Characterization and mapping of surface physical properties of Mars from CRISM multi-angular data : application to Gusev Crater and Meridiani Planum

International audienceThe analysis of particle physical properties (grain size, shape and internal structure) and its organization (surface porosity, roughness, and grain size distribution) provides information about the geological processes which formed and modified planetary surfaces. CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) multi-angular observations (varied emission angles) allow for the characterization of the surface scattering behavior, which depends on the composition and on the material physical properties such as the grain size, shape, internal structure, and the surface roughness. After an atmospheric correction (compensating mineral aerosol effects) by the Multi-angle Approach for Retrieval of the Surface Reflectance from CRISM Observations (MARS-ReCO), the surface reflectances at different geometries were analyzed by inverting the Hapke photometric model depending on six parameters: single scattering albedo, 2 phase function terms, macroscopic roughness and 2 opposition effects terms. In this work, surface photometric maps are created to observe the spatial variations of surface scattering properties as a function of geological units. Information regarding the single scattering albedo, the particle phase function and the macroscopic roughness are provided at the CRISM spatial resolution (200m/pixel). This article describes the application of this methodology to the data covering the Mars Exploration Rover (MER) landing sites located at Gusev Crater and Meridiani Planum where orbital and in situ observations are available. Complementary orbital observations (e.g., CRISM spectra, THermal EMission Imaging System (THEMIS), High Resolution Imaging Science Experiment, (HiRISE) images) were used for interpreting the modeled Hapke photometric parameters in terms of physical properties which can be used to constrain the geological processes. Available MER in situ observations were used as ground truth to validate the interpretations of the Hapke parameters. Varied scattering properties were observed within a CRISM observation (5x10km) suggesting that the surfaces are controlled by local geological processes (e.g., volcanic resurfacing, aeolian and impact processes) rather than regional or global processes. Results are consistent with the in situ observations, thus validating the approach and the use of photometry for the characterization of Martian surface physical properties