On the potential of orbital VHF sounding radars to locate shallow aquifers in arid areas using reflectometry

Abstract

Shallow aquifers are the primary water source to mitigate rising hydroclimatic fluctuations in arid areas, notably in North Africa and the Arabian Peninsula. The occurrence and dynamics of these expansive water bodies remain poorly characterized due to the reliance on sporadic monitoring wells. To address this deficiency, several studies are exploring the potential of low Earth orbit sounding radars as a large-scale mapping tool that can provide unique insights into the delineation and dynamics of these aquifers. Herein, we analyze the detectability of shallow aquifers (<10 m deep) using the radiometric analysis of surface reflections from a 45-MHz orbital sounder with an 8-MHz bandwidth. We use the ray tracing method to simulate the radar return from two realistic geoelectrical and topographic models of shallow aquifers in North African Sahara desert for omnidirectional and distributed array configurations. Our results suggest that the dielectric change induced by shallow aquifers that are up to 10-m deep can increase the 45-MHz radar surface return of the desiccated desert surface by 5 dB in areas with very low surface roughness of rms height <0.35 m. These preliminary results suggest a constrained potential for a monostatic VHF reflectometry to probe large sedimentary basins, which a distributed architecture can improve.