Evaluation of Sedimentary and Terrain Parameters from MARDI Camera Imaging and Stereogrammetry at Gale Crater

Abstract:

The Mars Descent Imager (MARDI) provides mm-resolution imaging of an ~0.92 m by 0.64 cm patch of the Martian surface beneath the rover. Since Sol 310, MARDI has acquired images under twilight illumination to optimize image quality for quantitative sedimentology analysis. This imaging, carried out after each rover drive, permits systematic measurement of clast size distribution, inter-clast spacing distribution, and surface areal coverage. Sedimentological parameters derived from these observations include clast sorting (mean/var of size) and other characteristics related to transport mechanisms or in-place weathering. Measured surface parameters (e.g., clast sorting) can be correlated with surface units qualitatively defined (e.g., smooth, rocky, outcrop) in images obtained by HiRISE, MSL Mastcam and MSL Navcam. In addition, a preliminary longitudinal analysis has been conducted to examine possible source regions for the bulk of the gravels by correlating sedimentary parameters with distance from either Peace Valles or Mt. Sharp, with evidence of trends associated with inter-clast spacing.

Sets of stereo MARDI images that allow the creation of high vertical precision (±2 mm) digital elevation models (DEMs) have also been acquired via two techniques. First, MARDI images taken at each step of comprehensive wheel imaging activities yield 5 MARDI images with ~50% overlap. Second, two MARDI sidewalk video imaging mode (SVIM) experiments yielded a continuous set of images during a rover drive with 75-82% overlap. DEMs created via either technique can be used to quantify terrain properties and measure clast cross-sectional shapes. The microtopographic properties of the Sol 651 surface (e.g., mean/sigma of local elevation and slopes) and its sub-cm texture as measured in the SVIM-derived DEM are consistent with the characterization of the terrain as smooth with few rocks >20 cm. Characterization of the Sol 691 surface as rockier than the Sol 651 surface is supported by a DEM with larger local slopes at cm scales (mean ~40°), slope variances over 20° and cm-scale height variance in excess of 2 cm. Ultimately, the analysis of clast sizes, spatial patterns, areal cover, and 3D shapes is expected to result in the identification of sub-populations, potentially tied to depositional events in the region and their sources.