A laboratory-based dielectric model for the radar sounding of the martian subsurface

International audienceFor the last decade, the SHARAD radar on board NASA's Mars Reconnaissance Orbiter, and the MARSIS radar on board ESA's Mars Express, have sounded the surface and subsurface of Mars from orbit to search for and characterise water ice reservoirs. When associated with dielectric models, the regolith composition (in terms of dust, ice and voids) of the surface and subsurface can be extracted from these data. These models describe the electromagnetic properties of the material as a function of its chemical and physical properties. With the goal of improving the currently available dielectric models for Martian icy regolith, we conducted laboratory measurements of the dielectric properties of the JSC Mars-1 Martian soil simulant mixed with water ice, varying the water ice mass fraction from 0 to 76%. Our measurements were performed between 50 MHz and 2 GHz, at ambient temperature, and at 243 K. The samples had porosities between 40% and 72%. Based on these, we propose a model that relates the dielectric constant of the sounded material to its volume fraction of water ice and/or of JSC Mars-1, its porosity, and its temperature. Tuned to the relevant frequencies, our dielectric model can be used to estimate the volume fraction of water ice from the radar sounding data of SHARAD and MARSIS. It is similarly relevant for the interpretation of data from the WISDOM radar, which will be part of the science payload of the ExoMars 2020 rover