Multisensor characterization of subsurface structures in a desert plain area in Egypt with implications for groundwater exploration

A combination of multispectral, thermal, and microwave data from ASTER and PALSAR satellites, supported by ground measurements from GPR, field spectroradiometry, and magnetometry, were used to investigate surface sediment characteristics of the El-Gallaba Plain area, northwest of Aswan. This desert plain once hosted an ancestral river system long before the Nile even existed. Nowadays, the fluvial deposits are largely covered by Aeolian and gravelly sands and thus only detectible with radar and thermal images. Results show two broad strips of thermal cooling anomalies arranged in a linear fashion and diagonally crossing the alluvial basin. Spectral signatures collected along the linear land surface temperature anomalies show generally higher reflectance values (higher albedo) than the surrounding sediments. Both, the cooler LST and higher albedo, suggest that the surface sediments within the anomaly strips have lower emissivity values (low heat storage capacity). The homogeneity of these sediments was measured with a ground penetrating radar (GPR) using 250 and 100 MHz shielded antenna. The 12 GPR profiles across the LST anomalies confirmed that the near-surface sediments (up to 10 m depth) consist of thin horizontal layers of sandstone with very low gravel content. These sediments show very different textural and compositional characteristics with respect to the surrounding areas, suggesting a different depositional environment. Magnetic profiles with 1.5 km average length were acquired across the LST anomalies to investigate deep-seated structures. The results confirmed the existence of graben-like structures with a maximum depth to the basement of 150 m and shallower depths toward the edges of the LST anomalies. Consequently, these structurally controlled basins could be promising areas for groundwater accumulation and exploration in the El-Gallaba Plain of the Western Desert in Egypt. The study uses a multi-sensor integrated approach to investigate and characterize an ancient buried alluvial fan, west of Aswan, and its potential for storing and supplying groundwater for land development by using non-invasive remote sensing techniques from space supported by limited ground surveys. This information is crucial for securing additional food sources and establishing new settlements away from the fertile Nile lands for a growing population in Egypt. The results of this study have implications for groundwater exploration in arid regions and highlight the potential of multisensor data integration for identifying areas of groundwater accumulation. The methodology used in this study involves the analysis of optical and radar satellite data, as well as ground surveys. Land surface temperature (LST) was calculated from ASTER images, and the resulting LST map revealed two broad strips of thermal cooling anomalies arranged in a linear fashion and diagonally crossing the alluvial basin. Radar data from ALOS/PALSAR were used to determine the range of backscatter coefficient values of the sediments along the thermal anomalies and their surroundings. Ground penetrating radar (GPR), field spectrometer, and magnetic measurements were used to validate the space-borne information and determine the nature of subsurface sedimentary layers and degree of homogeneity of the overlying unconsolidated materials.