain surface deformation and forest biomass, hence its quadrature-polarimetric SAR mode. The objective to provide quantitative information on a global scale imposes severe requirements on the radar to maximize coverage and to sustain reliable operational calibration. These requirements are best served by the hybrid-polarity architecture, in which the radar transmits in circular polarization, and receives on two orthogonal linear polarizations, coherently, retaining their relative phase. This architecture offers many significant advantages over conventional all-linearly-polarized SARs. This paper reviews those advantages, summarizes key attributes of hybrid-polarity dual- and quadrature-polarized SARs including conditions under which the signal-to-noise ratio is conserved, and describes the evolution of this architecture from first principles. -
Stefano Tebaldini and Fabio Rocca.
On the impact of propagation disturbances on SAR Tomography: Analysis and compensation.
In IEEE Radar Conference,
pages 1-6,
4-8 May 2009.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,.
Abstract: This paper is meant to discuss the role of propagation disturbances, such as those due to atmospheric disturbances or to residual platform motion, in SAR Tomography applications. It will be shown that phase stability requirements vary as a function of the number of targets within the system resolution cell, from which it follows that SAR Tomography applications require a higher phase stability, or a more accurate phase calibration, with respect to SAR Interferometry. Phase calibration will be discussed by comparing two approaches. The first is the traditional approach from Permanent Scatterers Interferometry, based on the assumption that it is possible to find stable targets in the imaged scene. The second is a new technique based on the Sum of Kronecker Products Decomposition, recently introduced in literature, which allows to isolate ground and volume contributions within the data provided the availability of multi-polarimetric acquisitions. As such, the latter approach is suited to carry out phase calibration in presence of volume scattering, as it is the case of forested areas. Experimental results will be provided basing on the analysis of the P-Band data-set relative to the forest site of Remningstorp, Sweden. -
Stefano Tebaldini and Fabio Rocca.
Polarimetric Options for SAR Tomography of Forested Areas.
In Proc. of PolInSAR - 4th Int. Workshop on Science and Applications of SAR Polarimetry and Polarimetric Interferometry,
Frascati, Italy,
January 2009.
ESA SP-668.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
E-SAR,
P-Band.
Abstract: The aim of this paper is to discuss the potentialities of SAR Tomography to infer information about the vertical structure of forested areas, basing on the availability of either multi-polarimetric or single-polarimetric data. The core of the analysis is represented by a model of the second order statistics of the multi-baseline, multi-polarimetric data that describes the imaged scene as the superposition of two distributed scattering mechanisms. In this framework, the well posing of the Tomographic problem can be discussed in a simple fashion, by considering the number of equations that arise from the data-set with respect to the number of the unknowns required to solve the model. As a result, it follows that through the exploitation of strongly structured models the vertical structure can be retrieved basing on single-polarimetric data as well, provided that a sufficient number of baselines is available. Still, the availability of multi-polarimetric and multi-baseline data offers the possibility to face the problem of the retrieval of the vertical structure of each scattering mechanism from a very general point of view, allowing to relax many of the assumptions that are otherwise mandatory. In other words, the availability of multipolarimetric data makes it possible to exploit not only model based approaches, but also model free, and hybrid approaches. As a result of this analysis, a new general methodology will be presented for the processing of multi-polarimetric and multibaseline data, that is consistent the inversion procedures usually exploited in single-baseline PolInSAR in the case where only single baseline data are available. Experimental results will be shown basing on a data-set of 9 P-Band SAR images of the forest site of Remningstorp, Sweden, acquired under the framework of the ESA campaign BioSAR 2007. -
Ping Zhang,
Jian Shang,
and Ruliang Yang.
A New algorithm improving SAR resolution based on SVA.
In Radar Conference, 2009 IET International,
pages 1-4,
20-22 2009.
ISSN: 0537-9989.
Keyword(s): SAR Processing,
Apodization,
Spatially Variant Apodization,
SVA.
Abstract: Resolution enhancement techniques in radar imaging have attracted considerable interest in recent years. The paper develops a new technique enhancing SAR resolution as well as suppressing sidelobes based on SVA technique. Spatially variant apodization (SVA) is a nonlinear sidelobe reduction method without lose the resolution of mainlobe. The signal bandwidth is extrapolated after SVA, which is the basis of resolution enhancement. An inverse weight function is used to equalize the SVA spectrum. A modified noninteger Nyquist spatially variant apodization (SVA) formulation is used to suppress sidelobes after extrapolation. Examples of 1D case and 2D case demonstrate enhanced image resolution with sidelobe reduction. -
Xiao Xiang Zhu,
Nico Adam,
Ramon Brcic,
and Richard Bamler.
Space-borne high resolution SAR tomography: experiments in urban environment using TS-X Data.
In Urban Remote Sensing Event, 2009 Joint,
pages 1-8,
20-22 May 2009.
[bibtex-key = Xiao2009]
-
Marcelo Albuquerque,
Pau Prats,
and Rolf Scheiber.
Applications of Time-Domain Back-Projection SAR Processing in the Airborne Case.
In European Conference on Synthetic Aperture Radar (EUSAR),
pages 4,
06 2008.
VDE Verlag GmbH.
ISBN: 978-3-8007-3084-1.
Keyword(s): SAR Processsing,
Time-Domain Back-Projection,
TDBP,
Back-Projection,
Synthetic Aperture Radar (SAR),
motion compensation,
tomography,
Airborne SAR,
E-SAR,
Topography-dependent motion compensation,
Motion Compensation,
MoComp,
Interferometry,
Non-Linear SAR,
Non-Linear Flight Tracks.
Abstract: The Back-Projection Algorithm is a SAR processing approach that uses time-domain convolution of the SAR data in order to perform SAR focusing. Some benefits of this approach are exact inversion, ideal motion compensation including topography information and handling of general aperture geometries. The implementation of the Back-Projection Algorithm was done focusing on the parallelization aspects. Applications of the algorithm are presented with respect to topography adaptive processing, direct generation of map projections and consideration of non linear trajectories. -
Michael Brandfass and Luis Fernando Lobianco.
Modified Fast Factorized Backprojection as Applied to X-Band Data for Curved Flight Paths.
In European Conference on Synthetic Aperture Radar (EUSAR),
pages 4,
June 2008.
VDE Verlag GmbH.
ISBN: 978-3-8007-3084-1.
Keyword(s): SAR Processsing,
Time-Domain Back-Projection,
TDBP,
Back-Projection,
Fast Factorized Back-Projection,
FFBP,
Fast Back-Projection,
Synthetic Aperture Radar (SAR),
motion compensation,
tomography,
Airborne SAR,
X-Band,
Motion Compensation,
MoComp,
Non-Linear SAR,
Non-Linear Flight Tracks.
Abstract: A Fast Factorized Backprojection scheme modified to X-band frequencies and applicable to small aperture beamwidths is presented to compute SAR images from real and synthetic airborne data sets. The numerical complexity and memory consumption of the algorithm is verified and compared to ordinary Backprojection. The modified Fast Factorized Backprojection scheme is investigated for exceedingly curved flight paths and compared to an \u03c9-k algorithm in combination with a motion error correction. Excellent SAR image focusing results were found for the modified Fast Factorized Backprojection approach while keeping the numerical complexity to O(N2log(N)). -
Honglei Chen and D. Kasilingam.
Performance Analysis of Multivariate Super-resolution Processing of Polarimetric Synthetic Aperture Radar Tomography.
In Geoscience and Remote Sensing Symposium, 2008. IGARSS 2008. IEEE International,
volume 4,
pages IV-169-IV-172,
7-11 July 2008.
[bibtex-key = Chen2008]
-
A. Donnellan,
P. Rosen,
J. Graf,
A. Loverro,
A. Freeman,
R. Treuhaft,
R. Oberto,
M. Simard,
E. Rignot,
R. Kwok,
Xiaoqing Pi,
J.B. Blair,
W. Abdalati,
J. Ranson,
H. Zebker,
B. Hager,
H. Shugart,
M. Fahnestock,
and R. Dubayah.
Deformation, Ecosystem Structure, and Dynamics of Ice (DESDynI).
In Proc. IEEE Aerospace Conf.,
pages 1-13,
March 2008.
ISSN: 1095-323X.
Keyword(s): DESDynl mission,
National Research Council Earth Science Decadal Survey,
Earth Science Applications from Space,
biomass,
cryosphere objectives,
ecosystem function,
ecosystem structure,
ice dynamics,
integrated L-band InSAR,
multibeam Lidar mission,
solid Earth,
surface deformation,
topography,
vegetation structure,
deformation,
optical radar,
synthetic aperture radar,
topography (Earth),
vegetation mapping;.
Abstract: The National Research Council Earth Science Decadal Survey, Earth Science Applications from Space, recommends that DESDynl (Deformation, Ecosystem Structure, and Dynamics of Ice), an integrated L-band InSAR and multibeam Lidar mission, launch in the 2010- 2013 timeframe. The mission will measure surface deformation for solid Earth and cryosphere objectives and vegetation structure for understanding the carbon cycle. InSAR has been used to study surface deformation of the solid Earth and cryosphere and more recently vegetation structure for estimates of biomass and ecosystem function. Lidar directly measures topography and vegetation structure and is used to estimate biomass and detect changes in surface elevation. The goal of DESDynl is to take advantage of the spatial continuity of InSAR and precision and directness of Lidar. There are several issues related to the design of the DESDynl mission, including combining the two instruments into a single platform, optimizing the coverage and orbit for the two techniques, and carrying out the science modeling to define and maximize the scientific output of the mission. -
A. Donnellan,
P. Rosen,
J. Ranson,
and H. Zebker.
Deformation, Ecosystem Structure, and Dynamics of Ice (DESDynI).
In IEEE Int. Geoscience and Remote Sensing Symposium, IGARSS 2008,
volume 3,
pages 5-8,
July 2008.
Keyword(s): DESDynl mission,
Deformation,
Ecosystem Structure,
and Dynamics of Ice,
Earth Science Decadal Survey,
National Research Council,
biomass estimation,
carbon cycle,
cryosphere objectives,
ecosystem function,
integrated L-band InSAR,
multibeam Lidar mission,
solid Earth surface deformation,
surface elevation changes,
topography measure,
vegetation structure,
deformation,
optical radar,
radar interferometry,
remote sensing by radar,
topography (Earth),
vegetation;.
Abstract: The National Research Council Earth Science Decadal Survey, Earth Science Applications from Space, recommends that DESDynI (Deformation, Ecosystem Structure, and Dynamics of Ice), an integrated L-band InSAR and multibeam Lidar mission, launch in the 2010-2013 timeframe. The mission will measure surface deformation for solid Earth and cryosphere objectives and vegetation structure for understanding the carbon cycle. InSAR has been used to study surface deformation of the solid Earth and cryosphere and more recently vegetation structure for estimates of biomass and ecosystem function. Lidar directly measures topography and vegetation structure and is used to estimate biomass and detect changes in surface elevation. The goal of DESDynI is to take advantage of the spatial continuity of InSAR and the precision and directness of Lidar. There are several issues related to the design of the DESDynI mission, including combining the two instruments into a single platform, optimizing the coverage and orbit for the two techniques, and carrying out the science modeling to define and maximize the scientific output of the mission. -
G. Fornaro,
A. Pauciullo,
F. Lombardini,
and M. Pardini.
Detection of Single and Multiple Scatterers in Multibaseline Multitemporal SAR Data.
In Geoscience and Remote Sensing Symposium, 2008. IGARSS 2008. IEEE International,
volume 2,
pages II-453-II-456,
7-11 July 2008.
[bibtex-key = Fornaro2008]
-
Othmar Frey,
Christophe Magnard,
Maurice Rüegg,
and Erich Meier.
Focusing SAR Data Acquired From Non-Linear Sensor Trajectories.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS '08,
pages 415-418,
2008.
Keyword(s): SAR Processing,
Time-Domain Back-Projection,
Back-Projection,
Non-Linear Flight Tracks,
Curvilinear SAR,
Extended Chirp Scaling,
ECS,
Mosaicking,
Geocoding,
Integrated Focusing and Geocoding,
Georeferencing,
mapping,
corridor mapping.E-SAR,
L-Band,
digital elevation model,
Airborne SAR.
Abstract: Standard focusing of SAR data assumes a straight recording track of the sensor platform. Small non-linearities of airborne platform tracks are corrected for during a motion compensation step while keeping the assumption of a linear flight path. In the following, the processing of SAR data from nonlinear tracks is discussed as may originate from small aircraft or drones flying at low altitude. They fly not a straight track but one dependent on topography, influences of weather and wind, or dependent on the shape of dedicated areas of interest such as rivers or traffic routes. A time-domain backprojection based technique, is proposed and evaluated with the help of experimental data featuring a drop in height, a double bend, a 90-degree curve and a linear flight track. In order to assess the quality of the focused data, close-ups of amplitude images are compared and the coherence is evaluated. The experimental data was acquired by the German Aerospace Center's E-SAR L-band system. -
Othmar Frey,
Christophe Magnard,
Maurice Rüegg,
and Erich Meier.
Non-Linear SAR Data Processing By Time-Domain Back-Projection.
In Proc. of EUSAR 2008 - 7th European Conference on Synthetic Aperture Radar,
pages 165-168,
2008.
Keyword(s): SAR Processing,
Time-Domain Back-Projection,
Back-Projection,
Non-Linear Flight Tracks,
Curvilinear SAR,
Extended Chirp Scaling,
ECS,
Mosaicking,
Geocoding,
Integrated Focusing and Geocoding,
Georeferencing,
mapping,
corridor mapping.E-SAR,
L-Band,
digital elevation model,
Airborne SAR.
Abstract: Focusing of conventional stripmap SAR data assumes a straight recording track of the sensor platform. Small deviations from that linear trajectory are corrected by motion compensation steps while keeping the assumption of a linear acquisition path. In the following, the processing of SAR data from non-linear tracks is discussed as may originate from small aircraft or drones flying at low altitude. They fly not a straight track but one dependent on topography, influences of weather and wind, or dependent on the shape of dedicated areas of interest such as rivers or traffic routes. Experimental data featuring a drop in height, a double bend and a 90-degree curve have been processed using a time-domain back-projection approach. The data was acquired by the German Aerospace Center's E-SAR L-band system. -
Othmar Frey and Erich Meier.
Combining Time-Domain Back-Projection and Capon Beamforming for Tomographic SAR Processing.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS '08,
pages 445-448,
2008.
Keyword(s): SAR Processing,
SAR Tomography,
Tomographic Processing,
Multi-Baseline SAR,
Time-Domain Back-Projection,
Back-Projection,
E-SAR,
P-Band,
Forestry,
Capon,
Capon Beamforming,
Superresolution.
Abstract: Various tomographic processing methods have been investigated in recent years. The quality of the focused tomographic image is usually 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. Neither time-domain back-projection (TDBP) processing, although providing a very accurate processing framework, is able to overcome the problem of ambiguous target detection in the tomographic image. In this paper, a possible extension of the TDBP approach to multilooking based tomographic focusing methods like standard beamforming and Capon beamforming is discussed. Preliminary results obtained with a simulated and a real airborne tomographic P-band data set are shown. -
Othmar Frey and Erich Meier.
Tomographic Focusing by Combining Time-Domain Back-Projection and Multi-Looking Based Focusing Techniques.
In Proc. of EUSAR 2008 - 7th European Conference on Synthetic Aperture Radar,
pages 73-76,
2008.
Keyword(s): SAR Processing,
SAR Tomography,
Tomographic Processing,
Multi-Baseline SAR,
Time-Domain Back-Projection,
Back-Projection,
E-SAR,
P-Band,
Forestry,
Capon,
Capon Beamforming,
Superresolution.
Abstract: Various tomographic processing methods have been investigated in recent years. The quality of the focused tomographic image is usually 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. Neither time-domain back-projection (TDBP) processing, although providing a very accurate processing framework, is able to overcome the problem of ambiguous target detection in the tomographic image. In this paper, a possible extension of the TDBP approach to multi-looking based tomographic focusing methods like standard beamforming and Capon beamforming is discussed. -
Charles V. Jakowatz,
Daniel E. Wahl,
and David A. Yocky.
Beamforming as a foundation for spotlight-mode SAR image formation by backprojection.
In Edmund G. Zelnio and Frederick D. Garber, editors,
,
volume 6970,
pages 69700Q,
2008.
SPIE.
Keyword(s): SAR Processing,
Back-projection,
Time-Domain Back-Projection,
TDBP,
Fast Back-projection,
Fast-Factorized Back-Projection,
FFBP,
Spotlight SAR,
Spotlight-mode data,
Beamforming.
[bibtex-key = jakowatzWahlYockyBeamformingTDBPSpotlightMode2008]
-
F. Lombardini,
G. Fornaro,
M. Pardini,
D. Reale,
F. Serafino,
F. Soldovieri,
and M. Costantini.
SAR tomography for scene elevation and deformation reconstruction: Algorithms and potentialities.
In Radar Conference, 2008. RADAR '08. IEEE,
pages 1-7,
26-30 May 2008.
[bibtex-key = Lombardini2008]
-
Christophe Magnard,
Othmar Frey,
Maurice Rüegg,
and Erich Meier.
Improved Airborne SAR Data Processing by Blockwise Focusing, Mosaicking and Geocoding.
In Proc. of EUSAR 2008 - 7th European Conference on Synthetic Aperture Radar,
pages 375-378,
2008.
Keyword(s): SAR Processing,
Time-Domain Back-Projection,
Back-Projection,
Non-Linear Flight Tracks,
Curvilinear SAR,
Extended Chirp Scaling,
ECS,
Mosaicking,
Geocoding,
Integrated Focusing and Geocoding,
Georeferencing,
mapping,
corridor mapping.E-SAR,
L-Band,
digital elevation model,
Airborne SAR.
Abstract: Standard focusing of SAR data assumes a straight recording track of the sensor platform. Small non-linearities of airborne platform are corrected for during a motion compensation step while keeping the assumption of a stripmap geometry. In the case of high resolution and high frequency SAR systems, the navigation data may not be accurate enough to perform such a motion compensation; SAR systems mounted on small aircrafts or drones flying at low altitude do not follow a straight track but one dependent on topography and atmospheric conditions. We present a blockwise focusing, mosaicking and geocoding method which allows processing such data. For the experiments, MEMPHIS and E-SAR data were used. -
G. Margarit,
J.J. Mallorqui,
I. Corney,
and C. Lopez-Martinez.
A Public Database of Simulated Multidimensional SAR Data for Techniques Validation.
In Geoscience and Remote Sensing Symposium, 2008. IGARSS 2008. IEEE International,
volume 2,
pages II-601-II-604,
7-11 July 2008.
[bibtex-key = Margarit2008]
-
Matteo Nannini,
Rolf Scheiber,
and Alberto Moreira.
On the Minimum Number of Tracks for SAR Tomography.
In ,
volume 2,
pages 441-444,
July 2008.
Keyword(s): SAR Processing,
SAR Tomography,
Capon,
MUSIC,
image reconstruction,
airboren SAR,
image representation,
radar interferometry,
synthetic aperture radar3D representation,
German Aerospace Center,
DLR,
L-band,
SAR interferometry,
SARTom,
data acquisition,
equivalent targets,
experimental SAR system,
minimum tomographic aperture,
spheroidal wave functions,
subspace superresolution methods,
synthetic aperture radar tomography,
tracks minimum number determination,
volumetric source,
ESAR.
Abstract: The main drawback of SAR Tomography (SARTom) is the considerable number of tracks required to achieve the 3-dimensional (3D) representation of a viewed scene. The key point concerns the trade-off between the vertical resolution and the control on ambiguities phenomena. This paper deals with the problem of the determination of the minimum number of required tracks when super-resolution subspace methods are applied. The results are validated on real data acquired in L-band by the E-SAR system of the German Aerospace Centre. -
P.A. Rosen,
S. Hensley,
and C. Le.
Observations and mitigation of RFI in ALOS PALSAR SAR data: Implications for the DESDynI mission.
In IEEE Radar Conference,
pages 1-6,
May 2008.
ISSN: 1097-5659.
Keyword(s): DESDynI mission,
L-band polarimetric radar,
RFI,
SAR data,
radio frequency interference,
synthetic aperture radar,
radiofrequency interference,
synthetic aperture radar;.
Abstract: Initial examination of ALOS PALSAR synthetic aperture radar (SAR) data has indicated significant radio frequency interference (RFI) in several geographic locations around the world. RFI causes significant reduction in image contrast, introduces periodic and quasi-periodic image artifacts, and introduces significant phase noise in repeat-pass interferometric data reduction. The US National Research Council Decadal Survey of Earth Science has recommended DESDynI, a Deformation, Ecosystem Structure, and Dynamics of Ice satellite mission comprising an L-band polarimetric radar configured for repeat-pass interferometry. There is considerable interest internationally in other future L-band and lower frequency systems, as well. Therefore, the issues of prevalence and possibilities of mitigation of RFI in these crowded frequency bands are of considerable interest. RFI is observed in ALOS PALSAR in California and Hawaii, USA, and in southern Egypt in data examined to date. Application of several techniques for removing it from the data prior to SAR image formation, ranging from straight-forward spectral normalization to time-domain, multi-phase filtering techniques, are considered. Considerable experience has been gained from the removal of RFI from P-band acquired by the GeoSAR system. These techniques applied to the PALSAR data are most successful when the bandwidth of any particular spectral component of the RFI is narrow. Performance impacts for SAR imagery and interferograms are considered in the context of DESDynI measurement requirements. -
Stefano Tebaldini.
Forest SAR tomography: A covariance matching approach.
In IEEE Radar Conference, 2008. RADAR '08.,
pages 1-6,
May 2008.
ISSN: 1097-5659.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
E-SAR,
P-Band,
radar imaging,
radar interferometry,
radar polarimetry,
radar resolution,
synthetic aperture radar,
tomographyP-band SAR images,
covariance matching approach,
forest SAR tomography,
multipolarimetric channel data,
single polarimetric channel data,
single target interferometric analysis,
synthetic aperture radar interferometry,
system resolution cell.
Abstract: In this paper a technique to conduct tomographic analyses of forested areas through multiple, coherent SAR images is presented. This technique differs from other methods existing in literature in that it may be regarded as a natural extension of SAR interferometry to the case where several distributed targets are present within the system resolution cell. In this way, it is possible to estimate the position of each target in the resolution cell with virtually the same accuracy obtainable by a single target interferometric analysis. Furthermore, this approach is suited to both single and multi polarimetric channel data. As a validation, this paper reports the results of a tomographic analysis of the forest site of Remningstorp, Sweden, basing on a data-set of 9 P-band SAR images acquired by DLRpsilas E-SAR. -
Stefano Tebaldini,
Fabio Rocca,
and A Monti-Guarnieri.
Model Based SAR Tomography of Forested Areas.
In IEEE International Geoscience and Remote Sensing Symposium,
volume 2,
pages 593-596,
July 2008.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
E-SAR,
P-Band.
Abstract: In this paper a technique is described for the tomographic characterization of forested areas through multiple SAR observations. This technique is based on a model of the second order statistics of the multi baseline, multi polarimetric, data which accounts for the presence of multiple distributed targets within the system resolution cell. The results of an experiment performed on a real P-band, multi-baseline, fully polarimetric data set relative to the forested site of Remningstorp, Sweden, are reported. Such results show the feasibility of performing a model based tomographic analysis of forests, resulting in a characterization of both the ground and the canopy in terms of elevation, spatial structure, and scattered power. -
Daniel E. Wahl,
David A. Yocky,
and Charles V. Jakowatz.
An implementation of a fast backprojection image formation algorithm for spotlight-mode SAR.
In Edmund G. Zelnio and Frederick D. Garber, editors,
,
volume 6970,
pages 69700H,
2008.
SPIE.
Keyword(s): SAR Processing,
Back-projection,
Time-Domain Back-Projection,
TDBP,
Fast Back-projection,
Fast-Factorized Back-Projection,
FFBP,
Spotlight SAR,
Spotlight-mode data.
[bibtex-key = wahlYockyJakowatzFastBackprojectionSpotlight2008]
-
Yanping Wang,
Bin Wang,
Wen Hong,
Lei Du,
and Yirong Wu.
Imaging Geometry Analysis of 3D SAR using Linear Array Antennas.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2008,
volume 3,
pages 1216-1219,
July 2008.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
linear antenna arrays,
radar imaging,
radar interferometry,
synthetic aperture radar,
3D SAR,
elevation direction,
imaging geometry analysis,
linear array antennas,
signal model.
Abstract: Linear array antennas SAR has a resolving capability in the elevation direction, and can get the 3D image of the target. In this paper, we derive the signal model of 3D SAR using a linear array antenna, and get the 3D resolutions and 3D point spread function of array antenna SAR, at the same time the sampling space of array antennas is given. The variance of the resolution in the elevation direction with array antenna angle and referenced look angle is studied. The geometry to reach the best resolution in the elevation direction is analyzed. Meanwhile the resolution for horizontal and vertical antenna array are calculated and compared. -
E.C. Zaugg and D.G. Long.
Along-Track Resolution Enhancement Forwide-Bandwidth, Low-Frequency SAR by Accounting for the Wavelength Change over the Bandwidth.
In Geoscience and Remote Sensing Symposium, 2008. IGARSS 2008. IEEE International,
volume 4,
pages IV-1272-IV-1275,
7-11 July 2008.
Keyword(s): SAR Processing.
[bibtex-key = Zaugg2008]
-
A. Ahlander,
H. Hellsten,
K. Lind,
J. Lindgren,
and B. Svensson.
Architectural Challenges in Memory-Intensive, Real-Time Image Forming.
In Int. Conf. on Parallel Processing,
pages 35-35,
Sept. 2007.
ISSN: 0190-3918.
Keyword(s): SAR Processing,
Backprojection,
Time-Domain Back-Projection,
Fast-Factorized Back-Projection,
FFBP,
GBP,
interpolation,
parallel algorithms,
parallel architectures,
radar imaging,
real-time systems,
storage management,
synthetic aperture radarcomplex memory access pattern,
computer architecture,
flight path error compensation,
memory-intensive real-time image forming,
parallel algorithm,
performance-intensive data interpolation,
synthetic aperture radar system.
Abstract: The real-time image forming in future, high-end synthetic aperture radar systems is an example of an application that puts new demands on computer architectures. The initial question is whether it is at all possible to meet the demands with state-of-the-art technology or foreseeable new technology. It is therefore crucial to understand the computational flow, with its associated memory, bandwidth and processing demands. In this paper we analyse the application in order to, primarily, understand the algorithms and identify the challenges they present on a basic architectural level. The processing in the radar system is characterized by working on huge data sets, having complex memory access patterns, and doing real-time compensations for flight path errors. We propose algorithm solutions and execution schemes in interplay with a two-level (coarse-grain/fine-grain) system parallelization approach, and we provide approximate models on which the demands are quantified. In particular, we consider the choice of method for the performance- intensive data interpolations. This choice presents a trade-off problem between computational performance and size of working memory. The results of this "upstream " study will serve as a basis for further, more detailed architecture studies. -
Christian Andres,
Torben Keil,
Raik Herrmann,
and Rolf Scheiber.
A multiprocessing framework for SAR image processing.
In ,
pages 524-527,
July 2007.
Keyword(s): SAR Processing,
Airborne SAR,
application program interfaces,
geophysics computing,
grid computing,
image processing,
multiprocessing systems,
synthetic aperture radar,
workstation clusters,
F-SAR,
SAR image processing,
airborne SAR sensor,
application programming interface,
cluster grids,
different architectures,
multiprocessing framework,
source code,
synthetic aperture radar,
workstation cluster.
Abstract: This paper introduces a framework developed for image processing of synthetic aperture radar (SAR) images. It encapsulates features of modern hardware architectures, including symmetric and asymmetric multiprocessing, within an easy and intuitive to use application programming interface (API). The multiprocessing part is designed for unified usage of different architectures reaching from multicore processors to cluster of workstations to grids of clusters. So an application using the framework can be ported from one architecture to another without any changes in the source code. The framework builds the bottom layer of the processing system developed for the German Aerospace Center's (DLR) new airborne SAR sensor, the F-SAR. -
Wang Bin,
Wang Yanping,
Hong Wen,
and Wu Yirong.
Simulation research of parametric methods for multi-baseline SAR tomography.
In Synthetic Aperture Radar, 2007. APSAR 2007. 1st Asian and Pacific Conference on,
pages 203-206,
5-9 Nov. 2007.
[bibtex-key = Bin2007]
-
Hubert M. J. Cantalloube,
Élise Colin-Koeniguer,
and Hélène Oriot.
High resolution SAR imaging along circular trajectories.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2007,
pages 850-853,
July 2007.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus,
PGA,
Autofocus by Deterministic Trajectory Triangulation Technique,
data acquisition,
Motion Compensation,
MoComp,
Residual Motion Errors,
radar antennas,
radar polarimetry,
remote sensing by radar,
synthetic aperture radar,
L-band radar,
P-band radar,
Sweden,
X-band sensor,
Airborne SAR,
aircraft attitude fluctuation,
circular trajectories,
Non-Linear Flight Track,
high resolution SAR imaging,
joint FOI-ONERA campaign,
narrower antenna pattern,
polarimetric full circle radar acquisition,
steerable antenna.
Abstract: After a first series of full circle SAR acquisitions in L- and P-bands during a 2004 joint FOI-ONERA campaign in Sweden, ONERA experimented in 2006 high resolution (15 cm) polarimetric, full circle acquisitions in France and Germany using its X-band sensor. In order to cope with narrower antenna pattern and aircraft attitude fluctuations, a steerable antenna was used. Furthermore, an experimental setup for retrieving high accuracy trajectory was installed. This paper describes the processing of this signals. -
Karlus A. Câmara de Macedo,
Rolf Scheiber,
and Alberto Moreira.
An autofocus approach for residual motion errors with application to airborne repeat-pass SAR interferometry.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2007,
Barcelona, Spain,
pages 4886 - 4889,
July 2007.
Keyword(s): SAR Processing,
Autofocus,
Residual Motion Errors,
WPCA,
Weighted PCA,
Weighted Phase Curvature Autofocus,
Phase Curvature Autofocus,
PCA,
Phase Gradient Autofocus,
PGA,
Repeat-Pass Interferometry,
Interferometry,
E-SAR,
airborne SAR,
Baseline Calibration,
Tomography,
SAR Tomography.
Abstract: Airborne repeat-pass SAR data are very sensible to sub-wavelength deviations from the reference track. To enable repeat-pass interferometry a high-precision navigation system is needed. Due to the limit of accuracy of such systems, deviations in the order of centimeters remain between the nominal and the processed reference track causing mainly undesirable phase undulations and misregistration in the interferograms, referred as residual motion errors. Up to now only interferometric approaches, as multi-squint, are used to estimate those deviations to compensate for such residuals. In this paper we present for the first time the use of the Autofocus technique for residual motion errors. A very robust autofocus technique has to be used since the accuracy of the estimated motion has to be at millimeter scale. Because we deal with low-altitude-stripmap mode data we propose a new robust autofocus technique based on the WLS (Weighted Least-Squares) phase estimation and Phase Curvature Autofocus (PCA) extended to the rangedependent case. We call this new technique WPCA (Weighted PCA). While the multi-squint approach is only able to estimate the baseline variation from coregistered images, the autofocus approach has the advantage of being able to estimate motion deviations independendtly for each image. Repeat-pass data of the E-SAR system of the German Aerospace Center (DLR) are used to demostrate the performance of the proposed approach. -
G. Fornaro,
F. Lombardini,
M. Pardini,
F. Serafino,
F. Soldovieri,
and M. Costantini.
Spaceborne multi-dimensional SAR imaging: Current status and perspectives.
In Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007. IEEE International,
pages 5277-5280,
23-28 July 2007.
[bibtex-key = Fornaro2007]
-
Othmar Frey,
Felix Morsdorf,
and Erich Meier.
Tomographic Processing of Multi-Baseline P-Band SAR Data for Imaging of a Forested Area.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS '07,
2007.
Keyword(s): SAR Processing,
SAR Tomography,
Tomographic Processing,
Multi-Baseline SAR,
Time-Domain Back-Projection,
Back-Projection,
E-SAR,
P-Band,
Forestry.
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. -
Othmar Frey,
Felix Morsdorf,
and Erich Meier.
Tomographic SAR Imaging of a Forested Area by Time-Domain Back-Projection.
In M.E. Schaepman,
S. Liang,
N.E. Groot,
and M. Kneubühler, editors,
10th Intl. Symposium on Physical Measurements and Spectral Signatures in Remote Sensing,
volume XXXVI,
2007.
Intl. Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences.
Keyword(s): SAR Processing,
SAR Tomography,
Tomographic Processing,
Multi-Baseline SAR,
Time-Domain Back-Projection,
Back-Projection,
E-SAR,
P-Band,
Forestry.
Abstract: Recently, various attempts have been undertaken to retrieve information about the three-dimensional structure of vegetation from multibaseline synthetic aperture radar data. Although tomographic processing of such data has been demonstrated, yet, there are still several problems that limit the focusing quality. In particular, the frequency-domain based focusing methods are susceptible to irregular and sparse sampling, two problems, which are unavoidable in case of multi-pass, multi-baseline radar data acquired by an airborne system. We propose a time-domain back-projection algorithm, which maintains the original geometric relationship between the original sensor positions and the imaged target and is therefore able to cope with irregular and sparse sampling without introducing any geometric approximations. Preliminary results obtained with a newly acquired P-band tomographic data set consisting of eleven flight tracks are shown and discussed. -
Wang Jinfeng,
Zhou Peng,
and Pi Yiming.
SAR tomography imaging based on high-order spectrum analysis.
In Synthetic Aperture Radar, 2007. APSAR 2007. 1st Asian and Pacific Conference on,
pages 364-367,
5-9 Nov. 2007.
[bibtex-key = Jinfeng2007]
-
F. Lombardini.
New potentials of differential SAR tomography: Volumetric differential interferometry and robust DEM generation.
In Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007. IEEE International,
pages 5281-5284,
23-28 July 2007.
[bibtex-key = Lombardini2007b]
-
Fabrizio Lombardini,
Matteo Pardini,
and Fulvio Gini.
Sector interpolation for 3D SAR imaging with baseline diversity data.
In Waveform Diversity and Design Conference, 2007. International,
pages 297-301,
4-8 June 2007.
[bibtex-key = Lombardini2007a]
-
Fabrizio Lombardini,
Ludwig Rössing,
Joachim H. G. Ender,
and F. Viviani.
Towards a Complete Processing Chain of Multibaseline Airborne InSAR Data for Layover Scatterers Separation.
In Urban Remote Sensing Joint Event, 2007,
pages 1-6,
11-13 April 2007.
Abstract: Interest is continuing to grow in exploiting the advanced multibaseline operation of synthetic aperture radar interferometry (InSAR) to solve layover effects, that can degrade conventional InSAR topographic mapping. In this work we report about experiments of the functionality of “layover-free†or “higher-order†interferometry with the dual-baseline single-pass SAR interferometer AER-II. Estimation of the number of multiple layover scatterers, i.e. of the interferometric order, and model-based spatial spectral estimation are integrated to process the three-antenna non uniform array data. Results are discussed for a bridge over the valley test site. -
Andrea Monti-Guarnieri and Stefano Tebaldini.
A new framework for multi-pass SAR interferometry with distributed targets.
In IEEE International Geoscience and Remote Sensing Symposium,
pages 5289-5293,
July 2007.
Keyword(s): Monte Carlo methods,
digital elevation models,
radar interferometry,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
topography (Earth)DEM,
InSAR,
LOS displacement,
Monte Carlo simulation,
distributed scattering,
multipass spaceborne SAR interferometry,
repeated pass ENVISAT images,
residual topography,
synthetic aperture radar interferometry.
Abstract: This paper focuses on multi-pass spaceborne synthetic aperture radar interferometry (InSAR) in presence of distributed scattering, paying particular attention to the role of target decorrelation in the estimation process. This phenomenon is accounted for by splitting the analysis into two steps. In the first step we estimate the interferometric phases from the data, while in the second step we use these phases to retrieve the physical parameters of interest, such as LOS displacement and residual topography. This approach is suited both to derive the performances of InSAR with different decorrelation models and for providing an actual estimate of LOS motion and DEM. Results achieved from Monte-Carlo simulations and a set of repeated pass ENVISAT images are shown. -
Matteo Nannini and Rolf Scheiber.
Height dependent motion compensation and coregistration for airborne SAR tomography.
In International Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007,
pages 5041-5044,
July 2007.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
geophysical signal processing,
image registration,
Motion Compensation,
radar imaging,
remote sensing by radar,
synthetic aperture radar2D SAR repeat-pass processing,
E-SAR system,
L-Band,
German Aerospace Centre,
SAR imaging,
airborne SAR tomography,
data acquisition,
height dependent motion compensation,
image coregistration,
multiple phase center separation,
processing correction,
tomogram quality,
volumetric target.
Abstract: SAR tomography (SARTom) is an imaging technique that allows multiple phase centers separation in the vertical (height) direction. It is performed after standard 2D SAR repeat-pass processing and operates on a stack of coregistered SAR images. Theoretically, the coregistration between two images is height dependent and the use of a reference height (or a DEM) is needed, although not ideal in the case of volumetric target (multiple phase centers in one resolution cell). In this paper, the drawbacks related to the choice of this reference in a tomographic context are analysed and a height dependent coregistration approach is proposed. In order to do this, it is also necessary to remove processing corrections related to the reference height, such as motion compensation, and make them height dependent. The inclusion of the height dependency during the tomographic SAR processing results in a better quality of the final tomograms in terms of pseudo-power and phase centers separation. The results of the proposed approach are validated on real data acquired by the E-SAR system of the German Aerospace Centre - DLR. -
Pau Prats,
Christian Andres,
Rolf Scheiber,
Karlus A. Câmara de Macedo,
Jens Fischer,
and Andreas Reigber.
Glacier displacement field estimation using airborne SAR interferometry.
In IEEE International Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007.,
pages 2098-2101,
July 2007.
Keyword(s): SAR Processing,
SAR interferometry,
InSAR,
DInSAR,
Spectral Diversity,
Residual Motion Errors,
Motion Compensation,
MoComp,
Airborne SAR,
ESAR,
airborne radar,
glaciology,
hydrological techniques,
radar interferometry,
synthetic aperture radar2D displacement map,
Aletsch glacier,
E-SAR,
Experimental SAR,
German Aerospace Center,
Swiss Alps,
across-track displacement,
airborne SAR data,
airborne,
along-track displacement,
extended multisquint approach,
glacier displacement field estimation,
slant-range geometry.
Abstract: This paper deals with the methodology in the processing of airborne SAR data to measure glacier displacement fields. The possibility to retrieve a 2D displacement map of the deformation in slant-range geometry with an airborne platform is discussed. A new extended multisquint approach is proposed to simultaneously estimate residual motion errors and the along-track displacement of the glacier, while the across-track displacement is obtained by means of differential interferomatry. Experimental results are shown with data acquired by the Experimental SAR (E-SAR) of the German Aerospace Center over the Aletsch glacier in the Swiss Alps. -
Rolf Scheiber,
Pau Prats,
Matteo Nannini,
Karlus A. Câmara de Macedo,
Christian Andres,
Jens Fischer,
and Ralf Horn.
Advances in airborne SAR interferometry using the experimental SAR system of DLR.
In European Radar Conference, EuRAD 2007.,
2007.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
InSAR,
Interferometry,
PTA,
SATA,
Residual Motion Errors,
Motion Compensation,
DInSAR,
Differential InSAR,
Differential Interferometry,
E-SAR.
Abstract: During recent years the experimental SAR (E-SAR) system of the German Aerospace Center (DLR) has continuously been operated to acquire data for different scientific applications in forestry, agriculture and glaciology. In this context, the data where mainly used to develop new scattering models in preparation of future space-borne missions posing increasing accuracy requirements especially for the processing of repeat-pass interferometric data. Also direct model-free methods like differential SAR interferometry for measuring displacements in the order of the wavelength or SAR tomography for real 3D microwave imaging of scattering volumes determined the development of advanced and very accurate motion compensation techniques. This paper first gives an overview of the updates of the E-SAR system performed during the last couple of years and then focusses on the recently developed airborne interferometric processing methods and their applications. -
Philipp Thompson,
Matteo Nannini,
and Rolf Scheiber.
Target separation in SAR image with the MUSIC algorithm.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2007.,
pages 468-471,
July 2007.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
radar imaging,
synthetic aperture radar,
DLR,
E-SAR system,
Fourier SAR image,
MUSIC,
MUSIC algorithm,
Spectral Estimation,
X-band,
corner reflectors,
post-processing implementation,
super-resolution experiment,
target separation,
targets geometry.
