Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p23a1606t&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P23A-1606
Physics
[5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties
Scientific paper
For lunar orbital synthetic aperture radars, such as the Chandrayaan Mini-RF operating at S-Band (13cm) wavelength and the Lunar Reconnaissance Orbiter Mini-RF operating at S-Band and X-Band (3-cm) wavelengths, it is important to understand and model the radar backscattering characteristics of the icy regoliths. If ice in the permanently shadowed areas of the lunar poles backscatters like the ices on Mercury, Mars and the Galilean satellites, then it will have a substantial radar enhancement characterized by a Circular Polarization Ratio (CPR) greater than unity. We examine the possibilities that these distinct signatures may be diminished by factors such as a thin regolith covering, and/or the ice occupies small patches within a larger radar pixel. Our first model for scattering from lunar surface assumes a simple mixing model consisting of diffuse and quasi-specular components. The quasi-specular component results from the surface and sub-surface layers that are oriented perpendicular to the radar’s line-of-sight. The diffuse component associated with either rocks or ice is assumed to be uniformly bright, with the backscatter being proportional to the cosine of the incidence angle. Rocks are assumed to have CPRs of unity while ices are assumed to have CPRs of 2 like those observed on Mercury, Mars and Galilean Satellites. This first model shows that radar signatures for ice and rocks are separable if the same-sense circular (SC) enhancements are greater than about 2-4. A preliminary validation using LRO radar data for a few polar and mid-latitude craters indicate that the observed CPRs are consistent with our models for different regolith ice and roughness conditions. Our second model addresses CPR variations for ice filling the pores of the regolith. Here the quasi-specular backscatter from the surface and buried crater ejecta as well as diffuse backscatter from sub-surface rocks will change with increased abundances of ice in the regolith. This second model indicates that only small indistinguishable changes in CPRs would occur.
Heggy Essam
Thompson William T.
Ustinov Eugene A.
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