Electromagnetic measurements on Martian soil analogs: Implications for MARSIS and SHARAD radars in detecting subsoil water

摘要

In this work a laboratory investigation on the electrical and magnetic properties of magnetite-bearing and water-bearing granular mixtures, selected as Martian soil simulants, is presented. The objective of these measurements is the estimation of the performance of space-borne ground penetrating radars for detection of subsurface water (both solid and liquid) on Mars (MARSIS on-board Mars Express, and SHARAD on Mars Reconnaissance Orbiter). A simplified two-layers soil model is proposed to estimate the radio wave maximum penetration depth. The upper layer contains different magnetite volume fractions, whereas the lower one, representing the target to be detected, consists of pure water ice, or basaltic sand mixed with either liquid or solid water. The material constitutive parameters are measured in the megahertz frequency region, to obtain the soil electromagnetic characterization in a band consistent with the MARSIS and SHARAD sounders. Complex dielectric permittivity and magnetic permeability of the tested materials are obtained by measuring the impedance of a capacitive cell (for the dielectric measurements), and a toroidal solenoid (for the magnetic measurements). The attenuation of radar signals and the target detection depth are computed as a function of the operating frequency, the upper layer magnetite content, and the receiver-to-transmitter signal power ratio.