Generation of DEM using SAR interferometry technique - a case study of bankura test site
Satyendra K. Khare, M. Sudhakar Rao and K. S. Rao
Centre of Studies in Resources Engineering
Indian Institute of Technology, Mumbai - 400 076
SAR Interferometry (InSAR) is a powerful technique for the generation of Digital Elevation Model (DEM). In this technique, the phases of two SAR Scenes of the same area are made to interfere to generate Interference fringes. The distortion of these fringes is a measure of the surface topography. This technique is different from conventional stereo technique. From the literature, the accuracy of DEM of InSAR is of the order of 5 - 10 meters depending on the frequency, base line, terrain slope, decorrelation of the signal etc. Differential InSAR technique has the capability to detect the movements of the order of a few mm. DEM has several applications in different fields such as Hydrology, Agriculture, Geo-technical, Transportation Engineering etc. In Hydrology DEM is useful for the delineation of watersheds, Dam and canal construction. In Agriculture DEM is useful for Irrigation planning, Laying of the roads is hilly terrain, Cut-and-fill etc.
In this paper an attempt is made to generate DEM using SAR Interferometry technique for the test site Bankura located in West Bengal. We have SAR tandem data of 9-4-96 and 10-4-96 and 14-5-96 and 15-5-96 of ERS-1/2 (Two pairs). The base lines are 99 and 165 meters respectively. Using GAMMA interferometric software, the raw SAR data is processed to focus and get the SLC (single look complex) data using Modular SAR Processor (MSP). The data quality is very good. Using Interferometric SAR Processor (ISP), the two SAR SLC data sets are processed to register the images to get Interference fringes. Flat terrain fringes are subtracted to get fringes related to the terrain topography. The trajectory of the satellite is tuned with the help of Ground Control Points (GCPs) derived from the topomaps. This step is required for the accurate estimation of the baseline. The phases, after unwrapping, are converted to terrain heights. Finally, the DEM is geo-coded to map the DEM in NS - WE directions and also to correct for the displacement of the locations due to slant viewing geometry of the SAR system. The final DEM is compared with the GPS measurements at selective locations. The results are in good agreement. Detailed discussion of the results will be presented.
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