Abstract: The aim of this work is to exploit the MUSIC algorithm performance in order to enhance target separability in range and azimuth, i.e. achieve point targets separation inside a resolution cell. Simulations have been done in order to plan and check the feasibility of a super-resolution experiment that took place in September 2006 on the test site of Oberpfaffenhofen (Germany). The data set has been acquired with the E-SAR system of the DLR in X-band. The targets to be separated were seven small corner reflectors that have been placed in a way that their response falls in one or, at maximum, two resolution cells of the standard Fourier SAR image. A post-processing implementation of the MUSIC algorithm has been proposed allowing, in the already focused SAR image, to retrieve the targets geometry. Conditions and analysis of the results have been carried out. -
Tan Wei-xian,
Hong Wen,
Wang Yan-ping,
and Wu Yi-rong.
A novel imaging approach for multi-baseline SAR tomography.
In Synthetic Aperture Radar, 2007. APSAR 2007. 1st Asian and Pacific Conference on,
pages 423-426,
5-9 Nov. 2007.
[bibtex-key = Wei-xian2007]
-
Tan Weixian,
Wang Yanping,
Hong Wen,
Wu Yirong,
Li Nanjing,
Hu Chufeng,
and Zhang Linxi.
SAR Three-Dimensional Imaging Experiments with Microwave Anechoic Chamber SAR Data.
In Microwave Conference, 2007. APMC 2007. Asia-Pacific,
pages 1-4,
11-14 Dec. 2007.
[bibtex-key = Weixian2007]
-
Evan C. Zaugg and David G. Long.
Full motion compensation for LFM-CW synthetic aperture radar.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2007.,
pages 5198-5201,
23-28 July 2007.
Keyword(s): SAR Processing,
LFM-CW,
LFM-CW SAR,
MoComp,
motion compensation,
CSA,
ECS,
Chirp Scaling,
Extended Chirp Scaling,
FSA,
Frequency Scaling Algorithm,
Range-Doppler Algorithm,
synthetic aperture radar,
Brigham Young University,
muSAR system,
LFM-CW signal model,
SAR image quality,
aircraft,
atmospheric turbulence,
high-resolution synthetic aperture radar systems,
linear frequency-modulated continuous-wave signal,
motion compensation,
motion correction algorithms,
unmanned aerial vehicle,
Airborne SAR,
geophysical techniques,.
[bibtex-key = Zaugg2007]
-
H. Chen and D. Kasilingam.
Auto-Regressive Aperture Extrapolation for Multibaseline SAR Tomography.
In Geoscience and Remote Sensing Symposium, 2006. IGARSS 2006. IEEE International Conference on,
pages 3743-3745,
July 31 2006-Aug. 4 2006.
[bibtex-key = Chen2006]
-
Karlus A. Câmara de Macedo,
Rolf Scheiber,
and Alberto Moreira.
First Evaluations of Airborne InSAR Time-Series.
In Proc. of EUSAR 2006 - 6th European Conference on Synthetic Aperture Radar,
2006.
Keyword(s): SAR Processing,
SAR Interferometry,
Interferometry,
Permanent Scatterers,
Phase Gradient Autofocus,
PS-PGA,
Autofocus,
Motion Compensation,
Residual Motion Error,
Repeat-Pass Interferometry,
Phase Calibration,
Baseline Calibration,
Tomographic Baseline Calibration,
Airborne SAR,
E-SAR.
Abstract: To allow time-series analysis of airborne SAR images using PSs (Permanent Scatterers), this paper has two main objectives. The first is to show, in a quantitative way, that there is a compromise between the number of images used to detect PSs, their probability of being detected and their stability. This tradeoff is derived based on estimation and detection theories. The second objective is to investigate the possibility of the use of permanent scatterers to estimate undesired phase undulations in ariborne data due to residual motion errors. A new technique is proposed, the so-called PS-PGA, where we apply the Phase Gradient algorithm on the PSs in order to obtain sub-wavelength estimations of residual motion errors for both master and slaves, separately, differently from current approaches. Compensation of these residual errors will lead to more reliable airborne D-InSAR measurements. -
An Daoxiang,
Huang Xiaotao,
and Wang Liang.
Contrast Optimized PGA Algorithm for P-band UWB SAR.
In Radar, 2006. CIE '06. International Conference on,
pages 1-4,
Oct. 2006.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus,
Contrast Optimization.
Abstract: The Phase Gradient Autofocus (PGA) technique has been proved to be a superior method for higher order autofocus. However, given the different nature of P-band Ultra-Wideband Synthetic Aperture Radar (UWB SAR) imagery and very low signal-to-clutter ratio in the data, conventional PGA algorithm usually fail to yield robust focusing result on raw data without distortion. We proposed the modified PGA algorithm that combines the traditional PGA with contrast optimization principle and reference scatterer coregistration. Our method is successfully applied on raw P-band UWB SAR image and excellent results are attained. -
Cao Fang,
Hong Wen,
and Wu Yirong.
An improved Cloude-Pottier decomposition using H/α/SPAN and complex Wishart classifier for polarimetric SAR classification.
In International Conference on Radar, 2006. CIE '06.,
pages 1-4,
October 2006.
Keyword(s): image classification,
radar imaging,
radar polarimetry,
synthetic aperture radarCloude-Pottier decomposition,
H/α,
/SPAN,
IHSL transform,
Wishart classifier,
polarimetric SAR classification,
synthetic aperture radar.
Abstract: An improvement is proposed for the Cloude-Pottier decomposition using H/α/SPAN and IHSL transform. Based on this decomposition, an unsupervised classification with SPAN is also given in this paper. The main advantages of this decomposition are that it uses SPAN to maintain the space information for further polarimetric analysis and provides a straight way to present the result. Our experiments show that this decomposition method provides better results than the general Cloude-Pottier method and the corresponding Wishart H/α/SPAN classification also achieves better performance than the current Wishart H/α/A method -
Othmar Frey,
Erich Meier,
and Daniel Nüesch.
An Integrated Focusing and Calibration Procedure for Airborne SAR Data.
In Proc. of EUSAR 2006 - 6th European Conference on Synthetic Aperture Radar,
2006.
Keyword(s): SAR Processing,
Time-Domain Backprojection,
Backprojection,
Terrain Correction,
Radiometry,
Radiometric Calibration,
Radiometric Correction,
Terrain,
Topography,
DEM Geocoding,
Geocoding,
DLR,
E-SAR,
Airborne SAR,
L-Band.
Abstract: Topography-induced variation of radar brightness still poses a problem in terms of radiometric calibration of SAR data, which is undoubtedly an indispensable step in order to deduce bio- or geophysical parameters from amplitude images. We propose an integrated focusing and calibration procedure for airborne SAR data based on the time-domain backprojection technique. With the help of sensor position and attitude data as well as a digital elevation model (DEM) the true acquisition geometry is maintained throughout the combined focusing and calibration step. The effectiveness of the method is evaluated by means of an E-SAR L-band data set acquired over undulating terrain. -
Per-Olov Frölind and Lars M. H. Ulander.
Evaluation of angular interpolation kernels in fast back-projection SAR processing.
In IEE Proceedings -- Radar, Sonar and Navigation,
volume 153,
pages 243-249,
June 2006.
ISSN: 1350-2395.
Keyword(s): SAR Processing,
Time-Domain Back-Projection,
Backprojection,
Back-Projection,
Fast Factorized Back-Projection,
Comparison of Algorithms,
interpolation,
interpolation kernels,
angular interpolation kernels,
radar imaging,
synthetic aperture radar,
ultra wideband radar,
UWB SAR,
interpolation method,
phase error,
polar version,
subimage version,
time domain SAR algorithm,
Factorized Backprojection.
Abstract: This paper presents a comparative study of the polar and the subimage based variants of the time domain SAR algorithm Fast Factorized Backprojection. The difference between the two variants with regard to the phase error, which causes defocusing in the image, is investigated. The difference between the algorithms in interpolation between stages is also discussed. To investigate the sidelobes in azimuth, the paper gives simulation results for a low frequency UWB SAR system for both algorithms. How the algorithms differ with regard to amount of beams and length of beams is also discussed. -
Charles V. Jakowatz and Neall Doren.
Comparison of polar formatting and back-projection algorithms for spotlight-mode SAR image formation.
In Edmund G. Zelnio and Frederick D. Garber, editors,
,
volume 6237,
pages 62370H,
2006.
SPIE.
Keyword(s): SAR Processing,
Polar Format Algorithm,
PFA,
Convolution Backprojection Algorithm,
CPB,
Comparison of Algorithms,
Spotlight SAR,
Spotlight-mode data.
[bibtex-key = jakowatzDorenPFABackprojectionComparison2006]
-
Charles V. Jakowatz and Daniel E. Wahl.
Correction of propagation-induced defocus effects in certain spotlight-mode SAR collections.
In Edmund G. Zelnio and Frederick D. Garber, editors,
,
volume 6237,
pages 62370I,
2006.
SPIE.
Keyword(s): SAR Processing,
Polar Format Algorithm,
PFA,
Atmospheric Influence,
Phase Gradient Algorithm,
PGA,
Autofocus,
Residual Phase Errors,
Residual Error,
Spotlight SAR,
Spotlight-mode data.
[bibtex-key = jakowatzWahlPGASpotlightmode2006]
-
Fabrizio Lombardini,
Ludwig Rössing,
Joachim H. G. Ender,
and F. Cai.
Interferometric Model Order Selection: Validation of ITC Methods with Airborne Three-antenna SAR Data.
In Geoscience and Remote Sensing Symposium, 2006. IGARSS 2006. IEEE International Conference on,
pages 2565-2568,
July 31 2006-Aug. 4 2006.
[bibtex-key = Lombardini2006]
-
J.M. Munoz-Ferreras,
J. Calvo-Gallego,
F. Perez-Martinez,
A. Blanco-del-Campo,
A. Asensio-Lopez,
and B.P. Dorta-Naranjo.
Motion compensation for ISAR based on the shift-and-convolution algorithm.
In Radar, 2006 IEEE Conference on,
pages 5pp.,
24-27 April 2006.
Keyword(s): ISAR.
[bibtex-key = Munoz-Ferreras2006]
-
Matteo Nannini and Rolf Scheiber.
A Time Domain Beamforming Algorithm for SAR Tomography.
In Proc. of EUSAR 2006 - 6th European Conference on Synthetic Aperture Radar,
2006.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
Time-Domain Beamforming,
Phase Calibration,
Baseline Calibration,
Tomographic Baseline Calibration,
Airborne SAR,
E-SAR.
Abstract: Interest on 3D imaging in a remote sensing frame has grown in the recent years and it finds in SAR Tomography (TomSAR) a natural way to resolve for targets in the third dimension. In this paper we compare the performance of a pure beamforming technique with the SpecAn algorithm. This comparison has the goal to estabilish if the time domain beamforming (TDB) performance are efficient in order to perform tomographic focusing. A tomographic baseline calibration is also presented. The TDB is applied on simulated and real airborne data in L-band. The real data have been acquired during a tomographic campaign in May 1998 on the test site of Oberpfaffenhofen (Germany) with the E-SAR system of the German Aerospace Center (DLR). -
P. Prats,
A. Reigber,
J. Mallorqui,
P. Blanco,
and A. Moreira.
Estimation of the Deformation Temporal Evolution Using Airborne Differential SAR Interferometry.
In Geoscience and Remote Sensing Symposium, 2006. IGARSS 2006. IEEE International Conference on,
pages 1894-1897,
July 31 2006-Aug. 4 2006.
Keyword(s): SAR Processing,
D-InSAR,
ESAR,
Airborne SAR,
L-Band,
differential interferometry,
Interferometry,
Motion Compensation,
RME,
Residual Motion Errors,
deformation measurement.
[bibtex-key = PratsReigberMallorquiBlancoMoreira2006a:DInSAR]
-
J. Sanz-Marcos,
J. Mallorqui,
A. Aguasca,
and P. Prats.
First ENVISAT and ERS-2 Parasitic Bistatic Fixed Receiver SAR Images Processed with the Subaperture Range-Doppler Algorithm.
In Geoscience and Remote Sensing Symposium, 2006. IGARSS 2006. IEEE International Conference on,
pages 1840-1843,
July 31 2006-Aug. 4 2006.
[bibtex-key = SanzMarcosMallorquiAguascaPrats2006:Bistatic]
-
D. Yocky and D. Wahl.
Minimum-Latency Polar Format Algorithm.
In Proc. IEEE Int. Geosci. Remote Sens. Symposium,
pages 3177-3179,
July 2006.
Keyword(s): SAR Processing,
Real-Time,
Real-Time Processing,
Real-Time SAR,
Video SAR,
Polar Format Algorithm,
PFA.
Abstract: The polar format algorithm (PFA) is a computationally efficient image formation method for high-resolution spotlight-mode SAR data collections. Yet, its usual real-time implementation waits until the entire synthetic aperture has been collected before beginning image formation. This results in a latency time. This paper presents a new approach to PFA that performs range and azimuth interpolation and range compression as the aperture is collected. Thus, the remaining latency is approximately the azimuth compression time. Performing image formation during aperture collection makes minimum-latency PFA a viable real-time image formation algorithm. -
D. Yocky,
D. Wahl,
and C. V. Jakowatz Jr..
Spotlight-Mode SAR Image Formation Utilizing the Chirp Z-Transform in Two Dimensions.
In Proc. IEEE Int. Geosci. Remote Sens. Symposium,
pages 4180-4182,
July 2006.
Keyword(s): SAR Processing,
SPECAN-like Processing,
SPECAN,
Chirp-Z Transform,
Chirp-Z Transform-based Focusing,
Spotlight SAR,
Spotlight-mode data.
Abstract: A new spotlight-mode synthetic aperture radar image formation approach is presented that directly utilizes the reflected electromagnetic returns collected on a polar grid. This approach eliminates polar-to-rectangular grid interpolation by employing chirp z-transforms in two dimensions. Since the chirp z-transform can be implemented via fast Fourier transforms (FFTs), this image formation algorithm consists almost entirely of FFTs allowing it to exploit computationally-efficient FFT engines for fast image formation speeds. This paper presents the algorithm, and compares the operation counts and execution time between the new algorithm and traditional polar formatting, which employs interpolation. The paper also presents conditions for which the chirp z-transform in two dimensions is advantageous. -
E.C. Zaugg,
D.L. Hudson,
and D.G. Long.
The BYU SAR: A Small, Student-Built SAR for UAV Operation.
In Geoscience and Remote Sensing Symposium, 2006. IGARSS 2006. IEEE International Conference on,
pages 411-414,
July 31 2006-Aug. 4 2006.
Keyword(s): SAR Processing,
BYU SAR,
UAV.
[bibtex-key = Zaugg2006]
-
X. Zheng,
W. Yu,
and Z. Li.
A Novel Algorithm for Wide Beam SAR Motion Compensation Based on Frequency Division.
In IEEE International Geoscience and Remote Sensing Symposium, 2006. IGARSS 2006.,
pages 3160-3163,
August 2006.
Keyword(s): SAR Processing,
Motion Compensation,
MoComp,
P-Band,
Wide Beamwidth,
Airborne SAR,
Frequency Division,
Frequency-Division Motion Compensation,
FD-MOCO.
Abstract: This paper proposes a novel motion compensation algorithm for wide beam Synthetic Aperture Radar (SAR) based on frequency division. It applies motion compensation in time domain and corrects both low- and high- frequency motion errors. The rationale and procedure of this algorithm are introduced in detail. Point scatterers of a P-band airborne SAR with different motion errors are tested to validate this algorithm. Compared with traditional narrow beam motion compensation and available wide beam compensation, the proposed algorithm has better performance. -
M. Blom and P. Follo.
VHF SAR image formation implemented on a GPU.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS '05.,
volume 5,
pages 3352-3356,
July 2005.
Keyword(s): SAR Processing,
Time-Domain Back-Projection,
TDBP,
GPU,
Graphic Processing Unit,
GPU Processing,
3D Graphics Card,
VHF,
Airborne SAR,
FOI,
CARABAS.
Abstract: This paper will describe how off-the-shelf 3D graphics cards can be used for scientific computation like SAR processing. In particular, a highly efficient one-dimensional FFT and a fast direct (global) backprojection implementation will be presented and analyzed. - F. Bordoni, A. Jakobsson, F. Gini, and F. Lombardini. On the Effects of Nonuniform Sampling for Interferometric Phase Estimation in the Presence of Layover. In Statistical Signal Processing, 2005 IEEE/SP 13th Workshop on, pages 645-650, July 17-20 2005. [bibtex-key = Bordoni2005]
-
Karlus A. Câmara de Macedo,
Christian Andres,
and Rolf Scheiber.
On the requirements of SAR processing for airborne differential interferometry.
In Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International,
volume 4,
pages 2693-2696,
25-29 July 2005.
Keyword(s): SAR Processing,
PTA-MoComp,
Postprocessing,
Motion Compensation,
Topography-Based Motion Compensation,
Chirp Scaling Algorithm,
Extended Chirp Scaling Algorithm,
fast Fourier transform-based postprocessing methodology,
FFT,
D-InSAR,
German Aerospace Center,
DLR,
airborne repeat-pass interferometry,
differential interferometry,
geometric fidelity,
motion errors,
phase accuracy,
residual phase errors,
topographic heights,
Topography,
DEM,
Terrain,
wide beamwidth,
Airborne SAR,
ESAR.
Abstract: Airborne Differential SAR Interferometry (DInSAR) is still a challenging task when compared to the spaceborne case due to the fact that airborne platforms are unable to describe a stable flight track. For that reason a very precise motion compensation which includes the correction of topographic-induced phase errors has to be performed in the airborne SAR data. This paper presents the required steps of phase correction to achieve accurate airborne D-InSAR data. The latest airborne D-InSAR processing chain of the E-SAR system is shown. Differential interferograms results using the proposed processing chain are also shown. -
Armin W. Doerry.
Autofocus correction of SAR images exhibiting excessive residual migration.
In Robert N. Trebits and James L. Kurtz, editors,
Proceedings of SPIE Vol. 5788, Radar Sensor Technology IX,
volume 5788,
pages 34-45,
2005.
SPIE.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus.
Abstract: Relatively small motion measurement errors manifest themselves principally as a phase error in Synthetic Aperture Radar (SAR) complex data samples, and if large enough become observable as a smearing, blurring, or other degradation in the image. The phase error function can be measured and then deconvolved from the original data to compensate for the presumed motion error, ultimately resulting in a well-focused image. Techniques that do this are termed ?autofocus? algorithms. A very popular autofocus algorithm is the Phase Gradient Autofocus (PGA) algorithm. The nearly universal, and typically reasonable, assumption is that the motion errors are less than the range resolution of the radar, allowing solely a phase correction to suffice. Very large relative motion measurement errors manifest themselves as an unexpected additional shifting or migration of target locations beyond any deterministic migration during the course of the synthetic aperture. Degradation in images from data exhibiting errors of this magnitude are substantial, often rendering the image completely useless. When residual range migration due to either real or apparent motion errors exceeds the range resolution, conventional autofocus algorithms fail. Excessive residual migration is increasingly encountered as resolutions become finer, less expensive inertial sensors are used, and operating ranges become longer (due to atmospheric phenomena). A new migration-correction autofocus algorithm has been developed that estimates the excessive residual migration and applies phase and frequency corrections to properly focus the image. This overcomes the conventional constraint that motion errors not exceed the SAR range resolution. -
Armin W. Doerry,
Dale F. Dubbert,
Martin Thompson,
and Vivian D. Gutierrez.
A portfolio of fine resolution Ka-band SAR images: part I.
In Robert N. Trebits and James L. Kurtz, editors,
Proc. of SPIE Vol. 5788, Radar Sensor Technology IX,
number 1,
pages 13-24,
2005.
SPIE.
Keyword(s): SAR Processing,
High Resolution,
Fine Resolution,
Sandia National Laboratoiries,
Ka-Band.
Abstract: Sandia National Laboratories designs and builds Synthetic Aperture Radar (SAR) systems capable of forming highquality exceptionally fine resolution images. During the spring of 2004 a series of test flights were completed with a Ka-band testbed SAR on Sandia?s DeHavilland DHC-6 Twin Otter aircraft. A large data set was collected including real-time fine-resolution images of a variety of target scenes. This paper offers a sampling of high quality images representative of the output of Sandia?s Ka-band testbed radar with resolutions as fine as 4 inches. Images will be annotated with descriptions of collection geometries and other relevant image parameters. -
Armin W. Doerry,
Dale F. Dubbert,
Martin Thompson,
and Vivian D. Gutierrez.
A portfolio of fine resolution Ka-band SAR images: part II.
In Robert N. Trebits and James L. Kurtz, editors,
Proc. of SPIE Vol. 5788, Radar Sensor Technology IX,
number 1,
pages 185-196,
2005.
SPIE.
Keyword(s): SAR Processing,
High Resolution,
Fine Resolution,
Sandia National Laboratoiries,
Ka-Band.
Abstract: Sandia National Laboratories designs and builds Synthetic Aperture Radar (SAR) systems capable of forming highquality exceptionally fine resolution images. During the spring of 2004 a series of test flights were completed with a Ka-band testbed SAR on Sandia?s DeHavilland DHC-6 Twin Otter aircraft. A large data set was collected including real-time fine-resolution images of a variety of target scenes. This paper offers a sampling of high quality images representative of the output of Sandia?s Ka-band testbed radar with resolutions as fine as 4 inches. Images will be annotated with descriptions of collection geometries and other relevant image parameters. -
Othmar Frey,
Erich Meier,
and Daniel Nüesch.
A Study on Integrated SAR Processing and Geocoding by Means of Time-Domain Backprojection.
In Proceedings of the Int. Radar Symposium, Berlin,
2005.
Keyword(s): SAR Processing,
Time-Domain Backprojection,
Backprojection,
Geocoding,
Radiometry,
Calibration,
Radiometric Calibration,
ENVISAT/ASAR,
Spaceborne SAR.
Abstract: Geocoded products of synthetic aperture radar data are of great interest for many applications. The conventional processing chain, which leads to geographically referenced synthetic aperture data consists of two main steps: first, the raw data are focused and, in a second step, the resulting single look complex image is geocoded to the favoured coordinate system. We investigate a time-domain backprojection approach that replaces the two steps, focusing and geocoding, by one algorithm leading directly to terrain-geocoded images. The technique is evaluated with ENVISAT/ASAR image mode data. We assess the geolocation accuracy and the radiometric performance of dedicated point targets such as transponders and a corner reflector. In addition, we compare our findings with results from corresponding level 1 products processed at the European Space Agency (ESA), which were validated within the scope of ENVISAT/ASAR Cal/Val activities. -
Othmar Frey,
Erich Meier,
and Daniel Nüesch.
Processing SAR data of rugged terrain by time-domain back-projection.
In SPIE Vol. 5980: SAR Image Analysis, Modeling, and Techniques X,
2005.
Keyword(s): SAR Processing,
Time-Domain Backprojection,
Backprojection,
Terrain Correction,
Radiometry,
Radiometric Calibration,
Radiometric Correction,
Terrain,
Topography,
DEM Geocoding,
ENVISAT/ASAR,
Spaceborne SAR.
Abstract: Processing of SAR images of rugged terrain deserves special care because the topography affects the focused image in a number of ways. In order to obtain geometrically and radiometrically corrected SAR images of mountainous areas additional knowledge about the topography and the sensor's trajectory and attitude has to be included in the processing or post-processing steps. Various well-known focusing techniques are available to transform SAR raw data into a single look complex image such as the range-Doppler, the chirp scaling or the omega-k algorithm. While these algorithms perform the azimuth focusing step in the frequency domain the time-domain back-projection processing technique focuses the data geometrically, i.e., in the time domain. In contrast to the frequency-domain techniques, time-domain back-projection maintains the entire geometric relationship between the sensor and the illuminated area. This implies a couple of advantages: a stringent, terrain-based correction for the elevation antenna gain pattern may be implemented and topography-induced variation of radar brightness can be eliminated in a single step. Further, the SAR image is focused directly onto an arbitrary reconstruction grid and in the desired geodetic reference frame without requiring any additional processing steps. We discuss the influence of rugged terrain on the radiometric properties of focused SAR data and demonstrate how the time-domain back-projection approach accounts for these effects within one integrated processing framework by incorporating both a correction for terrain slope induced variation of radar brightness and a stringent correction for the elevation antenna gain pattern. The algorithm is evaluated for ENVISAT/ASAR image mode data of a mountainous area. -
U. Gebhardt,
Ottmar Loffeld,
H. Nies,
S. Knedlik,
and Joachim H. G. Ender.
Bistatic airborne/spaceborne hybrid experiment: basic considerations.
In Roland Meynart,
Steven P. Neeck,
and Haruhisa Shimoda, editors,
Proc. of SPIE Vol.5978, Sensors, Systems, and Next-Generation Satellites IX,
number 1,
2005.
SPIE.
Keyword(s): SAR Processing,
Bistatic SAR,
Hybrid Bistatic SAR,
Bistatic Airborne/Spaceborne SAR,
Airborne SAR,
Spaceborne SAR,
Hybrid,
Spotlight Mode,
Sliding Spotlight Mode,
Simulation,
TerraSAR-X.
Abstract: Collecting data using different sensors mounted on different platforms is the challenge of multisensorics. Applications in Synthetic Aperture Radar (SAR) normally lead to extreme bi- or multistatic constellations in the multisensorial case. This paper describes basic considerations concerning the geometry, especially the antenna steering for a bistatic SAR experiment. Using the TerraSAR-X as a transmitter and a SAR system mounted on a plane as a receiver we want to record experimental raw data for further processing. Because of the high difference between the velocity of the transmitter platform and that of the receiver platform relative to a point target, stripmap mode is not useful in this case. By operating the transmitter in sliding spotlight or spotlight mode and using antenna steering to provide footprint chasing on the side of the receiving system, a useful scene extension in azimuth can be achieved. This is of course at the cost of a shorter time interval in which the point target is both illuminated by the transmitter and seen by the receiver. First simulations of a point target response will show that nevertheless we can expect a useful Doppler bandwidth and thus an adequate resolution in azimuth. -
Stéphane Guillaso and Andreas Reigber.
Polarimetric SAR Tomography (POLTOMSAR).
In Proceedings of POLINSAR'05,
Frascati, Italy,
2005.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
MUSIC,
Beamforming,
Capon,
Modified MUSIC,
DoA,
Direction of Arrival,
Fourier,
Pol-InSAR,
L-Band,
ESAR.
Abstract: In this paper, different approaches of airborne SAR tomography are presented. A SAR tomographic data acquisition system can be represented like an antenna array. The use of high-resolution methods is indicated to the concept of aperture synthesis for 3D-imaging using SAR data. Techniques presented are the standard Fourier-, Capon-based beamforming methods to improve the resolution quality. In order to estimate the nature of retrieved target, a polarimetric approach is introduced based on the modified high-resolution MUSIC algorithm. Finally, experimental results are shown using a multibaseline data set acquired in L-band by DLR?s experimental SAR (E-SAR) on a test site near Oberpfaffenhofen / Germany. - S. Guillaso and A. Reigber. Scatterer characterisation using polarimetric SAR tomography. In Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International, volume 4, pages 2685-2688, 25-29 July 2005. [bibtex-key = Guillaso2005a]
-
S. Guillaso,
A. Reigber,
and L. Ferro-Famil.
Evaluation of the ESPRIT approach in polarimetric interferometric SAR.
In Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International,
volume 1,
pages 4 pp.,
2005.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
airborne radar,
data acquisition,
radar imaging,
radar polarimetry,
radiowave interferometry,
remote sensing by radar,
stereo image processing,
synthetic aperture radar,
tomography,
vegetation mapping,
3D images,
ESPRIT approach,
German Aerospace Center,
SAR tomography,
airborne L-band repeat-pass interferometric data,
data acquisition,
experimental airborne SAR,
polarimetric interferometric SAR,
tomographic image,
vegetation,
volumetric area,
E-SAR.
Abstract: This paper presents a first evaluation of the ESPRIT approach in polarimetric interferometric SAR. This evaluation is carried out by using 3D images obtained by SAR tomographic like an alternative to the acquisition of ground-truth data, which is an extremely complex task in the case of volume areas. All parameters over a volumetric area are directly visible in a tomographic image and can, therefore, be employed to validate the ESPRIT approach by comparing parameters generated by ESPRIT and the SAR tomography approach. This allows to identify the principal deficiencies of the ESPRIT method, which occur over high vegetation areas, where there is a misinterpretation of the ESPRIT results. Whereas, the ESPRIT approach is useful for building characterisation, identifying a good applicability area. Airborne L-band repeat-pass interferometric data of the German Aerospace Center (DLR) experimental airborne SAR are used to perform this evaluation. -
V. C. Koo,
T. S. Lim,
and H. T. Chuah.
A Comparison of Autofocus Algorithms for SAR Imagery.
In Progress In Electromagnetics Research Symposium,
volume 1,
Hangzhou, China,
pages 16-9,
2005.
Keyword(s): SAR Processing,
Autofocus,
Motion Compensation,
MoComp,
Residual Motion Errors,
Comparion of Algorithms,
Comparison of Autofocus Algorithms,
Airborne SAR,
Phase Gradient Autofocus,
PGA,
Eigenvector Method,
Maximum Likelihood Estimation.
Abstract: A challenge in SAR system development involves compensation for nonlinear motion errors of the sensor platform. The uncompensated along-track motions can cause a severe loss of geometry accuracy and degrade SAR image quality. Autofocus techniques improve image focus by removing a large part of phase errors present after conventional motion compensation. It refers to the computer-automated error estimation and subsequent removal of the phase errors. Many autofocus algorithms have been proposed over the years, ranging from quantitative measurement of residual errors to qualitative visual comparison. However, due to the fact that different data sets and motion errors were employed, it is difficult to perform comparative studies on various algorithms. This paper compares and discusses some practical autofocus algorithms by using a common data set. Standard focal quality metrics are defined to measure how well an image is focused. Their implementation schemes and performance are evaluated in the presence of various phase errors, which include polynomial-like, high frequency sinusoidal, and random phase noise. -
Shu Li and Ian Cumming.
Improved beat frequency estimation in the MLBF Doppler ambiguity resolver.
In Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International,
volume 5,
pages 3348-3351,
2005.
Keyword(s): SAR Processing,
Doppler Centroid Estimation,
Doppler Ambiguity Resolver,
DAR,
MLBF,
Multilook Beat Frequency,
Improved Multilook Beat Frequency.
Abstract: Among the current Doppler ambiguity resolvers, the Multi-Look Beat frequency (MLBF) algorithm proves to be the most reliable one, especially in high contrast areas. The existing MLBF algorithm uses FFTs to measure the central frequency of the beat signal but the estimation accuracy is limited by quantization errors. This paper proposes an improved method of estimating the beat frequency in the MLBF algorithm that is based on phase increments. In our work, we examined five established frequency estimators and found that the Iterative Linear Prediction (ILP) method has the best performance. The experimental results on RADARSAT-1 data show that the new MLBF algorithm using ILP can obtain the correct ambiguity number in a higher percentage of blocks and that the RMS error of the results is less than half that of the existing method. -
F. Lombardini.
Analysis of non-gaussian speckle statistics in high-resolution SAR images.
In Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International,
volume 2,
pages 1337-1340,
25-29 July 2005.
[bibtex-key = Lombardini2005]
- F. Lombardini and G. Fornaro. First trials of fourier and adaptive tomo-doppler sar imaging. In Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International, volume 4, pages 2656-2659, 25-29 July 2005. [bibtex-key = Lombardini2005a]
-
C. Lopez-Martinez and E. Pottier.
Topography independent InSAR coherence estimation in a multiresolution scheme.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS'05,
volume 4,
pages 2689-2692,
July 2005.
Keyword(s): SAR Processing,
Coherence,
Coherence Estimation,
InSAR,
Interferometry,
SAR Interferometry,
Speckle Noise,
Wavelet Transform.
[bibtex-key = lopezMartinezPottier2005:Coherence]
-
Andreas Muschinski,
Fred M. Dickey,
and Armin W. Doerry.
Possible effects of clear-air refractive-index perturbations on SAR images.
In Robert N. Trebits and James L. Kurtz, editors,
Proc. of SPIE Vol. 5788, Radar Sensor Technology IX,
number 1,
pages 25-33,
2005.
SPIE.
Keyword(s): SAR Processing,
Atmospheric Modelling,
clear-air radar,
thin-lens approximation,
clear-air refractive index,
sheets,
gravity waves,
diffraction patterns.
Abstract: Airborne synthetic aperture radar (SAR) imaging systems have reached a degree of accuracy and sophistication that requires the validity of the free-space approximation for radio-wave propagation to be questioned. Based on the thin-lens approximation, a closed-form model for the focal length of a gravity wave-modulated refractive-index interface in the lower troposphere is developed. The model corroborates the suggestion that mesoscale, quasi-deterministic variations of the clear-air radio refractive-index field can cause diffraction patterns on the ground that are consistent with reflectivity artifacts occasionally seen in SAR images, particularly in those collected at long ranges, short wavelengths, and small grazing angles. -
P. Prats,
A. Reigber,
and J.J. Mallorqui.
Topography accommodation during motion compensation in interferometric repeat-pass SAR images.
In Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International,
volume 1,
pages 4pp.,
25-29 July 2005.
Keyword(s): SAR Processing,
Motion Compensation,
Topography-Based Motion Compensation,
ESAR,
L-Band,
Airborne SAR,
radar imaging,
synthetic aperture radar,
Topography,
German Aerospace Center E-SAR,
DLR,
SAR data processing,
airborne L-band repeat-pass interferometric data,
Interferometry,
Chirp Scaling Algorithm,
Extended Chirp Scaling Algorithm,
azimuth compression,
azimuth coregistration errors,
external digital elevation model,
DEM,
image enhancement,
image registration,
impulse response degradation,
phase artifacts,
repeat-pass interferometric SAR systems,
Calibration,
image registration,
repeat-pass interferometry.
[bibtex-key = PratsReigberMallorqui2005a:MoComp]
-
A. Reigber,
M. Neumann,
S. Guillaso,
S. Sauer,
and L. Ferro-Famil.
Evaluating PolInSAR parameter estimation using tomographic imaging results.
In Radar Conference, 2005. EURAD 2005. European,
pages 189-192,
2005.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
forestry,
matrix algebra,
radar imaging,
radar polarimetry,
radiowave interferometry,
remote sensing by radar,
synthetic aperture radar,
tomography,
vegetation mapping,
PolInSAR parameter estimation,
canopy,
forest height,
ground topography estimation,
polarimetric SAR interferometry,
tomographic imaging results.
Abstract: This paper concentrates on the forest height and ground topography estimation by means of polarimetric SAR interferometry and tomography. In polarimetric SAR interferometry, one of the most important methods described in literature is the line-fitting approach in the complex unitary circle (S.R. Cloude and K.P. Papathanassiou, 2003). Although it has shown their principal potential, an open issue is still the precise validation of the estimated parameters, as ground-truth collection is an extremely complex task in the case of forest parameters. SAR tomography is an alternative technique, which generates a fully three-dimensional representation of the imaged scene through coherent combination of a greater number of tracks (A. Reigber and A. Moreira, 2000) (S. Guillaso and A. Reigber, 2005). Forest ground and canopy are directly visible in a tomographic image; a tomographic image can therefore be used as an ideal validation base for PolInSAR forest parameter estimation. This paper compares high-resolution polarimetric SAR tomograms with PolInSAR forest height estimations, both derived from the same data set. This allows to identify areas of good applicability, as well as principal deficiencies of the different PolInSAR approaches. -
A. Reigber,
P. Prats,
and J.J. Mallorqui.
Refined estimation of time-varying baseline errors in airborne SAR interferometry.
In Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International,
volume 7,
pages 4799-4802,
25-29 July 2005.
Keyword(s): SAR Processing,
Airborne SAR,
calibration,
Interferometry,
L-Band,
Baseline refinement,
calibration,
interferometry,
InSAR,
Motion Compensation,
repeat-pass interferometry,
Residual Motion Errors,
RME,
Squinted SAR,
Multi-Squint Processing.
[bibtex-key = ReigberPratsMallorqui2005:MoComp]
-
J. Sanz-Marcos,
P. Prats,
and J.J. Mallorqui.
Bistatic fixed-receiver parasitic SAR processor based on the back-propagation algorithm.
In Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International,
volume 2,
pages 1056-1059,
25-29 July 2005.
[bibtex-key = SanzMarcosPratsMallorqui2005:Bistatic]
- F. Serafino, F. Soldovieri, F. Lombardini, and G. Fornaro. Singular value decomposition applied to 4D SAR imaging. In Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International, volume 4, pages 2701-2704, 25-29 July 2005. [bibtex-key = Serafino2005]
-
G. Shippey,
S. Banks,
and J. Pihl.
SAS image reconstruction using Fast Polar Back Projection: comparisons with Fast Factored Back Projection and Fourier-domain imaging.
In Oceans 2005 - Europe,
volume 1,
pages 96-101 Vol. 1,
June 2005.
Keyword(s): SAR Processing,
Time-Domain Back-Projection,
TDBP,
Fast-Factorized Back-Projection,
FFBP,
Fast Polar Back-Projection,
FPBP,
fast Fourier transforms,
image reconstruction,
radar imaging,
sonar imaging,
synthetic aperture radar,
synthetic aperture sonar FFBP,
FPBP,
Fast Factored Back Projection,
Fast Polar Back Projection,
Fourier-domain imaging,
SAS image reconstruction,
Synthetic Aperture Radar,
Synthetic Aperture Sonar,
autopositioning purposes,
azimuth sidelobe level,
computation time reduction,
intermediate physical aperture images,
multielement sonar arrays,
nonlinear platform trajectories,
preset approximation error,
review,
standard FFT-based method,
time-domain methods,
ultra-wideband airborne SAR,
wide bandwidths,
wide swaths.
Abstract: Fast Polar Back-Projection (FPBP) is a variant of the Fast-Factored Back-Projection (FFBP) algorithm, originally developed for ultra-wideband airborne Synthetic Aperture Radar (SAR), but since applied with success to Synthetic Aperture Sonar (SAS). The paper outlines the FPBP and FFBP algorithms, comparing computation time and memory requirements for the two methods. Processing time comparisons with a standard FFT-based method are also given. Since FFBP and FPBP are both approximation methods, computation time also depends on the preset approximation error, which particularly affects azimuth sidelobe level. The paper provides an opportunity to review speed and accuracy estimates made in previous literature. However reduction in computation time is not the decisive advantage of these time-domain methods. The difference from the FFT-based methods lies in the flexibility with which nonlinear platform trajectories, wide swaths, wide bandwidths, and multielement sonar arrays can be handled. It is also straightforward to obtain a set of intermediate physical aperture images for autopositioning purposes. -
Zhigang Su,
Yingning Peng,
and Xiutan Wang.
Non-Iterative Imaging Algorithm for CLSAR.
In Acoustics, Speech, and Signal Processing, 2005. Proceedings. (ICASSP '05). IEEE International Conference on,
volume 2,
pages 577-580,
2005.
ISSN: 1520-6149.
Keyword(s): SAR Processing,
Non-Linear Flight Path,
SAR Tomography,
Curvilinear SAR,.
Abstract: Curvilinear synthetic aperture radar (CLSAR), which aperture is formed via a curvilinear trajectory, is considered as a more practical three-dimensional (3-D) imaging system. The 3-D images obtained by using non-parametricmethods, however, have little practical use because the data collected by CLSAR is sparse in the 3-D frequency space. Some parametric methods have been successfully applied into CLSAR for imaging but have expensive computational cost since they are iteration methods. In this paper, a non-iterative imaging (NII) algorithm is proposed. The new algorithm estimates the range parameters of all scatterers via modern spectrum method, and then using these range estimates and the received data to form the two-dimensional (2-D) data slices, from which the cross-range parameters are estimated. Once the position (range and cross-range) estimates are obtained, the radar cross section (RCS) can be calculated from the data. Simulation results show that the new algorithm can efficiently form the target’s 3-D image via CLSAR. -
Zhigang Su,
Yingning Peng,
and Xiutan Wang.
Three-dimensional target features extraction in curvilinear SAR with aperture errors.
In Communications and Information Technology, 2005. ISCIT 2005. IEEE International Symposium on,
volume 2,
pages 1227-1230,
2005.
Keyword(s): SAR Processing,
Non-Linear Flight Path,
SAR Tomography,
feature extraction,
radar imaging,
synthetic aperture radar,
aperture errors compensation,
curvilinear SAR,
curvilinear synthetic aperture radar,
inverse SAR,
phase compensation technique,
phase information,
range information,
reference bins,
three-dimensional target features extraction.
