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A Numerical Model of CPR of Rough Surface With Discrete Scatterers for Analysis of Mini‐RF Data

Circular polarization ratio (CPR) was regarded as an important index for detecting water ice in the permanently shaded region (PSR) of the Moon poles. However, many studies have intuitively described that the double‐bounce scatte ring caused by dihedral consisting of rock facets and the lunar rough surface may yield high CPR. Under a large local incidence angle, single scattering is reduced. Double‐bounce scattering of the dihedral governs the echoes and leads to an enhanced CPR. In this paper, a numerical model of the lunar rough surface with discrete scatterers, for example, rock bodies, is developed. The bidirectional analytic ray tracing (BART) method is applied to numerically solve high‐order scattering of this surface/rocks model. The lunar surface is modeled by the Digital Elevation Model (DEM) data from Lunar Reconnaissance Orbiter (LRO) Lunar Orbiter Laser Altimeter (LOLA). This paper quantitatively analyzes how the surface topography, rocks, radar local incidence, etc, affect the CPR. It is found that at a small local incident angle, the single scattering is usually dominant and results in a small CPR. When the local incident angle becomes large, the radar wave reflected in the specular direction is more likely to be reflected again and increases the CPR.