Modeling radar scattering from icy lunar regoliths

The data from two orbital synthetic aperture radars - the Chandrayaan Mini-RF, at 13-cm wavelength (S-band) and the Lunar Reconnaissance Orbiter Mini-RF at 4 cm and 13 cm (X-band)-can provide evidence of presence of ice deposits in the polar shadowed areas. The performance and scientific return from those two experiments require that we understand the radar backscattering characteristics of the icy lunar regoliths sufficiently to assess the possibility of frozen volatiles in the surface and shallow subsurface (defined here as 10 times the wavelength). If ices in the permanently shadowed areas of the lunar poles have the radar characteristics similar to the ices on Mercury, Mars and the Galilean satellites, then these ices will have a substantial radar enhancement characterized by a circular polarization ratio (CPR) greater than unity. Here we examine the possibilities that this distinct CPR signature may be diminished by factors such as a thin regolith covering the ice, the ice occupying small patches within a larger radar pixel and/or the high CPRs resulting from blocky crater ejecta.