Abstract: In curvilinear synthetic aperture radar (SAR), it is difficult to compensate the curvilinear aperture errors. The algorithm proposed in this paper, based on the phase compensation technique in inverse SAR (ISAR), compensates the aperture errors by using the range and phase information in the reference bins. Consequently, the scatterers' three-dimensional (3-D) features are extracted from the compensated data. Simulation results show that the distribution obtained via the new algorithm, compared with the original distribution, only shifts in three-dimensional position without structure changing. So, the new algorithm is a novel 3-D features extraction algorithm for curvilinear SAR. - Qulin Tan, Zhou Fu, Zhengjun Liu, and Jiping Hu. An experiment for high resolution airborne SAR imaging based on phase gradient autofocus. In Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International, volume 5, pages 3322-3324, 25-29 July 2005. Keyword(s): SAR Processing, Autofocus, Phase Gradient Autofocus. [bibtex-key = Tan2005]
-
G.J. Vigurs,
M.S. Wood,
and M.L. Jarrett.
Non-linear synthetic aperture radar techniques.
In Radar Conference, 2005. EURAD 2005. European,
pages 13-16,
6-7 Oct. 2005.
Keyword(s): SAR Processing,
Non-Linear Flight Path,
Simulation,
MTI,
Moving Target Indication.
Abstract: The Non-Linear Synthetic Aperture Radar (SAR) technique uses a combination of platform manoeuvre and novel processing to separate the effects of a target’s radial velocity and cross-range displacement, giving accurate estimates of both. The technique provides high resolution images free from the image distortion caused in conventional SAR imagery by moving targets, and allows the accurate target location of both stationary and moving objects. The technique also allows the platform to fly a wide range of planned and unplanned manoeuvres, improving platform survivability in potentially hostile environments. -
Emmanouil Alivizatos,
Athanasios Potsis,
Andreas Reigber,
Alberto Moreira,
and Nikolaos K. Uzunoglou.
SAR Processing with Motion Compensation using the Extended Wavenumber Algorithm.
In Proc. of EUSAR 2004 - 5th European Conference on Synthetic Aperture Radar,
pages 157-160,
2004.
Keyword(s): SAR Processing,
omega-k,
Range Migration Algorithm,
Wavenumber Domain Algorithm,
Extended omega-k,
Extended Wavenumber Domain Algorithm,
Motion Compensation,
Squinted SAR,
Airborne SAR.
Abstract: Modern Synthetic Aperture Radar (SAR) systems are continuously developing into the direction of higher spatial resolution and new modes of operation. This requires the use of high bandwidths, combined with wide azimuthal integration intervals. For focusing such data, a high quality SAR processing method is necessary, which is able to deal with more general sensor parameters. Wavenumber domain (Omega-K) processing is commonly accepted to be an ideal solution of the SAR focusing problem [1]. However, it is mostly applicable on spaceborne SAR data where a straight sensor trajectory is given. In case of airborne SAR data, wavenumber domain processing has certain limitations in performing high-precision motion compensation. In this paper, a detailed description of the motion errors in the wavenumber domain, as well as a motion compensation technique in this domain is formulated. The correction of the motion errors in the two dimensional spectral domain can result in very accurate second order motion compensation. This procedure can also be combined with a 2D sub-aperture technique, which results in a fully azimuth-frequency adaptive block processing scheme. The reason why the wavenumber MoCo can be very critical especially in low frequency-widebeam and high squinted SAR data, is that in these cases wavelength dependent corrections become mandatory. -
Elke Boerner,
Hauke Fiedler,
Gerhard Krieger,
and Josef Mittermayer.
A new Method for Total Zero Doppler Steering.
In IGARSS '04, International Geoscience and Remote Sensing Symposium,
Sept 2004.
Keyword(s): SAR Processing,
Steering,
Yaw Steering,
Attitude Steering,
Doppler Centroid,
Zero Doppler Steering,
Total Zero Doppler Steering.
Abstract: This paper describes a new method to perform zero Doppler steering, namely Total Zero Doppler Steering. It is developed for spaceborne synthetic aperture radar (SAR) systems. This new method combines the yaw-steering with an additional pitch-steering, resulting in a Doppler centroid of theoretically zero Hertz over the whole desired range of incidence angles for the whole orbit and simultaneously for left and right looking geometry. -
F. Bordoni,
A. Jakobsson,
F. Lombardini,
and F. Gini.
Layover solution in multibaseline InSAR using interpolated arrays.
In Proceedings of the Fourth IEEE International Symposium on Signal Processing and Information Technology, 2004,
pages 175-178,
2004.
Keyword(s): SAR Processing,
Interferometry,
SAR Tomography,
Tomography,
Layover,
Array Interpolation,
MUSIC,
WSF.
Abstract: This work deals with the problem of direction of direction of arrival estimation of interferometric synthetic aperture radar (InSAR) signals in presence of layover. The focus here is on realistic acquisition systems with a low number of phase centres and nonuniform array geometry. An interpolated array approach is proposed, in order to apply spectral estimation techniques designed for uniform linear arrays. In particular, interpolated MUSIC and weighted subspace fitting (WSF) algorithms are developed and investigated. -
Knut Eldhuset.
Raw signal simulation for very high resolution SAR based on polarimetric scattering theory.
In IGARSS '04, International Geoscience and Remote Sensing Symposium,
Sept 2004.
Keyword(s): SAR Processing,
Simulation,
SAR Simulator,
Raw Data Simulator,
Polarimetric Scattering Theory.
Abstract: A method for raw signal simulation for extended SAR scenes with very high resolution is described. This simulator shall handle resolution better than 1 m, squinted geometry, elliptical orbit motion and use a polarimetric reflectivity matrix. Classical polarimetric scattering theory is based on electromagnetic harmonic fields using Maxwell s equations, Green s function, Huygens principle and Kirchhoff s approximation. Here, the scattering theory is modified for a chirp field. Calculated expressions for the scattered chirp field or the reflectivity matrix are presented. Such a reflectivity matrix can then be input to the inverse-EETF4 for raw data generation. -
Joachim H. G. Ender,
I. Walterscheid,
and Andreas R. Brenner.
New aspects of bistatic SAR: processing and experiments.
In IGARSS '04, International Geoscience and Remote Sensing Symposium,
Sept 2004.
Keyword(s): SAR Processing,
Bistatic SAR,
Bistatic Processing,
Backprojection,
omega-k,
Range Migration Algorithm,
Wavenumber Domain Algorithm,
Range-Doppler Algorithm,
Airborne SAR.
Abstract: The interest in bistatic synthetic aperture radar, using separated transmitter and receiver flying on different platforms, has been increasing rapidly over the last years. The reason for this are specific advantages, like the reduced vulnerability in military systems, forward looking SAR imaging, additional information about the target, or increased RCS (see e.g. [1]). Nevertheless, besides technical problems (see [2]) - like the synchronisation of the oscillators, the involved adjustment of transmit pulse versus receive gate timing, antenna pointing, flight coordination, double trajectory measurement and motion compensation - the processing of bistatic radar data is still not sufficiently solved. Some of the possibilities and problems will be discussed. The second part of this paper deals with a bistatic experiment performed in November 2003: Two SAR systems of FGAN have been flown on two different airplanes, the AER-II system has been used as a transmitter and the PAMIR system as a receiver. Different spatially invariant flight geometries have been tested. High resolution bistatic SAR images were generated successfully. -
G. Fornaro,
Giorgio Franceschetti,
and S. Perna.
Motion Compensation of Squinted Airborne SAR Raw Data: Role of Processing Geometry.
In IGARSS '04, International Geoscience and Remote Sensing Symposium,
Sept 2004.
Keyword(s): SAR Processing,
omega-k,
Range Migration Algorithm,
Wavenumber Domain Algorithm,
Extended omega-k,
Extended Wavenumber Domain Algorithm,
Motion Compensation,
Squinted SAR,
Airborne SAR.
Abstract: We discuss the role of processing geometry and the problem of motion compensation for non zero squint in airborne SAR processing. -
G. Fornaro and F. Serafino.
Spaceborne 3D SAR Tomography: experiments with ERS data.
In Geoscience and Remote Sensing Symposium, 2004. IGARSS '04. Proceedings. 2004 IEEE International,
volume 2,
pages 1240-1243,
2004.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
data acquisition,
image processing,
radar cross-sections,
radar imaging,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
tomography,
3D back-scattering property,
ERS data,
European Remote Sensing,
multibaseline SAR experiment,
spaceborne 3D SAR tomography.
Abstract: This paper presents the first results of a multibaseline SAR experiments for the reconstruction of the 3D back-scattering properties of ground scenes by using ERS data. -
Othmar Frey,
Erich Meier,
Daniel Nüesch,
and Achim Roth.
Geometric Error Budget Analysis for TerraSAR-X.
In Proc. of EUSAR 2004 - 5th European Conference on Synthetic Aperture Radar,
Ulm, Germany,
pages 513-516,
May 25-27 2004.
Keyword(s): SAR Processing,
SAR Geocoding,
Geocoding,
Error Budget Analysis,
TerraSAR-X,
Atmospheric Correction,
Atmospheric Path Delay,
Ionosheric Path Delay,
Antenna Gain Pattern Correction.
Abstract: The impact of potential error sources on geocoded products has been investigated with respect to the high resolution capabilities of the TerraSAR-X sensor. Datum shift parameters, maps, digital terrain and surface models have been identified as external error sources. The accuracy of the geocoded products depends heavily on the quality and availability of this information, which underlies regional variations. Error sources closely related to the sensor are its position, sampling window start time and Doppler centroid frequency. Another error source is given by atmospheric refraction. Ionospheric and atmospheric path delays have a considerable impact. Appropriate modeling can mitigate this effect. Further, high requirements on radiometric accuracy ask for an improved antenna gain pattern correction, which depends on the actual elevation angle and the terrain height. -
F. Gini and F. Lombardini.
Multibaseline post-processing for SAR interferometry.
In Sensor Array and Multichannel Signal Processing Workshop Proceedings, 2004,
pages 20-29,
2004.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
radar detection,
radar imaging,
radiowave interferometry,
synthetic aperture radar,
3D mapping,
XTI-SAR,
additive white Gaussian noise,
cross-track InSAR system,
multibaseline InSAR processing,
multicomponent signal corruption estimation,
multiplicative noise,
radar reflectivity retrieval,
semitransparent volume scattering layer,
signal detection,
synthetic aperture radar,
tomography.
Abstract: In this paper we provide a tutorial description of recent results of the research activity at the University of Pisa on multibaseline (MB) InSAR processing. The main focus is on the problem of retrieving both heights and radar reflectivities of natural layover areas by means of a cross-track InSAR (XTI-SAR) system. It is formulated as the problem of detecting and estimating a multicomponent signal corrupted by multiplicative noise and by additive white Gaussian noise. The problem of estimating the number of signal components in the presence of speckle is also addressed. Finally, a brief mention is given to recent research trends on robust methods for non-perfectly calibrated arrays and on MB-SAR tomography, which is an extension of MB-InSAR for full 3D mapping of semitransparent volume scattering layers. -
B. Hallberg,
G. Smith,
A. Olofsson,
and Lars M. H. Ulander.
Performance Simulation of Spaceborne P-band SAR for Global Biomass Retrieval.
In IGARSS '04, International Geoscience and Remote Sensing Symposium,
Sept 2004.
Keyword(s): SAR Processing,
Simulation,
P-Band,
Biomass Retrieval,
Forest.
Abstract: This paper evaluates the use of a spaceborne lowfrequency synthetic aperture radar (SAR) for forest biomass retrieval. Airborne radar data are used as input to a SAR simulator in which SAR system parameters of the assumed spaceborne system and propagation effects in the ionosphere (primarily scintillation and Faraday rotation) are modelled. The simulations are performed for different iononospheric perturbation states. Some simulated spaceborne low-frequency SAR images over boreal forest are shown and their usefulness for forest biomass retrieval are studied and discussed. The results indicate that it is possible to separate boreal forest into three classes assuming a moderate distorted ionosphere. -
Charles V. Jakowatz,
Daniel E. Wahl,
David A. Yocky,
Brian K. Bray,
Wallace J. Bow,
and John A. Richards.
Comparison of algorithms for use in real-time spotlight-mode SAR image formation.
In Edmund G. Zelnio and Frederick D. Garber, editors,
,
volume 5427,
pages 108-116,
2004.
SPIE.
Keyword(s): SAR Processing,
Real-Time,
Real-Time Processing,
Real-Time SAR,
Video SAR,
Polar Format Algorithm,
PFA,
Range Migration Algorithm,
RMA,
omega-k,
Comparison of Algorithms,
Comparison of Focusing Algorithms,
overlapped subaperture algorithm,
OSA,
Spotlight SAR,
Spotlight-mode data.
[bibtex-key = jakowatzWahlYockyBrayBowRichardsSpotlightComparisonOfAlgorithms2004]
-
Michael Jehle,
Othmar Frey,
David Small,
Erich Meier,
and Daniel Nüesch.
Improved Knowledge of SAR Geometry through Atmospheric Modelling.
In Proc. of EUSAR 2004 - 5th European Conference on Synthetic Aperture Radar,
Ulm, Germany,
pages 909-911,
May 25-27 2004.
Keyword(s): Geocoding,
Geometry,
Atmospheric Path Delay,
Ionosheric Path Delay,
Tropospheric Path Delay,
Atmospheric Modelling.
Abstract: Satellites observing and measuring the Earth s surface with electromagnetic waves are subject to atmospheric path delays. These atmospheric effects on radar signal propagation modify the signal velocity and direction and can be considered by simple modeling. In order to increase the geolocation accuracy of spaceborne SAR applications we developed a software tool that accounts for atmospheric path delays. Well-calibrated spaceborne ENVISAT-ASAR data are used to investigate improvements to knowledge of the geometry of the scene. -
David Kettler,
Doug Gray,
and Nick Redding.
The Point Spread Function for UWB SAR Imaging using Inversion of the Circular Radon Transform.
In Proc. of EUSAR 2004 - 5th European Conference on Synthetic Aperture Radar,
Ulm, Germany,
pages 175-178,
May 25-27 2004.
Keyword(s): SAR Processing,
Fourier-Hankel Inversion,
Hankel Transform,
Abel Transform,
Circular Radon Transform,
CRT,
Radon Transform,
Ultra-Wideband SAR,
Airborne SAR.
Abstract: This paper summarises how SAR data collection can be viewed as taking the Circular Radon Transform of the ground reflectivity and outlines how image formation can be achieved by inverting the CRT via a Fourier-Hankel transform. An expression for the point spread function (PSF) of the imaging process is arrived at by means of an analytic inversion for a Gaussian. This PSF shows the effect on the image of the finite synthetic aperture. Illustrations of the PSF to show its range and aperture dependence are given. -
John C. Kirk,
Don Woods,
and Joe Salzman.
Efficient Motion-Tolerant Fopen SAR Processing.
In Proc. of EUSAR 2004 - 5th European Conference on Synthetic Aperture Radar,
volume 1,
Ulm, Germany,
pages 179-182,
May 25-27 2004.
Keyword(s): SAR Processing,
omega-k,
Range Migration Algorithm,
Wavenumber Domain Algorithm,
Motion Compensation,
Thinned Range Migration Algorithm,
Airborne SAR.
Abstract: The Range Migration Algorithm (RMA) is an efficient approach to process strip map data with large range cell migration. However, it is sensitive to cross track motion of the radar. To provide for a degree of motion tolerance, an applicable approach is to retain only a portion of the full processed image around a central reference point (CRP) where motion compensation is applied. This results in throwing away that part of the image that is potentially defocused with the result that this discarded data area has to be reprocessed with additional CRPs. This results in a processing in-efficiency that can greatly drive up the processing requirements. An efficient algorithm is being developed which alleviates this wasted data processing in-efficiency problem. This new algorithm, called tyhe Thinned RMA, operates by filtering the data to just the area to be processed and then resampling the data at a much lower rate. The RMA then proceeds normally, but now operates on a much reduced cross track data size. This approach can also provide a much greater tolerance to cross track motion. To date the algorithm as been developed and tested on simulated data and recorded phase history data. Processing speed-ups of approximately 4 to 1 are being achieved compared to a full RMA algorithm that retains a small patch about the CRP. Ultimately the algorithm will progress to a two stage version that will provide the optimum in motion tolerance and processing efficiency. -
Gerhard Krieger,
Nicolas Gebert,
and Alberto Moreira.
SAR Signal Reconstruction from Non-Uniform Displaced Phase Centre Sampling.
In IGARSS '04, International Geoscience and Remote Sensing Symposium,
Sept 2004.
Keyword(s): SAR Processing,
Bistatic SAR,
Bistatic Processing,
Dual Receive Antenna.
Abstract: The displaced phase centre (DPC) technique will enable a wide swath SAR with high azimuth resolution. In a classic DPC system, the PRF has to be chosen such that the SAR carrier moves just one half of its antenna length between subsequent radar pulses. Any deviation from this PRF will result in a nonuniform sampling of the synthetic aperture. This paper shows that an unambiguous reconstruction of the SAR signal is also possible in case of such a non-optimum PRF. For this, an innovative reconstruction algorithm is derived, which enables a recovery of the unambiguous Doppler spectrum also in case of a non-uniform sampling of the synthetic aperture. This algorithm will also have a great potential for multistatic satellite constellations as well as the dual receive antennas in Radarsat II and TerraSAR-X. -
J. Li and P. Stoica.
Versatile robust Capon beamforming: theory and applications.
In Sensor Array and Multichannel Signal Processing Workshop Proceedings, 2004,
pages 38-42,
July 2004.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
Capon,
Robust Capon Beamforming,
RCB,
acoustic imaging,
array signal processing,
beam steering,
channel bank filters,
covariance matrices,
ground penetrating radar,
image resolution,
interference (signal),
landmine detection,
radar imaging CBRCB,
CPRCB,
DCRCB,
FLGPR imaging system,
RCF,
SCB,
acoustic imaging,
constant-beamwidth RCB,
constant-powerwidth RCB,
covariance fitting formulation,
doubly constrained robust Capon beamformer,
forward-looking ground penetrating radar,
interference rejection,
landmine detection,
rank-deficient robust Capon filter-bank approach,
resolution,
spectral estimation,
standard Capon beamformer,
steering vector.
Abstract: The standard Capon beamformer (SCB) has better resolution and much better interference rejection capability than the data-independent beamformer provided that the array steering vector corresponding to the signal-of-interest (SOI) is accurately known. However, whenever the knowledge of the SOI steering vector is imprecise (as is often the case in practice), the performance of the Capon beamformer may become worse than that of the data-independent beamformer. Most of the early suggested robust adaptive methods are rather ad hoc in that the choice of their parameters are not directly related to the uncertainly of the steering vector. In this paper we provide a review of the recently proposed robust Capon beam-former (RCB) and doubly constrained robust Capon beamformer (DCRCB), which directly address the uncertainty of the steering vector and naturally extend the covariance fitting formulation of SCB to the case of uncertain steering vectors by enforcing a double constraint on the steering vector, viz. a constant norm constraint and an uncertainty set constraint. We also present several extensions and applications of RCB including constant-powerwidth RCB (CPRCB) and constant-beamwidth RCB (CBRCB) for acoustic imaging, rank-deficient robust Capon filter-bank (RCF) approach for spectral estimation, and rank-deficient RCB for landmine detection using forward-looking ground penetrating radar (FLGPR) imaging systems. The excellent performances of RCB, DCRCB, and the various extensions of RCB are demonstrated by simulated and experimental examples. -
M. Limbach,
B. Gabler,
and Ralf Horn.
Fine Resolution, fully Polarimetric P-band subsystem for E-SAR -- Technique and Results.
In Proc. of EUSAR 2004 - 5th European Conference on Synthetic Aperture Radar,
pages 275-278,
2004.
Keyword(s): SAR Processing,
ESAR,
P-Band,
Airborne SAR,
Polarimetry,
Polarimetric P-Band.
Abstract: The design of the P-band subsystem of DLR's E-SAR system is presented in this paper. With a new microstrip patch antenna and other key hardware components a bandwidth of more than 28% at a lower centre frequency is achieved. The system parameters correspond to a range resolution better than 2.1m. Measurements of system gain, cross polarisation suppression, system sensitivity and some antenna parameters are shown. -
F. Lombardini,
Joachim H. G. Ender,
L. Rössing,
M. Galletto,
and L. Verrazzani.
Experiments of interferometric layover solution with the three-antenna airborne AER-II SAR system.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS '04,
volume 5,
pages 3341-3344,
September 2004.
Keyword(s): SAR Processing,
Capon,
MUSIC,
airborne radar,
antenna arrays,
radar imaging,
radiowave interferometry,
remote sensing by radar,
synthetic aperture radar,
terrain mapping,
InSAR,
SAR imagery,
SAR Interferometry,
advanced multibaseline operation,
airborne experimental radar,
calibration,
dual-baseline single-pass SAR interferometer,
electromagnetic tomography,
higher-order interferometry,
hybrid spatial spectral estimation,
interferometric layover solution,
layover-free interferometry,
multichannel operation,
nonparametric spectral estimation,
parametric spectral estimation,
spectral analysis,
synthetic aperture radar,
three-antenna airborne AER-II SAR System,
three-antenna nonuniform array data.
Abstract: Interest is recently growing in exploiting the advanced multibaseline operation of synthetic aperture radar interferometry (InSAR) to solve layover effects, that can degrade conventional SAR and InSAR imagery. In this work we report about: experiments of the functionality of "layover-free" or "higher-order" interferometry with the dual-baseline single-pass SAR interferometer AER-II. Non-parametric, parametric and hybrid spatial spectral estimators are applied to process the three-antenna non uniform array data. Calibration issues, first real data results and impact of order selection are discussed for a bridge over the valley scene -
José Márquez-Martìnez and Josef Mittermayer.
Analysis of Range Ambiguity Suppression methods in SAR by using a Novel Range Ambiguity Raw Data Simulator.
In Proc. of EUSAR 2004 - 5th European Conference on Synthetic Aperture Radar,
volume 1,
Ulm, Germany,
pages 593-596,
May 25-27 2004.
Keyword(s): SAR Processing,
Simulation,
SAR Simulator,
Raw Data Simulator,
Range Ambiguity Suppression,
ESAR,
Airborne SAR.
Abstract: This paper presents a novel range ambiguity raw data simulator (RAS). The simulator was used to investigate range ambiguity suppression obtained by means of up and down chirp coding for point targets and realistic scenes including extended targets. A pre-processing technique for up and down-chirp processing has also been developed. Different applications are investigated using data from the experimental SAR system from DLR (ESAR), either oriented to point target detection or to extended target analysis. Several image processing results with different range ambiguities ratios are presented. -
Yibo Na,
Hongbo Sun,
Yee Hui Lee,
Ling Chiat Tai,
and Hian Lim Chan.
Performance evaluation of back-projection and range migration algorithms in foliage penetration radar imaging.
In Image Processing, 2004. ICIP '04. 2004 International Conference on,
volume 1,
pages 21-24,
2004.
ISSN: 1522-4880.
Keyword(s): SAR Processing,
Backprojection,
omega-k,
Comimage reconstruction,
radar imaging,
synthetic aperture radar,
FOPEN SAR imaging,
back-projection algorithm,
computer-aided tomography,
foliage penetration radar imaging,
image reconstruction,
range migration algorithm,
seismic migration techniques,
synthetic aperture radar.
Abstract: In this paper, two relatively novel synthetic aperture radar (SAR) imaging techniques, namely the back-projection algorithm and range migration algorithm, are discussed. The back-projection algorithm originates from the medical imaging reconstruction technique called computer-aided tomography whereas the range migration algorithm is derived from seismic migration techniques. In this paper, both the back-projection and range migration algorithms are applied to foliage penetration (FOPEN) SAR imaging and performance comparisons are made. The simulations and experimental data processing results show that both algorithms are suitable for FOPEN radar imaging and that theoretical performances can be achieved. -
Lam H. Nguyen,
Marc Ressler,
and Mehrdad Soumekh.
Signal Processing and Image Formation Using Low-Frequency Ultra-Wideband Radar Data.
In Russell S. Harmon,
J. Thomas Broach,
and John H. Holloway(Jr.), editors,
Proceedings of SPIE: Detection and Remediation Technologies for Mines and Minelike Targets IX,
volume SPIE5415,
pages 1053-1064,
2004.
Keyword(s): SAR Processing,
Ultra-Wideband SAR,
Backprojection,
Wavefront Reconstruction,
Wavenumber Domain Algorithm,
omega-k,
Image Formation,
RFI Suppression,
Digital Spotlighting.
Abstract: In support of the U.S. Army Night Vision And Electronic Sensors Directorate (NVESD), the U.S. Army Research Laboratory (ARL) has developed infrastructures, tools, and algorithms to evaluate the data set. This paper focuses on the signal processing and image formation using data from a low-frequency ultrawideband sensor. We examine various issues that are associated with this class of SAR databases such as radio frequency interference (RFI), the effects of spectral notches, and errors in motion measurement to image quality. We show the pre-processing steps such as frequency and phase calibration, radio frequency interference extraction. We also show the application of digital spotlight technique to correct motion errors introduced by the measurement system. Finally, we show the resulting SAR imagery of various minefields. -
Lam H. Nguyen,
Marc Ressler,
D. Wong,
and Mehrdad Soumekh.
Enhancement of backprojection SAR imagery using digital spotlighting preprocessing.
In Radar Conference, 2004. Proceedings of the IEEE,
pages 53-58,
2004.
Keyword(s): SAR Processing,
Backprojection,
Time-Domain Backprojection,
Digital Spotlighting,
Boom-SAR,
Self-Induced Resonance Suppression,
SIR Suppression,
RFI Suppression,
Doppler effect,
antialiasing,
image enhancement,
radar imaging,
synthetic aperture radar,
ARL boom-SAR data,
Doppler aliasing suppression,
PRF,
SAR data filtering scheme,
SAR imagery enhancement,
azimuth-compressed SAR data,
backprojection SAR imagery,
digital spotlighting preprocessing,
image fidelity improvement,
radar radiation pattern,
side lobe artifacts.
Abstract: This paper examines signal processing methods for improving the fidelity of backprojection SAR imagery using a preprocessing method that suppresses Doppler aliasing as well as other side lobe artifacts that are introduced by the radar radiation pattern. The algorithm, known as digital spotlighting, imposes a filtering scheme on the azimuth-compressed SAR data, and manipulates the resultant spectral data to achieve a higher PRF to suppress the Doppler aliasing. The merits of the algorithm are studied using the ARL boom-SAR data. -
Lam H. Nguyen,
Tuan Ton,
David Wong,
and Mehrdad Soumekh.
Adaptive coherent suppression of multiple wide-bandwidth RFI sources in SAR.
In Edmund G. Zelnio and Frederick D. Garber, editors,
Algorithms for Synthetic Aperture Radar Imagery XI,
volume 5427,
pages 1-16,
2004.
SPIE.
Keyword(s): SAR Processing,
RFI Suppression,
Ultra-Wideband SAR,
Wide-Bandwidth RFI,
Boom-SAR,
Self-Induced Resonance Suppression,
SIR Suppression,
RFI Suppression.
Abstract: This paper is concerned with suppressing multiple wide-bandwidth radio frequency interference (RFI) sources in SAR systems. A coherent processing of passive radar (sniff) data is presented to diminish the effects of wide-bandwidth as well as narrow-bandwidth RFI sources in the active radar data that are collected by a SAR system. The approach is based on a two-dimensional adaptive filtering of the active SAR data using the passive sniff data as the reference signal. A similar mathematical (signal) model and processing is also utilized to suppress self-induced resonance (SIR) signals that are generated by the interaction of the radar-carrying platform and the transmitted radar signal. Results are shown using the Army Research Laboratory (ARL) low-frequency, ultra-wideband (UWB) imaging radar (Boom-SAR). -
David Small,
Michael Jehle,
Erich Meier,
and Daniel Nüesch.
Radiometric Terrain Correction Incorporating Local Antenna Gain.
In Proc. of EUSAR 2004 - 5th European Conference on Synthetic Aperture Radar,
Ulm, Germany,
pages 929-932,
May 25-27 2004.
Keyword(s): SAR Geocoding,
Radiometric Correction,
Radiometric Terrain Correction,
Radiometric Calibration,
Calibration,
Local Antenna Gain.
Abstract: Radiometric terrain correction consists of normalising a SAR image for well-understood backscatter contributions in order to amplify less easily apparent influences (e.g. thematic land cover variance). A rigorous modelling of the SAR image formation process includes consideration of how foreshortening and layover create ambi guity when connecting map geometry grid points to and from counterparts in radar geometry (slant or ground range vs. azimuth). A radar amplitude image simulation is formed by iterating through a facetted DEM, calcu lating the accumulated illuminated area at every range and azimuth coordinate in radar geometry. We show how DEM-based image simulations gain further realism by incorporating knowledge of the SAR antenna's elevation an-tenna gain pattern (AGP). Although typical AGP corrections assume an ellipsoidal Earth, the AGP is actually draped upon the Earth's terrain. We quantify differences between estimates of local antenna gain and illuminated area performed using (a) the typical ellipsoid assumption, (b) a DEM. We demonstrate application of local antenna gain knowledge within the image simulation process using ENVISAT ASAR images acquired over Switzerland. We introduce a weighted resolution approach for robust combination of multiple radiometrically normalised terrain geocoded backscatter maps. -
David Small,
Erich Meier,
and Daniel Nüesch.
Robust radiometric terrain correction for SAR image comparisons.
In IGARSS '04, International Geoscience and Remote Sensing Symposium,
volume 3,
pages 1730-1733,
2004.
Keyword(s): backscatter,
radiometry,
remote sensing by radar,
terrain mapping,
AGP,
ENVISAT ASAR images,
Earth ellipsoid,
Earth rolling terrain,
SAR imagery,
Switzerland,
composite radar map,
ideal flat terrain,
local antenna gain pattern,
mountainous terrain,
normalized images,
radar backscatter coefficient,
radar brightness coefficient,
radar equation,
radiometric errors,
radiometrically calibrated images,
robust radar image simulation,
robust radiometric terrain correction,
robust technique,
terrain geocoded images,
terrain induced modulations,
terrain variations.
Abstract: We demonstrate a robust technique for radiometric terrain correction, whereby terrain-induced modulations of the radiometry of SAR imagery are modelled and corrected. The resulting normalized images may be more easily compared with other data sets acquired at different incidence angles, even opposing look directions. We begin by reviewing the radar equation, pointing out simplifications often made to reduce the complexity of calculating the backscatter coefficient, normalized either by ground area (/spl sigma//sup 0/), or illuminated area projected into the look direction (/spl gamma//sup 0/). The integral over the illuminated area is often approximated by a scale factor modelling a simple planar slope, departing only slightly from "ideal" flat terrain: for /spl gamma//sup 0/, the radar brightness (/spl beta//sup 0/) is normalized via modulation with the tangent of the local incidence angle. We quantify the radiometric errors introduced by ignoring terrain variations, comparing results based on (a) a robust radar image simulation-based approach properly modelling variations in local illuminated area, and (b) an ellipsoidal Earth assumption. A second simplification often made in solving for backscatter using the radar equation is the assumption that the local antenna gain does not vary significantly from a simple model draping the antenna gain pattern (AGP) across an Earth ellipsoid, returning the local antenna gain as a function of slant range alone. In reality, the AGP is draped across the Earth's rolling terrain retrieval of properly calibrated backscatter values should model these variations and compensate for them: although smaller than the errors caused by not property modelling variations in local illuminated area, they can be significant. We use well-calibrated and annotated ENVISAT ASAR images acquired over Switzerland to show how robust radiometric terrain correction, incorporating models for the variations of local illuminated area with terrain enables calibrated mixture of imagery acquired at differing incidence angles. Only robust retrieval of backscatter values enables such inter-mode comparisons - a capability that significantly reduces the required revisit time for monitoring changes to the radar backscatter. In conclusion, we describe a techn- ique for combining a set of terrain-geocoded and radiometrically calibrated images derived from ascending and descending passes and multiple incidence angles to create composite radar backscatter maps. At each point, the contribution of each image to the composite is weighted according to its local resolution. The resulting composite image manifests relatively uniform high ground resolution, even in highly mountainous terrain. -
David Small,
Betlem Rosich,
Erich Meier,
and Daniel Nüesch.
Geometric Calibration and Validation of ASAR Imagery.
In CEOS SAR Workshop 2004,
Ulm,
May 2004.
Keyword(s): SAR Geocoding,
Calibration,
Validation,
Quality Assessment,
ASAR,
ENVISAT.
Abstract: We describe work conducted to calibrate and then validate the geometry of ENVISAT ASAR products. A systematic error in range location was observed in ASAR products during the commissioning phase. A careful and complete analysis has been performed to establish the precise error. It has been compensated by updating the range gate bias (or sampling window start time bias). Validation of the absolute location accuracy of most ASAR products was performed subsequently. The location of surveyed targets is predicted using the satellite state vectors and ancillary timing information via the range and Doppler equations. The prediction's accuracy is affected by instrument bias, ionospheric and atmospheric path delay, as well as target survey errors. Transponders are in addition subject to internal delay uncertainty. The positions of the strong transponder and corner reflector targets in the images are measured to sub-sample accuracy by employing large oversampling factors. Initial and residual bias determinations were made using image acquisitions covering transponders and corner reflectors in the Netherlands, Canada, and Switzerland. Using a large number of independent targets helps reduce the influence of their independent survey errors. The highest resolution slant range single look complex (SLC) products (IMS, APS) were mainly used for testing. In addition, absolute location error was also measured on selected ground range products (IMP, APP, IMM, APM, WSM). Some ground range products also require treatment of multiple slant/ground range polynomials - proper handling is validated. For all test cases processed with precise orbits to date, the residual bias in the slant range direction has been smaller than the size of a single range sample. Predictability of target image location within ASAR image products is very high - better than experience with ERS-1/2, JERS-1, and RADARSAT-1. This result is encouraging, as it opens possibilities for ground control point (GCP) free terrain-geocoding and simplified interferometric processing. - David Small, Betlem Rosich, Adrian Schubert, Erich Meier, and Daniel Nüesch. Geometric Validation of Low and High-Resolution ASAR Imagery. In Proc. of the 2004 Envisat & ERS Symposium, ESA SP-572, Salzburg, Sep. 2004. Keyword(s): SAR Processing, SAR Geocoding, Geocoding, Validation, Geometric Validation, ASAR, ENVISAT. [bibtex-key = smallRosichSchubertMeierNueesch04:SubmittedBistatic]
-
Junfeng Wang and Xingzhao Liu.
SAR Automatic Range-Migration Correction.
In IGARSS '04, International Geoscience and Remote Sensing Symposium,
Sept 2004.
Keyword(s): SAR Processing,
range-Doppler Algorithm,
omega-k,
Range Migration Algorithm,
Wavenumber Domain Algorithm,
Range-Migration Correction.
Abstract: A new idea is presented to correct range migration in SAR imaging. In the range-Doppler domain, all the samples at a given Doppler frequency constitute a Doppler slice. Different Doppler slices are found to have similar envelopes. According to this similarity, the Doppler slices are shifted in range to correct range migration. This technique applies even without the prior information about the relative motion between the radar and the target. -
W. - M. Boerner.
Recent Advances in Extra-Wide-Band Polarimetry, Interferometry and Polarimetric Interferometry in Synthetic Aperture Remote Sensing and its Applications.
In IEE Proceedings - Radar, Sonar and Navigation,
volume 150,
pages 113-124,
June 2003.
Keyword(s): SAR Processing,
Interferometry,
Pol-InSAR,
RFI Suppression,
Extra-WideBand SAR,
WideBand SAR.
Abstract: The development of radar polarimetry and radar interferometry is advancing rapidly, and these novel radar technologies are revamping 'synthetic aperture radar imaging' decisively. The successive advancements are sketched beginning with the fundamental formulations and highlighting the salient points of these diverse remote sensing techniques. Whereas with radar polarimetry the textural fine-structure, target orientation and shape, symmetries and material constituents can be recovered with considerable improvements above that of standard 'amplitude-only polarisation radar'; with radar interferometry the spatial (in depth) structure can be explored. In 'polarimetric-interferometric synthetic aperture radar (POL-IN-SAR) imaging' it is possible to recover such co-registered textural plus spatial properties simultaneously. This includes the extraction of 'digital elevation maps (DEM)' from either 'fully polarimetric (scattering matrix)' or 'interferometric (dual antenna) SAR image data takes' with the additional benefit of obtaining co-registered three-dimensional 'POL-IN-DEM' information. Extra-wide-band POL-IN-SAR imaging - when applied to 'repeat-pass image overlay interferometry' - provides differential background validation and measurement, stress assessment, and environmental stress-change monitoring capabilities with hitherto unattained accuracy, which are essential tools for improved global biomass estimation and also for wetland assessment and monitoring. More recently, by applying multiple parallel repeat-pass EWB-POL-D(RP)-IN-SAR imaging along stacked (altitudinal) or displaced (horizontal) flight-lines will result in 'tomographic (multi-interferometric) polarimetric SAR stereo-imaging', including foliage- and ground-penetrating capabilities. In addition, various closely related topics of (i) acquiring additional and protecting existing spectral windows of the 'natural electromagnetic spectrum (NES)' pertinent to remote sensing; and (ii) mitigation against common 'radio frequency interference (RFI)' and intentional 'directive jamming of airborne and spaceborne POL-IN-SAR imaging platforms' are appraised. - H.J. Callow, M.P. Hayes, and P.T. Gough. Autofocus of stripmap SAS data using the range-variant SPGA algorithm. In OCEANS 2003. Proceedings, volume 5, pages 2422-2426Vol.5, 22-26 Sept. 2003. Keyword(s): SAR Processing, Autofocus, Phase Curvature Autofocus, Phase Gradient Autofocus, PGA, SPGA, Stripmap Phase Gradient Algorithm, Synthetic Aperture Sonar, SAS. [bibtex-key = Callow2003a]
-
H.J. Callow,
M.P. Hayes,
and P.T. Gough.
Stripmap phase gradient autofocus.
In OCEANS 2003. Proceedings,
volume 5,
pages 2414-2421,
September 2003.
Keyword(s): SAR Processing,
Autofocus,
Phase Curvature Autofocus,
Phase Gradient Autofocus,
PGA,
SPGA,
Stripmap Phase Gradient Algorithm,
Synthetic Aperture Sonar,
SAS.
Abstract: Current sonar autofocus techniques for blur removal originate in the radar community but have not provided a complete solution for Synthetic Aperture Sonar (SAS) imagery. The wide-beam, wide-band nature of SAS imagery makes implementation of Synthetic Aperture Radar (SAR) autofocus techniques difficult. This paper describes a generalisation of the standard Phase Gradient Antofocus (PGA) algorithm used in spotlight SAR that allows operation with stripmap SAS geometries. PGA uses prominent points within the target scene to estimate image blurring and phase errors. We show how PGA can be generalised to work with wide-band, wide-heam stripmap geometries. The SPGA method works by employing wavenumher domain 2D phase estimation techniques. The 2D phase errors are related to aperture position errors using the wavenumber transform. Robust sway estimates are obtained by using redundancy over a number of target points. We also present an improved Phase Curvature Autofocus (PCA) algorithm using the wavenumher transform. Preliminary results from the two algorithms (both on field-collected and simulated data sets) are presented and related to those obtained using previous methods. A discussion of SPGA's benefits over traditional algorithms and the limitations of the SPGA algorithm. The SPGA algorithm was found to perform better than 2-D PCA on both simulated and field-collected data sets. Further testing on a variety of target scenes and imagery is required to investigate avenues of autofoeus improvement. -
Hubert-M.J. Cantalloube and Pascale Dubois-Fernandez.
Airborne X-band SAR imaging with 10 cm resolution - technical challenge and preliminary results.
In ,
volume 1,
pages 185-187 vol.1,
July 2003.
Keyword(s): SAR Processing,
Motion Compensation,
Autofocus,
radar cross-sections,
radar imaging,
radar resolution,
remote sensing by radar,
synthetic aperture radar 2 1/2 D surface modelling,
Doppler algorithms,
Ku bands,
RAMSES,
X-Band,
X-band SAR imaging,
Airborne SAR,
antenna pattern compensation method,
back-injection synthesis algorithm,
carrier trajectory,
clutter appearance,
differential GPS-hybridized inertial navigation unit,
high resolution clutters,
isotropic echoes,
matching cross-range resolution,
optical surface modelling,
phase tracking,
point-like echoes,
Range Migration Algorithm,
resolution cell,
synthetic aperture radar,
TDBP,
Time-Domain Back-Projection,
temporal-domain synthesis algorithm,
texture simulations,
omega-k algorithm.
