A Comprehensive Approach in Understanding the Martian Geoelectrical and Geomagnetic Context for the Interpretation of Futur Radar Sounding Data.

Low frequency sounding radars on Mars can probes the subsurface layers to varying depths depending on the sounding geometry and the geoelectrical and geomagnetic properties of the soil at the sounded sites. Hence a good knowledge of the electric and magnetic properties of the rocks and sediments constituting the investigated media is crucial for any future data analysis and interpretation. We have undertaken a comprehensive investigation of the potential electrical and magnetic losses that may be encountered on Mars based on three steps: The first is the laboratory characterization of Mars-like volcanic and sedimentary materials in the low frequency band of 1-30 MHz, which covers the frequency range of the MARSIS experiment onboard the Mars Express orbiter (ESA-2003), the SHARAD shallow sounder that will be flown in 2005 (NASA-ASI) and possible ground penetrating radars that may be flown as part of future rover and geophysical network missions. The electromagnetic properties of these analog Mars materials will be presented as a function of various important geophysical parameters, such as porosity, bulk density and temperature. The second step is the integration of these measurements into a series of frequency dependent geoelectrical models representing the distribution and state of subsurface water under variety of geologic conditions, with the intent of identifying those locations on Mars that offer the best opportunity for an unambiguous detection of subsurface liquid water. We then use the Finite Difference Time Domain method to simulate the radar wave propagation across those models and hence getting a possible preview of the backscattered echo corresponding to different geological context and radar characteristics. These simulations will be compared with the data returned by MARSIS and SHARAD in an effort to better understand the nature and characteristics of the subsurface Martian environment. Finally, these analyses will be supplemented by field investigations of simple terrestrial analogue sites using 2-30 MHz GPR instruments. Recent soundings conducted in the West Egyptian Desert by a 2 MHz GPR demonstrated the ability of this technique to detect the Nubian Aquifer at a depth around 900 m beneath thick layer of marine sedimentary quaternary and tertiary structures constituted mainly of dry porous dolomite, illinite, limestone and sandstone, given a reasonable knowledge of the local geoelectrical properties of the crust. In this talk we will summarize our efforts date and discuss their implications for the interpretation of data from future Mars radar sounding investigations.