Absrtact
Shallow fossil aquifers are the largest freshwater bodies in the North African Sahara and the Arabian Peninsula. Their groundwater dynamics and response to climatic variability and anthropogenic discharge remain largely unquantified due to the absence of large-scale monitoring methods. Currently, the assessment of groundwater dynamics in these aquifer systems is made primarily from sporadic well logs that barely cover a few percent of the geographical extent of these water bodies. To address this deficiency, we develop the use of an Ultra-Wide Band (UWB) Very High Frequency (VHF) interferometric airborne sounding radar, under a Space Act Agreement between NASA and the Qatar Foundation, to characterize the depth and geometry of the shallowest water table in large hyper-arid hydrological basins in North Africa and the Arabian Peninsula. We describe herein the science objectives, measurement requirements, instrument design, expected performance, flight implementation scenarios, primary targets for investigation, and the first technology demonstration of the concept. Our performance analyses suggest that an airborne, nadir-looking sounding radar system operating at 70-MHz center frequency with a linearly polarized folded-dipole antenna array—enabling a bandwidth of 50 MHz—and a surface SNR of 85 dB flying at an altitude of 500-2000 m, can map the uppermost water table depths of aquifer systems spanning tens of kilometers at a vertical resolution of 3 m in desiccated terrains to an average penetration depth of 50 m, with a spatial resolution of 200 m. For the first time, this airborne concept will allow time-coherent high-resolution mapping of the uppermost water tables of major aquifer systems in hyperarid areas, providing unique insights into their dynamics and responses to increasing climatic and anthropogenic stressors, which remain largely uncharacterized. The above significantly surpasses the existing capabilities for mapping shallow aquifers in these harsh and remote environments, which today rely on data collected on different time scales from sparse well logs that do not cover their geographic extents.
Keywords: Airborne sounding radar; VHF radar; Synthetic aperture radar; Desert hydrology; Subsurface imaging; Groundwater and aquifers