Abstract: RAMSES airborne SAR system bandwith was recently increased to 1.2 GHz in X and Ku bands, yielding (unweighted) 3 dB range resolution of 11 cm. Synthesis of SAR images with matching cross-range resolution, requires long integration time thus disqualifies temporal-domain back-injection synthesis algorithm as impractically slow. The wider relative bandwidth also disqualifies simplified range/Doppler types of algorithms because the hypothesis of proportionality between Doppler and squint is no more valid. Therefore, we implemented a fast frequency-domain synthesis algorithm (Ω-k or range-migration algorithm) and designed a new deterministic motion and antenna pattern compensation method for it. Since the required accuracy on carrier trajectory exceeded the performance of our differential GPS-hybridized inertial navigation unit, we implemented an autofocus based on the phase tracking of several isotropic point-like echoes. Since the resolution cell is only a few wavelength wide, clutter appearance and statistics is unusual. We present here some typical examples for high resolution clutters and compare with texture simulations from optical 2 1/2 D surface modelling. -
Shane R. Cloude and Konstantinos P. Papathanassiou.
Three-stage inversion process for polarimetric SAR interferometry.
In ,
volume 150,
pages 125-134,
June 2003.
ISSN: 1350-2395.
Keyword(s): SAR Processing,
decorrelation,
electromagnetic wave scattering,
inverse problems,
parameter estimation,
radar imaging,
radar polarimetry,
remote sensing by radar,
synthetic aperture radar geometrical approach,
ground topography,
interferograms,
inversion accuracy,
mean extinction estimation,
model structure,
multiple polarisation channels,
parameter estimates,
parameter estimation,
polarimetric SAR interferometry,
random canopy,
simulated vector coherent SAR data,
single frequency sensor,
temporal decorrelation,
three-stage inversion process,
two-layer coherent scattering model,
vegetation height,
vertical tree structure.
Abstract: The authors provide a new geometrical approach for the inversion of a two-layer coherent scattering model, widely used for the interpretation of polarimetric interferometric SAR data. It has been shown in several recent publications that, by using interferograms in multiple polarisation channels, estimation of vegetation height, underlying ground topography and mean extinction is possible. Furthermore, this can be achieved with a single frequency sensor without the need for a separate reference DEM, other a priori information or the use of data-specific regression formulas. The authors first review the details of this approach and then develop a three-stage inversion procedure to illustrate the steps involved in parameter estimation. They then consider several possible sources of error in the inversion. In particular, they concentrate on the effects of vertical tree structure and on the effects of temporal decorrelation on inversion accuracy. It is shown that the former leads to errors, mainly in the extinction estimation, while the latter does not change the model structure but reduces the available parameter set and increases the variance of the parameter estimates. Finally, the new algorithm is applied to simulated vector coherent SAR data for a random canopy. -
C. Colesanti,
A. Ferretti,
C. Prati,
and F. Rocca.
Multi-image satellite SAR interferometry: state of the art and future trends.
In Proc. Int. Radar Conf.,
pages 239-244,
September 2003.
Keyword(s): SAR Processing,
InSAR,
SAR Interferometry,
electromagnetic wave scattering,
radar imaging,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
ground deformation data,
high precision elevation data,
multi-image satellite SAR interferometry,
permanent scatterers technique,
spaceborne interferometric SAR images,
sparse privileged point-wise radar target grid,
synthetic aperture radar.
Abstract: In this paper, we wish to review briefly the principles underlying a recently developed approach, known as the permanent scatterers (PS) technique and aimed at the joint exploitation of a series of spaceborne interferometric SAR images for the retrieval of high precision elevation and ground deformation data on a sparse grid of privileged point-wise radar targets. -
Ian G. Cumming,
Y. L. Neo,
and Frank Wong.
Interpretations of the Omega-K Algorithm and Comparisons with other Algorithms.
In IGARSS '03, International Geoscience and Remote Sensing Symposium,
2003.
Keyword(s): SAR Processing,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Stolt Mapping,
Chirp Scaling Algorithm,
Range-Doppler Algorithm,
Comparison of Algorithms.
Abstract: This paper presents a Fourier interpretation of the Omega-k SAR processing algorithm that helps explain the key Stolt mapping operation. An approximate form of the algorithm is sometimes used, and we explain how both forms of the Omega-k compare with the range Doppler and the chirp scaling algorithms. Finally, a brief discussion is given on which radar parameters allow the accurate use of each algorithm. -
M. De Stefano and Andrea Monti-Guarnieri.
Robust Doppler Centroid estimate for ERS and ENVISAT.
In Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International,
volume 6,
pages 4062-4064,
2003.
Keyword(s): SAR Processing,
Doppler Centroid Estimation,
Doppler Ambiguity Resolver,
DAR,
ENVISAT,
ERS,
MLBF,
RADARSAT,
Wavelength Diversity,
WDAR,
Multilook Beat Frequency,
fine polynomial estimation,
higher order technique,
robust Doppler centroid estimation,
robustness,
second order statistic estimator,
unambiguous Doppler estimation.
Abstract: The algorithm presented is capable of retrieving the correct DC ambiguity and to fit a fine polynomial estimate both on uniform and contrasted scenes. The core of the algorithm exploits a block wise processing: in each block a coarse unambiguous estimate is provided by exploiting both a second order statistic estimator (WDAR) and a higher order technique (MLBF). The final, fine estimate of the unambiguous Doppler is achieved by jointly exploiting the coarse unambiguous estimate with a fine, ambiguous one. The proposed algorithm accounts carefully for large variation of DC with range, like for recent Emergency Backup Mode of ERS and RADARSAT. The final estimate and its confidence is provided by a weighted average of the block measures. Tuning of the weights and additional check ensure robustness. The estimate of the offset frequency constant is then approached and a solution for calibrating its value is provided. -
Joachim H. G. Ender.
SAR/MTI with Multi-Subaperture Phased Arrays.
In Proceedings of the Tyrrhenian International Workshop on Remote Sensing TIWRS,
pages 313-331,
September 2003.
Keyword(s): SAR,
Multi-Channel SAR,
MTI,
AER-II,
PAMIR,
Subaperture Processing,
Phased Array Radar,
SAR Processing,
Multi-Channel SAR,
MTI,
AER-II,
PAMIR,
Subaperture Processing,
Phased Array Radar,
Tomography,
SAR Tomography.
Abstract: SAR systems equipped with a phased array antenna and several receiver channels offer additional flexibility and extended target signatures. Besides of the electronic beam-steering permitting interesting operational modes, the partitioning into subarrays with parallel receiving channels opens the possibility to receive multichannel signals containing much more information about the scene than in the classical single channel case. In this paper, we start from a general signal model for wideband multi-channel data. This signal model serves as a basis for the development of algorithms for some special array configurations and applications. The approach is done from a signal theoretical point of view including statistical analysis. Most of the methods apply also to small groups of classical antennas, so the considerations are not limited to phased arrays. The airborne experimental multi-channel SAR systems AER and PAMIR serve as demonstrators for extended possibilities of imaging radars equipped with active phased arrays and parallel receiving channels. The presented examples have been achieved with these demonstrators. Comments: + Much und MTI, but topics like SAR tomography are covered as well. Anything that is multi-channel. -
Joachim H.G. Ender and Andreas R. Brenner.
PAMIR - a wideband phased array SAR/MTI system.
In IEE Proceedings - Radar, Sonar and Navigation,
number 3,
pages 165-172,
June 2003.
Keyword(s): SAR Processing,
PAMIR,
MTI,
GMTI,
Time-Domain Backprojection,
Backprojection,
Spotlight SAR,
FGAN,
X-Band,
InSAR 1.8 GHz,
ISAR,
IfSAR,
Phased Array Multifunctional Imaging Radar,
X-band radar,
airborne imaging radar,
electronically steerable phased array,
ground moving objects,
ground moving target indication,
ground-moving target indication,
inverse SAR,
long-range imaging capabilities,
multichannel capability,
operational modes,
receive channels,
reconfigurable phased array antenna,
reconnaissance tasks,
resolution,
signal bandwidth,
single-pass interferometric SAR,
space-time adaptive processing,
spaceborne imaging radar,
subapertures,
surveillance,
synthetic aperture radar,
wideband phased array SAR/MTI system,
wideband system design.
Abstract: Air- and spaceborne imaging radar systems in forthcoming surveillance and reconnaissance tasks have to meet increasingly severe demands. The next generation of top-level synthetic aperture radar (SAR) systems will comprise, among others, high resolution and long-range imaging capabilities, highly sensitive ground moving target indication and a multitude of sophisticated operational modes. The variety of tasks can be fulfilled only by the use of a reconfigurable phased array antenna together with a comprehensive wideband system design and a multichannel capability. At FGAN a new experimental X-band radar has been conceived, which will possess in its final upgrade an electronically steerable phased array consisting of 16 autonomous and reconfigurable subapertures, five independent receive channels, and a total signal bandwidth of about 1.8 GHz. The sensor is called PAMIR (Phased Array Multifunctional Imaging Radar). It is envisaged to demonstrate SAR imaging at a very high resolution and for a long range. The fine resolution will also be achieved with inverse SAR (ISAR) imaging of ground moving objects. Furthermore, the number of receive channels will allow ground-moving target indication (GMTI) by space?time adaptive processing and single-pass interferometric SAR (IfSAR) with a very high 3-D resolution. In its current stage of extension PAMIR is operable with one receive channel and a mechanically steerable antenna array. The system design and the intended capabilities of PAMIR are described. Ground-based and airborne experimental results concerning high-resolution SAR and ISAR imaging are also presented. -
Tuo Fu,
Meiguo Gao,
and Yuan He.
An improved scatter selection method for phase gradient autofocus algorithm in SAR/ISAR autofocus.
In Neural Networks and Signal Processing, 2003. Proceedings of the 2003 International Conference on,
volume 2,
pages 1054-1057Vol.2,
14-17 Dec. 2003.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus.
[bibtex-key = Fu2003]
-
A. Jakobsson,
F. Gini,
and F. Lombardini.
Layover solution in multibaseline INSAR using robust beamforming.
In Signal Processing and Information Technology, 2003. ISSPIT 2003. Proceedings of the 3rd IEEE International Symposium on,
pages 328-331,
14-17 Dec. 2003.
[bibtex-key = Jakobsson2003]
-
A. Jakobsson,
F. Lombardini,
and F. Gini.
Weighted subspace fitting of interferometric phases for multibaseline SAR interferometry.
In Signal Processing and Its Applications, 2003. Proceedings. Seventh International Symposium on,
volume 1,
pages 321-324vol.1,
1-4 July 2003.
[bibtex-key = Jakobsson2003a]
-
J.S. Lee,
D.L. Schuler,
T.L. Ainsworth,
and W.-M. Boerner.
Polarization orientation estimation and applications: a review.
In IEEE International Geoscience and Remote Sensing Symposium, 2003. IGARSS '03.,
volume 1,
pages 428-430,
July 2003.
Keyword(s): SAR Processsing,
calibration,
covariance matrices,
data acquisition,
radar polarimetry,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
terrain mapping DEM generation,
AIRSAR,
L-band,
polarimetric SAR images,
P-band,
polarimetric SAR images,
SIR-C,
circular polarization covariance matrix,
estimation algorithms,
ocean surface feature characterization,
polarimetric SAR data compensation,
polarimetric calibration,
polarization orientation angle shifts,
polarization orientation estimation,
radar frequency,
scattering media,
terrain slopes,
Airborne SAR.
Abstract: We review estimation algorithms and applications of polarization orientation angle shifts induced by terrain slopes. We develop a unified analysis of estimation algorithms based on circular polarization covariance matrix. The effect of radar frequency, scattering media, and polarimetric calibration will also be discussed. Applications to DEM generation, polarimetric SAR data compensation and ocean surface feature characterization will be mentioned. SIR-C, and JPL AIRSAR L-band and P-band polarimetric SAR images are used for demonstration. -
F. Lombardini.
Differential tomography: a new framework for SAR interferometry.
In Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International,
volume 2,
pages 1206-1208vol.2,
21-25 July 2003.
[bibtex-key = Lombardini2003]
-
F. Lombardini and F. Gini.
Multiple reflectivities estimation for multibaseline InSAR imaging of layover extended sources.
In Radar Conference, 2003. Proceedings of the International,
pages 257-263,
3-5 Sept. 2003.
[bibtex-key = Lombardini2003b]
-
Fabrizio Lombardini and Andreas Reigber.
Adaptive spectral estimation for multibaseline SAR tomography with airborne L-band data.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS '03.,
volume 3,
pages 2014-2016,
2003.
Keyword(s): SAR Processing,
Tomography,
SAR Tomography,
Capon spectral estimator,
adaptive Capon spectral estimator,
spectral estimation,
multibaseline 3D SAR focusing,
multi-baseline SAR,
InSAR,
Multibaseline InSAR,
Forestry.
Abstract: In the recent years there has been growing interest in exploiting multibaseline (MB) SAR interferometry in a tomographic framework, to produce full 3D imaging e.g. of forest layers. However, Fourier-based MB SAR tomography is generally affected by unsatisfactory imaging quality due to a typically low number of baselines and their irregular distribution. In this work, we apply the more modern adaptive Capon spectral estimator to the vertical image reconstruction problem, using real airborne MB data. A first demonstration of possible imaging enhancement in real-world conditions is given. -
A. Löw and W. Mauser.
Generation of geometrically and radiometrically terrain corrected ScanSAR images.
In IEEE International Geoscience and Remote Sensing Symposium, 2003. IGARSS '03,
volume 6,
pages 3995-3997,
2003.
Keyword(s): SAR Processing,
SAR Geocoding,
Radiometric Calibration,
Calibration,
Radiometric Correction,
backscatter,
microwave imaging,
radiometry,
synthetic aperture radar,
terrain mapping,
topography (Earth),
ENVISAT,
ASAR,
RADARSAT,
biophysical parameters,
geometrically terrain corrected ScanSAR images,
ScanSAR,
geophysical parameters,
microwave imagery,
quantitative image analysis,
radiometrically terrain corrected ScanSAR images,
surface topography,
synthetic aperture imagery.
Abstract: Inclined surface topography diminishes the geometric and radiometric quality of synthetic aperture imagery. The correction of these effects becomes indispensable when quantitative image analysis is performed with respect to the derivation of geo- and biophysical parameters. Due to their spatial extent and frequent availability, ScanSAR image products extend the operative range of microwave imagery and have a high potential for numerous operational applications over larger areas. The study presents a procedure for a pre-operational terrain correction of ScanSAR imagery as acquired by RADARSAT and ENVISAT ASAR. -
P. Prats,
J.J. Mallorqui,
and A. Broquetas.
Calibration of interferometric airborne SAR images using a multisquint processing approach.
In Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International,
volume 7,
pages 4353-4355vol.7,
21-25 July 2003.
Keyword(s): SAR Processing,
Motion Compensation,
ESAR,
L-Band,
X-Band,
Airborne SAR,
Squinted SAR,
Interferometry,
azimuth phase undulations,
calibration,
image pairs,
interferometric airborne synthetic aperture radar systems,
InSAR,
multisquint processing,
phase error correction,
phase error detection,
single-pass interferometrie data.
[bibtex-key = PratsMallorquiBroquetas2003a:MoComp]
-
A. Reigber,
A. Potsis,
E. Alivizatos,
N. Uzunoglu,
and A. Moreira.
Wavenumber domain SAR focusing with integrated motion compensation.
In Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International,
volume 3,
pages 1465-1467,
2003.
Keyword(s): SAR Processing,
omega-k,
Range Migration Algorithm,
Wavenumber Domain Algorithm,
Extended omega-k,
Extended Wavenumber Domain Algorithm,
Motion Compensation,
Squinted SAR,
Airborne SAR.
Abstract: In this paper a new SAR data processing algorithm denoted with Extended Omega-K (EOK) is analytically presented and formulated. EOK algorithm combines the advantages of the high accurate focusing of the wavenumber domain algorithms with high precision motion compensation. The new EOK algorithm integrates a two-step range adaptive motion compensation correction in the general formulation of the wavenumber domain algorithm, leading to a new SAR processing scheme, which is much more robust concerning long synthetic apertures and squint angle than for example the chirp-scaling method. Additionally it offers the possibility of processing wideband low-frequency airborne SAR data up to near-wavelength resolution. The performance and the accuracy of the new EOK SAR data processing algorithm is demonstrated using simulated data. -
A. Reigber,
P. Prats,
R. Scheiber,
and J.J. Mallorqui.
Options for high-precision motion compensation for airborne differential SAR interferometry.
In Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International,
volume 7,
pages 4356-4358vol.7,
21-25 July 2003.
Keyword(s): SAR Processing,
D-InSAR,
InSAR,
ESAR,
Airborne SAR,
L-Band,
differential interferometry,
Interferometry,
Motion Compensation,
RME,
Residual Motion Errors,
Spectral Diversity,
Multi-Squint Processing,
Digital Elevation Model,
DEM.
[bibtex-key = ReigberPratsScheiberMallorqui2003:MoComp]
-
M. Rombach and João Moreira.
Description and applications of the multipolarized dual band OrbiSAR-1 InSAR sensor.
In Radar Conference, 2003. Proceedings of the International,
volume 5,
pages 245-250,
2003.
Keyword(s): electromagnetic wave reflection,
electromagnetic wave scattering,
radar polarimetry,
remote sensing by radar,
Spaceborne SAR,
synthetic aperture radar,
terrain mapping,
topography (Earth),
vegetation mapping,
OrbiSAR-1 InSAR sensor,
area mapping,
bald earth height information,
biomass,
canopy top foliage scattering,
digital elevation,
forest-classification,
ground elevation,
interferometric SAR,
multipolarized dual band InSAR sensor,
permanent cloud covered tropical areas,
soil reflection,
surface elevation,
topographic maps,
trunk reflection,
vegetation density,
vegetation height,
vegetation/microwave interaction.
Abstract: In the last decade, interferometric SAR (InSAR) has reached a wide acceptance as being a suitable tool to generate high-precision digital elevation models. Especially in tropical areas, with nearly permanent cloud coverage, InSAR provides a cost-efficient means for mapping large areas in short time periods. However, the interaction of microwaves with vegetation is strongly dependant on their frequency, demanding a careful interpretation of the extracted information. Short waves like X-band are mainly scattered back from the top of the canopy, whereas P-band penetrates the foliage and gets reflected from trunk and soil, thus carrying the phase information (and therefore the height information as well) from bald earth. For the generation of topographic maps, generally the ground elevation rather than the surface elevation is required, whereas the surface and ground elevation together enable the estimation of additional physical parameters like vegetation height, density, or biomass. -
R. Scheiber.
A three-step phase correction approach for airborne repeat-pass interferometric SAR data.
In Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International,
volume 2,
pages 1190-1192vol.2,
21-25 July 2003.
[bibtex-key = Scheiber2003]
-
David Small,
Jürgen Holzner,
Hannes Raggam,
Detlef Kosmann,
and Adrian Schubert.
Geometric performance of ENVISAT ASAR products.
In IGARSS '03, International Geoscience and Remote Sensing Symposium,
volume 2,
pages 1121-1123,
2003.
Keyword(s): SAR Processing,
SAR Geocoding,
Geocoding,
synthetic aperture radar,
terrain mapping,
topography (Earth),
ASAR geolocation accuracy,
ASAR images,
ASAR slant range products,
DEM,
ENVISAT,
ASAR,
ENVISAT ASAR products,
ESA,
alternating polarization,
corner reflectors,
derivative geocoded products,
ellipsoid-geocoded products,
estimation techniques,
geometric performance,
ground control points,
ground range precision,
ground range products,
ground range transformation,
map features,
medium resolution products,
multiple validation,
nominally geocoded GTC locations,
radar geometry image products,
radar image,
single look complex,
topographic maps,
transponders,
wide swath mode acquisitions,
zero-Doppler iteration.
Abstract: We describe validation measurements of the geometric accuracy of ASAR images, measured redundantly via independent methods. Our tests include image (IM), alternating polarization (AP), and wide swath (WS) mode acquisitions over a variety of test sites. ASAR's slant range products (IMS/APS) require a slightly different validation methodology than ground range precision (IMP, APP) and medium resolution products (IMM, APM, WSM). A third approach is required for ellipsoid-geocoded products (IMG, APG). The most highly accurate validation is possible with single look complex (SLC) data (IMS and APS products), as all other product types lose resolution during multilooking. For a library of ground control points (GCPs) including map features such as bridges or road intersections, as well as (where available) transponders and corner reflectors, we use surveyed or map-measured position information (together with the delay value in the case of transponders) to solve the zero-Doppler iteration and predict the position of the GCP as an azimuth and slant range coordinate in the radar image. In the case of ground range products (e.g. IMP, APP, IMM, APM, WSM) the predicted slant range value is additionally transformed by a slant to ground range transformation tro determine the predicted image coordinate. The GCP feature is then either measured by inspection of a detected image, or localized automatically within the neighborhood of the prediction. GCPs are measured within the radar geometry image products, derivative geocoded products, and topographic maps, providing their measured map, radar geometry, and nominally geocoded GTC locations. Radar image locations are compared to map reference values and statistics of differences are tabulated. We compare the accuracies of the estimates achievable using transponders and map GCPs. Based on the suite of products (and accompanying orbit information) available to us, we establish a methodology for estimating a preliminary sampling window start time bias. The multiple validation and estimation techniques used ensure robust determination of ASAR geolocation accuracy. -
Gordon C. Staples and Joost van der Sanden.
RADARSAT-2 Polarimetry Applications.
In Anais XI SBSR, Simposio Brasileiro de Sensoriamento Remoto 2003, INPE, Belo Horizonte, Brasil,
volume 1,
pages 2383-2389,
2003.
Keyword(s): Radarsat-2,
Polarimetry,
Applications.
Abstract: RADARSAT-2, planned for a mid 2004 launch, is an advanced polarimetric SAR satellite. Key features of RADARSAT-2 are high resolution (3 m), polarimetric modes, enhanced ground system providing rapid satellite tasking and near-real time data processing, improved image location accuracy, and on-board solid state recorders. The focus of this paper is on the RADARSAT-2 polarimetric applications including agriculture, cartography, disaster management, forestry, geology, hydrology, oceans, and sea ice. -
B. Subiza,
E. Gimeno-Nieves,
J.M. Lopez-Sanchez,
and J. Fortuny-Guasch.
An Approach to SAR Imaging by Means of Non-Uniform FFTs.
In IEEE International Geoscience and Remote Sensing Symposium, 2003. IGARSS '03.,
volume 6,
pages 4089-4091,
July 2003.
Keyword(s): SAR Processing,
Range Migration Algorithm,
RMA,
omega-k,
NUFFT,
Non-Uniform Fast Fourier Transform,
Fast Fourier Transform,
FFT,
geophysical techniques,
interpolation,
radar imaging,
synthetic aperture radar,
SAR imaging algorithm,
Stolt interpolation,
computation time,
computational efficiency,
numerical simulations,
seismic migration SAR processing.
Abstract: In this study, the potential use of the non-uniform FFT (NUFFT) in SAR imaging is analyzed. The main objective has been the improvement of the computational efficiency and image accuracy of seismic migration SAR processing. Different NUFFT methods have been implemented and tested in order to choose an adequate technique for the imaging problem. Our approach consists in substituting both the Stolt interpolation and the final range inverse FFT, in the omega-k algorithm, by a single NUFFT. Numerical simulations illustrate the performance of the new method and the influence of the selection of NUFFT parameters in the precision and computation time of the SAR imaging algorithm. - T.J. Sutton, H.D. Griffiths, S.A. Chapman, R. Crook, and M. Way. Optimizing a three-stage autofocus system for synthetic aperture imaging using a UUV. In OCEANS 2003. Proceedings, volume 5, pages 2433-2437Vol.5, 22-26 Sept. 2003. [bibtex-key = Sutton2003a]
-
T.J. Sutton,
H.D. Griffiths,
A.P. Hetet,
Y. Perrot,
and S.A. Chapman.
Experimental validation of autofocus algorithms for high-resolution imaging of the seabed using synthetic aperture sonar.
In Radar, Sonar and Navigation, IEE Proceedings -,
volume 150,
pages 78-83,
April 2003.
[bibtex-key = Sutton2003]
-
L. R. Varshney and D. Thomas.
Sidelobe reduction for matched filter range processing.
In Proc. IEEE Radar Conf.,
pages 446 - 451,
5-8 2003.
ISSN: 1097-5659.
Keyword(s): SAR Processing,
Apodization,
Spatially Variant Apodization,
Dual Apodization,
leakage energy minimization,
linear frequency modulation,
matched filtering,
nonlinear frequency modulation,
pulse compression ratio,
range sidelobes,
sidelobe control,
sidelobe reduction,
chirp modulation,
frequency modulation,
matched filters,
minimisation,
nonlinear filters,
radar detection,
radar interference,
radar signal processing.
Abstract: Linear frequency modulation (LFM) matched filtering results in range sidelobes. These sidelobes are often objectionable because they may mask small targets or may be mistaken for targets themselves. Various methods of sidelobe control are investigated and their performance is measured. The methods of sidelobe reduction include dual apodization, spatially variant apodization, and leakage energy minimization. Nonlinear frequency modulation (NLFM) matched filtering is also investigated. A simulation was run to compare LFM with sidelobe control and NLFM, all using moderately low pulse compression ratios. Results suggest that generally, NLFM matched filtering has better detection and estimation characteristics than LFM with sidelobe control. -
David A. Yocky and Charles V. Jakowatz.
Automated wide-angle SAR stereo height extraction in rugged terrain using shift-scaling correlation.
In Andrew G. Tescher, editor,
,
volume 5203,
pages 10-20,
2003.
SPIE.
Keyword(s): SAR Processing,
Stereo SAR,
Rugged Terrain,
Polar Format Algorithm,
PFA,
Spotlight SAR,
Spotlight-mode data.
[bibtex-key = yockyJakowatzStereoHeightExatraction]
-
P. Berardino,
G. Fornaro,
R. Lanari,
E. Sansosti,
F. Serafino,
and F. Soldovieri.
Multi-pass synthetic aperture radar for 3-D focusing.
In Geoscience and Remote Sensing Symposium, 2002. IGARSS '02. 2002 IEEE International,
volume 1,
pages 176-178 vol.1,
2002.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
geophysical techniques,
radar imaging,
radar theory,
remote sensing by radar,
synthetic aperture radar,
terrain mapping,
3D focusing,
SAR,
SVD,
geophysical measurement technique,
land surface,
multipass method,
penetration depth,
radar imaging,
radar remote sensing,
radar tomography,
singular value decomposition,
synthetic aperture radar,
terrain mapping.
Abstract: In the area of tomographic synthetic aperture radar processing we present a new technique that makes use of the singular value decomposition method to improve the resolution limits by including a-priori information about the radiation penetration depth. -
P. Berens.
Estimation of Carrier Track For High Precision SAR
Imaging Using Active Reference Reflectors.
In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar,
pages 241-244,
2002.
Keyword(s): SAR Processing,
Active Reflector,
Transponder,
Autofocus,
Carrier Track Estimation,
Flight Track Estimation,
Kalman Filter,
PAMIR,
X-Band. DGPS,
INS.
Abstract: Synthetic aperture radar (SAR) processing needs precise information about the path of the radar sensor. Modern DGPS and INS systems are commonly used. However, for highest resolution, additional auto focus algorithms have to be implemented. The success of these algorithms depends strongly on the scene. For a reliable estimation of the flight path, a new idea is presented: active reference reflectors (transponders) within the scene receive the pulses of the radar system and reradiates them with an additional amplitude modulation. The echoes from these transponders can be separated from the echoes of the scene and offer an excellent basis for the estimation of the antenna track. The paper describes the processing steps to separate the echoes of the transponders from the scene echoes. The range histories from the antenna to the transponders can be determined very precisely afterwards. A Kalman filter combines the measured ranges and motion information given by a DGPS system to estimate the carrier track. -
Andreas R. Brenner.
DISTRIBUTED SAR PROCESSING IN THE TIME DOMAIN.
In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar,
2002.
Keyword(s): SAR Processing,
Backprojection,
Time-Domain Backprojection,
PAMIR,
Distributed Processing,
Parallel Processing.
Abstract: The next generation airborne SAR sensors will comprise among others high resolution imaging capabilities (< 1 dm) and long range surveillance (> 100 km). This wide band and wide angle scenario requires an accurate modeling for SAR image formation with respect to motion compensation and focusing. This paper reports on the feasibility to jointly realise two approaches: First, a non-approximative time domain based SAR processor was developed. Second, because of its high computational burden, a distributed implementation on a heterogeneous workstation cluster by means of message passing interfaces was carried out. The evaluation of the processor on simulated data as well as an assessment of the distributed implementation is presented. The distributed time domain processor is successfully applied to data acquired with the new very wideband SAR sensor PAMIR of FGAN-FHR as well. -
Andreas R. Brenner and Joachim H. G. Ender.
First Experimental Results Achieved With The New Very Wideband SAR System PAMIR.
In Proc. of EUSAR 2002 - 4rd European Conference on Synthetic Aperture Radar,
pages 81-86,
2002.
Keyword(s): SAR Processing,
Time-Domain Backprojection,
Backprojection,
PAMIR,
Phased Array Multifunctional Imaging Radar,
AER-II,
X-Band,
High Resolution,
Wideband SAR.
Abstract: Imaging radar systems in forthcoming surveillance and reconnaissance tasks have to meet increasingly severe demands. The next generation airborne SAR should comprise high resolution imaging capabilities (< 1 dm), long range surveillance (> 100 km), moving target indication (< 1 m/s) and a multitude of complex operational modes like MultipleSpotlight, ScanMTI and ISAR imaging of ground moving targets. At FGAN-FHR, where the experimental SAR system AER-II is successfully operational since 1996, a new experimental X-band system was conceived, which will possess in its final stage of realisation an electronically steerable phased array, five independent receive channels, a total signal bandwidth of about 1.8 GHz and will support novel multifunctional radar modes. The system is termed PAMIR (Phased Array Multifunctional Imaging Radar) and operates in its current realization with one channel and two horn antennas. In this paper, the first experimental results concerning calibration, synthetic bandwidth, motion compensation and high resolution image formation are presented. -
Yu Ding and David C. Munson, Jr..
A fast back-projection algorithm for bistatic SAR imaging.
In Proc. Int. Conf. on Image Processing,
volume 2,
pages 449-452,
2002.
ISSN: 1522-4880.
Keyword(s): SAR Processing,
Backprojection,
Time-Domain Back-Projection,
Back-projection,
Bistatic SAR,
image reconstruction,
integral equations,
radar imaging,
synthetic aperture radar,
tomography 2D interpolation,
FFT,
Fourier domain,
Fourier domain data,
bistatic SAR imaging,
computational cost reduction,
direct Fourier reconstruction,
fast back-projection algorithm,
image formation algorithms,
integral equations,
near-field imaging,
nonCartesian grid,
simulation results,
synthetic aperture radar,
tomography.
Abstract: Using a far-field model, bistatic synthetic aperture radar (SAR) acquires Fourier data on a rather unusual, non-Cartesian grid in the Fourier domain. Previous image formation algorithms were mainly based on direct Fourier reconstruction to take advantage of the FFT, but the irregular coverage of the available Fourier domain data and the 2-D interpolation in the Fourier domain may adversely affect the accuracy of image reconstruction. Back-projection techniques avoid Fourier-domain interpolation, but ordinarily have huge computational cost. We present a fast back-projection algorithm for bistatic SAR imaging, motivated by a fast back-projection algorithm previously proposed for tomography. It has a reduced computational cost, on the same order as that of direct Fourier reconstruction. Furthermore, this approach can be used for near-field imaging. Simulation results verify the performance of this new algorithm. -
Armin W. Doerry,
Fred M. Dickey,
Louis A. Romero,
and John M. DeLaurentis.
Difficulties in Superresolving Synthetic Aperture Radar Images.
In Edmund G. Zelnio, editor,
Proc. of SPIE Vol. 4727, Algorithms for Synthetic Aperture Radar Imagery IX,
number 1,
pages 122-133,
2002.
SPIE.
Keyword(s): SAR Processing,
Superresolution,
Super Resolution,
High Resolution,
Fine Resolution,
Spectral Estimation.
Abstract: The ability to resolve Synthetic Aperture Radar (SAR) images to finer resolutions than the system bandwidths classically allow is a tantalizing prospect. Seemingly superresolution offers something for nothing, or at least something better than the system was designed for if only we process enough or right. Over the years this has proved to be a rather popular area of investigation, generating a wide variety of algorithms and corresponding claims of performance. Nevertheless, the literature on the fundamental underlying principles of superresolution as applied to SAR has been rather anemic. This paper addresses the following questions: What exactly is superresolution? and What is not really superresolution, but perhaps more aptly described as image enhancement? Is true superresolution possible? and to what degree? What constrains superresolution? and very importantly, How should we objectively test whether an image is in fact superresolved? Whereas superresolution concepts offer the potential of resolution beyond the classical limit, this great promise has not generally been realized. That is not to say that many reported algorithms have no useful effect on images. True superresolution is defined herein as the recovery of true scene spectrum, that allows more accurate scene rendering. The analytical basis for superresolution theory is outlined, and the application to SAR is then investigated as an operator inversion problem, which is generally ill posed. Noise inherent in radar data tends to severely inhibit significant enhancement of image resolution. A criterion for judging superresolution processing of an image is presented. -
Joachim H.G. Ender and Andreas R. Brenner.
PAMIR - A Wideband Phased Array SAR/MTI System.
In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar,
pages 157-162,
2002.
Keyword(s): SAR Processing,
PAMIR,
MTI,
GMTI,
Time-Domain Backprojection,
Backprojection,
Spotlight SAR,
FGAN,
X-Band,
InSAR 1.8 GHz,
ISAR,
IfSAR,
Phased Array Multifunctional Imaging Radar,
X-band radar,
airborne imaging radar,
electronically steerable phased array,
ground moving objects,
ground moving target indication,
ground-moving target indication,
inverse SAR,
long-range imaging capabilities,
multichannel capability,
operational modes,
receive channels,
reconfigurable phased array antenna,
reconnaissance tasks,
resolution,
signal bandwidth,
single-pass interferometric SAR,
space-time adaptive processing,
spaceborne imaging radar,
subapertures,
surveillance,
synthetic aperture radar,
wideband phased array SAR/MTI system,
wideband system design.
Abstract: Future air- and spacebased reconnaissance systems will be equipped with long range radar platforms of high flexibility, very high resolution in the order of one decimetre, covering a large angular sector and operating in sophisticated modes using multi channel signal processing. This variety of tasks can be fulfilled only by use of a phased array antenna. The need for a large bandwidth rises a lot of problems to be solved. To study the achievable performance in practice, FGAN-FHR has decided to build up an experimental system: PAMIR, the Phased Array Multifunctional Imaging Radar. Now, the system has come to a first stage allowing to gather preliminary radar data using a simple horn antenna. The phased array antenna is planned to be available in 2003. -
Andrea Monti-Guarnieri.
Processing Strategies for Phase Unwrapping for InSAR Applications.
In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar,
volume 1,
Ulm, Germany,
pages 349-352,
May 25-27 2002.
Keyword(s): SAR Processing,
Interferometry,
Phase Unwrapping,
Multifractal Modelling of Earth Topography.
Abstract: We exploit the terrain statistics derived from multifractal modelling of earth topography to derive some statistical properties of SAR interferogram, with particular reference to the gradient of the unwrapped phase. -
R.L. Morrison, Jr. and David C. Munson, Jr..
An experimental study of a new entropy-based SAR autofocus technique.
In Image Processing. 2002. Proceedings. 2002 International Conference on,
volume 2,
pages II-441-II-444vol.2,
22-25 Sept. 2002.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus.
[bibtex-key = Morrison2002]
-
Clifford J. Nolan and Margaret Cheney.
Synthetic Aperture Inversion For Non-Flat Topography.
In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar,
volume 1,
pages 105-108,
2002.
Keyword(s): SAR Processing,
Backprojection,
Non-Flat Topography.
Abstract: This paper considers Synthetic Aperture Radar and other synthetic aperture imaging systems in which a backscattered wave is measured from positions along a single flight track. We assume that the ground topography is known but not necessarily flat. We consider two cases, corresponding to the degree of directionality of the antenna. For the high-directivity case, we propose an imaging algorithm involving backprojection and a spatially varying filter that corrects for the antenna beam pattern, source waveform, and other geometrical factors. We give conditions on the relationship between the flight track and the topography to avoid artifacts. We show that the algorithm correctly reproduces certain features of the scene. For the case of an antenna with poor directionality, the image produced by the above algorithm contains artifacts. For this case, we analyze the strength of the artifacts relative to the strength of the true image. The analysis of this paper shows that the artifacts can be somewhat suppressed by increasing the curvature of the flight track and by keeping the desired target in view for as long as possible. -
Mats I. Pettersson.
Detection of Moving Target in Wideband SAR Using Fast Time Backprojection Processing.
In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar,
volume 1,
pages 217-220,
2002.
Keyword(s): SAR Processing,
Backprojection,
Fast Backprojection,
Time Domain Backprojection,
Moving Target Indication,
Ultra-Wideband SAR.
Abstract: A likelihood ratio test is proposed for moving target detection in an ultra wide frequency band and wide antenna beam (wide band) SAR system. The developed method combines time domain fast backprojection SAR processing methods with moving target detection. It saves computational load when all relative speeds can be tested using the same clutter suppressed sub-aperture beams. The proposed method is tested on narrow band radar data. -
Athanasios Potsis,
Andreas Reigber,
Emmanouil Alivizatos,
Alberto Moreira,
and Nikolaos K. Uzunoglou.
Comparison of Chirp Scaling and Wavenumber Domain Algorithms for Airborne Low-Frequency SAR.
In Francesco Posa, editor,
SAR Image Analysis, Modeling, and Techniques V,
volume 4883,
pages 25-36,
March 2002.
Keyword(s): SAR Processing,
Chirp Scaling Algorithm,
Extended Chirp Scaling Algorithm,
omega-k,
Range Migration Algorithm,
Wavenumber Domain Algorithm,
Comparison of Algorithms,
P-Band,
Wideband SAR,
Airborne SAR.
Abstract: In recent years a new class of Synthetic Aperture Radar (SAR) systems, using low frequencies, have emerged. The combination of low frequencies with high bandwidths allows a variety of new applications. Several new fields arise in forestry, biomass estimation and in archaeological and geological exploration. The P-band SAR technology benefits from technological advances in antenna design, low noise amplifiers, band pass filters, digital receiver technology, as well as new processing algorithms. For all the new applications of an airborne P-band SAR system, the high-resolution imaging is an important parameter, but it cannot be easily achieved with conventional processing techniques. In this paper, the performance and limitations of the Extended Chirp Scaling (ECS) algorithm and wavenumber domain Omega-K processing algorithm are analysed and discussed. Additionally, modifications of both algorithms are proposed, which optimise the respective algorithm for processing low frequency, wide-beam and wide-band SAR data. Despite of the inherent limitations of the above mentioned processing algorithms, a deterministic phase error, called "digital phase error", due to digital signal processing characteristics is formulated and its effect to the processed SAR data is analytically described. The analysis is carried out, using simulated low frequency airborne SAR data. -
Rolf Scheiber and V. M. Bothale.
Application of Multi-Look Techniques for Interferometric SAR Data.
In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar,
Cologne, Germany,
pages 77-80,
June 2002.
Keyword(s): SAR Processing,
Extended Chirp Scaling,
ECS,
Chirp Scaling,
CS,
Azimuth Focusing,
Multi-Look Processing,
Non-Linear Flight Paths,
Non-Linear SAR,
Interferometry,
InSAR,
E-SAR,
Airborne SAR,
SAR interferometry,
azimuth registration,
geophysical measurement technique,
image registration,
interferometric SAR,
land surface,
motion compensation,
multi-look method,
multi-pass airborne method,
multilook method,
radar remote sensing,
residual motion errors,
spectral domain multi-look approach,
synthetic aperture radar,
terrain mapping.
Abstract: Two different multi-look techniques for interferometric SAR data are investigated in the first part of this paper. The first one uses the box-car type of filter on the complex interferogram in the spatial domain, whereas the second one performs look-wise filtering of the individual images in the spectral domain with subsequent coherent addition of the look-wise interferograms. Next, it is shown that the flexibility of the spectral domain multi-look technique can be used for improved motion compensation and further for precisely updated estimation of azimuth misregistration offsets. This leads finally to the compensation of residual motion errors in case of multi-pass SAR interferometry. Investigations using data of the DLR owned airborne ESAR system are presented. -
Rolf Scheiber and V.M. Bothale.
