Figure 1. Two CRISM false color images overlain onto a HiRISE image mosaic. Curiosity ’s traverses from the Bradbury Landing Site to sol 3052 at the base of Mont Mercou are shown. The CRISM data RGB band center wavelengths are 2.496, 1.802, and 1.237 µm, respectively. The reddish-brown color of the Bagnold dune field as opposed to the darker, less red sand fields to the southeast is a consequence of the increased reflectance with increasing wavelength for the Bagnold dune deposits as opposed to the deposits located to the southeast. The white box delineates the location of the detailed study area (Figure 3) and the yellow lines show the outline of CRISM along-track oversampled scene FRT00021C92, the focus of this paper. The footprints of CRISM scenes HRL0000BABA (left) and FRT0000C518 (right) are also shown. VRR stands for Vera Rubin ridge, GT for Glen Torridon, and GP for Greenheugh pediment. NB stands for the Namib barchan dune, MDI stands for Mount Desert Island, and SoF for Sands of Forvie. In this paper we focus on comparisons of results for MDI and SoF areas, which have distinctly different color and thus spectral properties. CRISM data have been processed to single scattering albedo (SSA), as described in Section 2 of the text.
We first review previous rover- and orbital-based results for the Bagnold dunes, with a focus on the MDI location within the linear Bagnold dunes and results from Curiosity ’s measurements on the northern edge of the SoF sand sheet. The CRISM ATO observation (Figures 2 and 3) is then used to retrieve single scattering albedo (SSA) spectra from 0.50 to 2.6 µm at 12 m/pixel scale, i.e., a high enough spatial resolution to properly sample both the MDI and SoF sand deposits. The Bagnold linear dunes, including MDI, show a reddish-brown color, whereas the southern sand deposits, including SoF, are darker and lack the reddish-brown color (Figures 1-3). We employed CRISM spectra to determine the reasons for these color differences, focusing on retrieval of mineral abundances and grain sizes for these two deposits.