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Analysis of Polarimetric Mini-SAR and Mini-RF Datasets for Surface Characterization and Crater Delineation on Moon
Himanshu Kumari, Ashutosh Bhardwaj *
1  Indian Institute of Remote Sensing, Dehradun, India


ISRO's Chandrayaan-1 and NASA's Lunar Reconnaissance Orbiter (LRO) were launched on 22 October 2008 and June 18, 2009, respectively with an aim of exploration along with identification of possible safe sites for future robotic and human lunar missions. These missions have used Miniature Synthetic Aperture Radar (Mini SAR) and Miniature Radio Frequency (Mini-RF) instrument payloads developed by NASA and flown aboard India's Chandrayaan-1 spacecraft and LRO, NASA respectively. These sensors are used for hybrid polarimetry to image shadowed polar regions, where there is a possibility of water to exist. NASA estimates that there are chances of over 600 million metric tons of water ice on the moon, which further prompts the interest of researchers in exploring the moon. The hybrid polarimetric architecture of mini-SAR supports the calculation of Stokes parameters of the backscattered signal, which further allows the derivation of decomposition parameters required to obtain the sub-surface information of the craters. This research aims to study the surface properties of polar and non-polar regions of the Moon and find an approach to detect the boundaries of the Lunar craters. The ArcGIS add-in crater tool was used for delineating the boundaries of the lunar craters using the openly accessible digital elevation model (DEM) generated from Terrain Mapping Camera (TMC) data. The polar craters Nobile, Haworth, Gioja, and an unnamed crater near Byrd along with non-polar craters named Arago and Moltke were investigated for surface characteristics. The Eigenvalues and Eigenvectors were estimated to calculate entropy (H) and the Poincare ellipticity (α) which were used to characterize the scattering mechanism. The three polarimetric decomposition techniques m-δ, m-χ, and H-α applied along with the circular polarization ratio (CPR) were used to obtain the sub-surface information, and identify the shreds of evidence of water ice deposits inside the craters near the polar regions. The results found the dominance of surface scattering inside the craters and double-bounce scattering in the outer region of craters which were graphically analyzed using a transect and box plot. The analytical view of the results proved the hypothesis of the possibility of water ice deposits for the polar craters with the use of decomposition techniques with CPR greater than 1, which further needs validation through other techniques, such as dielectric constant analysis.

Keywords: circular polarization ratio; polarimetric decomposition techniques; Terrain Mapping Camera; digital elevation model; Nobile; Moltke