Interferometric multi-look techniques for SAR data.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS '02,
volume 1,
pages 173-175,
2002.
Keyword(s): SAR Processing,
Extended Chirp Scaling,
ECS,
Chirp Scaling,
CS,
Azimuth Focusing,
Multi-Look Processing,
Non-Linear Flight Paths,
Non-Linear SAR,
Interferometry,
InSAR,
E-SAR,
Airborne SAR,
airborne radar,
geophysical signal processing,
geophysical techniques,
radar imaging,
remote sensing by radar,
synthetic aperture radar,
terrain mapping,
SAR interferometry,
azimuth registration,
geophysical measurement technique,
image registration,
interferometric SAR,
land surface,
motion compensation,
multi-look method,
multi-pass airborne method,
multilook method,
radar remote sensing,
residual motion errors,
spectral domain multi-look approach,
synthetic aperture radar,
terrain mapping.
Abstract: This paper addresses the benefits of the spectral domain multi-look approach for SAR interferometry. A comparison with the wide spread spatial averaging filter is included in the beginning. Next, it is shown that the flexibility of the spectral domain multi-look technique can be used for improved motion compensation and further for precisely updated estimation of azimuth misregistration offsets. This leads finally to the compensation of residual motion errors in case of multi-pass airborne SAR interferometry, e.g. for the E-SAR system of DLR. -
David Small,
Detlev Kosmann,
Jürgen Holzner,
Hannes Raggam,
Mauro Pirri,
Adrian Schubert,
Urs Krüttli,
Wolfgang Hummelbrunner,
and Martina Franke.
ASAR Level 1 Geolocation.
In Huguette Sawaya-Lacoste, editor,
Proceedings of the Envisat Calibration Review,
2002.
Keyword(s): SAR Geocoding,
Calibration,
Validation,
Quality Assessment,
ASAR,
ENVISAT.
Abstract: The localisation of ASAR products is vital to the ground segment, as overlays with independent information sources (typically in a map geometry) are only possible when the transformation between radar and map geometry is well calibrated. In this paper we describe calibration and validation steps undertaken to ensure that the transformations from radar to map geometry and back again are as accurate as possible. The ground segment of every new system must validate its geocoding chain to ensure that all parameters are treated consistently and are compatible with the product specifications. Special attention is devoted to the range and azimuth timing, as well as the orbit quality, cartographic and geodetic parameters describing the reference map projections. ASAR IMS and APS products are in the radar's native slant-range geometry. IMP, APP, IMM, APM, and WSM products are arranged in ground-range geometry. IMG and APG products are ellipsoid-geocoded (no terrain corrections applied), and delivered in map geometry. Each product type requires a slightly different calibration and validation methodology. -
David Small,
Adrian Schubert,
Urs Krüttli,
Erich Meier,
and Daniel Nüesch.
Preliminary Validation of ASAR Geometric Accuracy.
In Proceedings of ENVISAT Validation Workshop,
ESA-ESRIN, Frascati,
Dec. 2002.
Keyword(s): SAR Processing,
SAR Geocoding,
Geometric Accuracy,
Geometric Calibration,
Calibration,
Validation,
Quality Assessment,
ASAR,
ENVISAT.
Abstract: We describe preliminary validation experiments performed to validate the geometric accuracy of ENVISAT ASAR data acquired in image (IM) and alternating polarisation (AP) modes. ESA?s ASAR transponders in The Netherlands were used primarily as reference locations. Corner reflectors were deployed at test sites in Switzerland for comparison, and conventional ground control points such as bridges and road intersections were also used. The location of the reference points in radar geometry was predicted based upon the reflector?s geographical position (and delay term in the case of transponders) and compared with the actual measured location in the image products. We form tentative conclusions on the residual error sources. -
M. Weiss and P. Berens.
Motion compensation of wideband synthetic aperture radar with a new transponder technique.
In IEEE International Geoscience and Remote Sensing Symposium, 2002. IGARSS '02.,
volume 6,
pages 3649-3651,
June 2002.
Keyword(s): SAR Processing,
Motion Compensation,
calibration,
Autofocus,
phased array radar,
radar imaging,
synthetic aperture radar,
transponder,
PAMIR,
SAR,
active transponders,
calibration,
coherent integration,
echoes,
large synthetic aperture,
phased array multifunctional imaging radar,
radar pulses,
transponder technique,
wideband synthetic aperture radar.
Abstract: A high resolution synthetic aperture radar (SAR) system called phased array multifunctional imaging radar (PAMIR) is currently under development at FGAN. This system uses a very high bandwidth and performs a coherent integration along a large synthetic aperture. Problems in the area of calibration and motion compensation arise which can't be solved using common tools like corner reflectors. This paper describes the construction of active transponders which modulate and re-radiate radar pulses, discusses the advantages for calibration and shows how the echoes can be used for motion compensation in the SAR processing. -
Charles L. Werner,
Urs Wegmüller,
and Tazio Strozzi.
Processing Strategies for Phase Unwrapping for InSAR Applications.
In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar,
volume 1,
pages 353-356,
2002.
Keyword(s): SAR Processing,
Interferometry,
Phase Unwrapping,
Minimum Cost Flow,
Branch Cut.
Abstract: One of the most challenging aspects in the successful application of SAR interferometry (INSAR) is unwrapping the interferometric phase. The difficulties arise in attempting to find global optimization procedures with the best possible cost criteria for data that are both noisy and incomplete. Recent progress in this problem includes introduction of network flow optimization, and the use of triangular irregular networks for sparse data. Interferograms differ greatly in the difficulty to unwrap depending on the interferogram fringe complexity and correlation. We examine the characteristics of these types and present phase unwrapping strategies for each of these. -
Xiaojian Xu and R. M. Narayanan.
SAR image enhancement using noninteger Nyquist SVA technique.
In Proc. IEEE Antennas and Propagation Society International Symposium,
volume 4,
pages 298-301,
2002.
Keyword(s): SAR Processing,
Apodization,
Spatially Variant Apodization,
SVA,
ISAR,
image enhancement,
image resolution,
inverse SAR imaging,
iterative super SVA procedure,
noninteger Nyquist SVA,
nonlinear filtering,
sidelobe level reduction,
spatially variant apodization,
synthetic aperture radar,
iterative methods,
nonlinear filters.
Abstract: In SAR and inverse SAR (ISAR) imaging, conventional Fourier transform (FT) based image reconstruction techniques result in images with limited resolution. The down-range and cross-range resolutions of these algorithms are inversely proportional to the radar signal waveform bandwidth and to the synthetic aperture size, respectively. On the other hand, when modem spectral estimation methods are applied to radar imaging, these nonlinear techniques, usually called super resolution algorithms, offer improved resolution, better contrast, and reduced speckle. Spatially variant apodization (SVA) is a nonlinear filtering operation which significantly reduces the sidelobe levels without degrading mainlobe resolution of the sinc impulse response. In this work, we propose a modified version of noninteger Nyquist SVA and develop an iterative super SVA procedure for SAR and ISAR image enhancement. The proposed technique was successfully applied to various SAR/ISAR images. -
Richard Abrahamsson,
Jian Li,
Petre Stoica,
and Gunnar Thordarson.
Sensitivity of two autofocus algorithms to spatially variant phase errors.
In E. G. Zelnio, editor,
Proceedings of SPIE Vol. 5788,,
volume 4382 of Presented at the Society of Photo-Optical Instrumentation Engineers (SPIE) Conference,
pages 29-40,
August 2001.
Keyword(s): SAR Processing,
Phase Gradient Autofocus,
PGA,
AUTOCLEAN,
CLEAN,
Polar Format Algorithm,
Autofocus,
Residual Motion Errors,
Motion Errors,
Motion Compensation,
MoComp,
Motion Through Resolution Cells,
Spatially Variant Phase Errors,
Airborne SAR.
Abstract: In this paper we study the performance of two existing autofocus algorithms in a difficult SAR scenario. One algorithm is the well known phase gradient autofocus (PGA) algorithm and the other is the more recent AUTOCLEAN. The latter was introduced particularly with ISAR autofocus of a small target in mind and has been shown to outperform the PGA when range misalignment is present. This was expected as AUTOCLEAN, as opposed to PGA, has a built-in ability to compensate for range misalignment. In most available studies of the above autofocus algorithms spatially variant phase errors are absent or insignificant. The data used here is far-field SAR data collected over a large range of aspect angles. The target area is large, hence significant motion through resolution cells (MTRC) occurs due to target scene rotation. The polar format algorithm (PFA) is applied prior to autofocus to handle MTRC and compensate for off-track platform motion. However, the platform motion measurements used in PFA are not precise enough to compensate for the off-track motion and left after PFA are phase errors corrupting the data. These phase errors are spatially variant due to the large target scene and this violates the models for the autofocus algorithms above. This in contrast with the previously mentioned studies. We show that the performances of the autofocus algorithms considered are much deteriorated by the presence of spatially variant phase error but in different ways since the averaging of the phase error estimates is made differently in the two algorithms. Based on our numerical study of the two autofocus methods we try to rank them with respect to their sensitivity to spatially variant phase errors. -
Arnold Barmettler,
Erich Meier,
and Daniel Nüesch.
Development of an Ultra-Wideband SAR Processor.
In CEOS SAR Workshop 2001,
April 2001.
Keyword(s): SAR Processing,
Time Domain Backprojection,
Backprojection,
Ultra-Wideband SAR,
VHF SAR,
CARABAS,
Airborne SAR.
Abstract: Ultra-wideband SAR (UWB) has a high potential for applications because it makes high-resolution low-frequency imaging radar feasible. In combination with other SAR frequency bands, topographic or even tomographic mapping will be possible and geophysical parameters determinable. RSL has its own SAR processor for frequency bands from P- to X-band for various space- and airborne SAR sensors. For the processing of VHF UWB data, a new module for azimuth focusing was developed, due to the special system requirements at these wavelengths. We present first results from RSL's VHF processing chain based upon rangecompressed data from the Swedish CARABAS sensor system. -
Matthew C. Cobb and James H. McClellan.
Omega-k Quadtree UWB SAR Focusing.
In Proceedings of the 2001 IEEE Radar Conference,
pages 311-314,
May 2001.
Keyword(s): SAR Processing,
Wavefront Reconstruction,
Wavenumber Domain Algorithm,
omega-k Quadtree Processing,
omega-k,
Quadtree Processing,
Backprojection,
Ultra-Wideband SAR,
Ghost Target Elimination,
FOPEN.
Abstract: A variation on the quadtree algorithm for ultra- wideband, wide-angle (UWB-WA) SAR imaging that uses the omega-k algorithm for final stage focusing is introduced. Several signal processing techniques appropriate to the requirements of UWB-WA SAR, and that prevent errors and artifacts in the omega-k focusing will be reviewed. These techniques include spatial and temporal shifts for spotlight data, elimination of ghost targets, and adjustments needed to account for the virtual sampling of the quadtree algorithm. In order to justify these techniques, a simple Fourier-based model of the imaging problem appropriate to UWB-WA SAR is presented. -
Ian G. Cumming.
Model-Based Doppler Estimation for Frame-Based SAR Processing.
In IGARSS '01, International Geoscience and Remote Sensing Symposium,
volume 6,
pages 2645-2647,
2001.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Clutterlock.
Abstract: This paper presents a new method of Doppler centroid estimation whereby estimates are made over small blocks of data covering a whole frame of data, and examined for strong SNR and lack of bias. Poor estimates are rejected, and the remaining estimates are used to fit a surface model of the Doppler centroid vs. range and azimuth. The method is applied to both the fractional and integer PRF part of the centroid. A geometric model is used to constrain the model to allowable roll, pitch and yaw values of satellite attitude. The method is tested with RADARSAT-1 and SRTM/X-SAR data. -
Joachim H. G. Ender.
The meaning of k-space for classical and advanced SAR techniques.
In International Symposium Physics in Signal and Image Processing, PSIP 2001,
Marseille,
pages 23-38,
January 2001.
Keyword(s): SAR Processing,
k-Space,
Airborne SAR,
Bistatic SAR.
Abstract: Synthetic aperture radar (SAR) has proven to be a powerful technique for imaging the surface of the earth and other celestial bodies with high resolution in the microwave region. As sensor a radar is used which is mounted on a moving platform - an airplane or satellite. By its motion a synthetic aperture is formed; the image is processed from the radar raw data using focusing algorithms of high complexity. Similar to SAR imaging is the technique of inverse SAR (ISAR), which allows to image turning or moving objects with a fixed radar. The k-space as the domain of the spatial Fourier transform presents an important mathematical tool for general imaging problems. As an example, in biomedical ultrasonic imaging, k-space techniques are widely used, for instance for the analysis of imaging systems and evaluation of data collection strategies, see e.g. [33]. In the field of radar imaging, the k-space can serve as a system analysis tool as well as the basis for reconstruction algorithms: Many of the phenomena arising for SAR and ISAR can be explained by analysis in the k-space. Some of the algorithms like polar reformatting are based on k-space formulation. To get a deeper insight into physical effects, it is also worthwile to look at advanced techniques like bistatic SAR in the light of k-space. On the other hand, the k-space is also a domain for the synthesis of imaging conditions: Thanks to the fast development of technical components, it will be more and more possible to create flexible waveforms and geometries, i.e.: to design the measurement configuration in the k-space opening new exciting possibilities. In this tutorial, a unified view of such techniques in terms of k-space is presented. Here, the aim of this tutorial is not to give a comprehensive summary of the numerous focussing algorithms, but to give aspects of the way of thinking in the three-dimensional Fourier domain. Though it is also possible to handle the k-space in terms of electromagnetic theory (e.g.[20]), we will concentrate to the signal-theoretical view. -
F. Gini,
F. Lombardini,
P. Matteucci,
and L. Verrazzani.
System and estimation problems for multibaseline InSAR imaging of multiple layovered reflectors.
In Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International,
volume 1,
pages 115-117vol.1,
9-13 July 2001.
[bibtex-key = Gini2001]
-
Xiaotao Huang,
Zhimin Zhou,
and Diannong Liang.
Effects of RFI on UWB-SAR Using LFM Waveforms.
In CIE International Conference on Radar, 2001,
pages 631-633,
October 2001.
Keyword(s): SAR Processing,
RFI Suppression,
Ultra-Wideband SAR,
VHF SAR.
Abstract: The dual requirement of ultra-wide band synthetic aperture radar (UWB-SAR) for high range resolution and low frequency penetration proposes the problem of radio frequency interference (RFI) suppression. Although careful design of the receiver hardware can reduce this difficulty, a great amount of RFI will still distort the actual target returns. The effects of RFI on both of the design of hardware and the task of signal processing are studied. We focus our analysis on the basic pulse compression in linear frequency modulated (LFM) UWB-SAR. The output of a typical sinusoidal RFI after pulse compression is derived and proved to be closely related to the frequency of the RFI. Computer simulations successfully verify our conclusions. -
Roger R.-Y. Lee,
James S. Verdi,
and Mehrdad Soumekh.
Enhancements of NP-3 UHF Image Quality Using Digital Spotlighting Technique.
In Proceedings of the 2001 IEEE Radar Conference,
pages 1-6,
May 2001.
Keyword(s): SAR Processing,
Wavefront Reconstruction,
Wavenumber Domain Algorithm,
omega-k,
RFI Suppression,
Subaperture Processing,
Digital Spotlighting,
Slow-Time Upsampling,
Alias-free Processing,
Quadband SAR,
P-Band,
X-Band,
L-Band,
C-Band,
Airborne SAR.
Abstract: This paper is concerned with signal processing issues that are associated with foliage penetrating (FOPEN) USA Navy NP-3 ultra-wideband (UWB) synthetic aperture radar. The digital signal processors that were developed for the NP-3 data commonly used a radar beamwidth angle that was limited to 35 degrees. Provided that the NP-3 radar beamwidth angle was 35 degrees, the NP-3 SAR system would approximately yield alias-free data in the slow-time Doppler domain. We show that the NP-3 data possess a 50-degree beamwidth angle within the entire 215-730 MHz band of the NP-3 radar that is imposed by the radar (radial) range swath gate. The 50-degree beamwidth of the NP-3 system results in slow-time Doppler aliasing within the frequency band of 444-730 MHz. We outline a slow-time processing of the NP-3 data, that we refer to as digital spotlighting and PRF upsampling, to minimize the Doppler aliasing. The digital spotlighting is also used for in-scene target calibration -
F. Lombardini,
F. Gini,
and P. Matteucci.
Application of array processing techniques to multibaseline InSAR for layover solution.
In Radar Conference, 2001. Proceedings of the 2001 IEEE,
pages 210-215,
1-3 May 2001.
[bibtex-key = Lombardini2001]
-
F. Lombardini,
F. Gini,
and P. Matteucci.
Multibaseline ATI-SAR for robust ocean surface velocity estimation in presence of bimodal Doppler spectrum.
In Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International,
volume 1,
pages 578-580vol.1,
9-13 July 2001.
[bibtex-key = Lombardini2001a]
-
J.J. Mallorqui,
I. Rosado,
and M. Bara.
Interferometric calibration for DEM enhancing and system characterization in single pass SAR interferometry.
In Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International,
volume 1,
pages 404-406vol.1,
9-13 July 2001.
[bibtex-key = Mallorqui2001]
-
Seung-Mok Oh and James H. McClellan.
Multiresolution Imaging with Quadtree Backprojection.
In The Record of the Thirty-Fifth Asilomar Conference on Signals, Systems and Computers, 2001,
volume 1,
pages 105-109,
November 2001.
Keyword(s): SAR Processing,
Backprojection,
Quadtree Processing,
Divide and Conquer Methods.
Abstract: The quadtree backprojection is an efficient space-time synthetic aperture radar (SAR) imaging algorithm that is based on the spectral decomposition of SAR data. Normally the quadtree backprojection is represented as a multiple stage imaging process that performs the space-time domain imaging over a number of sub-patches separately at each stage. By representing the contents of each sub-patch with a predefined energy function, it is possible to form a sequence of multi-resolution images. In this paper, we discuss various applications where this quadtree imaging can be applied to provide the multiresolution imaging. These include SAR, tomographic medical imaging and beamforming. -
Tim Payne.
Phase analysis for the limitations of the tomographic paradigm on a 3D scene.
In Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International,
volume 7,
pages 3030-3032,
2001.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
geophysical techniques,
radar theory,
remote sensing by radar,
synthetic aperture radar,
terrain mapping,
3D Fourier transform,
3D scene,
SAR,
complex surface reflectivity,
demodulated pulses,
geophysical measurement technique,
land surface,
phase analysis,
phase errors,
spotlight mode,
synthetic aperture radar,
terrain mapping,
three dimensional scene.
Abstract: The tomographic paradigm argues that the demodulated pulses from a spotlight mode SAR system trace a 2D slice of the 3D Fourier transform of the complex surface reflectivity. This paper derives the phase errors that result from imaging a 3D surface from a non planar collection geometry and shows how correct projection to the true surface can eliminate many of the errors. The response from an ideal scatterer is derived and then approximated to simplify the expression into a manageable and meaningful form and so that insight can be gained into the artifacts produced. The theory indicates that warping an image by distorting the final image to correct for layover doesn't eliminate the second order blurring terms produced by the relief and that both the layover and these blurring affects can be properly eliminated through correct projection to the real ground plane -
Mats I. Pettersson.
Moving Target Detection in Wide Band SAR.
In CIE International Conference on Radar, 2001,
pages 614-618,
October 2001.
Keyword(s): SAR Processing,
Backprojection,
Fast Backprojection,
Time Domain Backprojection,
Moving Target Indication,
Ultra-Wideband SAR.
Abstract: A likelihood ratio test is proposed for moving target detection in a ultra wide frequency band and wide antenna beam (wide band) SAR systems. The developed method combines time domain fast backprojection SAR processing methods with moving target detection. It saves the computational load when all relative speeds can be tested using the same clutter suppressed sub-aperture beams. The proposed method is tested on narrow band radar data -
M. Preiss,
D. Gray,
and N.J.S. Stacy.
The effect of polar format resampling on uncompensated motion phase errors and the phase gradient autofocus algorithm.
In Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International,
volume 3,
pages 1442-1444vol.3,
9-13 July 2001.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus.
[bibtex-key = Preiss2001]
-
Lars M. H. Ulander,
Per-Olov Frölind,
A. Gustavsson,
H. Hellsten,
T. Jonsson,
B. Larsson,
and G. Stenstrom.
Performance of the CARABAS-II VHF-Band Synthetic Aperture Radar.
In IGARSS '01, International Geoscience and Remote Sensing Symposium,
volume 1,
pages 129 - 131,
Jul. 2001.
Keyword(s): SAR Processing,
RFI Suppression,
Backprojection,
Ultra-Wideband SAR,
VHF SAR,
CARABAS,
Airborne SAR.
Abstract: CARABAS-II is an airborne SAR operating in the 20-90 MHz band. The low operating frequency enables detection of concealed objects in dense forests as well as mapping of forest stem volume. A number of calibration experiments have recently been conducted to evaluate system performance. In this paper, we report on some of the results from the analysis. Spatial resolution, measured using 5-m trihedrals, is typically 2.5 m in both slant range and azimuth. The right-left ambiguity ratio, measured using 5-m trihedrals on both sides of the flight track, is about 10 dB for a single antenna element on receive. The noise level varies in the images and includes both multiplicative (integrated sidelobe ratio, right-left ambiguity ratio) and additive (radio-frequency interference, receiver noise) terms. Analysis of images from a recent campaign in northern Sweden shows that the additive noise term is less than -20 dB (noise-equivalent beta ?) for slant ranges less than 14 km. -
Lars M. H. Ulander,
Hans Hellsten,
and Gunnar Stenström.
Performance analysis of fast backprojection for synthetic-aperture radar processing.
In Edmund G. Zelnio, editor,
Proc. of SPIE Vol. 4382, Algorithms for Synthetic Aperture Radar Imagery VIII,
number 1,
pages 13-21,
2001.
SPIE.
Keyword(s): SAR Processing,
Backprojection,
Time-Domain Backprojection,
Fast Backprojection,
inversion,
back-projection,
fast,
performance.
Abstract: Exact SAR inversion for a linear aperture may be obtained using fast transform techniques. Alternatively, backprojection in time domain may be used which can also handle general curved apertures. In the past, however, backprojection has seldom been used due to its heavy computational burden. We show in the paper that the backprojection method can be formulated as an exact recursive method based on factorization of the aperture. By sampling the backprojected data in local polar coordinates it is shown that the number of operations is drastically reduced and can be made to approach that of fast transform algorithms. -
M. Bara,
A. Broquetas,
and J. Closa.
Precise geometry simulation of interferometric SAR signal for air and spaceborne sensors.
In Geoscience and Remote Sensing Symposium, 2000. Proceedings. IGARSS 2000. IEEE 2000 International,
volume 2,
pages 746-748vol.2,
24-28 July 2000.
[bibtex-key = Bara2000]
- D. G. Falconer. Radar imaging using statistical orthogonality. In E. G. Zelnio, editor, Proc. SPIE Vol. 4053, p. 10-19, Algorithms for Synthetic Aperture Radar Imagery VII, Edmund G. Zelnio; Ed., volume 4053 of Presented at the Society of Photo-Optical Instrumentation Engineers (SPIE) Conference, pages 10-19, August 2000. Keyword(s): SAR Processing, Non-Linear Flight Path, SAR Tomography, Curvilinear SAR. [bibtex-key = falconer2000:NonLinearSAR]
-
Guoyongmei,
Chenhao,
Hongwen,
and Maoshiyi.
Resample in the first order motion compensation of real-time SAR processor.
In 5th International Conference on Signal Processing Proceedings, 2000. WCCC-ICSP 2000,
volume 3,
pages 1830-1833,
2000.
Keyword(s): SAR Processsing,
Airborne SAR,
Motion Compensation,
MoComp,
airborne radar,
error compensation,
image sampling,
motion compensation,
radar imaging,
real-time systems,
synthetic aperture radarSAR image,
airborne radar,
azimuth focus,
first order motion compensation,
image defocus,
image distortion,
motion error model,
phase errors,
real-time SAR processor,
resample problem,
signal amplitude,
synthetic aperture radar.
Abstract: The resample problem in the first order motion compensation of real-time SAR processor is presented. The motion error model is properly established, and the simulation shows that the formation of the motion error with liner or second phase term gives rise to the image defocus and distortion. The magnitude of motion error poses changes in the range gate drift. When the motion error exceeds a range bin during synthetic time, resample should be taken into consideration; the resample inaccuracy within one bin does not have impact on azimuth focus, but the signal amplitude, so resample is necessary and important in motion compensation -
Lance M. Kaplan,
Seung-Mok Oh,
Matthew C. Cobb,
and James H. McClellan.
Error Analysis for Quadtree Image Formation.
In International Conference on Image Processing, ICIP 2000,
volume 1,
pages 717-720,
Sept 2000.
Keyword(s): SAR Processing,
Backprojection,
Quadtree Processing,
Error Analysis,
Ultra-Wideband SAR.
Abstract: The quadtree image formation technique is a computationally efficient approximation to standard backprojection. Where the computational load of backprojection is O(N^3) for N sensors forming an N?N image, the quadtree method uses a divide-and-conquer strategy similar to the fast Fourier transform (FFT) to reduce the computational load down to O(N^2*log(N)). However, the quadtree introduces errors in the relative time shifts used to focus pulses. These errors reduce the signal gain in the mainlobe response for isotropic point-like targets. In addition, the oscillations of the sidelobes increase from stage to stage. This paper develops performance bounds for the mainlobe losses under far field conditions and relates these bounds to the slow-time Nyquist rate -
Lance M. Kaplan,
Seung-Mok Oh,
and James H. McClellan.
Detection of Broadside Targets During Image Formation Using a Quadtree Approach.
In The Record of the 2000 IEEE Radar Conference,
pages 104-109,
May 2000.
Keyword(s): SAR Processing,
Backprojection,
Quadtree Processing,
Ultra-Wideband SAR,
Boom-SAR,
Multiscale Detection.
Abstract: The military is interested in using ultra-wideband (UWB) synthetic aperture radar (SAR) systems to detect ground targets. Standard automatic target detection methods search the entire scene for regions of interest (ROI) after image formation. In order to save computations, we introduce a multiscale detection algorithm that uses partially processed radar data during the intermediate stages of a quadtree-based backprojection image formation algorithm. When the detector accrues enough information to determine that a patch of ground is free of potential targets, it then cues the image former to terminate the processing that would further resolve that patch. The detector combines a feature that estimates the coherent signal to noise ratio with another feature that exploits the broadside flash scattering phenomenon. The new approach is evaluated over a measured database generated by the ARL Boom-SAR radar. -
Yunjin Kim and Jakob van Zyl.
Overview of Polarimetric Interferometry.
In Aerospace Conference Proceedings, 2000 IEEE,
volume 3,
pages 231-236,
2000.
Keyword(s): SAR Processing,
radar polarimetry,
radiowave interferometry,
synthetic aperture radar,
SAR interferometry,
InSAR,
SAR polarimetric interferometry,
SAR polarimetry,
synthetic aperture radar,
Pol-InSAR.
Abstract: SAR (Synthetic Aperture Radar) interferometry has enabled twoimportant science applications: surface change detection and topographicmapping. SAR interferometry is sensitive to the location of the imagedarea and the scattering geometry. SAR polarimetry makes use of thepolarization dependent scattering response of each pixel within theimaged area. The polarimetric response is highly sensitive to thescattering mechanism of a pixel. S.R. Cloude and K.P. Papathanassioufirst published the formulation of polarimetric interferometry thatcombines both SAR interferometry and SAR polarimetry. The main purposeof using polarimetric interferometry is to extract scattering mediuminformation that may be difficult to obtain from scalar interferometry.Even though the formulation and initial demonstrations appear to be verypromising, potential applications of polarimetric interferometry canonly be verified by comparing polarimetric interferometry signatureswith ground truth data. In this talk, we present the theory andimplementation of SAR polarimetric interferometry. Especially, we reviewSAR polarimetry, SAR interferometry, and SAR polarimetric interferometryin a unified manner. In addition, a new calibration technique suitablefor polarimetric interferometry is suggested in this paper -
J.M. Lopez-Sanchez,
J. Fortuny,
A.J. Sieber,
L. Sagues,
M. Bara,
X. Fabregas,
and A. Broquetas.
Experimental comparison of different scattering mechanism selections for vegetation height retrieval by POLINT.
In Geoscience and Remote Sensing Symposium, 2000. Proceedings. IGARSS 2000. IEEE 2000 International,
volume 1,
pages 138-140vol.1,
24-28 July 2000.
[bibtex-key = Lopez-Sanchez2000]
-
J.J. Mallorqui,
M. Bara,
and A. Broquetas.
Sensitivity equations and calibration requirements on airborne interferometry.
In Geoscience and Remote Sensing Symposium, 2000. Proceedings. IGARSS 2000. IEEE 2000 International,
volume 6,
pages 2739-2741vol.6,
24-28 July 2000.
[bibtex-key = Mallorqui2000]
-
David Small,
Stefan Biegger,
and Daniel Nüesch.
The Topology of SAR Imagery in Rough Terrain.
In Proc. of EUSAR 2000 - 3rd European Conference on Synthetic Aperture Radar,
2000.
Keyword(s): SAR Processing,
SAR,
Calibration,
Terrain,
DEM,
Image Simulation,
Terrain-Geocoding,
Topology,
Heteromorphism.
[bibtex-key = smallBieggerNueschEUSAR2000:ImgRoughTerrain]
-
Mehrdad Soumekh,
Gernot Gunther,
Mark Linderman,
and Ralph Kohler.
Digitally-Spotlighted Subaperture SAR Image Formation Using High Performance Computing.
In Edmund G. Zelnio, editor,
Algorithms for Synthetic Aperture Radar Imagery VII,
volume SPIE4053,
pages 260-271,
2000.
Keyword(s): SAR Processing,
Wavefront Reconstruction,
Wavenumber Domain Algorithm,
omega-k,
RFI Suppression,
Subaperture Processing,
Parallel Processing,
Digital Spotlighting,
Slow-Time Upsampling,
Alias-free Processing,
Real-Time Processing,
High Performance Computing,
FFTW.
Abstract: This paper is concerned with the implementation of the SAR wavefront reconstruction algorithm on a high performance computer. For this purpose, the imaging algorithm is reformulated as a coherent processing (spectral combination) of images that are formed from a set of subapertures of the available synthetic aperture. This is achieved in conjunction with extracting the signature of a specific target region (digital spotlighting). Issues that are associated with implementing the algorithm on SMP-HPCs and DMP-HPCs are discussed. The results using the FOPEN P-3 SAR data are provided. -
Mehrdad Soumekh,
Steve Worrell,
Edward G. Zelnio,
and Brett Keaffaber.
SAR Wavefront Reconstruction Using Motion Compensated Phase History (Polar Format) Data and DPCA-Based GMTI.
In Edmund G. Zelnio, editor,
Algorithms for Synthetic Aperture Radar Imagery VII,
volume SPIE4053,
pages 64-75,
2000.
Keyword(s): SAR Processing,
Wavefront Reconstruction,
Wavenumber Domain Algorithm,
omega-k,
Polar Format Algorithm,
X-Band,
Squinted SAR,
Motion Compensation,
Monopulse SAR,
MTI,
GMTI.
Abstract: This paper address the problem of processing an X-band SAR database that was originally intended for processing via a polar format imaging algorithm. In our approach, we use the approximation-free SAR wavefront reconstruction. For this, the measured and motion compensated phase history (polar format) data are processed in a multi-dimensional digital signal processing algorithm that yields alias-free slow-time samples. The resultant database is used for wavefront image formation. The X-band SAR system also provides a two channel along-track monopulse database. The alias-free monopulse SAR data are used in a coherent signal subspace algorithm for Ground Moving Target Indication (GMTI). Results are provided. -
David A. Yocky and Charles V. Jakowatz.
Two-target height effects on interferometric synthetic aperture radar coherence.
In Edmund G. Zelnio, editor,
,
volume 4053,
pages 102-108,
2000.
SPIE.
Keyword(s): SAR Processing,
SAR Tomography,
InSAR,
SAR Interferometry,
Polar Format Algorithm,
PFA,
Spotlight SAR,
Spotlight-mode data.
[bibtex-key = yockyJakowatzTwoTargetsInSAR2000]
-
Güner Arslan,
Magesh Valliappan,
and Brian L. Evans.
Quality Assessment of Compression Techniques for Synthetic Aperture Radar Images.
In International Conference on Image Processing, ICIP 1999,
volume 3,
pages 857-861,
October 1999.
Keyword(s): Data Compression,
Quality Assessment,
Quality Measures,
Edge Correlation Quality Measure.
Abstract: Synthetic aperture radar (SAR) systems are mounted on airplanes and satellites, which have limited downlink and storage capacity, yet SAR image sequences may be produced at rates of several Gbps. Compression is difficult because SAR images contain significant high-frequency information, such as terrain boundaries and terrain texture. In assessing the quality of compressed images, peak signal-to-noise ratio and men-squared error are inadequate because they assume that distortion is solely due to image-independent additive noise. In this paper, we provide objective measures to assess the visual quality of SAR images compressed by JPEG and SPIHT coders. The human visual system responds differently to linear distortion and noise injection (nonlinear distortion plus additive noise). Our key contributions are that we first decouple and quantify the linear distortion and noise injection in JPEG and SPIHT coders, and second introduce a new edge correlation quality measure which we use to quantify nonlinear distortion -
M. Bara,
J. Monne,
and A. Broquetas.
Navigation systems requirements for airborne interferometric SAR platforms.
In Geoscience and Remote Sensing Symposium, 1999. IGARSS '99 Proceedings. IEEE 1999 International,
volume 4,
pages 2158-2160vol.4,
28 June-2 July 1999.
[bibtex-key = Bara1999]
-
M. Bara,
O. Mora,
M. Romero,
and A. Broquetas.
Generation of precise wide-area geocoded elevation models with ERS SAR data.
In Geoscience and Remote Sensing Symposium, 1999. IGARSS '99 Proceedings. IEEE 1999 International,
volume 4,
pages 1924-1926vol.4,
28 June-2 July 1999.
[bibtex-key = Bara1999a]
-
Svante Björklund and David Rejdemyhr.
A MATLAB Toolbox for Radar Array Processing.
In ISSPA '99, International Symposium on Signal Processing and its Applications,
pages 547-550,
1999.
Keyword(s): Radar Array Processing,
MATLAB Toolbox for Radar Array Processing.
Abstract: This paper describes the design, implemented possibilities and usage of a MATLAB Toolbox for radar signal processing. The Toolbox is especially suited for processing in the spatial dimension using signals from an antenna array. Both simulated and measured signals can be used. Both conventional processing, e.g. conventional beamforming, and model based processing is possible. -
Ian G. Cumming,
Frank Wong,
and Bob Hawkins.
RADARSAT-1 Doppler Centroid Estimation Using Phase-Based Estimators.
In CEOS SAR Workshop 1999,
1999.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Multilook Cross Correlation,
MLCC,
Multilook Beat Frequency,
MLBF,
Clutterlock,
Doppler Ambiguity Resolver,
DAR,
Satellite SAR.
Abstract: Doppler Centroid (DOPCEN) estimation continues to be an important and sometimes overlooked component of SAR processing. This is especially true in the case of ScanSAR, where the estimate must be accurate to approximately 5 Hz in order to avoid radiometric artifacts in the processed images. In the last 10 years, a new class of estimator has been developed based on the phase of the received signal, rather than on the spectral amplitude. The concepts were developed by Madsen, Bamler and Runge, and more recently by Wong and Cumming. It is generally acknowledged that the phase-based estimators can be more accurate than the amplitude-based estimators, provided their limitations are understood, and they are applied properly. We consider the DLR (Bamler & Runge), the MLCC and the MLBF (the latter two both Wong & Cumming). We show how their performance differs as a function of radiometric discontinuities, partially-exposed targets, noise levels, scene contrast and radar squint angle. The 3 algorithms provide different estimation accuracies with respect to each of these data attributes. RADARSAT data has tighter DOPCEN estimation requirements, because of ScanSAR operation, and because of its higher noise equivalent sigma naught. We have made improvements to the existing phase-based estimators and tested their performance on RADARSAT data. In the paper, we will review the operation of the DOPCEN algorithms, compare their performance, and explain why it is advantageous to use an algorithm which combines features of more than one of the 3 algorithms. Finally, we describe our recommendations for a reliable, combined algorithm. -
Marina Dragosevic.
On Accuracy of Attitude Estimation and Doppler Tracking.
In CEOS SAR Workshop 1999,
1999.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Clutterlock,
Doppler Tracker,
Attitude Angles,
Doppler Ambiguity Resolver,
DAR,
Satellite SAR.
Abstract: A precise physical model of the Doppler effects is based on the spacecraft state vectors, earth model and spacecraft attitude. Thus, the problem of Doppler tracking can be posed as the problem of adaptive estimation of the satellite attitude. The same physical model and general approach to Doppler/attitude tracking can be applied to ERS and RADARSAT. However, in the case of RADARSAT there are two additional problems: 1) Since RADARSAT is not zero-Doppler steered, attitude estimation must be combined with PRF (pulse repetition frequency) ambiguity resolution. An efficient and reliable method that achieves this will be presented and discussed. 2) For RADARSAT there is a beam peak dislocation in the azimuth direction and the amount of this dislocation depends on the elevation angle. This is especially significant for the wide beams and for ScanSAR due to the large elevation aperture of the combined beams. It is shown how this effect can be modeled as equivalent elevation-dependent yaw and pitch in addition to the ordinary (very small) RADARSAT attitude angles. It is also shown how these equivalent yaw and pitch values can be incorporated in the generic Doppler centroid model. This representation of the beam peak dislocation feature is very useful because it facilitates the verification of the existing (or new) characterizations of the RADARSAT beam peak dislocation. Ideally, when the elevation-dependent yaw and pitch is taken into account, all beams should provide the same value for the true attitude (via independent Doppler centroid measurements). Thus, a mismatch can be used to correct the dislocation model. Based on these geometric/kinematic models, a complete procedure for very accurate Doppler and attitude tracking for ERS, RADARSAT single beam and RADARSAT ScanSAR modes will be outlined. Results regarding theoretical estimation accuracy and observed variability will be compared. The paper will include comparison with other similar published methods and results. For ScanSAR, all beams are used simultaneously and the sensitivity of the attitude estimates to the proper beam dislocation modeling will be considered. -
Gerard J. Genello(Jr.),
Michael C. Wicks,
and Mehrdad Soumekh.
Alias-free Processing of P-3 Data.
In Edmund G. Zelnio, editor,
Algorithms for Synthetic Aperture Radar Imagery VI,
volume SPIE3721,
pages 189-200,
1999.
Keyword(s): SAR Processing,
Backprojection,
Wavefront Reconstruction,
Wavenumber Domain Algorithm,
omega-k,
RFI Suppression,
Digital Spotlighting,
Slow-Time Upsampling,
Alias-free Processing,
P-Band,
Ultra-Wideband SAR,
FOPEN,
Airborne SAR.
Abstract: This paper is concerned with multidimensional signal processing and image formation with FOliage PENetrating (FOPEN) airborne radar data which were collected by a Navy P-3 ultra wideband (UWB) radar in 1995 [Raw]. A commonly-used assumption for the processing of the P-3 data is that the beamwidth angle of the radar is limited to 35 degrees [Bes],[Goo]; provided that this assumption is valid, the PRF of the P-3 SAR system yields alias-free data in the slow-time Doppler domain. However, controlled measurements with the P-3 radar have indicated a beamwidth which exceeds 35 degrees [Raw]. In this paper, we examine a method for processing of the P-3 data in which the incorrect assumption that its radar beamwidth angle is limited to 35 degrees is not imposed. In this approach, a SAR processing scheme which enables the user to extract the SAR signature of a specific target area (digital spotlighting) is used to ensure that the resultant reconstructed SAR image is not aliased [S94], [S95], [S99]. The images which are formed via this method with 8192 pulses are shown to be superior in quality to the images which are formed via the conventional P-3 processor with 16386 pulses which was developed at the MIT Lincoln Laboratory [Bes]. In the presentation, we also introduce a method for converting the P-3 deramped data into its alias-free baseband echoed data; the signature of the Radio Frequency Interference (RFI) signals in the two-dimensional spectral domain of the resultant data is examined. -
Rüdiger Gens.
On Phase Unwrapping Based on Minimum Cost Flow Networks.
In FRINGE '99, Advancing ERS SAR Interferometry from Applications towards Operations,
1999.
Keyword(s): SAR Processing,
Interferometry,
Phase Unwrapping,
Minimum Cost Flow.
