Potential of RISAT-1 SAR data in detecting palaeochannels in parts of the Thar Desert, India

摘要

In the present study, we have demonstrated the potential of RISAT-1 Synthetic Aperture Radar (SAR) data to detect palaeochannels in parts of Thar Desert, India, which may be utilized as one of the guides of geoarchaeological exploration, besides forming groundwater prospective zones. Palaeochannels have been detected using RISAT-1 SAR MRS datasets in the southern parts of Jaisalmer and northeastern parts of Barmer districts, Rajasthan. These palaeochannels of length varying between 14 and 36 km and width varying between 20 and 65 m are present within parabolic sand dune complexes. Palaeochannels have been detected as distinct dark tone on RISAT-1 SAR data compared to feeble expression on corresponding LANDSAT-OLI FCC datasets. This is due to sand-filled valleys, acting as radar smooth surface and absorbing the radar energy with negligible backscatter and enhanced topography due to side-looking capability of RISAT-1 SAR. High-resolution Cartosat DEM has been utilized to prepare topographical profiles, supporting the geomorphological interpretation. Merging of RISAT-1 SAR and LANDSAT ETM datasets using PCA techniques led to enhancements of palaeochannels on merged FCC data products. Like polarization of RISAT-1, SAR data could further enhance and aid in detecting palaeochannels. The entire region was flooded in August 2006 and water had flown through these palaeochannels, which subsequently dried up and facilitated their easy detection; they are otherwise difficult to interpret using pre-flood images. Analysis of sequential post-flood images has been taken up for detailed study of the area, as there is scope to detect additional hitherto unknown palaeochannels.