SAR Remote Sensing of Buried Faults: Implications for Groundwater Exploration in the Western Desert of Egypt
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- Gaber, A., Koch, M., Helmi Griesh, M. et al. Sens Imaging (2011) 12: 133. doi:10.1007/s11220-011-0066-1
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The hydrological setting of a desert plain area located in Egypt, west of Aswan city, is still not well understood, and thus, its groundwater potential remains largely unknown. Images from the ALOS/PALSAR L-band sensor have been used to detect and delineate the subsurface structures in this area. Linear, elliptical and circular polarization transformations were applied to the ALOS/PALSAR full polarimetric data by changing the orientation angle (ψ°) and elliptical angle (χ°). The circular polarization (ψ = 0° and χ = 45°) proved to be the best transformation for revealing buried faults in various strike directions, which have not been reported in the last version of the official geologic map of this area. Such derived circular polarization images were further enhanced by applying the Optimal Polarization Contrast Enhancement method. The moisture content (ӨS) of the study sites was generally low, with an average of roughly 0.01%. The average Root Mean Square Height (hRMS) of the surface roughness was also low with 0.01 cm across all sites. The relative dielectric constant (εr) of the sand in the study area produced a very low value of 3.04. The effects of ӨS, εr and hRMS on the radar backscattered signals turned out to be very low, thus providing, optimal conditions for L-band to penetrate relatively deeply. Moreover, 21 GPR profiles were acquired using 270 MHz shielded antennas to validate the radar remote sensing results. These GPR profiles reveal obvious offsets in the subsurface stratigraphy suggesting that such highly fractured zones are possibly favorable zones for groundwater accumulation.