Abstract: Phase unwrapping is a key step in the SAR interferometric processing chain as it converts the phase information derived from an interferometric image pair into valuable height information. Many algorithms have been developed to solve the phase unwrapping problem. None of the algorithms implemented so far has met with all the requirements for an optimal solution. Recently, a very promising approach has been introduced by Costantini (1998). The new method formulates the phase unwrapping problem as a global minimisation problem which can be solved by using minimum cost flow (MCF) networks. These MCF networks in general have been well studied and efficient algorithms exist. However, application of the MCF for phase unwrapping is a new approach and requires further research. This paper deals with the investigation of this particular algorithm and focuses on the optimisation of the cost function used to define the MCF network. -
Harry Jackson,
Ian Sinclair,
and Sebastian Tam.
ENVISAT/ASAR Precision Transponders.
In CEOS SAR Workshop 1999,
Toulouse,
Oct. 1999.
Keyword(s): Transponders,
ASAR,
ASAR Transponders,
ENVISAT,
ENVISAT Transponders.
Abstract: MPB Technologies Inc. is currently building the Radio Frequency (RF) and control units for a suite of three transponders for the European Space Agency. The transponders are instrumental in the external characterization of the Advanced Synthetic Aperture Radar (ASAR) mounted on board ENVISAT. The prototype transponder was designed and built at ESTEC [1]. This paper presents the operation of the transponders, and describes the final design, integration and testing of the production RF and control transponder units. Like the earlier ERS-1/2 and RADARSAT-1 transponders [2,3], these units provide a constant RCS mode, with constant gain radiometric response, and an azimuth pattern mode to allow for amplitude recording of the satellite pass. In the ASAR transponders, two further modes have been added - a characterization mode to assist in the commissioning and monitoring of ASAR, and an experimental phase-stable mode to provide point target echoes with stabilized phase response. -
Richard T. Lord and Michael R. Inggs.
Efficient RFI Suppression in SAR Using a LMS Adaptive Filter with Sidelobe Suppression Integrated with the Range-Doppler Algorithm.
In IGARSS '99, International Geoscience and Remote Sensing Symposium,
volume 1,
pages 574-576,
June 1999.
Keyword(s): SAR Processing,
RFI Suppression,
P-Band,
Range-Doppler Algorithm.
Abstract: The LMS adaptive filter has been used successfully to suppress radio frequency interference (RFI) from SAR images. This paper describes a method to efficiently implement this filter by integrating it with the range-Doppler algorithm. A technique to reduce the sidelobes created by the filter is described and illustrated on simulated data and on real P-band data -
Andrea Monti-Guarnieri,
Fabio Rocca,
Pietro Guccione,
and Ciro Cafforio.
Optimal Interferometric ScanSAR Focusing.
In IGARSS '99, International Geoscience and Remote Sensing Symposium,
volume 3,
pages 1718-1720,
1999.
Keyword(s): SAR Processing,
Interferometry,
ScanSAR,
Focusing.
Abstract: This paper deals with phase preserving focusing for very low resolution ScanSAR. Conventional techniques get ScanSAR focusing by exploiting the SAR matched reference, and compensate scalloping by an inverse antenna weighting. Yet, this approach introduces a space-variant distortion in the focused impulse response (IRF). A rather different focusing technique is then proposed, where the set of space-variant focusing kernels is computed by means of Wiener deconvolution. They perform ScanSAR focusing and descalloping at one time, achieving the finest resolution and without distorting the impulse response. -
A. Potsis,
A. Reigber,
and K.P. Papathanassiou.
A phase preserving method for RF interference suppression in P-band.
In Geoscience and Remote Sensing Symposium, 1999. IGARSS '99 Proceedings. IEEE 1999 International,
volume 5,
pages 2655-2657,
1999.
Keyword(s): SAR Processing,
interference suppression,
radar interference,
radar theory,
radiowave interferometry,
synthetic aperture radar,
ESAR,
P-Band,
Airborne SAR,
P-band synthetic aperture radar interferometric data,
RFI Suppression,
Solothurn,
Switzerland,
interferometric SAR data applications,
least mean square method,
phase preserving method,
phase preserving notch filter,
polarimetric interferometric SAR data.
Abstract: Addresses the least mean square method for estimation and coherent subtraction of the RF interference in interferometric SAR data applications. The authors also compare the results with a phase preserving notch filter. For this purposes the authors use polarimetric interferometric SAR data from a test site in Solothum/Switzerland collected by the DLR's Experimental SAR (ESAR) -
Richard Rau and James H. McClellan.
Data Efficient Implementation of UWBWA SAR Algorithms.
In ICASSP '99, International Conference on Acoustics, Speech, and Signal Processing,
volume 6,
pages 3525-3528,
1999.
Keyword(s): SAR Processing,
Backprojection,
Ultra-Wideband SAR,
Fan Filter,
Quincunx Grid.
Abstract: It is shown that the particular form of the frequency support of raw data and focused imagery obtained from an ultra-wideband, wide beamwidth synthetic aperture radar system can be exploited in nonseparable sampling schemes to reduce the overall amount of raw data samples and image pixels that need to be stored and computed. Furthermore, it is demonstrated that the constant integration angle backprojection (CIAB) image former implicitly applies a fan filter that interpolates raw data sampled on a quincunx grid back onto the underlying rectangular grid. This subtle property of the CIAB has not been exploited so far. It leads to higher quality images with less computational complexity. -
Z. She,
D.A. Gray,
R.E. Bogner,
and J. Homer.
Three-dimensional SAR imaging via multiple pass processing.
In Geoscience and Remote Sensing Symposium, 1999. IGARSS '99 Proceedings. IEEE 1999 International,
volume 5,
pages 2389-2391,
1999.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
geophysical techniques,
radar imaging,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
terrain mapping,
topography (Earth),
DFT,
InSAR,
SAR,
SAR image,
beamforming,
eigenvector method,
elevation,
geophysical measurement technique,
image registration,
land surface topography,
multiple pass processing,
phase correction,
radar imaging,
radar remote sensing,
spaceborne radar,
subspace method,
superresolution,
synthetic aperture radar,
terrain mapping,
three-dimensional imaging.
Abstract: This paper develops a novel approach to reconstruct a three-dimensional (3D) SAR image with multiple pass processing. It involves image registration, phase correction and beamforming in elevation. An eigenvector method is proposed for the phase correction and the beamforming in elevation is carried out by a DFT or a subspace method for superresolution. 3D SAR images are demonstrated by processing ERS-1 real data with the proposed approach -
D.G. Thompson,
J.S. Bates,
and D.V. Arnold.
Extending the phase gradient autofocus algorithm for low-altitude stripmap mode SAR.
In The Record of the 1999 IEEE Radar Conference,
pages 36-40,
April 1999.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus,
Strip-map,
Range-Dependent.
[bibtex-key = thompsonBatesArnold1999a:PGA]
-
D.G. Thompson,
J.S. Bates,
D.V. Arnold,
and David G. Long.
Extending the phase gradient autofocus algorithm for low-altitude stripmap mode SAR.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS '99,
volume 1,
pages 564-566,
28 June-2 July 1999.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus,
Strip-map,
Range-dependent.
[bibtex-key = thompsonBatesArnold1999b:PGA]
-
P. Tsakalides and C.L. Nikus.
A new phase gradient autofocus technique for high resolution image formation based on fractional lower-order statistics.
In Electronics, Circuits and Systems, 1999. Proceedings of ICECS '99. The 6th IEEE International Conference on,
volume 2,
pages 667-670vol.2,
5-8 Sept. 1999.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus.
[bibtex-key = Tsakalides1999]
-
Lars M. H. Ulander and Per-Olov Frölind.
Precision Processing of CARABAS HF/VHF-Band SAR Data.
In IGARSS '99, International Geoscience and Remote Sensing Symposium,
volume 1,
pages 47-49,
June 1999.
Keyword(s): SAR Processing,
RFI Suppression,
Backprojection,
Time Domain Backprojection,
Ultra-Wideband SAR,
VHF SAR,
CARABAS,
Airborne SAR,
Motion Compensation.
Abstract: A stream-lined precision processor has been developed for the CARABAS-II HF/VHF-band SAR system. The authors describe the basic system characteristics, the normal waveform used, and the signal processing techniques to form images. In particular, challenges related to the stepped-frequency waveform, the radio-frequency interference environment, and widebeam motion-compensation are discussed and processing solutions are devised. -
Ali F. Yegulalp.
Fast Backprojection Algorithm for Synthetic Aperture Radar.
In The Record of the 1999 IEEE Radar Conference,
pages 60-65,
1999.
Keyword(s): SAR Processing,
Backprojection,
Convolution Backprojection,
FOPEN,
Ultra-Wideband SAR,
Image Formation,
Focusing,
Motion Compensation.
Abstract: We introduce a new algorithm for time-domain backprojection of synthetic aperture radar (SAR) data. The algorithm reproduces images generated by standard backprojection pixel-for-pixel to any required tolerance, but it runs roughly ?N times faster for an N by N pixel image. Fast backprojection retains the advantages of standard backprojection: perfect motion compensation for any flight path, low artifact levels, unlimited scene size, perfect focus for arbitrarily wide bandwidths and integration angles, and strictly local processing (i.e., pulses can be processed as they are collected without along-track buffering or corner turns). The new algorithm also makes it possible to store the image in progress on disk (rather than in memory) with only a mild penalty in processing speed. -
P. Zavattero.
Distributed target SAR image de-blurring using phase gradient autofocus.
In Radar Conference, 1999. The Record of the 1999 IEEE,
pages 246-249,
20-22 April 1999.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus.
Abstract: A new analysis of errors in blur function estimate formed by the real-time Phase Gradient Autofocus (PGA) algorithm is presented for synthetic aperture radar images of distributed targets in correlated noise clutter. It is shown that the PGA algorithm, like the Attia-Steinberg and Vachon-Raney focusing algorithms, can estimate a translation-invariant blur function when no point reflectors are present. The analysis shows that simulation evaluations of PGA performance which do not include sufficient simulated clutter can tend to underestimate the performance of the algorithm in initial iterations. Implications of the error analysis for performance optimization of real-time PGA implementations are presented for the algorithm steps that involve range bin selection, circular shifting, and windowing. It is shown that range bins selected for processing should be widely spaced if possible. If distributed targets are present which cause locally spatially correlated imagery, then it is desirable that the circular shifting segment of the algorithm maintain maximum decorrelation of the intermediate windowed and aligned images used for iterative phase error estimation. -
Stefan Buckreuss and Ralf Horn.
E-SAR P-band SAR subsystem design and RF-interference suppression.
In Geoscience and Remote Sensing Symposium Proceedings, 1998. IGARSS '98. 1998 IEEE International,
volume 1,
pages 466-468,
1998.
Keyword(s): SAR Processing,
airborne radar,
interference suppression,
microstrip antenna arrays,
radar interference,
radar polarimetry,
synthetic aperture radar,
450 MHz,
E-SAR P-band SAR subsystem design,
Germany,
Institut fur Hochfrequenztechnik,
P-Band,
P-band radar front-end,
RFI Suppression,
RF-interference suppression,
Weilheim,
carrier frequency,
experimental airborne synthetic aperture radar,
microstrip patch array antenna,
polarimetric radar,
signal bandwidth.
Abstract: Since the beginning of 1994 the Institut f{\"u}r Hochfrequenztechnik of the German Aerospace Center (DLR) has been operating an experimental airborne SAR E-SAR with a P-band radar front-end. The microstrip patch array antenna allows a signal bandwidth of slightly more than 10% of the 450 MHz carrier frequency. The radar is polarimetric on a pulse-to-pulse basis. -
Francesco Holecz,
Paolo Pasquali,
João Moreira,
and Daniel Nüesch.
Rigorous radiometric calibration of airborne AeS-1 InSAR data.
In IGARSS '98, Geoscience and Remote Sensing Symposium,
volume 5,
pages 2442-2444,
1998.
Keyword(s): SAR Processing,
Radiometry,
Radiometric Calibration,
Airborne SAR,
Topography,
Interferometry,
calibration,
geophysical techniques,
remote sensing by radar,
synthetic aperture radar,
9.6 GHz,
AeS-1,
InSAR,
X-band,
airborne radar,
elevation data,
geophysical measurement technique,
interferometric SAR,
land surface,
radar remote sensing,
radiometric calibration,
synthetic aperture radar,
terrain mapping,
topographic data.
Abstract: The processing of synthetic aperture radar images usually does not -
Charles V. Jakowatz,
Daniel E. Wahl,
and Paul H. Eichel.
Refocus of constant-velocity moving targets in synthetic aperture radar imagery.
In Edmund G. Zelnio, editor,
,
volume 3370,
pages 85-95,
1998.
SPIE.
Keyword(s): SAR Processing,
Moving Target Indication,
MTI.
[bibtex-key = jakowatzWahlEichelRefocusMovingTargets]
-
Bruno Juhel,
Yannick Chevalier,
Marc Le Goff,
Emmanuel Legros,
and Georges Vezzosi.
Experimental Ultra Wide Band SAR Images of Canonical Targets.
In IGARSS '98, International Geoscience and Remote Sensing Symposium,
volume 2,
pages 1153-1155,
1998.
Keyword(s): SAR Processing,
Backprojection,
Time Domain Backprojection,
Ultra-Wideband SAR.
Abstract: This paper describes one technique for ultra wide band (UWB) time domain radar signal processing. Usually a radar is a narrow band system, but in this case transmitted signals are nanosecond short pulses without carrier which have a spectral content from 100 MHz to 1 GHz. Time domain backprojection is used to focus SAR images. The algorithm is tested with experimental data measured with an UWB prototype radar. The configuration of this radar is described and some UWB SAR images of canonical targets are presented -
Bruno Juhel,
Georges Vezzosi,
and Marc Le Goff.
Radio Frequency Interferences Suppression for Noisy Ultra Wide Band SAR Measurements.
In Ultra-Wideband Short-Pulse Electromagnetics 4, 1998,
pages 387-393,
June 1998.
Keyword(s): SAR Processing,
Backprojection,
Ultra-Wideband SAR,
RFI Suppression.
Abstract: A back projection algorithm dedicated to Ultra Wide Band (UWB) signals for synthetic aperture radar (SAR) imaging is described. The time domain aspect is all the more important that the transient nature of UWB signal supplies a vast amount of information on the electromagnetic scattering mechanisms. But, during UWB measurements, radio frequency interferences (RFI) can appear and obscure target detection. We have described how RFI can be an important noise source in UWB system and how they can be suppressed. The Least Mean Square (LMS) method for extracting RFI give good results, which are quantified with simulated data. Next, we would like to improve our sinusoidal model of the RFI to include a more complete description of the RFI signal and to apply the LMS algorithm to measured data -
Kenneth Knaell.
Progress in three-dimensional SAR from curvilinear apertures.
In William J. Miceli, editor,
,
volume 3462,
pages 110-121,
1998.
SPIE.
Keyword(s): SAR Processing,
Non-Linear Flight Path,
SAR Tomography,
Curvilinear SAR.
[bibtex-key = knaell:110]
-
Riccardo Lanari,
Scott Hensley,
and Paul Rosen.
Modified SPECAN algorithm for ScanSAR data processing.
In IEEE International Geoscience and Remote Sensing Symposium,
volume 2,
pages 636-638,
July 1998.
Keyword(s): SAR Processing,
Modified SPECAN,
SPECAN,
Spectral Analysis,
geophysical signal processing,
geophysical techniques,
radar imaging,
remote sensing by radar,
spaceborne radar,
synthetic aperture radarSAR,
ScanSAR,
ScanSAR image,
chirp z-transform,
chirp-z,
geophysical measurement technique,
land surface,
modified SPECAN algorithm,
phase-preserving algorithm,
radar imaging,
radar remote sensing,
range-dependent correction factor,
synthetic aperture radar,
terrain mapping.
Abstract: The authors present a new phase-preserving algorithm for ScanSAR data processing that extends the SPECAN procedure. The proposed technique allows one to avoid the range dependent scaling of the azimuth pixel dimension, obtained by applying the standard SPECAN approach; this result is achieved by replacing the standard Fourier transform included in the SPECAN algorithm with a chirp z-transform, whose kernel includes a range-dependent correction factor. ScanSAR images generated via the proposed procedure have a constant azimuth pixel spacing whose dimension can be selected according to the application requirements -
Li Liwei,
Asif Raza,
and Mao Shiyi.
Improvement of rank one phase estimation (ROPE) autofocusing technique.
In Signal Processing Proceedings, 1998. ICSP '98. 1998 Fourth International Conference on,
volume 2,
pages 1461-1464vol.2,
12-16 Oct. 1998.
[bibtex-key = Liwei1998]
-
F. Lombardini,
H.D. Griffiths,
and F. Gini.
A ML multichannel ATI-SAR technique for measuring ocean surface velocities.
In OCEANS '98 Conference Proceedings,
volume 2,
pages 778-782vol.2,
28 Sept.-1 Oct. 1998.
[bibtex-key = Lombardini1998]
-
F. Lombardini and P. Lombardo.
A ML thinned array SAR interferometric sensor for high accuracy absolute phase retrieval.
In Radar Conference, 1998. RADARCON 98. Proceedings of the 1998 IEEE,
pages 263-268,
11-14 May 1998.
[bibtex-key = Lombardini1998a]
-
Richard T. Lord and Michael R. Inggs.
Approaches to RF interference suppression for VHF/UHF synthetic aperture radar.
In Communications and Signal Processing, 1998. COMSIG '98. Proceedings of the 1998 South African Symposium on,
pages 95-100,
1998.
Keyword(s): SAR Processing,
adaptive filters,
adaptive signal processing,
interference suppression,
least mean squares methods,
radar imaging,
radar interference,
synthetic aperture radar,
LMS adaptive filter,
P-Band,
RF interference suppression,
RFI Suppression,
SAR imagery,
VHF/UHF SAR applications,
VHF/UHF synthetic aperture radar,
coherent subtraction algorithms,
filter approaches,
image quality,
interference power,
least-mean-squared filter,
radio frequency interference,
receiver noise,
spectral estimation.
Abstract: An increasing amount of interest has developed in VHF/UHF SAR applications. Unfortunately the VHF-UHF portion of the spectrum is already in heavy use by other services, such as television and mobile communications. Even in remote locations the interference power often exceeds receiver noise by many dB, becoming the limiting factor on system sensitivity and severely degrading the image quality. This paper addresses the problem of radio frequency (RF) interference and its impact on SAR imagery. Several RF interference suppression methods are described and discussed. These include spectral estimation and coherent subtraction algorithms, as well as various filter approaches. The least-mean-squared (LMS) adaptive filter is described in detail, and its effectiveness in suppressing RF interference is demonstrated on simulated data and on real P-band data. -
Stefan Nilsson and Lars-Erik Andersson.
Application of Fast Backprojection Techniques for some Inverse Problems of Synthetic Aperture Radar.
In Edmund G. Zelnio, editor,
Algorithms for Synthetic Aperture Radar Imagery V,
volume SPIE3370,
pages 62-72,
1998.
Keyword(s): SAR Processing,
Backprojection,
Fast Backprojection,
Quadtree Processing,
Time Domain Backprojection,
Circular Averages,
Wideband SAR,
Focusing,
Motion Compensation.
Abstract: In certain radar imaging applications one encounters the problem of reconstructing a reflectivityfunction from information about its averages over circles with center on a straight line. A robust inversion method is afiltered backprojection method, similar to the one used in medical tomography. We will present a fast algorithm for this backprojection operator. Numerical examples are given. -
Richard Rau and James H. McClellan.
A Directional Image Decomposition for Ultra-Wideband SAR.
In ICASSP '98, International Conference on Acoustics, Speech, and Signal Processing,
volume 5,
pages 2877-2880,
May 1998.
Keyword(s): SAR Processing,
Backprojection,
Ultra-Wideband SAR,
Directional Filterbanks.
Abstract: This paper presents a theoretical analysis of the structure of wide angle, ultra-wideband SAR images formed by a constant integration angle backprojection image former. It is shown that the effects of the image former can be modeled as a filtering operation on the original data. Furthermore, SAR images for different squint angles can be obtained from the original images by directional filtering. As a result, it is shown that perfect reconstructing directional filterbanks can be used as a unitary transform between SAR images and a 3-D representation containing additional aspect-angle information. It is demonstrated, how this new representation can be used to enhance targets. -
Andreas Reigber and Andreas Ulbricht.
P-band repeat-pass interferometry with the DLR experimental SAR.
In Geoscience and Remote Sensing Symposium Proceedings, 1998. IGARSS '98. 1998 IEEE International,
volume 4,
pages 1914-1916,
1998.
Keyword(s): SAR Processing,
airborne radar,
geophysical techniques,
remote sensing by radar,
synthetic aperture radar,
DLR experimental SAR,
ESAR,
P-Band,
RF interference removal,
RFI Suppression,
SAR interferometry,
Interferometry,
UHF,
geophysical measurement technique,
ground parameters,
land surface,
radar remote sensing,
repeat-pass interferometry,
repeat-pass mode,
surface topography,
synthetic aperture radar,
terrain mapping.
Abstract: SAR interferometry is a powerful tool for the determination of surface topography and for estimation of ground parameters. In particular the analysis of different frequencies has the capability to provide a broad set of useful information. Therefore long wavelengths like the P-band of great interest, because they often show different interactions with scatterers than shorter wavelengths like the C-band. The authors address the implementation of a P-band repeat-pass mode for the DLR's experimental SAR (ESAR), including the problematic removal of RF-interferences in the data. Recent results on a test site in Solothurn/Switzerland are shown. -
Olle Seger,
Magnus Herberthson,
and Hans Hellsten.
Real time SAR processing of low frequency ultra wide band radar data.
In Proc. of EUSAR '98 - European Conference on Synthetic Aperture Radar,
pages 489-492,
May 1998.
Keyword(s): SAR Processing,
Backprojection,
Time-Domain Backprojection,
Local Backprojection,
Real Time Operation,
Ultra-Wideband SAR,
FOPEN,
Image processing,
Ground Penetrating Radar,
Low-Frequency SAR,
Image Reconstruction,
Radar Resolution,
Parallel Processing.
Abstract: CARABAS (Coherent All RAdio BAnd Sensing) is a synthetic aperture radar with high relative bandwidth. Furthermore, CARABAS operates at radio band frequencies, which enables the radar to penetrate foliage. In this paper, we propose and analyze a reconstruction algorithm suitable for parallel implementation. The core idea of the method is a subdivision of the radar raw data into subapertures, from which coarse resolution subimages can be reconstructed. These subimages are then distributed to the nodes of a powerful parallel computer in order to achieve fine resolution at real-time rate. -
David Small,
Francesco Holecz,
Erich Meier,
and Daniel Nüesch.
Absolute radiometric correction in rugged terrain: A plea for integrated radar brightness.
In IGARSS '98, International Geoscience and Remote Sensing Symposium,
volume 1,
pages 330-332,
1998.
Keyword(s): geophysical signal processing,
geophysical techniques,
radar imaging,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
absolute radiometric correction,
biomass estimation,
geophysical measurement technique,
integrated radar brightness,
integrative faceted heteromorphic approach,
land surface,
multimode SAR imagery,
multimode image comparison,
radar remote sensing,
radiometric normalisation,
rugged terrain,
spaceborne radar,
synthetic aperture radar,
terrain mapping,
terrain-induced variation.
Abstract: Rigorous intercomparison of multimode SAR imagery requires not -
David Small,
Francesco Holecz,
Erich Meier,
and Daniel Nüesch.
Radiometric Normalization for Multimode Image Comparison.
In Proc. of EUSAR '98 - European Conference on Synthetic Aperture Radar,
pages 191-194,
1998.
Keyword(s): SAR Processing,
SAR Geocoding,
Geocoding,
Calibration,
Radiometric Calibration,
Radiometric Correction,
Digital Elevation Model,
Image Simulation,
Terrain-Geocoding.
Abstract: Intercomparison of backscatter collected by SAR sensors at heterogeneous radar look angles gives rise to highly variable ground areas being associated with each pixel location within a radar geometry (slant or ground range) image. Many elements within a digital elevation model (in map geometry) can be mapped to a single location in the radar image (range / Doppler coordinates). An image simulation technique uses a faceted high resolution elevation model to integrate all backscatter returned to each range and Doppler location in the radar image (incorporating knowledge of local radar shadow). Modelling the imaging process in this manner, a map of illuminated area is produced in radar geometry, and used to normalize the true backscatter returned by the radar sensor. Although radar shadow must be considered specially, no extraordinary treatment is required of layover regions, as they are correctly accounted for by integration of the illuminated area. The image simulation approach improves on the conventional consideration of 2D incidence angles, as the 3D configuration defining the illuminated area (in both the range and azimuth dimensions) is captured. RADARSAT images acquired over Switzerland are used to demonstrate the benefit of such normalization for thematic interpretation. A high resolution digital elevation model (DEM) with 25m pixel spacing is used as input to the image simulation. The deterioration of the normalization with progressively poorer input DEMs is studied empirically to gauge the required DEM resolution for acceptable normalization of images acquired over pre-alpine topography. -
Mehrdad Soumekh.
Range Stacking: An Interpolation-free SAR Reconstruction Algorithm.
In Edmund G. Zelnio, editor,
Algorithms for Synthetic Aperture Radar Imagery V,
volume SPIE3370,
pages 13-24,
1998.
Keyword(s): SAR Processing,
Range Stacking Algorithm,
Wavefront Reconstruction,
Wavenumber Domain Algorithm,
omega-k,
Backprojection,
Wideband SAR,
Squinted SAR,
FOPEN,
Motion Compensation.
Abstract: A method for digital image formation in Synthetic Aperture Radar (SAR) systems is presented. The proposed approach is based on the wavefront reconstruction theory for SAR imaging systems. However, this is achieved without image formation in the spatial frequency domain of the target function which requires interpolation. The proposed method forms the target function at individual range points within the radar range swath; this is referred to as range stacking. The range stacking reconstruction method is applicable in stripmap and spotlight (broadside and squint) SAR systems. Results using a wide-beamwidth FOliage PENetrating (FOPEN) SAR database are provided, and the effect of beamwidth filtering on the signature of moving targets in the imaging scene is shown. -
D.G. Thompson,
J.S. Bates,
D.V. Arnold,
David G. Long,
and A. Robertson.
Range dependent phase gradient autofocus.
In IEEE International Geoscience and Remote Sensing Symposium Proceedings, IGARSS '98,
volume 5,
pages 2634-2636,
6-10 July 1998.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus,
PGA,
Range-dependent.
Abstract: The Phase Gradient Autofocus (PGA) algorithm has been widely used in Spotlight Synthetic Aperture Radar (SAR) to remove motion-induced blurs in the images. The PGA algorithm has been proven to be a superior autofocus method. PGA assumes a narrow beam, which is valid for most SAR systems. However, lower altitude SAR have large range dependencies that cannot be ignored. A new phase estimator for PGA is introduced and extended to allow range dependence. An ERS-1 image of Death Valley is used in simulations comparing the new estimator to the widely used maximum likelihood approach and in demonstrating the range-dependent PGA algorithm. - F. Berizzi, G. Corsini, M. Diani, F. Lombardini, and G. Pinelli. Simulation model and performance analysis of a three-antenna InSAR system. In Radar 97 (Conf. Publ. No. 449), pages 119-123, 14-16 Oct. 1997. [bibtex-key = Berizzi1997]
-
G. Corsini,
M. Diani,
F. Lombardini,
and G. Pinelli.
Reduction of the phase-unwrapping drawbacks by the three-antenna interferometric SAR system.
In Geoscience and Remote Sensing, 1997. IGARSS '97. 'Remote Sensing - A Scientific Vision for Sustainable Development'., 1997 IEEE International,
volume 4,
pages 1536-1538vol.4,
3-8 Aug. 1997.
[bibtex-key = Corsini1997]
-
Charles V. Jakowatz,
Daniel E. Wahl,
Paul A. Thompson,
and Neall E. Doren.
Space-variant filtering for correction of wavefront curvature effects in spotlight-mode SAR imagery formed via polar formatting.
In Edmund G. Zelnio, editor,
,
volume 3070,
pages 33-42,
1997.
SPIE.
Keyword(s): SAR Processing,
Polar Format Algorithm,
PFA,
Range Migration Algorithm,
RMA,
omega-k,
correction of wavefront curvature effects,
Spotlight SAR,
Spotlight-mode data.
[bibtex-key = jakowatzWahlThompsonDorenSpotlightPolarFormat1997]
-
Michael Y. Jin.
High Quality Spotlight SAR Processing Algorithm Designed for LightSAR Mission.
In IGARSS '97, International Geoscience and Remote Sensing Symposium,
volume 29,
pages 477-480,
August 1997.
Keyword(s): SAR Processing,
Subband Images,
LightSAR,
SIR-C,
Spotlight SAR.
Abstract: A high quality spotlight SAR processing algorithm is presented. In this algorithm, subband images of the radar illuminated spot are processed using well known strip mode processing algorithms. A full resolution image is then formed by (1) merging the spectra of subband images into a full band spectrum, and (2) taking an inverse FFT. Advantages of this algorithm include (1) higher image quality, (2) higher processing throughput rate, and (3) lower S/W development cost. The image quality achieved by this algorithm is better than that previously achieved by the backprojection algorithm. The fine image quality is demonstrated by the SIR-C spotlight SAR images. -
Chan Hian Lim and Yeo Tat Soon.
Non-iterative spotlight SAR autofocusing using a modified phase-gradient approach.
In Geoscience and Remote Sensing, 1997. IGARSS '97. 'Remote Sensing - A Scientific Vision for Sustainable Development'., 1997 IEEE International,
volume 1,
pages 484-486vol.1,
3-8 Aug. 1997.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus.
[bibtex-key = Lim1997]
-
P. Lombardo and F. Lombardini.
Multi-baseline SAR interferometry for terrain slope adaptivity.
In Radar Conference, 1997., IEEE National,
pages 196-201,
13-15 May 1997.
[bibtex-key = Lombardo1997]
-
S. Lawrence Marple, Jr..
Computing the discrete-time analytic signal via FFT.
In Signals, Systems and Computers, 1997. Conference Record of the Thirty-First Asilomar Conference on,
volume 2,
pages 1322-1325,
1997.
Keyword(s): Analytic Signal,
discrete time systems,
fast Fourier transforms,
frequency-domain analysis,
signal sampling,
FFT,
complex-valued decimated N/2-point discrete-time analytic signal,
complex-valued interpolated NM-point discrete-time analyticsignal,
complex-valued standard N-point discrete time analytic signal,
discrete-time analytic signal,
frequency-domain algorithms,
real-valued N-point discrete-time signal,
sample rate,
transform end points,
Hilbert Transform.
Abstract: Starting with a real-valued N-point discrete-time signal,frequency-domain algorithms are provided for computing (1) thecomplex-valued standard N-point discrete time `analytic' signal of thesame sample rate, (2) the complex-valued decimated N/2-pointdiscrete-time analytic signal of half the original sample rate, and(3) the complex-valued interpolated NM-point discrete-time `analytic'signal of M times the original sample rate. Special adjustment oftransform end points is shown to generate proper discrete-time`analytic' signals -
H. Rudolf,
D. Tarchi,
and A.J. Sieber.
Combination of linear and circular SAR for 3-D features.
In Geoscience and Remote Sensing, 1997. IGARSS '97. 'Remote Sensing - A Scientific Vision for Sustainable Development'., 1997 IEEE International,
volume 4,
pages 1551-1553,
1997.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
geophysical techniques,
radar imaging,
remote sensing by radar,
synthetic aperture radar,
InSAR,
LISA,
buried object detection,
circular SAR,
circular aperture,
geophysical measurement technique,
ground penetrating radar,
interferometric SAR,
land surface,
linear SAR,
linear SAR outdoor system,
mine detection,
radar imaging,
radar remote sensing,
terrain mapping,
three dimensional feature,
vegetation mapping.
Abstract: An economic and fast change of an existing radar system with alinear synthetic aperture into a system with 3D capabilities ispresented. For actual and future fields of radar in remote sensing, suchas high precision mine detection, highly accurate vegetationmeasurements and interferometric SAR applications the importance ofresolution in the third dimension is growing fast. Until now a such aradar required an expensive phased array antenna, a costly narrow-beamscanning system, or a combination of both of them. In order to overcomethese problems, the combination of an existing linear SAR outdoor system(LISA) with a circular aperture for vertical resolution led to a fastand economic additional 3rd dimension feature. A test experiment hasbeen performed to validate the system and the implemented SAR processor.The very promising results are presented. -
Shunhua Wang and Xiaotao Huang.
Autofocus techniques for reducing phase errors in UWB-SAR.
In IEEE National Aerospace and Electronics Conference, NAECON 1997,
volume 2,
pages 1009-1014,
July 1997.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Autofocus,
PGA,
Residual Motion Errors,
UWB SAR.
[bibtex-key = wangHuang1997:Autofocus]
-
Weidong Yu and Zhaoda Zhu.
Comparison of Doppler Centroid Estimation Methods in SAR.
In IEEE National Aerospace and Electronics Conference NAECON,
volume 2,
pages 1015-1018,
1997.
Keyword(s): SAR Processing,
Doppler Centroid Estimation,
Energy Balancing,
Matched Correlation Estimator,
Maximum Likelyhood Estimator,
Sign Doppler Estimator,
SDE,
Correlation Doppler Estimator,
CDE,
ERS.
Abstract: This paper compares five Doppler centroid estimation methods which are: energy balancing, matched-correlation maximum likelihood, correlation Doppler estimator (CDE) and sign Doppler estimator (SDE). Their estimation performances in raw data domain and image domain are studied. The computer simulation results are presented. ERS-1 raw data are also used to test the performances of every method. -
G. Cazzaniga and Andrea Monti-Guarnieri.
Removing RF interferences from P-band airplane SAR data.
In Geoscience and Remote Sensing Symposium, 1996. IGARSS '96. 'Remote Sensing for a Sustainable Future.', International,
volume 3,
pages 1845-1847,
1996.
Keyword(s): SAR Processing,
geophysical signal processing,
geophysical techniques,
interference,
interference (signal),
interference filters,
notch filters,
radar imaging,
radar interference,
remote sensing by radar,
synthetic aperture radar,
MUSIC,
P-Band,
RFI Suppression,
RF interference removal,
UHF radar,
adaptive signal processing,
airborne radar,
airborne SAR,
geophysical measurement technique,
in-phase subtraction,
land surface,
notch filtering,
radar imaging,
radar remote sensing,
synthetic aperture radar,
terrain mapping,
urban area.
Abstract: This paper approaches the problem of canceling the disturbances due to RF interferences in P-band, airborne SAR missions. Two techniques are introduced: one exploits MUSIC to estimate the interferences' frequencies, and then performs notch filtering at that frequencies; whereas the other adaptively estimate the interference contributions and cancel them by means of in-phase subtraction. Both techniques have been successfully tested on the data acquired by the DLR E-SAR sensor over urban areas. -
F. Gatelli,
Andrea Monti-Guarnieri,
Claudio Prati,
and Fabio Rocca.
Medium resolution efficient phase preserving focusing for interferometry.
In IGARSS '96, International Geoscience and Remote Sensing Symposium,
volume 1,
pages 671-673,
1996.
Keyword(s): SAR Processing,
Presumming,
Interferometry,
geophysical signal processing,
geophysical techniques,
image processing,
image resolution,
radar imaging,
radar signal processing,
synthetic aperture radar,
SAR imagery,
SAR interferometry,
Unix Workstations,
algorithm,
coherence map,
geophysical measurement technique,
geophysics computing,
image pair,
image processing,
image resolution,
land surface,
medium resolution efficient phase preserving focusing,
radar imaging,
radar remote sensing,
radar signal processing,
real time method,
strip-map SAR interferogram,
synthetic aperture radar,
terrain mapping.
Abstract: A real time technique to get strip-map SAR interferograms and coherence maps with common Unix Workstations is presented. For the ERS mission, the ?real time? throughput corresponds to approximately 1/8 of PRF: e.g. ~4 min for processing a 100?100 km image pair. The proposed algorithm achieves that goal on a medium cost 160 Mflops/s Unix Workstation. The output is a 5 looks averaged interferogram, with a geometric resolution of 50?50. - H. Hellsten, Lars M. H. Ulander, A. Gustavsson, and B. Larsson. Development of VHF CARABAS II SAR. In Proc. SPIE, volume 2747, pages 48-60, June 1996. [bibtex-key = hellstenUlanderGustavsson1996:CARABASII]
-
J. Homer,
I.D. Longstaff,
and G. Callaghan.
High resolution 3-D SAR via multi-baseline interferometry.
In IEEE International Geoscience and Remote Sensing Symposium, IGARSS'96,
volume 1,
pages 796-798,
May 1996.
Keyword(s): SAR Processing,
SAR Tomography,
Tomography,
geophysical techniques,
radar imaging,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
topography (Earth)3D imagery,
InSAR,
Multi-baseline Interferometry,
SAR imaging,
azimuth resolving capability,
geophysical measurment technique,
interferometric SAR,
land surface topography,
node aperture,
normal-to-slant-range direction,
procedural outline,
radar remote sensing,
spaceborne radar,
synthetic aperture radar,
terrain height,
terrain mapping,
theoretical analysis,
three dimensional SAR method.
Abstract: The ability of interferometric SAR (InSAR) to provide terrain height estimation can be interpreted as being due to the baseline (of the two SAR imaging flight paths) acting as an aperture in the normal-to-slant-range (n&oarr;) direction. However, the aperture, because it consists of only two nodes, has effectively no resolving power. The authors introduce and examine a technique which synthesises an N>2 node aperture in the n&oarr; direction from N-1 connected baselines. This, together with the slant-range and azimuth resolving capability of SAR imaging systems, enables the generation of high resolution 3D imagery. A theoretical analysis and procedural outline of the proposed technique are presented -
Charles V. Jakowatz,
Daniel E. Wahl,
and Paul A. Thompson.
Ambiguity resolution in SAR interferometry by use of three phase centers.
In Edmund G. Zelnio and Robert J. Douglass, editors,
,
volume 2757,
pages 82-91,
1996.
SPIE.
Keyword(s): SAR Processing,
InSAR,
SAR Interferometry,
multibaseline,
Multibaseline InSAR,
Three phase centers,
Terrain Mapping,
Topography,
Spotlight SAR,
Spotlight-mode data.
[bibtex-key = jakowatzWahlThompsonAmbiguityResolutionInSARByThreeAntennas]
-
Kenneth Knaell.
Three-dimensional SAR from curvilinear apertures.
In Radar Conference, 1996., Proceedings of the 1996 IEEE National,
pages 220-225,
1996.
Keyword(s): SAR Processing,
Non-Linear Flight Path,
SAR Tomography,
curvilinear SAR,
image enhancement,
interference suppression,
maximum likelihood estimation,
radar antennas,
radar clutter,
radar cross-sections,
radar imaging,
synthetic aperture radar,
IMP algorithm,
aperture configuration,
artifacts,
coherent CLEAN algorithm,
curvilinear apertures,
dynamic range,
image sidelobes,
image size,
imaging techniques,
likelihood extremization,
maximum likelihood estimation,
scatterers,
sidelobe leakage effects,
three-dimensional SAR.
Abstract: Three-dimensional information content in radar data taken from suitably curved aperture paths is sufficient to allow useful 3D images to be produced by appropriate imaging techniques. The coherent CLEAN algorithm, the IMP algorithm, and maximum likelihood estimation have been used to produce 3D images from data obtained for two such scenarios. The IMP algorithm in conjunction with likelihood extremization produces images free of sidelobe leakage effects found in the CLEAN algorithm. The CLEAN and IMP algorithms find use initiating likelihood extremization on or near its global maximum. Dynamic range of such images appears dependent upon levels at which artifacts appear although valid scatterers are indicated below such levels. Artifacts appear to be a function of the image sidelobes determined by the aperture configuration. Reduction of this problem and methods to increase image size will extend the general usefulness of this technique -
Jung Ah C. Lee,
Orhan Arikan,
and David C. Munson, Jr..
Formulation of a General Imaging Algorithm for High-Resolution Synthetic Aperture Radar.
In ICASSP '96, International Conference on Acoustics, Speech, and Signal Processing,
volume 4,
pages 2092-2095,
May 1996.
Keyword(s): SAR Processing,
Backprojection,
Convolution Backprojection.
