Derivation of the complete (3d) displacement field using interferometric Synthetic Aperture Radar (SAR) technique; Case Study on the Bam fault



Investigation and monitoring of the displacement field derived from deformation is among the important studies in earth science and geophysics topics, which plays a main role in the prevention and praxeology of natural disasters such as earthquake, subsidence, land slide et cetera. Here we can mention the several methods in geodetic measurement and deformation monitoring such as spirit leveling, the positioning systems like (SLR, Satellite laser range finding), (VLBI, Very long baseline interferometer) and (GPS, Global positioning system), and Interferometric Synthetic aperture Radar (InSAR) technique. Of the above methods, the InSAR technique with the ability to generate large, continual and contiguous ground overlays, so with high spatial and temporal resolution it turns out to be one of the important techniques.
The goal of this study is derivation of a continual map for three orthogonal components of the co-seismic surface displacement field with InSAR data. The displacement components observed with radar are in the direction of satellite line of sight. The satellite LOS displacement vector has a lower sensitivity to north displacements than to the other two components of a surface displacement, i.e. east and up, due to the near-polar satellite orbits. This act caused a reduction in the accuracy of the calculated deformation components. There are several solutions to this problem and in this paper, the azimuth offset data of ascending and descending passes is used solve this problem. So as regards efficacy of atmosphere errors on radar imaging, the calculation of displacement components is relative, so with far field data derived from coherence images, the necessary shift to converting the relative values to absolute was calculated with the detrending process and reduced from the calculated deformation components.
The case study of this research is on the 2003 Bam earthquake using co-seismic and pre-seismic pairs of Envisat radar images in ascending and descending orbits. The images were processed with Doris Software in Linux systems. Finally the 3D reconstruction process was accomplished with Matlab software in Windows. The derived results in this study have compared well with other publications.