Radar subsurface mapping of the polar layered deposits on Mars

[ 1] Determining the three-dimensional (3-D) structure of the Martian polar caps is fundamental to understanding their hydrologic history, dynamic behavior, past climatic changes, and the underlying lithosphere, and radar sounding is the most promising technique to do so. We model the dielectric profile of the Martian polar layered deposits (PLD), apply it to a 1-D electromagnetic plane wave propagation model, and calculate the relative strength of radar reflections produced by layering within these deposits. Variations in dust fraction with depth derive from albedo profiles of a northern polar trough and a radiative transfer model. Detection of the fine-scale layering present in the polar deposits with SHARAD is likely under a wide range of possible dielectric properties of the ice and silicate inclusions as long as minimum inclusion volumetric fractions are larger than 10(-3). Our models indicate also that stratigraphic mapping of the PLD is feasible with a vertical resolution of similar to 20 m under ideal conditions. Penetration depths depend greatly on the dielectric properties of silicate inclusions, reaching at least 250 m for ice rich in highly conductive altered basaltic dust to at least 2 km for weakly conducting silicate inclusions. Because of the wide parameter space and unconstrained composition, interpretation of polar radar data will be best accomplished in conjunction with updated thermal models and other data sets, such as the recently published results from orbital infrared remote sensing that impose limits on ice grain size and dust.