Abstract: We consider the application of an alternative imaging algorithm to the inversion of strip-mapping synthetic aperture radar (SAR) data. The algorithm was originally developed and successfully applied in the area of geophysics to estimate the conductivity distribution from wellbore induction measurements. The SAR measurement relation satisfies the same form of integral equation describing the wellbore problem. By exploiting the form of the measurement kernel, we derive a SAR image formation algorithm involving deconvolution-backprojection. Unlike correlation-based SAR image formation, our approach is more general, without simplifying assumptions on the range function, and is robust to measurement noise, at the expense of increased computational complexity. Simulation results are presented that demonstrate the effectiveness of the proposed algorithm. -
F. Lombardini.
Absolute phase retrieval in a three-element synthetic aperture radar interferometer.
In Radar, 1996. Proceedings., CIE International Conference of,
pages 309-312,
8-10 Oct. 1996.
[bibtex-key = Lombardini1996]
-
F. Lombardini and P. Lombardo.
Maximum likelihood array SAR interferometry.
In Digital Signal Processing Workshop Proceedings, 1996., IEEE,
pages 358-361,
1-4 Sept. 1996.
[bibtex-key = Lombardini1996a]
-
John W. McCorkle and Martin Rofheart.
Order N^2 log(N) Backprojector Algorithm for Focusing Wide-Angle Wide-Bandwidth Arbitrary-Motion Synthetic Aperture Radar.
In Gerald S. Ustach, editor,
Radar Sensor Technology,
volume SPIE2747,
pages 25-36,
1996.
Keyword(s): SAR Processing,
Backprojection,
Fast Backprojection,
Quadtree Processing,
Time Domain Backprojection,
Wideband SAR,
Focusing,
Motion Compensation.
Abstract: A new, fast algorithm for synthetic aperture radar (SAR) image formation is introduced. The algorithm is based on a decomposition of the time domain backprojection technique. It inherits the primary advantages of time domain backprojection: simple motion compensation, simple and spatially unconstrained propagation velocity compensation, and localized processing artifacts. The computational savings are achieved by using a divide-and-conquer strategy of decomposition, and exploiting spatial redundancy in the resulting sub-problems. The decomposition results in a quadtree data structure that is readily parallelizable and requires only limited interprocessor communications. For a SAR with N aperture points and an N by N image area, the algorithm is seen to achieve O(N^2 logN) complexity. The algorithm allows a direct trade between processing speed and focused image quality. - B. Walker, G. Sander, M. Thompson, B. Burns, R. Fellerhoff, and D. Dubbert. A high-resolution, four-band SAR Testbed with real-time image formation. In Geoscience and Remote Sensing Symposium, 1996. IGARSS '96. 'Remote Sensing for a Sustainable Future.', International, volume 3, pages 1881-1885vol.3, 27-31 May 1996. [bibtex-key = Walker1996]
-
Zhu Zhaoda,
Qiu Xiaohui,
and She Zhishun.
Modified Doppler centroid tracking method for phase compensation in ISAR.
In Radar, 1996. Proceedings., CIE International Conference of,
pages 751-754,
8-10 Oct. 1996.
Keyword(s): ISAR.
[bibtex-key = Zhaoda1996]
-
Zhaoda Zhu,
Xiaohui Qiu,
and Zhishun She.
ISAR motion compensation using modified Doppler centroid tracking method.
In Aerospace and Electronics Conference, 1996. NAECON 1996., Proceedings of the IEEE 1996 National,
volume 1,
pages 359-363vol.1,
20-23 May 1996.
Keyword(s): ISAR.
[bibtex-key = Zhu1996]
-
Kenneth Abend and John W. McCorkle.
Radio and TV interference extraction for ultrawideband radar.
In Dominick A. Giglio, editor,
Algorithms for Synthetic Aperture Radar Imagery II, Dominick A. Giglio; Ed.,
volume 2487,
pages 119-129,
1995.
SPIE.
Keyword(s): SAR Processing,
RFI Suppression,
Ultra-Wideband SAR,
Airborne SAR.
Abstract: This paper describes a computationally efficient, high-performance, UWB radar interference suppression algorithm. An adaptive FIR (finite impulse response) prediction-error noise- whitening filter exhibits minimal computational complexity and achieves 30 dB interference reduction per pulse (1 microsecond(s) long) with 16-bit simulated interference. Using measured interference data digitized to 8-bits with a 6.5 effective bit digitizer, collected just north of Washington, DC at the Army Research Laboratory, the technique achieved 20 to 27 dB of reduction. To minimize the computational load, the filter weights are periodically determined from data collected during a fraction of a radar range sweep. These weights are found to be effective for hundreds of subsequent radar pulses. Previous work on an estimate-and-subtract, tone-extraction technique resulted in 20 dB average interference reduction on the same measured data with a computational load linearly related to the number of tones extracted. The adaptive filtering approach uses an over-determined system producing an FIR filter with N taps, independent of the number of interference signals. An iterative technique to reduce the range sidelobes caused by the filter's impulse response is also presented. The computational load of this iterative stage is, at worst, linearly related to the number of targets whose sidelobes are extracted. It is shown that, with a small reduction in performance, the sidelobe reduction can be accomplished with a relatively small increase in the overall computational load. The computational complexity of the proposed technique relative to the estimate-and- subtract technique depends on the signal and interference environment and on the acceptable sidelobe level. A comprehensive radio and TV interference simulator was developed to test the interference suppression algorithm. It avoids difficulties in memory requirements and code complexity typically encountered in high-sample rate, long duration, and UWB simulations. Data was generated for various population densities, sampling rates, and quantization levels. Results using the simulation data showed that the performance of the algorithm was related to the quantization level with more bits producing better results. -
A. Beaudoin,
N. Stussi,
D. Troufleau,
N. Desbois,
L. Piet,
and M. Deshayes.
On the use of ERS-1 SAR data over hilly terrain: Necessity of radiometric corrections for thematic applications.
In Geoscience and Remote Sensing Symposium, 1995. IGARSS '95,
volume 3,
pages 2179-2182,
1995.
Keyword(s): SAR Processing,
SAR Geocoding,
Geocoding,
Radiometric Calibration,
Radiometric Correction,
Calibration,
DEM,
ERS-1,
Mediterranean forest,
acquisition geometry,
empirical cosine model,
geophysical measurement technique,
geophysical techniques,
hilly terrain mapping,
land surface,
quantitative use,
radar imaging,
radar remote sensing,
radiometric correction,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
thematic applications,
vegetation mapping.
Abstract: A radiometric correction method for the quantitative use of ERS SAR data acquired over hilly terrain is illustrated over a Mediterranean forest test-site. It is based on a DEM coupled to the SAR acquisition geometry. It is shown that uncorrected ?0 information is mainly related to the ground scattering area (8 dB variations), and the useful thematic information (2-3 dB) is therefore masked. Once calibrated, pixel intensity decreases with local incidence angle (variations up to 1.5 dB) and this variability can be reduced using an empirical cosine model. Then, the thematic benefits of such corrections are illustrated for surface discrimination and parameter estimation, along with a discussion on applicability and limitations -
Fulvio Gini and Fabrizio Lombardini.
A novel linear-quadratic technique for coherent radar detection in mixed clutter environment.
In European Microwave Conference, 1995. 25th,
volume 1,
pages 360-364,
Oct. 1995.
[bibtex-key = Gini1995a]
-
Fulvio Gini,
Fabrizio Lombardini,
and Lucio Verrazzani.
A robust approach to decentralized CFAR detection in spiky clutter.
In European Microwave Conference, 1995. 25th,
volume 1,
pages 584-588,
Oct. 1995.
[bibtex-key = Gini1995]
-
Ron S. Goodman,
Sreenidhi Tummala,
and Walter G. Carrara.
Issues in Ultra-Wideband, Widebeam SAR Image Formation.
In The Record of the 1995 IEEE Radar Conference,
pages 479-485,
May 1995.
Keyword(s): SAR Processing,
Range Migration Algorithm,
Wavefront Reconstruction,
Wavenumber Domain Algorithm,
omega-k,
RFI Suppression,
Motion Compensation,
Autofocus Techniques,
Ultra-Wideband SAR,
Sidelobe Control,
P-Band,
FOPEN,
Airborne SAR.
Abstract: The formation of low-frequency, ultra-wideband/widebeam (UWB/WB) SAR imagery faces inherent challenges not present in conventional SAR systems operating at higher frequencies. Small angle approximations and other shortcuts taken in conventional SAR processors may be inappropriate for the UWB/WB SAR processor. The severe range migration associated with fine resolution UWB/WB SAR poses a significant problem for the image formation algorithm. The combination of a long synthetic aperture and a wide azimuth beamwidth has important implications for motion compensation implementation and performance. We survey the major challenges to UWB/WB SAR image formation. The emphasis is on the formation of fine resolution digital imagery from low frequency UWB/WB data collected in the stripmap mode by an airborne SAR system. We examine the differences in image formation and data processing between UWB/WB systems and conventional SAR systems. We illustrate aspects of UWB/WB image formation with imagery from the P3 ultra-wideband radar system - a 0.3 m resolution SAR which operates in the VHF/UHF frequency bands -
F. Holecz,
A. Freeman,
and J. van Zyl.
Topographic effects on the antenna gain pattern correction.
In IGARSS '95, Geoscience and Remote Sensing Symposium,
volume 1,
pages 587-589,
1995.
Keyword(s): SAR Processing,
SAR Geocoding,
Geocoding,
SIR-C,
X-SAR,
antenna gain pattern correction,
antenna radiation patterns,
radiometric calibration,
calibration,
Radiometric Correction,
remote sensing by radar,
satellite antennas,
Spaceborne SAR,
terrain effect,
terrain mapping,
topographic effect,
ERS-1,
ERS-2,
JERS-1,
RADARSAT,
SIR-C,
X-SAR.
Abstract: The purpose of this paper is to analyse and quantify the topographic effects on the antenna gain pattern correction of existing spaceborne Synthetic Aperture Radar systems, namely ERS-1, JERS-1, SIR-C, and X-SAR. Simulations and real SAR data of a test site are used. The corrections are carried out taking into account the local surface topography and compared with the standard method based on a reference ellipsoid. Results show that elevation variations in the ERS-1 and JERS-1 cases do not. affect significantly the antenna gain pattern correction. For extreme topographic differences, greater than 3000 m, a reference altitude for the radiometric calibration is suggested. On the other hand, for the low-orbit SRL-1J2 terrain information is strongly recommended, particularly, if relief differences within the image are significant, namely greater than 1000 m. Furthermore, it will be shown that in the SIR-C case, even if the polarizations of the am tenna gain patterns are slightly different, polarimetric calibration errors due to relief variations can be neglected. Finally, implications for forthcoming spaceborne SAR systems, i.e. ERS-2 and RADARSAT, are discussed. -
P. Pasquali,
C. Prati,
F. Rocca,
M. Seymour,
J. Fortuny,
E. Ohlmer,
and A.J. Sieber.
A 3-D SAR experiment with EMSL data.
In Geoscience and Remote Sensing Symposium, 1995. IGARSS '95. 'Quantitative Remote Sensing for Science and Applications', International,
volume 1,
pages 784-786,
1995.
Keyword(s): SAR Processing,
Tomography,
SAR Tomography,
radar applications,
radar imaging,
remote sensing by radar,
synthetic aperture radar,
topography (Earth),
EMSL,
European Microwave Signature Laboratory o,
JRC,
geodesy,
geophysical measurement technique,
horizontal slice,
interferometric SAR image,
land surface topography,
multi-baseline SAR,
radar remote sensing,
synthetic aperture radar,
target reconstruction,
terrain mapping,
three dimensional structure.
Abstract: In usual SAR systems the image spectrum is regularly sampled along azimuth and slant range. A third dimension is found in the baseline of interferometric SAR images. An experiment on the use of multi-baseline SAR images far 3D target reconstruction is presented. The data have been collected in the European Microwave Signature Laboratory of JRC. The volume is presented as horizontal slices of the target at different depths. -
Matthew Braunstein,
James M. Ralston,
and David A. Sparrow.
Signal processing approaches to radio frequency interference (RFI) suppression.
In Dominick A. Giglio, editor,
Algorithms for Synthetic Aperture Radar Imagery,
volume 2230,
pages 190-208,
1994.
SPIE.
Keyword(s): SAR Processing,
RFI Suppression,
Ultra-Wideband SAR,
Airborne SAR.
Abstract: Ultra-wideband radar (UWB) has been shown to be among the most powerful techniques available for underground and obscured object detection. The value of such systems is that they combine the penetration enhancement associated with VHF/UHF (and lower) frequencies with the resolution of wide absolute bandwidth. Such systems necessarily make use of much of the frequency spectrum already in heavy use by other services, such as television and mobile communications. Although this spectral overlap provides occasion for adverse consequences in both directions, to date the principal consequence has been often-severe impact on UWB radar measurements. Even in remote locations, the average interference power often exceeds receiver noise by many dB, becoming the limiting factor on system sensitivity. Nor are UWB radar designers free to overcome this interference by increasing radar power, since regulatory sanction for UWB operation will depend on maintaining sufficiently low spectral power densities to assure that other, prior, services are not appreciably degraded. Given the importance of radio frequency interference (RFI) on practical ultrawide band ground penetrating radar systems, it is important to consider how and to what extent the effects of RFI noise may be reduced. The overall problem of RFI and its impacts will be described and several signal processing approaches to removal of RFI will be discussed. These include spectral estimation and coherent subtraction algorithms and various filter approaches, which have been developed and applied by the signal processing community in other contexts. These methods will be applied to several different real-world experimental data sets, and quantitative measures of the effectiveness of each of these algorithms in removing RFI noise will be presented. Although computationally-intensive, most of the techniques to be described achieve substantial increases in S/RFI without requiring concomitant increases in radar average power. -
Charles V. Jakowatz,
Daniel E. Wahl,
Paul H. Eichel,
and Paul A. Thompson.
New formulation for interferometric synthetic aperture radar for terrain mapping.
In Dominick A. Giglio, editor,
,
volume 2230,
pages 411-418,
1994.
SPIE.
Keyword(s): SAR Processing,
InSAR,
SAR Interferometry,
Terrain Mapping,
Topography,
Spotlight SAR,
Spotlight-mode data.
[bibtex-key = jakowatzWahlEichelThompsonInSAR1994]
-
Alberto Moreira and Rolf Scheiber.
Doppler parameter estimation algorithms for SAR processing with the chirp scaling approach.
In Geoscience and Remote Sensing Symposium, 1994. IGARSS '94. 'Surface and Atmospheric Remote Sensing: Technologies, Data Analysis and Interpretation'., International,
volume 4,
pages 1977-1979,
1994.
Keyword(s): SAR Processing,
Doppler Centroid Estimation,
Doppler Ambiguity Resolver,
DAR,
SDE,
CDE,
Sign Doppler Estimator,
Correlation Doppler Estimator,
Doppler radar,
FM radar,
airborne radar,
geophysical signal processing,
geophysical techniques,
radar applications,
radar imaging,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar,
Doppler parameter estimation algorithm,
Doppler parameters,
Doppler rate,
SAC,
SAR imaging,
SAR processing,
SPECAN,
airborne radar,
autocorrelation function,
Chirp Scaling Algorithm,
chirp scaling approach,
correlation method,
geophysical measurement technique,
image processing,
land surface,
range-frequency centroid,
remote sensing,
shift and correlate algorithm,
signal processing,
spaceborne SAR,
synthetic aperture radar,
terrain mapping.
Abstract: This paper presents several correlation based methods for estimation of the Doppler parameters from SAR raw data in connection with the chirp scaling algorithm. For the estimation of the Doppler rate, a modified approach of the shift and correlate (SAC) algorithm is proposed. In this case, the auto-correlation function of each data set and the standard deviation of the velocity calculations are used in order to monitor the validity of the estimations. For resolving the PRF ambiguity, a new approach is proposed, which is based on the estimation of the range-frequency centroid as a function of the azimuth frequency. Several results of the Doppler parameters estimation are presented for airborne and spaceborne SAR data -
Rolf Scheiber and Alberto Moreira.
Extension of the Correlation Doppler Estimator for Determination of the Doppler Rate and for Resolving the PRF-Ambiguity.
In Giorgio Franceschetti, editor,
SAR Data Processing for Remote Sensing,
volume SPIE2316,
pages 33-41,
1994.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Clutterlock,
Correlation Doppler Estimator,
CDE,
Sign Doppler Estimator,
SDE,
Doppler Ambiguity Resolver,
DAR,
Doppler Rate Estimation,
Autofocus.
Abstract: Recently the chirp scaling algorithm has been proposed for high quality SAR processing. The algorithm requires first a transformation of the range uncompressed SAR raw data into the range-Doppler domain, which does not permit conventional techniques for the estimation of the Doppler parameters to be introduced efficiently into the processing. This paper first reviews the so called 'correlation Doppler estimator' (CDE), which was proposed for the estimation of the Doppler centroid in the time domain. This estimation algorithm is further extended in order to allow also the estimation of the Doppler rate. To perform this only bright targets are considered. By continuous calculation of the first coefficient of the auto-correlation function, the slope of the frequency history of the Doppler signal is determined, giving an exact estimate of the Doppler rate. to obtain also an estimation of the Doppler rate for scenes without bright targets but with some contrast, a modified version of the SAC algorithm is presented. Further a new method is presented, which can solve the PRF-ambiguity by means of an evaluation of the signal envelope skew in the range-Doppler domain. This technique does not require any additional range FFT, since it is based on the estimation of the variation of a range centroid as a function of the azimuth frequency. Several results are presented, which show the performance of the proposed new approaches. Some remarks are made regarding the inclusion of the described methods into the extended chirp scaling algorithm. -
D.E. Wahl,
C.V. Jakowatz,
and P.A. Thompson.
New approach to strip-map SAR autofocus.
In Digital Signal Processing Workshop, 1994., 1994 Sixth IEEE,
pages 53-56,
2-5 Oct. 1994.
Keyword(s): SAR Processing,
Autofocus,
Phase Curvature Autofocus,
Phase Gradient Autofocus.
Abstract: This paper demonstrates how certain concepts from the Phase Gradient Autofocus (PGA) algorithm for automated refocus of spotlight mode SAR imagery may be used to design a similar algorithm that applies to SAR imagery formed in the conventional strip-mapping mode. The algorithm derivation begins with the traditional view of strip-map image formation as convolution (compression) using a linear FM chirp sequence. The appropriate analogies and modifications to the spotlight mode case are used to describe a working algorithm for strip-map autofocus. -
Pierre Duhamel,
Mohsen Montazeri,
and Katia Hilal.
Classical adaptive algorithms (LMS, RLS, CMA, decision directed)seen as recursive structures.
In Acoustics, Speech, and Signal Processing, 1993. ICASSP-93., 1993 IEEE International Conference on,
volume 3,
pages 496-499,
1993.
Keyword(s): RFI Suppression,
adaptive filters,
computational complexity,
correlation theory,
least squares approximations,
recursive functions,
FIR algorithm,
adaptive algorithms,
block algorithms,
constant modulus algorithm,
correlation coefficients,
decision-directed algorithm,
equilibrium states,
finite impulse response,
least mean square,
LMS,
recursive least squares,
RLS,
recursive structures.
Abstract: Any finite impulse response (FIR) adaptive algorithm has aninherent recursive structure, since the error at time n is fedback into the algorithm to provide the next tap vector. The authors explicitly provide this recursive structure and show that a least meansquare (LMS) adaptive algorithm can be expressed in terms of a recursivefilter, the coefficients of this recurrence being the correlation coefficients of the input signal. Corresponding structures are proposed for the recursive least squares (RLS) algorithm, the constant modulus algorithm (CMA), and the decision-directed (DD) algorithm. These schemes provide block algorithms that are equivalent to the corresponding sample-by-sample algorithm, while requiring fewer computations. The corresponding structures are easily used for studying equilibrium states of the adaptive algorithms. -
A. Martinez and Jean L. Marchand.
Implementation and Quality Analysis of a CSA SAR Processor.
In IGARSS '93, International Geoscience and Remote Sensing Symposium,
volume 3,
pages 1179-1181,
August 1993.
Keyword(s): SAR Processing,
Chirp Scaling Algorithm,
Quality Assessment,
Quality Measures,
ISLR,
PSLR.
Abstract: Recently, a new SAR processing algorithm has been proposed. The basis of the method is to equalize the range migration trajectories of the whole image with respect to a reference range. During azimuth compression, the range migration at the reference range can be exactly corrected, and its effect is extended to all ranges. In order to assess the quality of the resulting image, a number of quality criteria are evaluated. They include classical measurements, such as spatial resolution, ISLR and PSLR, as well as refined ones for better analysis of the pulse shape. The stability and variation of the quality criteria when changing several key input parameters (Doppler centroid, FM rate acid reference range) are also studied. The tests have been performed using real ERS-1 raw data. The selected scene is the Flevoland site where three transponders and several corners reflectors are deployed, thus allowing precise quality analysis to be performed. -
B.L. Robertson and David C. Munson, Jr..
Motion errors in ISAR imaging of approaching targets.
In Acoustics, Speech, and Signal Processing, 1993. ICASSP-93., 1993 IEEE International Conference on,
volume 5,
pages 449-452vol.5,
27-30 April 1993.
Keyword(s): ISAR.
[bibtex-key = Robertson1993]
-
Ian G. Cumming,
Frank Wong,
and R. Keith Raney.
A SAR Processing Algorithm With No Interpolation.
In IGARSS '92, International Geoscience and Remote Sensing Symposium,
pages 376-379,
May 1992.
Keyword(s): SAR Processing,
Differential Range Deramp - Frequency Domain Algorithm,
DRD-FD Algorithm,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Comparison of Algorithms.
Abstract: Current SAR processing algorithms incorporate interpolators to perform key functions. It turns out that the interpolators are difficult to implement, and are one of the largest sources of error in the processing. In this paper, we introduce a new algorithm which eliminates the use of the interpolation operation, yet achieves accurate range migration correction over the full range swath. The algorithm can handle large apertures and large squints, and has noticeably better phase and geometry accuracy than current algorithms, even when the apertures and squints are high. The new algorithm is called Differential Range Deramp - Frequency Domain (DRD-FD) Algorithm, because its key operation is to use the linear-FM property of the range chirp to differentially shift the range energy as a function of azimuth frequency, and then to do the remaining range cell migration correction in the two-dimensional frequency domain. In this paper, the new algorithm is described, and simulation results are given to demonstrate its focusing, phase and geometric performance with squinted SAR data. In addition, an image is shown made from SEASAT data. -
Didier Dendal and Jean L. Marchand.
Omega-k Techniques Advantages and Weaker Aspects.
In IGARSS '92, International Geoscience and Remote Sensing Symposium,
pages 366-368,
May 1992.
Keyword(s): SAR Processing,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Comparison of Algorithms.
Abstract: Wave equation techniques and the omega-k algorithm are very attractive for future SAR space missions with on board reconstruction. The aim of the present work is to point out the stronger advantages and the weaker aspects of this algorithm compared to current SAR processors. Theoretical assumptions and approximations, practical limitations and drawbacks of the method will be outlined in contradistinction to its more positive aspects. A sensitivity analysis, with some positive conclusions, has also been performed. It will appear that there is no great revolution with regard to the traditional algorithms and that the major problems and chief restrictions are always the same, as well as the unavoidable antagonism between processing speed and reconstruction precision, even if some secondary effects are more easily handled there. - P.H. Eichel, D.C. Ghiglia, C.V. Jakowatz, and D.E. Wahl. Phase Gradient Autofocus for SAR Phase Correction: Explanation and Demonstration of Algorithmic Steps. In Digital Signal Processing workshop, 1992. The, pages 6.6.1-6.6.2, September 13-16, 1992. Keyword(s): SAR Processing, Autofocus, Phase Gradient Autofocus. [bibtex-key = Eichel1992]
-
Ralf Horn and Erich Meier.
A Refined Procedure To Generate Calibrated Imagery From Airborne Synthetic Aperture Radar Data.
In Geoscience and Remote Sensing Symposium, 1992. IGARSS '92. International,
pages 406-408,
1992.
Keyword(s): SAR Processing,
AGC,
Automatic Gain Control,
STC,
Sensitivity Time Control,
Calibration,
Radiometry,
Radiometric Calibration,
Radiometric Correction,
APG,
Antenna Gain Pattern,
ESAR,
E-SAR.
Abstract: The paper desciibes a procedure realized at DLR to generate calibrated imagery from synthetic aperture radar systems installed on board of small aircrafts. It has been especially developed for the DLR experimental radar system E-SAR, which uses antennas fixed directly to the body of a DO 228 aircraft. A receiver gain control system (STC) is implemented. The correction of the STC variable receiver gain, the compensation of the translational and rotational motion errors of the aircraft and the calibration of the radar data in the SAR processor are described. First preliminary results obtained from a recent experiment in Switzerland are shown. -
Alberto Moreira,
Artur Brodscholl,
Jacob Dom,
Frank Kochsiek,
and Winfried Poetzsch.
Airborne Real-time SAR Processing Activities at DLR.
In Geoscience and Remote Sensing Symposium, 1992. IGARSS '92. International,
pages 412-414,
1992.
Keyword(s): SAR Processing,
Real-Time SAR Processing,
Subaperture Processing,
Real-Time Subaperture Processing,
Hardware Processor,
STC,
Sensitivity Time Control.
[bibtex-key = moreiraBrodschollDomKochsiekPotzsch92:realTimeSARProc]
-
R. Keith Raney.
A New and Fundamental Fourier Transform Pair.
In IGARSS '92, International Geoscience and Remote Sensing Symposium,
volume 1,
pages 106-107,
1992.
Keyword(s): SAR Processing,
Wavenumber Domain Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Stationary Phase Method,
Closed Form Fourier Transform.
Abstract: A closed form Fourier transform relationship between the range signal, azimuth signal domain and the range signal, azimuth frequency (or Doppler) domain is presented. The derivation assumes the presence of a large time-bandwidth pulse modulation in range. The expression is valid over a wide angular field of view, and expressed using the hyperbolic range equation. The resulting Fourier transform pair is of general utility in SAR, tomography, active seismics and related imaging problems, and allows more insight into the imaging process in the presence of range curvature than is normally available. -
Hartmut Runge and Richard Bamler.
A Novel High Precision SAR Focussing Algorithm Based On Chirp Scaling.
In IGARSS '92, International Geoscience and Remote Sensing Symposium,
pages 372 - 375,
May 1992.
Keyword(s): SAR Processing,
Chirp Scaling Algorithm,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Range-Doppler Algorithm,
Comparison of Algorithms,
Squinted SAR.
Abstract: Azimuth compression of synthetic aperture radar data is an inherently two-dimensional problem because the SAR reference function migrates through several range resolution cells. This effect is referred to as range cell migration. For perfect focusing of the image the fact has to be accounted for that the amount of range cell migration varies with range. In classical range-Doppler SAR processors as well as with two-dimensional frequency domain processors a space-variant interpolation is required in order to compensate for this effect. In general, interpolation will degrade the final image quality and is computation time consuming. The proposed new algorithm avoids any interpolation step. It is essential for the algorithm that the SAR data are transformed to the range-Doppler domain prior to range compression. In this domain each range line is premultiplied with a particular phase function which is designed to perfectly straighten the range cell migration trajectories even for arbitrarily wide swath by the subsequent range compression step. This new method for range migration correction is the key element of a new SAR processing algorithm described in detail. The proposed method is inherently phase preserving. Its focusing quality is neither limited by high squint nor by wide swath. The implementation is simple because only multiplications and Fourier transforms are required. The paper presents a detailed derivation of the algorithm theory and illustrates possible implementations. -
Richard Bamler.
A Systematic Comparison of SAR Focussing Algorithms.
In IGARSS '91, International Geoscience and Remote Sensing Symposium,
volume 2,
pages 1005-1009,
1991.
Keyword(s): SAR Processing,
Range-Doppler Algorithm,
Wavenumber Domain Algorithm,
omega-k,
Secondary Range Compression,
Comparison of Algorithms.
Abstract: Focussing of SAR data is an inherently space-variant two-dimensional correlation. Six different algorithms are compared with each other in terms of their focussing quality and their ability to handle the space-variance of the correlation kernel: range-Doppler with and without secondary range compression, a modified range-Doppler algorithm, and three versions of the wavenumber domain processor. Quantitative examples are given for SEASAT and ERS-1. -
Terry M. Calloway,
Charles V. Jakowatz,
Paul A. Thompson,
and Paul H. Eichel.
Comparison of synthetic-aperture radar autofocus techniques: phase gradient versus subaperture.
In Franklin T. Luk, editor,
,
volume 1566,
pages 353-364,
1991.
SPIE.
Keyword(s): SAR Processing,
Autofocus,
Comparison of Algorithms,
Comparison of Autofocus Algorithms,
Phase Gradient Algorithm,
PGA,
Subaperture-based Autofocus,
subaperture correlation,
look-misregistration autofocus,
Map Drift.
[bibtex-key = callowayJakowatzThompsonEichelAutofocusComparisonPGASubaperture1991]
- M. Cocard, A. Geiger, E. Meier, and D. Nuesch. X-SAR Geometric Error Budget Analysis. In Geoscience and Remote Sensing Symposium, 1991. IGARSS '91. Remote Sensing: Global Monitoring for Earth Management., International, volume I, pages 247-251, 1991. [bibtex-key = cocardGeigerMeierNuesch91:XSARGEBA]
-
Jorgen Dall.
A new frequency domain autofocus algorithm for SAR.
In IGARSS '91, Geoscience and Remote Sensing Symposium,
volume 2,
pages 1069 - 1072,
1991.
Keyword(s): SAR Processing,
Autofocus,
SAC,
Shift and Correlate Algorithm,
Doppler Rate Estimation,
Autofocus,
Map Drift,
Airborne SAR.
Abstract: A new autofocus algorithm with a very high computational efficiency is presented. Although based on a completely different principle, this 'shift-and-correlate' algorithm has some similarity with the traditional map drift algorithm. Theory and preliminary tests indicate that the two algorithms have comparable accuracies. However, with the new algorithm the number of arithmetic operations is reduced by a factor of about 50. This, in combination with its non-iterative nature, makes it very suitable for real-time processing. -
Tapan Misra and Alberto Moreira.
A New Method For Generation Of Optimum Matched Filter From Replica Data For Pulse Compression.
In Geoscience and Remote Sensing Symposium, 1991. IGARSS '91. 'Remote Sensing: Global Monitoring for Earth Management'., International,
volume 2,
pages 1011-1014,
1991.
Keyword(s): SAR Processing,
Range Compression,
Pulse Compression,
Matched Filter,
Replica,
Chirp Replica,
Optimum Matched Filter.
[bibtex-key = misraMoreira91:OptimMatchedFilt]
-
T.E. Scheuer and Frank Wong.
Comparison of SAR Processors Based on a Wave Equation Formulation.
In IGARSS '91, International Geoscience and Remote Sensing Symposium,
volume 2,
pages 635-639,
June 1991.
Keyword(s): SAR Processing,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm,
Range-Doppler Algorithm,
Comparison of Algorithms.
Abstract: In this paper, we utilize a wave equation framework to describe SAR processing. Within this framework, various conventional and new processing techniques can be reliably compared. In particular, we compare wave equation implementations of the conventional range-Doppler algorithm and the seismic/SAR algorithm recently proposed. The range-Doppler algorithm is a matched filter solution of the Kirchhoff integral in range-time and Doppler-wavenumber space, while the seismic/SAR algorithm is a frequency-wavenumber or plane wave solution to the wave equation using the measured data as a boundary condition. Thus, both processors can be viewed as boundary value solutions to the electromagnetic wave equation. Point spread function analysis, of simulated ERS-1 data and of actual SEASAT data, shows that both processors provide very accurate relative amplitude and phase results. Nevertheless, we expect that future SAR processors may incorporate features of both techniques. -
Carmine Tarantino.
Comparison Between Different Doppler Centroid Estimation Methods For Spaceborne SAR Processing.
In Geoscience and Remote Sensing Symposium, 1991. IGARSS '91. 'Remote Sensing: Global Monitoring for Earth Management'., International,
volume 2,
pages 1047-1049,
1991.
Keyword(s): SAR Processing,
Doppler Centroid Estimation,
Spectra Correlation Estimator,
SIR-B.
Abstract: High accuracy estimation of Doppler centroid values is an important input for precision SAR processing. This paper describes the resutls of the numberical comparison between two different algorithms for Doppler centroid estimation. The Spectra Correlation Estimator and the Clutterlock Algorithm Estimator are tested by processing real SIR-B SAR data. The comparison of these two algorithms according to the required accuracy, the scene type and the processing time is proposed and results are analyzed. Test resutls indicate that an estimation accuracy of a few Hz is obtained. -
Daniel E. Wahl,
Charles V. Jakowatz,
Dennis C. Ghiglia,
and Paul H. Eichel.
Relationships between autofocus methods for SAR and self-survey techniques for SONAR.
In Andrew G. Tescher, editor,
,
volume 1567,
pages 32-40,
1991.
SPIE.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Algorithm,
PGA,
Subaperture-based Autofocus,
subaperture correlation,
look-misregistration autofocus,
Map Drift,
SONAR.
[bibtex-key = wahlJakowatzGhiliaEichelAutofocusSARandSONAR1991]
-
Terry M. Calloway,
Paul H. Eichel,
and Charles V. Jakowatz.
Iterative registration of SAR imagery.
In Andrew G. Tescher, editor,
,
volume 1349,
pages 412-420,
1990.
SPIE.
Keyword(s): SAR Processing,
Image Registration,
Basic Geocoding,
Iterative Image Registration.
[bibtex-key = callowayEichelJakowatzIterativeRegistration1990]
-
Daniel E. Wahl,
Paul H. Eichel,
and Charles V. Jakowatz.
Implementation of the phase-gradient algorithm.
In Franklin T. Luk, editor,
,
volume 1348,
pages 528-535,
1990.
SPIE.
Keyword(s): SAR Processing,
Autofocus,
Phase Gradient Algorithm,
PGA.
[bibtex-key = wahlEichelJakowatzPGAImplementation1990]
-
J.L. Bauck and W. K. Jenkins.
Convolution-backprojection image resource for bistatic synthetic aperture radar.
In Proc. IEEE Int. Symp. on Circuits and Systems,
volume 3,
pages 1512-1515,
May 1989.
Keyword(s): SAR Processing,
Bistatic SAR,
Backprojection,
bistatic synthetic aperture radar,
Azimuth Focusing,
convolution-backprojection,
elliptical-arc projections,
final reconstructed image,
ground patch,
image resource,
pixel,
weighting,
radar cross-sections,
radar theory;.
Abstract: The algorithm presented accounts for the elliptical nature of the wavefronts over the ground patch (resulting in elliptical-arc projections) and is based on the convolution-backprojection (CBP) algorithm of computer tomography. Essentially, three changes were made to the CBP algorithm. First, instead of backprojection along straight lines, the backprojection is along the same elliptical arcs from which the data were taken. Second, each pixel in the image, during each backprojection, receives a weighting depending on its position in the image. Third, each projection receives an additional overall weighting depending on the positions of the transmitter and the receiver for the corresponding projection. As with CBP, each projection is convolved with a specified function before backprojection, and all of the backprojections are accumulated to form the final reconstructed image -
C. Y. Chang and John C. Curlander.
Doppler Centroid Estimation Ambiguity For Synthetic Aperture Radars.
In IGARSS '89, International Geoscience and Remote Sensing Symposium,
volume 4,
pages 2567-2571,
July 1989.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Clutterlock,
Doppler Ambiguity Resolver,
DAR,
Range Cross-Correlation Technique,
Multiple PRF Technique,
SIR-C.
Abstract: A technique for estimation of the Doppler centroid of synthetic aperture radar (SAR) in the presence of a large antenna boresight pointing uncertainty is described. Also investigated is the image degradation resulting from data processing using an ambiguous centroid. Two approaches for Doppler centroid estimation (DCE) ambiguity resolution are presented: The range cross-correlation technique and the multiple PRF technique. For the multiple PRF technique, since other design factors control the selection for SAR, a generalized algorithm is derived for PRFs not containing a common divisor. An example using the Shuttle Imaging Radar (SIR-C) parameters illustrates that this algorithm is capable of resolving the C-band DCE ambiguity for antenna pointing uncertainties of 2? ~ 3?. - P.H. Eichel, D.C. Ghiglia, C.V. Jakowatz, G.A. Mastin, L.A. Romero, and D.E. Wahl. Applications of phase gradient autofocus to aperture synthesis imaging. In Multidimensional Signal Processing Workshop, 1989., Sixth, pages 57-58, Sept. 1989. Keyword(s): SAR Processing, Autofocus, Phase Gradient Autofocus. [bibtex-key = Eichel1989]
-
João Moreira and Winfried Poetzsch.
Results Of The Real-time Adaptive Radiometric Correction Implemented In The Dfvlr L/C-band Sar.
In Geoscience and Remote Sensing Symposium, 1989. IGARSS'89. 12th Canadian Symposium on Remote Sensing., 1989 International,
volume 4,
pages 2232-2234,
1989.
Keyword(s): SAR Processing,
AGC,
Automatic Gain Control,
STC,
Sensitivity Time Control,
Calibration,
Radiometry,
Radiometric Calibration,
Radiometric Correction,
APG,
Antenna Gain Pattern,
ESAR,
E-SAR.
[bibtex-key = moreiraPoetzsch89:AGCSTC]
-
R. Keith Raney and Paris W. Vachon.
A Phase Preserving SAR Processor.
In IGARSS '89, International Geoscience and Remote Sensing Symposium,
volume 4,
pages 2588-2591,
July 1989.
Keyword(s): SAR Processing,
Phase Preserving,
Range Migration Algorithm,
omega-k,
Wavenumber Domain Algorithm.
Abstract: Synthetic aperture radar (SAR) image phase information is necessary to support many advanced SAR applications. The phase information in the complex image for conventional range-Doppler processors is not a robust estimate of scene phase. A SAR processor specifically designed to preserve phase information is being developed at the Canada Centre for Remote Sensing (CCRS). In addition to preserving vital phase information, this processor can support large degrees of range curvature and range migration. Therefore, it is possible, in principle, to use this processor for satellite SAR data, high resolution airborne SAR data, and for both squint mode and spotlight mode SAR data. This paper summarizes the theory and presents early results. -
Hartmut Runge and Richard Bamler.
PRF Ambiguity Resolving for SAR.
In IGARSS '89, International Geoscience and Remote Sensing Symposium,
volume 4,
pages 2572-2575,
July 1989.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Clutterlock,
Doppler Ambiguity Resolver,
DAR,
Look Correlation,
Comparison of Algorithms,
SIR-C,
X-SAR.
Abstract: For high precision SAR (Synthetic Aperture Radar) processing, the determination of the absolute Doppler centroid is indispensable. The Doppler frequency estimated from azimuth spectra, however, suffers from the fact that the data are sampled with the PRF and an ambiguity about the correct PRF-band remains. Five methods for ambiguity resolving are proposed and discussed together with the already known technique of look correlation. None of these methods have a requirement on the mission schedule. It is shown that the following effect can be used to measure the absolute Doppler frequency: the Doppler shift of range spectra, range migration, image geometric misregistration and the use of multifrequency radar data. -
J. Siewerth.
Theory And Quantitative Comparison Of Doppler Centroid Estimation Methods.
In Geoscience and Remote Sensing Symposium, 1989. IGARSS'89. 12th Canadian Symposium on Remote Sensing. 1989 International,
volume 4,
pages 2576-2578,
1989.
Keyword(s): SAR Processing,
Doppler Centroid Estimation,
Energy Balancing,
Sign Doppler Estimator,
SDE,
Correlation Doppler Estimator,
CDE,
ERS.
Abstract: The purpose of this paper is to describe the theory and implementation of three different Doppler centroid estimation methods and to present the first results of currently performed quantitative investigations. The Doppler centroid shift caused by the relative velocity between the sensor platform and the targets is derived by analysing the recieved SAR data. In contrast to the conventionally used Delta-E method (also called energy balancing), which is a frequency approach, the two other methods, the Correlation Doppler Estimator (CDE) and the Sign Doppler Estimator (SDE), are both performed in the time domain. -
J. L. Bauck and W. K. Jenkins.
Tomographic Processing of Spotlight-Mode Synthetic Aperture Radar Signals with Compensation for Wavefront Curvature.
In ICASSP '88, International Conference on Acoustics, Speech, and Signal Processing,
volume 2,
pages 1192-1195,
April 1988.
Keyword(s): SAR Processing,
Backprojection,
Convolution Backprojection,
Spotlight SAR,
Wavefront Curvature.
