Assessing the Textural Properties of Hyper-Arid Areas in the VHF Range in Support of Radar Probing of Shallow Aquifers

• Main Authors: Schaefer, S. J., Heggy, E., Normand, J., Farag, A. Z. A., Palmer, E. M., Chmielewski, A. B.
• Other Authors: Computer Science, Columbia University of New York, USC Viterbi School of Engineering, University of Southern California (USC), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2020
• Subjects: 1829 Groundwater hydrology; HYDROLOGY; 1847 Modeling; 1855 Remote sensing; 1894 Instruments and techniques: modeling; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Ice Sheet
• Online Access: https://hal.science/hal-04293023

International audience The Orbiting Arid Subsurface and Ice Sheet Sounder (OASIS) will be the first mission to explore subsurface signatures of climate change in hyper-arid warm deserts and polar ice sheets in cold ones. OASIS will perform detailed mapping of shallow aquifers (i.e., <100m) in Earth's hyper-arid regions using VHF subsurface sounding radars. Doing so will enhance our understanding of the groundwater budget and dynamic in fossil aquifers, as well as the paleoclimatic conditions in North Africa and the Arabian Peninsula during the Holocene. In preparation for the OASIS mission, we investigated the Arabian Peninsula's surface textural properties at the VHF frequencies from 20 to 60 MHz to identify areas with low surface roughness and clutter that will be the primary targets for mapping shallow aquifers. The results will also support refining the sounding radar measurement requirements, operations modes, and clutter removal efforts over areas with different textural properties. To achieve these objectives, we used the global 1-arcsecond DEM from the SRTM data to investigate the Arabian peninsula's surface textural properties at the metric and decametric scale as a first step, before extending our approach to the desert's area in North Africa. Using this dataset, we created maps for the topographic slopes and the root-mean-square height (HRMS) for a 1km-by-1km footprint for the Arabian peninsula. Finally, we classified the surface of the Arabian Peninsula into four categories: smooth, moderately rough, rough, and very rough, at 40, 50, and 60 MHz based on the Rayleigh roughness criterion. Our results suggest that the majority of the Arabian Peninsula is moderately rough to rough at those wavelengths. Such roughness can induce signal attenuation from -5 to -20 dB due to surface reflection. The largest portion of the peninsula's HRMS values fall below 15 m, which corresponds to the depth below which aquifers could be distinct without advanced clutter removal. Hence, water tables of aquifers more ...