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.