Measuring Earth Displacement with ENVISAT ASAR of Dec. 26, 2003 Earthquake in Bam, Iran
Contact Persons
Keywords
Synthetic Aperture Radar, Multipass-Interferometry, Digital Height Model, Bam, Iran, ASAR
Quick Reference
Differential SAR Interferometry was applied to investigate the displacement of the Earth's surface caused by the earthquake. Two interferometric pairs of images are shown here. Influences of both topography and variations in the spacecraft's orbit were modelled and compensated. Once that is done, the relative position of the Earth's surface during the second overpass as compared to the first becomes clear to see.
Some Results
Two interferometric pairs of images were acquired by ENVISAT ASAR sensor (beam IS2, VV polarisation).
Each pair has a nearly ideal zero "baseline", the distance between the position of the spacecraft during each respective overpass. The ascending pair of images were acquired on Nov. 16, 2003 and Feb. 29, 2004 respectively. The descending pair of images were acquired on Dec. 3, 2003 and Feb. 11, 2004.
To detect movement differences, the influence of topography is first removed by generating a synthetic interferogram. The public SRTM3 digital surface model (DSM) was used as the source of reference height information. Care was taken to model the spacecraft orbit as accurately as possible: DORIS precise orbit state vectors were therefore used whenever available. The best available radar timing annotations (see geometric calibration) were also employed.
To unwrap the phase values, the public domain software package SNAPHU was used. The resulting unwrapped phases are shown below in a UTM map projection. The phases are rewrapped to a 4pi interval to accentuate possible phase unwrapping errors (fortunately not in evidence). The ASAR backscatter is overlaid as the image amplitude.
Terrain-geocoded Unwrapped Displacement Phase
Time Frame
Software for differential SAR interferometry was implemented and has been used in investigations at RSL since 1995. For further information on Differential InSAR project at RSL, see: Differential InSAR.
Publications
- JÓNSSON S., MAI P., SMALL, D., MEIER E., SALICHON J., GIARDINI D. [2005]:
Using SAR Interferometry and Teleseismic Data to Determine Source Parameters for the 2003 Bam Earthquake, Proc. of ENVISAT/ERS Symposium, Salzburg, Austria, Sept. 6-10, 2004 (ESA SP-572, April 2005). - SMALL, D. [2004]: The Bam Earthquake - Preliminary Interferograms, http://eopi.esa.int/esa/esa, ESA Earth Observation Principal Investigator (EOPI) Portal, ESA, Jan. 2004.
Partnerships
The ASAR data was provided courtesy of the European Space Agency
This work is done under the auspices of the Inter-University Collaboration for Earth Observation and Geoinformatics by the
- Remote Sensing Laboratories, Department of Geography, University of Zürich, Switzerland
- Dept. of Earth Sciences, Institute of Geophysics, ETH Zürich, Switzerland