Searching for water-ice in the lunar media has been a key issue in the moon explorations. Missions of mini-SAR and mini-RF SAR made compact-pol (polarization) measurements on lunar polar permanent shadowed region (PSR). High circular polarization ratio (CPR) data and a two-layer model were applied to studying if water ice in PSR could be retrieved. However, it has been studied that high CPR is not simply due to the presence of water ice, and the Campbell model is a degenerated half-space model, which confused final inversion. In this letter, using the mini-RF data on the PSR of Hermite-A crater on the north pole, a two-layer model with the Kirchhoff and small perturbation approximations is presented. It takes account of the surface-layering topography, which makes changes of local incidence and polarimetric base rotation. Our results do not support Calla's conclusions based on the half-space model, suggesting that the inversion of mini-RF is not so straightforward in proving water-ice existence in the PSR media. It points out that the double- and high-order scattering of random volumetric scatters on the lunar surface might play a role, and high-resolution measurements and more elaborate modeling are needed for further studies.

Searching for water ice in the lunar media has been a key issue in the Moon explorations. Missions of Mini-SAR and Mini-RF SAR made compact-pol(polarization) measurements on lunar polar permanent shadowed region (PSR). High circular polarization ratio (CPR) data and two-layer model were applied to studying if water-ice in PSR could be retrieved. However, it has been studied that high CPR is not simply due to the presence of water-ice. We point out that the Campbell model is a degenerated half-space model, which confused dielectric inversion of Mini-RF data. In this paper, our numerical BART (Bi-directional Analytic Ray Tracing) is applied to simulate high-order scattering from the lunar rough surface with-and without-stone-scatters, the CPR is numerically simulated and analyzed. Furthermore, a two-layer model of KA surface (Kirchhoff-approximation)/SPA subsurface (small perturbation approximation) subsurface is developed to take account of all these topographic factors for PSR dielectric inversion. The Mini-RF data on the PSR of Hermite-A crater in the North pole (see Fig. 1) are employed for the inversion. Our results do not support previous conclusions based on the half space model, suggesting that the inversion of Mini-RF are not so straight forward in proving water-ice existence in the PSR media. It points out that double and high-order scattering of random volumetric scatters on the lunar surface can play a certain role, and high-resolution measurements and more elaborate modeling are needed for further studies.

Dielectric inversion of lunar permanently shadowed region (PSR) of moon poles has been studied for estimation of possible water-ice content. The Campbell model was directly applied to mini-SAR data for inversion on the Hermite-A crater region. However, this letter presents quantitative analysis that the lunar surface topography, i.e., surface roughness and slopes, and underlying dielectric media, and so on, can significantly affect this inversion. The model is actually degenerated into a half-space model without topographic account. This letter presents a two-layer model of Kirchhoff-approximation surface/small perturbation approximation subsurface to take account of all these topographic factors for PSR dielectric inversion.