Abstract: An algorithm is introduced which corrects for problems which arise in spotlight-mode synthetic aperture radar (SAR) when a significant amount of wavefront curvature is present. Wavefront curvature can be problematic when it is desired to reconstruct high-resolution images of ground patches which subtend a large angle at the radar. The proposed, non-Fourier, algorithm uses mappings to modify the convolution-backprojection method of computed tomography, providing reconstructions from circular-arc projections that are of the same high quality as those made from standard straight-line projections using the unmodified algorithm. In addition, other problems in high-resolution SAR imaging are identified which have solutions involving tomographic concepts, including situations which give rise to fan-beam-like projections. The new algorithm can be modified to deal with these problems as well. -
D.J. DiFilippo,
G.E. Haslam,
and W.S. Widnall.
Evaluation of a Kalman filter for SAR motion compensation.
In IEEE Position Location and Navigation Symposium, PLANS '88,
pages 259-268,
29 Nov-2 Dec 1988.
Keyword(s): SAR Processing,
Motion Compensation,
Residual Errors,
Kalman filters,
filtering and prediction theory,
military systems,
radar antennas,
Kalman filter,
SAR motion compensation,
SARMCS,
air turbulence,
airborne SAR,
aircraft maneuvers,
inertial measurement unit,
low-cost strapdown IMU,
radar antenna,
synthetic aperture radar.
Abstract: A synthetic aperture radar motion compensation system (SARMCS) is being developed at the Defence Research Establishment Ottawa to compensate an airborne SAR for spurious motions of the radar antenna that may be caused by air turbulence of aircraft maneuvers. A Kalman filter has been developed as part of this SAR motion compensation system which uses a low-cost strapdown IMU (inertial measurement unit), to measure antenna motion. The function of the Kalman filter is to control misalignments of the strapdown analytical platform, since analysis has indicated that these errors are dominant contributors to motion compensation error. Representative results from processing raw recorded flight data have verified the proper operation of all aspects of the Kalman filter and have indicated that the filter performance is consistent with the motion compensation requirements. Some examples of actual SAR strip-map imagery are shown in order to demonstrate the enhancement provided by the SARMCS. -
James E. Harris,
Randall S. Ostler,
Douglas M. Chabries,
and Richard W. Christiansen.
Quality Measures for SAR Images.
In IEEE International Conference on Acoustics, Speech, and Signal Processing ICASSP,
volume 2,
pages 1064-1067,
April 1988.
Keyword(s): SAR Processing,
Quality Assessment,
Quality Measures.
Abstract: Synthetic aperture radar (SAR) contains information features different from those of infrared images and conventional photography. Image quality measures specifically created for SAR are necessary to measure SAR processor performance especially in the context of lossy image data compression. The quality measures discussed include several existing measures and newly developed measures created to better gauge specific features of SAR imagery. Each quality performance measure is evaluated subjectively to determine the applicability to SAR image fidelity. -
Ian G. Cumming,
P. F. Kavanagh,
and M. R. Ito.
Resolving the Doppler Ambiguity for Spaceborne Synthetic Aperture Radar.
In IGARSS '86, International Geoscience and Remote Sensing Symposium,
volume 3,
pages 1639-1643,
1986.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Azimuth Look Correlation,
Clutterlock,
Doppler Ambiguity Resolver,
DAR,
Doppler Rate Estimation,
Autofocus.
Abstract: In spaceborne SAR systems, the radar beam pointing angle must be known to approximately one half the beamwidth in order to resolve the Doppler centroid ambiguity and provide accurate data processing. This constraint may place a heavy burden on the beam pointing and measurement error budget, unless an alternate means can be provided to estimate the beam pointing angle or Doppler centroid. In this paper, a new method is presented for estimating the Doppler centroid directly from the received radar data, during the image formation process. The algorithm has been programmed into the GSAR processor, and encouraging test results have been obtained. -
Ian G. Cumming and John R. Bennett.
Digital processing of SEASAT SAR data.
In Proc. Rec. IEEE Int. Conf. Acoust., Speech Signal,
volume 4,
Washington, DC,
pages 710-718,
April 1979.
Keyword(s): SAR Processing,
Seasat,
Spaceborne SAR,
Range Compression,
Azimuth Compression,
Azimuth Focusing.
Abstract: The Synthetic Aperture Radar (SAR), on board the Seasat-A satellite, provides an all-weather imaging capability which should prove useful in a number of remote sensing applications. Unlike optical (Landsat) data, the SAR data requires extensive two-dimensional, space variant signal processing before an image is formed. This paper describes the signal processing operations in a digital processor which has been built to produce images from the Seasat-A SAR data. It describes the operations of real-to-complex data conversion, range compression via fast convolution, matrix transformation of 40 MB disk arrays, range cell migration correction, look extraction via bandpass filtering, azimuth compression via fast convolution, interpolation and detection. - Report of the DESDynI Applications Workshop. Technical report, Version 1, April 2009. Keyword(s): DESDynI mission, BIOMASS mission, Earth explorer core mission candidate, P-band, forest area, forest biomass, forest disturbances, global maps, synthetic aperture radar, terrestrial carbon cycle, remote sensing by radar, spaceborne radar, DESDynl mission, Deformation, Ecosystem Structure, and Dynamics of Ice, Earth Science Decadal Survey, National Research Council, biomass estimation, carbon cycle, cryosphere objectives, ecosystem function, integrated L-band InSAR, multibeam Lidar mission, solid Earth surface deformation, surface elevation changes, topography measure, vegetation structure, deformation, optical radar, radar interferometry, remote sensing by radar, topography (Earth), vegetation. [bibtex-key = DESDynIApplicationsWorkshopReport]
-
Candidate Earth Explorer Core Mission BIOMASS - Report for Assessment.
Technical report,
ESA SP-1313/2,
November 2008.
Keyword(s): BIOMASS mission,
Earth explorer core mission candidate,
P-band,
forest area,
forest biomass,
forest disturbances,
frequency 425 MHz,
global maps,
synthetic aperture radar,
terrestrial carbon cycle,
remote sensing by radar,
spaceborne radar,
synthetic aperture radar.
[bibtex-key = BIOMASS_ESA_EARTH_EXPLORER_MISSION2008]
-
Mehrdad Soumekh.
Time Domain Non-Linear SAR Processing.
Technical report,
Department of Electrical Engineering,State University of New York,
2006.
Keyword(s): SAR Processing,
Backprojection,
Time-Domain Backprojection,
Non-Linear Flight Path,
Matlab,
MPI,
MatlabMPI,
Video SAR,
Parallel Processing,
Wavefront Reconstruction,
omega-k Algorithm,
omega-k,
Range Migration Algorithm.
[bibtex-key = soumekhReport2006:TDBP]
-
Betlem Rosich and Peter Meadows.
Absolute Calibration of ASAR Level 1 Products Generated with PF-ASAR.
Technical report Iss. 1 rev. 5,
ESA,
Oct. 2004.
Keyword(s): ASAR,
ENVISAT,
Calibration,
Validation,
Product Calibration,
Quality Measures,
Quality Assessment,
Level 1 Products,
SAR.
Abstract: The aim of this document is to describe the absolute calibration of high rate ASAR Level 1 products generated by ESA using the ASAR processing Facility (PF-ASAR). ESA ASAR level 1 products are generated at the Processing and Archiving Centres (PACs) and at the acquisitions stations: D-PAC, I-PAC, UK-PAC, PDHS-K (Kiruna), PDHS-E (Esrin). Since the same processor is used in all facilities, a unique methodology is described here, which is applicable to any product regardless of where it has been generated. The document is organised as follows: Section 3 describes the derivation of sigma and gamma nought over distributed targets. Section 4 presents the estimation of point targets Radar Cross Section. Annex A provides a procedure to derive the elevation angle for each image pixel, which is a key parameter for the absolute product calibration. Annex B describes how to perform the elevation antenna pattern correction, which is required for complex products calibration. Annex C defines the parameters required for the above operations. Annex D is provided for reference. It presents the evolution of the elevation antenna pattern since Aug. 2002. Comments: Reference: ENVI-CLVL-EOPG-TN-03-0010, Issue 1, revision 5, 07. Oct 2004 -
Michiel Otten and Henno Boomkamp.
Estimation of the Absolute Orbit Accuracy of Envisat.
Technical report,
European Space Operations Centre (ESOC),
Robert-Bosch Strasse 5, D-64283 Darmstadt,
2003.
Keyword(s): ENVISAT,
DORIS,
Precise Orbit,
Orbit,
Orbit Accuracy,
Accuracy,
ASAR.
Abstract: This paper presents the results of the orbit comparison campaign conducted at the European Space Operations Centre (ESOC) in May 2003. The goal of the comparison is to better quantify the absolute orbit accuracy of ENVISAT. For this comparison cycle 12 of ENVISAT was selected which corresponds to a period of 35 days starting at 10.12.2002 and ending at 13.01.2003. Two days, 18 and 19 December, were excluded within this period from the comparison. These days were selected because of the large inclination manoeuvre on 18 December and the resulting loss of DORIS and SLR tracking data for nearly a day. Six different centers contributed their POD solution to the comparison. The CNES POD solution used in this comparison is the same solution as the one that is found on the ENVISAT altimeter GDR. The JPL-DORIS solution only uses the DORIS tracking dataset and is based on the EGM- 96 gravity field where all the other centers use DORIS and SLR data and the GRIM5-C1 field. Three complementary analysis methods where applied to all contributions, namely pair-wise orbit comparison, SLR tracking data analysis and altimeter crossover analysis. -
ASAR-Cal-Val-Team.
Quality Measurements Definition for ASAR Level 1 Products.
Technical report Iss. 1,
ESA,
Mar. 2002.
Keyword(s): ENVISAT,
ASAR,
Product Calibration,
Calibration,
Quality Assessment,
Quality Measures,
ISLR,
PSLR,
SSLR,
Level 1 Products,
SAR,
ASAR,
ENVISAT,
Calibration,
Validation,
Quality Measures.
Abstract: The activities to verify and calibrate ASAR products during the ENVISAT Commissioning Phase (C.P.) will be carried out by the ASAR CAL/VAL team members at different centres and in some cases, using different product analysis tools. It is therefore important to establish the methodology for deriving all the quality parameters so that results from different team members are completely consistent. This document describes the procedures to be followed during the C.P. for measuring the ASAR product quality parameters on Level I products. -
Kenneth Knaell.
Three-Dimensional SAR from Curvilinear Apertures.
Technical report,
Carerock Division, Naval Surface Warfare Center,
1994.
Keyword(s): SAR Processing,
Non-Linear Flight Path,
SAR Tomography,
3D Feature Extraction,
Target Feature Extraction,
Curvilinear SAR.
[bibtex-key = knaellReport1994:NonLinearSARTomo]
- Fabio Rocca, Claudio Prati, and Andrea Monti-Guarnieri. New Algorithms for Processing of SAR Data. ESA Contract Report, ESRIN Contract no. 7998/88/F/FL(SC), 1989. Keyword(s): SAR Processing, Range Migration Algorithm, omega-k, Wavenumber Domain Algorithm, Range-Doppler Algorithm, Secondary Range Compression, Comparison of Algorithms. [bibtex-key = roccaPratiMontiGuarnieri89:omegak]
-
PolInSAR 2009 Sorted Recommendations,
January 2009.
[bibtex-key = PolInSAR2009SortedRecommendations]
- A. Colettaa, D. De Lisle, A. Moreira, A. Freeman, M. Shimada, T. Ainsworth, Konstatinos Papathanassiou, S. R. Cloude, P. Dubois-Fernandez, P. Lombardo, G. Trianni, K. Raney, A. Minchella, F. Charbonneau, L. Ferro-Famil, D. Floricioiu, S. Lehner, Irena Hajnsek, Ridha Touzi, Wolfgang Martin Boerner, Eric Pottier, and Fabio Rocca. Summaries and Recommendations of the POLInSAR 2009 Workshop, January 2009. [bibtex-key = PolInSAR2009Recommendations]
-
Andreas Reigber.
Multimodale Verarbeitung hochauflösender SAR Daten,
February 2008.
Note: Habilitationsschrift an der Fakultät IV -Elektrotechnik un Informatik - der Technischen Universität Berlin.
Keyword(s): SAR Processing,
airborne SAR,
omega-k,
Range Migration Algorithm,
Wave Number Domain Algorithm,
Extended Chirp Scaling,
ECS,
SAR Interferometry,
Interferometry,
InSAR,
Residual Motion Errors,
Residual Errors,
Motion Compensation,
MoComp,
PolInSAR,
Polarimetry.
Abstract: Abbildende Radartechnik ist ein Fernerkundungsverfahren, welches das Ziel hat, von einer beobachteten Gegend eine hochaufgel\"oste Reflektivit\"atskarte im Mikrowellenbereich zu erzeugen. Erreicht wird dies durch Abstrahlung und Empfang von elektromagnetischer Strahlung im Mikrowellenbereich, typischerweise durch Sensoren, die auf Flugzeugen oder Satelliten montiert sind. Unter einer ganzen Reihe von Mikrowellensensoren hat sich in den letzten Jahren ein besonderes Interesse in Radar mit synthetischer Apertur (SAR) herausgebildet. Der Grund hierf\"ur ist, dass das SAR als einziger Mikrowellensensor eine fl\"achige Abbildung mit einer hohen r\"aumlichen Aufl\"osung, die durchaus mit der optischer Systeme vergleichbar ist, erm\"oglicht. Die Entwicklungsgeschichte des Radars mit synthetischer Apertur begann bereits vor \"uber 50 Jahren mit der Idee, die Doppler-Verschiebung des Radarsignals zu nutzen, um die Azimutaufl\"osung des damals aktuellen side-looking airborne radar (SLAR) zu verbessern [215]. Zur Prozessierung der Daten war man, bis in die 1970er Jahre hinein, auf die Verwendung optischer, holographischer Verfahren angewiesen; erst danach war man in der Lage, mittels digitaler Datenverarbeitung hochaufgel\"oste SAR Aufnahmen in hoher Qualit\"at zu erzeugen [10],[216]. Seitdem entwickelte sich die Fernerkundung mit SAR Sensoren rasant weiter, hin zu immer h\"oheren Aufl\"osungen und Aufnahmemodi. In den letzten 10 Jahren gewannen dabei vor allem die mehrkanalige SAR Modi stark an Bedeutung, wie z.B. multispektrales SAR [66], SAR Interferometrie [8] und SAR Polarimetrie [13]. Diese Arbeit besch\"aftigt sich vor allem mit speziellen Datenverarbeitungstechniken solcher mehrkanaliger SAR Daten. SAR Sensoren arbeiten im Mikrowellenbereich des elektromagnetischen Spektrums bei Wellenl\"angen zwischen wenigen Millimetern und mehreren Metern. Betrachtet man das Transmissionsspektrum der Erdatmosph\"are, so stellt man fest, dass bei Wellenl\"angen gr\"osser als etwa 1cm praktisch keine nennenswerte Absorption mehr auftritt. Dies gilt sowohl f\"ur die Luft selbst als auch f\"ur Wolken und kleinere Wassertropfen. SAR Aufnahmen lassen sich daher praktisch unabh\"angig von den aktuell herrschenden Wetterbedingungen generieren, wohingegen Wolken und Nebel f\"ur optische Systeme oft eine grosse Einschr\"ankung darstellen. Als aktives System, das seine eigene Beleuchtung mitbringt, besteht weiterhin keinerlei Abh\"angigkeit von der jeweiligen Tageszeit. Zusammengenommen f\"uhren diese Punkte dazu, dass sich SAR Sensoren besonders gut f\"ur verl\"assliche und regelm\"assige Beobachtungen eignen. Der Informationsgehalt von Radaraufnahmen ist deutlich anders gelagert als der von optischen oder Infrarotsystemen. W\"ahrend im optischen Bereich vor allem die molekulare Zusammensetzung des Objekts f\"ur die charakteristische Reflektivit\"at des Objekts verantwortlich zeichnet, sind im Mikrowellenbereich vor allem die geometrische Form sowie die dielektrischen Eigenschaften f\"ur die St\"arke der R\"uckstreuung von Bedeutung. In Radaraufnahmen tritt daher das Relief und morphologische Strukturen besonders deutlich hervor. Auch \"Anderungen in der Leitf\"ahigkeit, z.B. durch unterschiedliche Bodenfeuchte, k\"onnen so beobachtet werden. Aufgrund der Sensitivit \"at auf dielektrische Eigenschaften k\"onnen im Prinzip sogar Informationen \"uber den Vegetationszustand gesammelt werden. Eine weitere wichtige Eigenschaft von Radaraufnahmen ergibt sich aus den Ausbreitungseigenschaften von Mikrowellen: Durch ihre lange Wellenl\"ange sind Mikrowellen bis zu einem gewissen Grad in der Lage, in Vegetationsschichten, in Schnee und Eis und sogar in den Boden einzudringen [203]. Das Eindringverm\"ogen h\"angt dabei von der Wellenl\"ange des Sensors, aber auch von den dielektrischen Eigenschaften und der Leitf\"ahigkeit des Objekts ab. K\"urzere Wellenl\"angen, wie das X-Band, werden stark ged\"ampft und daher vor allem von der Oberfl\"ache reflektiert. In k\"urzeren Wellenl\"angen sammelt man daher in erster Linie Informationen \"uber die oberen Schichten von Vegetation oder Boden. L\"angere Wellenl\"angen, wie L- oder P-Band, dringen hingegen oft tief in Vegetation ein. R\"uckstreuung in solchen Wellenl\"angen enthalten daher Anteile aus dem gesamten r\"uckstreuenden Volumen. An dieser Stelle zeigt sich bereits ein typisches Problem der Fernerkundung im allgemeinen: Die zu untersuchenden Objekte sind meist recht komplex, und ihre Eigenschaften wirken sich in vielerlei Weise auf das gemessene Bildergebnis aus. Ein Fernerkundungssensor liefert aber nur einen sehr niedrigdimensionalen Raum von Observablen, im Falle eines konventionellen SAR Sensors sogar nur einen einzigen Messwert. Es ist daher in vielen F\"allen sehr schwierig, oder sogar unm\"oglich, aus dem gemessenen Bildergebnis auf den gesuchten Objektparameter zu schliessen. Es besteht also ein Mehrdeutigkeitsproblem: Mehrere verschiedene S\"atze von Objektparametern k\"onnen zu exakt dem gleichem Satz an Observablen f\"uhren. Der einzige Weg dieses Problem zu umgehen, ist die Erh\"ohung der Dimensionalit\"at des Sensors, also die Verwendung mehrerer unabh\"angiger Empfangskan\"ale. Thema dieser Arbeit sind spezielle sogenannte multimodale Verarbeitungstechniken, die f\"ur die korrekte Bearbeitung solcher multidimensionaler Datens\"atze notwendig sind. Es soll dabei insbesondere aufgezeigt werden, dass durch Hinzunahme weiterer Datendimensionen generell eine verbesserte Informationsextraktion erreicht, bzw. mit ihnen eine verbesserte Datenverarbeitung erzielt werden kann. Generell ergeben sich in der SAR Fernerkundung vor allem folgende M\"oglichkeiten f\"ur multimodale Erweiterungen: Multifrequentes SAR: Alle bislang betriebenen satellitengest\"utzten SAR Systeme arbeiten nur in einem einzigen Band, besitzen also eine dedizierte zentrale Wellenl\"ange. Verwendet wird dabei meist das C-Band, wie z.B. bei den europ\"aischen ERS-1, ERS-2 [4] und ENVISAT [119] und den kanadischen RADARSAT-1 [161] und RADARSAT-2 [125]. Es kommt aber auch L-Band, z.B. beim japanischen ALOS-PALSAR [99], und X-Band, wie bei in K\"urze startenden TerraSAR-X [214], zum Einsatz. Prinzipiell stehen daher also SAR Daten in verschiedenen Wellenl\"angen zur Verf\"ugung. Trotzdem sind solche inhomogenen Datenquellen als nicht ideal anzusehen, da unterschiedliche Aufnahmezeitpunkte, sowie abweichende Bildaufl\"osungen und Sensorcharakteristika zu beachten sind. Die einzige Ausnahme stellen die Shuttle Missionen SIR-C/X-SAR im Jahr 1994 (X-, C- und L-Band) [92] und SRTM im Jahr 2000 (X- und C-Band) [213] dar, bei denen zum ersten Mal aus dem Orbit multifrequente SAR Daten simultan aufgezeichnet wurden. Im Gegensatz dazu bieten die allermeisten heutzutage betriebenen flugzeuggest\"utzten SAR Systeme die M\"oglichkeit mehrerer Wellenl\"angen. Zu nennen sind hier beispielsweise das E-SAR System des Deutschen Zentrums f\"ur Luft- und Raumfahrt (X-, C-, S-, L- und P-Band) [89], das franz\"osische RAMSES System von Onera (W-, Ka-, Ku-, X-, C-, S-, L- und P-Band) [45] oder das amerikanische AIRSAR System des JPLs (X-, C- und L-Band) [207]. Die Reflektivit\"at im Mikrowellenbereich kann stark von der verwendeten Wellenl\"ange abh\"angen, da die Dielektrizit\"atskonstante vieler Materialien stark frequenzabh\"angig ist [203]. Auch die Oberfl\"achenrauhigkeit hat in verschiedenen Wellenl\"angen einen unterschiedlichen Einfluss auf die St\"arke der R\"uckstreuung [203]. Aus diesen Gr\"unden erscheinen SAR Aufnahmen, die in unterschiedlichen B\"andern angefertigt worden sind, oft sehr verschieden. Genau diese Unterschiede erlauben es mache Oberfl\"achen oder Materialien zu trennen, die bei Betrachtung in nur einer Wellenl\"ange noch identisch erscheinen; dies l\"asst sich z.B. zu Klassifikationszwecken ausnutzen. Wie bereits zuvor erw\"ahnt, \"andert sich mit der Wellenl\"ange auch das Eindringverm\"ogen der Mikrowellen. Es wird in verschiedenen B\"andern also auch Informationen aus unterschiedlichen Schichten eines Volumens gewonnen; dies kann dazu benutzt werden um beispielsweise in Kombination mit interferometrischen Ans\"atzen Vegetationsh\"ohen zu bestimmen [217][205]. Dadurch dass sich die verschiedenen B\"ander im allgemeinen nicht spektral \"uberlappen, sind multifrequente SAR Daten untereinander inkoh\"arent. Die Datenverarbeitung der einzelnen Kan\"ale erfolgt daher in erster Linie unabh\"angig voneinander; erst zum Schluss werden die verschiedenen Aufnahmen kombiniert ausgewertet. In dieser Arbeit wird aus diesem Grund nicht weiter auf die Verarbeitung multifrequenter Daten eingegangen. Polarimetrisches SAR: Die SAR Polarimetrie (PolSAR) ist eine weitere wichtige M\"oglichkeit, den Beobachtungsraum von SAR Sensoren zu erweitern. Elektromagnetische Wellen sind transversaler Natur und erlauben daher zwei orthogonale Schwingungsrichtungen. Dies gilt sowohl f\"ur den Sende- als auch f\"ur den Empfangskanal, man erh\"alt also im Idealfall 4 unabh\"angige Messungen. Dies ist Gegenstand der Radarpolarimetrie, initiiert im Jahre 1948 durch G.W. Sinclair mit der Einf\"uhrung des Konzepts der Streumatrizen [188]. Da Radarpolarimetrie deutlich h\"ohere Hardwareanforderungen stellt, blieb sie lange nur ein theoretisches Konstrukt [90] [12], und ihr praktischer Nutzen wurde vor allem im zivilen Bereich lange nicht erkannt. Diese Situation \"anderte sich mit der Verf\"ugbarkeit polarimetrischer SAR Daten verschiedener flugzeuggest \"utzter SAR Systeme, wie beispielsweise dem AIRSAR oder dem E-SAR, sowie den beiden SIR-C/X-SAR Missionen, bei denen polarimetrische SAR Daten in mehreren Wellenl\"angen erzeugt wurden. Seitdem hat sich die SAR Polarimetrie zu einer etablierten Fernerkundungsmethode entwickelt, welche auch in zunehmenden Masse von den neuesten SAR Satelliten, wie dem kanadischen RADARSAT-2, dem japanischen ALOS-PALSAR und dem deutschen TerraSAR-X, unterst\"utzt wird. Eine besondere Eigenschaft der SAR Polarimetrie ist die prinzipielle M\"oglichkeit, verschiedenartige R\"uckstreumechanismen unterscheiden zu k\"onnen. Dies kann erreicht werden, da die gemessenen polarimetrischen Signaturen stark vom jeweils aufgetretenen Streuprozess abh\"angen. Im Vergleich zum herk\"ommlichen einkanaligen SAR ergibt sich damit eine signifikante Verbesserung bei der Unterscheidung verschiedener Oberfl\"achentypen, was sich beispielsweise in der Verbesserung von Landnutzungsklassifikationen [35],[111] ausn\"utzen l\"asst. Des weiteren erlaubt die SAR Polarimetrie durch ihren vergr\"osserten Raum an Observablen auch einfache physikalische Modellierungen. Durch Invertierung polarimetrischer Streumodelle lassen sich z.B. Bodenparameter wie Rauigkeit und Bodenfeuchte bestimmen [30]. Weiterhin lassen sich mit Hilfe der SAR Polarimetrie auch die Anteile verschiedener charakteristischer R\"uckstreuklassen ermitteln [65], selbst wenn sie sich innerhalb eines Pixels gegenseitig \"uberlagern. In Kapitel 3 wird auf die Besonderheiten der Verarbeitung polarimetrischer SAR Daten eingegangen. Aufbauend auf die grundlegenden Konzepte der SAR Polarimetrie, zusammengefasst in Abschnitt 3.1, wird in Abschnitt 3.2 eine Zeit-Frequenz Analyse polarimetrischer Daten vorgenommen. Der hierdurch weiter vergr\"osserter Raum an Observablen erlaubt die Detektion st\"orender anisotroper R\"uckstreumechanismen sowie die Entfernung ihres Einflusses aus den Daten. Des weiteren wird in Abschnitt 3.1.2 ein verbessertes polarimetrisches Klassifikationsverfahren unter Verwendung von Nachbarschaftsinformation als zus\"atzlicher Datendimension abgeleitet. Interferometrisches SAR: SAR Interferometrie (InSAR) ist eine multimodale Erweiterung in der SAR Fernerkundung, welche den Beobachtungsraum geometrisch durch mehrere Aufnahmen von leicht verschiedenen Orten erweitert. Anschaulich wird in der SAR Interferometrie eine leichte Variation des Einfallswinkels vorgenommen, wobei davon ausgegangen wird, dass sich die R\"uckstreueigenschaften dabei nicht signifikant ver\"andern. Analysiert wird dann der aufgetretene Phasenunterschied zwischen zwei oder mehreren solcher Aufnahmen, der einen direkten Zusammenhang zu der Topographie des Bodens aufweist und sich daher zur Erstellung von genauen H\"ohenmodellen eignet. Die ersten Experimente in diese Richtung wurden 1974 von L.C. Graham durchgef\"uhrt [79] und in den 1980ern experimentell in Form von InSAR Modifikationen am AIRSAR Sensor fortgef\"uhrt [220]. Popul\"ar wurde die SAR Interferometrie aber erst mit dem Start der ERS Satelliten, die erstmals operationelle satellitengest\"utzte SAR Interferometrie bieten konnten. Im Jahr 2000 kumulierte diese Entwicklung in der Shuttle Radar Topography Mission (SRTM), w\"ahrend der ein hochgenaues H\"ohenmodell der gesamten Landoberfl\"ache der Erde zwischen 60 deg N und 60 deg S erzeugt wurde [213]. Die SAR Interferometrie ist heutzutage eine etablierte Technik, welche mit einer Vielzahl von satellitengest\"utzten Sensoren m\"oglich ist [68][72][128]. Neben der Abbildung der Terraintopographie kann die SAR Interferometrie auch zur Bestimmung kleinster Topographie\"anderungen eingesetzt werden. Mit dieser sogenannten differentiellen SAR Interferometrie (DInSAR) lassen sich durch Phasenmessung Genauigkeiten unterhalb der Wellenl\"ange, also typischerweise bis in den Millimeterbereich hinein, erzielen. Dies ist in verschiedensten Anwendungsbereichen einsetzbar, wie z.B. in der Analyse tektonischer Prozesse, oder in der Beobachtung von Absenkungsprozessen als Folge menschlicher Bergbauaktivit\"aten [124],[48],[105]. Des weiteren l\"asst sich der erweiterte Beobachtungsraum der SAR Interferometrie auch mit dem der SAR Polarimetrie verschneiden [142]. In der sogenannten polarimetrischen SAR Interferometrie (PolInSAR) wird dies ausgenutzt, um physikalische R\"uckstreumodelle mehrerer sich \"uberlagernder Streumechanismen aufzustellen. Eine Modellinvertierung erlaubt dann die Bestimmung von Schichtdicken und anderer Parameter des Objekts, was sich z.B. zur Bestimmung von Waldh\"ohen und Bodentopographie ausnutzen l\"asst [31]. Kapitel 4 besch\"aftigt sich mit der Verarbeitung interferometrischer SAR Daten. In Abschnitt 4.1 werden wiederum zuerst die grundlegenden Konzepte von SAR Interferometrie und differentieller SAR Interferometrie vorgestellt. In der Folge wird auf die Besonderheiten von flugzeuggest\"utzter Repeat-Pass SAR Interferometrie eingegangen, eine wichtige Variante der Interferometrie, die aber bislang aufgrund verschiedener Fehlereinfl\"usse (siehe Abschnitt 4.2) nur sehr eingeschr\"ankt m\"oglich ist. In 4.3 werden mehrere Techniken zur Umgehung dieser Probleme eingef\"uhrt, wobei wiederum Zeit-Frequenz Analysen benutzt werden, um entweder erweiterte Beobachtungsm\"oglichkeiten zu erhalten oder genauere Korrekturen anbringen zu k\"onnen. Along-Track Interferometrie / MTI: Die im vorherigen Abschnitt beschriebene SAR Interferometrie wird pr\"azise auch als across-track Interferometrie bezeichnet. Des weiteren existiert auch noch eine zweite Variante, die sogenannte along-track Interferometrie (ATI). Bei ihr werden zwei oder mehr, in Flugrichtung versetzte, Antennenelemente simultan betrieben. Bewegt sich ein Objekt w\"ahrend der Aufnahme in Blickrichtung des Sensors, so kommt es durch die geringf\"ugig verschiedenen Empfangszeitpunkte zu einer Phasenverschiebung zwischen den beiden Aufnahmen, was sich ausnutzen l\"asst, um die Geschwindigkeit des Objekts zu bestimmen. Fr\"uhe Experimente in Richtung along-track Interferometrie fanden z.B. bereits in den 1980er Jahren mit einem modifizierten AIRSAR Sensor statt [74]; in der Folge wurde ATI verbreitet zur Messung von Str\"omungsgeschwindigkeiten von Wasseroberfl\"achen eingesetzt. \"Uber die Jahre entstanden mehrere Variationen dieses Konzepts, welche vor allem das Ziel hatten, durch Einf\"uhrung weiterer Empf\"angerkan\"ale die Genauigkeit der Geschwindigkeitmessung zu verbessern [22][98]. Mit den geplanten TerraSAR-X und RADARSAT-2 Sensoren wird auch erstmals operationelle Along-Track Interferometrie mit einem zivilen satellitengest\"utzten Sensor m\"oglich sein [179][137]. Eine weitere M\"oglichkeit von Sensoren mit mehreren simultanen betriebenen Antennenelementen in Azimut ist die Detektion von Position und Geschwindigkeit von Bewegtzielen am Boden (moving target detection, MTI) [184]. Die Anwendungsgebiete lagen bislang vor allem im milit \"arischen Bereich [46], in neuerer Zeit wird aber auch der Einsatz von MTI f\"ur die zivile Verkehrsbeobachtung vorgeschlagen [126][87]. Sind mehr als 2 Empf\"angerkan\"ale verf\"ugbar, wird zur Unterdr\"uckung der R\"uckstreuung nicht-bewegter Ziele bei MTI Anwendungen gerne auf sogenanntes space-time adaptive processing (STAP) zur\"uckgegriffen [101]. Diese Arbeit besch\"aftigt sich nicht weiter mit der Verarbeitung von Daten, die simultan von einem Antennenarray in Azimut aufgezeichnet wurden, die also simultan unter mehreren Squintwinkeln empfangen wurden. Zeit-Frequenz Analysen: Existiert nur ein Empf\"angerkanal, so l\"asst sich trotzdem eine gewisse Adaption auf den Squintwinkel \"uber sogenannte Zeit-Frequenz Analysen erreichen. Dabei wird das Doppler-Spektrum in Azimut in mehrere Subb\"ander aufgespalten, die jeweils eine leicht unterschiedliche mittlere Blickrichtung auf die Szene repr\"asentieren. Man erh\"alt damit gleichzeitig eine gewisse Aufl\"osung in Azimut (d.h. Zeit) als auch im Squintwinkel (d.h. Doppler-Frequenz). Gleiches ist auch in Entfernungsrichtung m\"oglich, wobei hier die verschiedenen Subb\"ander verschiedenen Wellenl\"angen entsprechen. Zeit-Frequenz Zerlegungen besitzen eine lange Geschichte in der SAR Fernerkundung und wurden vor allem zur optimierten Prozessierung von SAR Daten [129][190] und zur Analyse bzw. zur Fokussierung von bewegten Objekten verwendet [26]. In neuerer Zeit wurden ausserdem Zeit-Frequenzanalysen direkt in der SAR Bildanalyse eingesetzt. So l\"asst sich beispielsweise das Korrelationsverhalten zwischen Subaperturen ausnutzen, um koh\"arente Punktstreuer in der Szene zu detektieren [191][185]. Polarimetrische Signaturen weisen in vielen F\"allen eine starke Abh\"angigkeit vom Blickwinkel auf, was ein Problem f\"ur hochaufl\"osende SAR Systeme darstellt und durch polarimetrische Zeit-Frequenz Analysen gel\"ost werden kann [1][58]. Noch einen Schritt weiter geht die Kombination von Polarimetrie, Interferometrie und Zeit-Frequenzanalyse auf Basis von Waveletzerlegungen mit dem Ziel der optimalen Erzeugung von H\"ohenmodellen [37]. In dieser Arbeit wird an mehreren Stellen auf die Zeit-Frequenzanalyse von SAR Daten eingegangen. Kapitel 2.2.2 gibt eine Einf\"uhrung in der Bildung von Subaperturen mit Hilfe Fourier- Transformationen. In Abschnitt 2.3.2 und 2.3.3 wird eine Zeit-Frequenz Analyse teilprozessierter Daten verwendet, um Fehler der Bewegungskompensation in adaptiver Weise auszugleichen. In \"ahnlicher Weise wird in Kapitel 4.3.1 eine Zeit-Frequenz Analyse benutzt, um eine Adaption der Bewegungskompensation auf die Topographie der Szene zu erreichen. Kapitel 3.2 besch\"aftigt sich mit der Zeit-Frequenzanalyse polarimetrischer SAR Daten zur Eliminierung anisotroper R\"uckstreuung. Schliesslich wird in Kapitel 4.3.2 eine Zeit-Frequenz Analyse interferometrischer Daten vorgenommen, um kleinste Fehler in der Bestimmung der Basislinie aus den Daten selbst abzuleiten. Weitere Techniken: Die obige Aufstellung mehrkanaliger Erweiterungen des SAR Prinzips ist bei weitem nicht vollst\"andig und gibt nur einen \"Uberblick \"uber die wichtigsten Bereiche. Eine wichtige noch zu erw\"ahnende Technik ist die Bildung von Zeitreihen, d.h. die regelm\"assige Beobachtung eines Gebiets mit anschliessender kombinierter Auswertung der Datens\"atze. Dies l\"asst sich nat\"urlich in vielerlei Hinsicht direkt zur Beobachtung von zeitlich ver\"anderlichen Prozessen einsetzen. Aber auch im Sinne der differentiellen SAR Interferometrie werden solche Zeitreihen z.B. zur Filterung von atmosph\"arischen und topographischen Fehlern verwendet, was es erlaubt, minimalste Bodendeformationen sehr zuverl\"assig zu detektieren [47][48]. Eine andere M\"oglichkeit, einen solchen Datensatz mit vielen interferometrischen Basislinien kombiniert auszuwerten, stellt die sogenannte SAR Tomographie dar. Bei ihr wird eine zus\"atzliche synthetische Apertur senkrecht zu Azimut- und Entfernungsrichtung aufgebaut, um eine echte dreidimensionale Abbildung der Szene zu erreichen [168]. Dies Technik l\"asst sich wiederum auch mit der SAR Polarimetrie kombinieren [81]. Schwerpunkt dieser Arbeit wird die Verarbeitung multimodaler hochaufl\"osender SAR Daten bilden. Zu diesem Zweck wird ein Exkurs durch die drei aktuell wohl bedeutsamsten Themenkomplexe der SAR Fernerkundung unternommen - der SAR Prozessierung (Kapitel 2), der SAR Polarimetrie (Kapitel 3) und der SAR Interferometrie (Kapitel 4). Zus\"atzlich zu einer detaillierten Einf\"uhrung in das jeweilige Gebiet soll in allen Bereichen aufgezeigt werden, wie sich durch Hinzunahme multimodaler Verarbeitungstechniken, bzw. mit Hilfe der mehrkanaligen Information selbst, signifikante Verbesserungen in der Auswertung erzielen lassen. -
Daniel Svensson and Jan Johansson.
Suppression of Radio Frequency Interference in Low Frequency SAR.
Master's thesis,
Chalmers University of Technology,
2004.
Keyword(s): SAR Processing,
RFI Suppression,
CARABAS,
Airborne SAR,
Analogue TV,
VHF SAR.
Abstract: To acquire high resolution in airborne radar imaging, either minuscule wavelengths or incredibly large antennas must be used. Another way of solving that issue is to utilise moving radar to realise the effect of a large aperture; a technique called synthetic aperture radar (SAR). CARABAS is a low frequency SAR system, operating in the band of 20 ? 90 MHz, designed to minimise the influence from speckle by using wavelengths of the same order as the resolution cells of the ground image. Radio frequency interference (RFI) is, however, highly prevalent in that frequency band, and must be filtered before the SAR image formation is initialised. The purpose of this thesis is to investigate a proposed method of suppressing RFI, particularly from analogue TV, with a technique based on Doppler compression filtering, to conclude if that technique is applicable. The technique is based on the fact that temporal variations in the TV signal can be predicted. Thus, by synchronising the radar transmission to the line synchronisation pulse of the TV signal, the interference after pulse compression will be concentrated to a component at DC and components at the field rate and its harmonics, in the slow time unfolding of radar data, which enables efficient notch filtering in the range and Doppler domains. The thesis has been carried out at Ericsson Microwave Systems AB in M?lndal, under the supervision of Dr. Hans Hellsten, the originator of CARABAS. The thesis work comprised thorough literature studies, profound measurements of DVD signals, representing ordinary TV signals, implementation of the proposed RFI suppression system in MATLAB, and analysis of the system, regarding attained suppression for different parameter sets. From the results of the thesis it can be concluded that the suppression technique is indeed applicable, but that not all parameter sets provide the required mitigation of 30 dB. That requirement was only fulfilled for two cases: for one second of integration time, together with 4 Hz null-to-null notch widths, and for two seconds of integration time, together with 2 Hz notch widths ? both with a PRF of 15 kHz and a complete Doppler band-pass filtering outside the interval of ?100 to 100 Hz. -
Betlem Rosich.
Preliminary Doppler Analysis on ASAR Products,
2002.
Keyword(s): SAR Processing,
Doppler Centroid,
Doppler Centroid Estimation,
Clutterlock,
ASAR,
ENVISAT.
Abstract: This paper summarised the different Doppler estimation algorithms used in PF-ASAR for the different modes, how this information appears on the ASAR products and provides a first comparisons between measured and expected Doppler as well as a preliminary estimation of the in-flight antenna miss-pointing based on wave mode data products. -
David T. Sandwell.
SAR Image Formation: ERS SAR Processor Coded in Matlab.
Note: Lecture Notes - Radar and Sonar Interferometry,
2002.
Keyword(s): SAR,
SAR Processing,
Digitizing,
ERS,
MATLAB,
Range-Doppler,
Range Compression,
Range Migration,
Azimuth Processing,
SLC,
Raw Data,
Parameter Files,
Squinted SAR,
Example Processor.
[bibtex-key = San02d:SAR]
-
Clint Slatton.
Improving Segmented INSAR Processing Using Presumming.
,
1998.
Keyword(s): SAR Processing,
InSAR,
TOPSAR,
Presumming,
Range-Doppler Algorithm,
Azimuth Processing,
omega-k Algorithm.
Abstract: Literature Survey Comments: +/- Not much on presumming, but generally a good introduction to some SAR concepts.
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