Polarimetric decomposition-based analysis of Chandrayaan-2 L-band DFSAR data for potential water ice detection in lunar polar regions

Abstract The DFSAR (Dual-Frequency Synthetic Aperture Radar) onboard the Chandrayaan-2 spacecraft, launched on July 22, 2019, represents a significant advance in radar-based exploration of solid celestial bodies. Chandrayaan-2 is equipped with an array of sophisticated sensors, including the DFSAR, which operates in both the L-band and the S-band in Fully Polarimetric (FP) and compact polarimetric (CP) modes. In this study, we utilize L-band Synthetic Aperture Radar (SAR) data to analyze the lunar regolith. The L-band has superior penetration capabilities, allowing for more effective retrieval of subsurface parameters compared to previous S-band SAR missions. By using L-band in Fully Polarimetric (FP) mode, we can effectively characterize the lunar surface. This technology enables detailed polarimetric analysis of the lunar surface, particularly in the challenging Permanently Shadowed Regions (PSRs) at the lunar poles. These PSRs serve as cold traps for water molecules and are ideal locations for exploring water ice. DFSAR, SLI data is imported, and pre-processing is carried out after generating the scattering matrix. Multilooking is performed with a factor of 38. Refined Lee filter [5x5] window size is applied after coherency matrix generation to remove the speckle in the data, and also multiple decomposition techniques are employed, including the $$H/A/\\bar{\\alpha }$$ decomposition (based on eigenvalue-eigenvector analysis) and the Yamaguchi four-component decomposition model (based on double-bounce, surface, and volume scattering), which effectively characterize the variations in surface roughness, material composition, and topography of the crater’s inner and outer walls. This study focuses on the polar and non-polar regions (Hermite-A, Peary, Gardner, and Korolev X crater regions), utilizing DFSAR data to conduct a comprehensive polarimetric analysis aimed at identifying the potential presence of water ice deposits. The results reveal the dominance of volume scattering within the walls of the crater, which is verified across all decomposition methods. Circular Polarization Ratio (CPR) analysis further demonstrates a pronounced difference between the interior and exterior regions, with the interior values suggesting rough textures and a higher probability of water ice presence. This aligns with prior studies that associate elevated CPR values and volume scattering with ice deposits in the lunar Polar Regions. To validate the SAR-based analysis, high-resolution lunar surface images captured by the Navigation camera onboard Pragyan Rover at the Chandrayaan-3 landing site were examined. The change in surface roughness before and after landing was reflected in scattering powers, confirming changes in the lunar terrain.