Comparative analysis of photometric parameters over Apollo landing sites from Terrain Mapping Camera (Chandrayaan-1/2) and lab measured data

Abstract

Terrain Mapping Camera (TMC) onboard Chandrayaan-1/2 have provided high spatial resolution (∼5m) panchromatic images in three stereo-views of fore, nadir and aft, (-25⁰, 0⁰, 25⁰), respectively. This study presents the comparative analysis of photometric properties in visible domain from TMC and lab measured data over Apollo 11, 12, 16 and 17 landing sites. Photometric properties have also been analyzed over Apollo 14 landing site using TMC data. A complete framework involving various algorithms and computer programs have been developed to generate topographically corrected incidence and emergence zenith and azimuthal angles, phase angles and radiance factor images. Variations of Lommel-Seeliger corrected radiance factor with respect to phase bins have been analyzed and fit with a physics based simplified Hapke model to retrieve photometric parameters in the available phase angle ranges. Retrieved photometric parameters from TMC datasets were analyzed, compared and validated with the parameters retrieved from the available lab measurements over Apollo Landing sites soil samples using the same model over the same phase angle ranges. Differences in retrieved parameters from TMC with respect to lab measured data were observed, for example, retrieved albedo from TMC datasets were found to be less by 30-33% and 45-50% with respect to lab measurements at 550 nm and 750 nm respectively for both mare and highland regions (Apollo 11, 12 and 16 landing sites). These differences may be due to the changes in lunar soil properties such as compaction, disturbances in particle arrangement or soil structure, etc. caused during sample preparation. It has also been observed that retrieved asymmetry factor is closer and comparable for mare landing sites in comparison to highland landing sites. Phase ratio (slope of phase function) images have also been generated over Apollo 16 and 17 landing sites to identify surface structure anomalies and alterations in top layer of regolith caused by Lunar Modules' landing and liftoff. Phase ratio anomalies were also observed in North Ray crater due to the differences in physical properties of top layer of regolith caused by mass wasting events.