BAM Earthquake surface deformation pattern measured with radar interferometry
We computed the displacement caused by the Bam Earthquake in
corresponding to the major quake of Bam (Iran) which took place on 26 December 2003.
The ASAR data has kindly been provided by
ESA
in order to
promote the Envisat ASAR data for use in seismology
and to highlight the value of the ASAR data archive collected over seismic areas.
Data copyright ESA.
The interferogram created of two ASAR SLC
(master orbit 9192, 03 DEC 2003; slave orbit 9693, 07 JAN 2004)
images spanning the event is shown
here.
The interferometric phase is overlaid on the amplitude of the interferogram.
The color correspond to phase between -pi and pi.
Clearly visible is that the topographic signal is dominantly present
in the interferogram.
This is due to the large perpendicular baseline
(approximately 500 meters).
The topographic signal disguishes the deformation signal, so we have to
remove it from the interferogram.
Therefore, a 3 pass D-InSAR processing has been performed to correct the
topographic component.
A topo-pair interferogram has been computed using the same master and
slave orbit 6687, JUN 2003.
The perpendicular baseline in this case also was approximately 500 meters
(be it with a negative sign).
The
topo pair thus looks very similar.
The resulting interferogram is shown below.
The phase has not been unwrapped.
Each color cycle corresponds to approximately 2.8 cm in the line of sight
to the sensor. Due to the viewing angle of approximately 23 degrees,
this could be caused by 3 cm of vertical deformation, 7 cm of horizontal deformation,
or a combination of horizontal and vertical deformation.
We can count approximately 10 fringes from the center.
This could be interpreted as appoximately 70 cm of horizontal deformation.
The area that could be processed is about 100 km by 100 km.
The ground resolution is 20 meters in both direction.
Also see the
phase and
magnitude images.
No spectral filtering or phase filtering has been used to obtain this result.
Also, very moderate multilooking factor of 5 in azimuth and 1 in range has been
used.
The noise level is low however, but can thus be easily improved using a more
sophisticrated processing.
The full input files used by Doris for the processing are given here for
defo-pair processing input files and
topo-pair processing input files.
You can use these files to repeat the processing yourself!
(Use the run script provided by doris by copying these files to
the "Inputfiles" directory.)
The logging output that Doris created is stored for comparision at
defo-pair processing output files and
topo-pair processing output files.
Petar Marinkovic re-computed the differential interferogram using the DEOS precise
orbits.
The
phase image using precise orbits
clearly does not contain a large orbit trend anymore.
dinsar with external SRTM DEM
shows a result obtained by Dr. Rao,
where the 2-pass method using the SRTM DEM with step COMPREFDEM and SUBTRREFDEM
is used.
Other sources of information:
ESA
Bert Kampes
12-Mar-2004
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