An Approach for Finding Possible Presence of Water Ice Deposits on Lunar Craters Using MiniSAR Data

Abstract

Investigating the feasibility of water-ice deposits on lunar surface has been a very challenging task, which requires meticulous effort. Conceptualization of MiniSAR was a breakthrough because it had capability to image the shadowed regions that may have higher possibility of water-ice. Earlier studies have found that circular polarization ratio (CPR) is greater than unity in regions having volume scattering due to dielectric mixing (or water-ice deposits). However, later experiments revealed that ${\rm CPR} >1$ might also occur due to surface roughness. Thus, instead of using single polarimetric parameter CPR, it is required to use textural (or roughness) behavior of lunar surface along with scattering mechanisms, for obtaining the regions having higher possibility of dielectric mixing. For this purpose, information of two different approaches namely, polarimetric approach (i.e., $m - \delta $ decomposition and $m - \chi $ decomposition) and fractal approach have been fused together. The polarimetric approaches, i.e., $m - \delta $ decomposition and $m - \chi $ decomposition, help in identifying scattering mechanisms associated with lunar surface, whereas fractal-based approach helps in characterizing lunar surface on the basis of surface roughness using a measure called fractal dimension “ $\bm{D}.$ ” Finally, a decision tree algorithm has been proposed, in which decision criteria are decided on the basis of CPR, $m - \delta $ decomposition, $m - \chi $ decomposition, and fractal dimension “ $\bm{D}.$ .” The proposed approach seems to resolve the vagueness caused by ${\rm CPR} >1$ assumption, and to segregate areas representing volume scattering in relatively smooth surfaces inside anomalous craters, where possibility of dielectric mixing (or water-ice) may be high.