Title: The Thermophysical Properties of the Bagnold Dunes, Mars: Ground-truthing Orbital Data,
Abstract: In this work, we compare the thermophysical properties and particle sizes
derived from the Mars Science Laboratory (MSL) rover's Ground Temperature
Sensor (GTS) of the Bagnold dunes, specifically Namib dune, to those derived
orbitally from Thermal Emission Imaging System (THEMIS), ultimately linking
these measurements to ground-truth particle sizes determined from Mars Hand
Lens Imager (MAHLI) images. In general, we find that all three datasets report
consistent particle sizes for the Bagnold dunes (~110-350 microns, and are
within measurement and model uncertainties), indicating that particle sizes of
homogeneous materials determined from orbit are reliable. Furthermore, we
examine the effects of two physical characteristics that could influence the
modeled thermal inertia and particle sizes, including: 1) fine-scale (cm-m
scale) ripples, and 2) thin layering of indurated/armored materials. To first
order, we find small scale ripples and thin (approximately centimeter scale)
layers do not significantly affect the determination of bulk thermal inertia
from orbital thermal data determined from a single nighttime temperature.
Modeling of a layer of coarse or indurated material reveals that a thin layer
(< ~5 mm; similar to what was observed by the Curiosity rover) would not
significantly change the observed thermal properties of the surface and would
be dominated by the properties of the underlying material. Thermal inertia and
grain sizes of relatively homogeneous materials derived from nighttime orbital
data should be considered as reliable, as long as there are not significant
sub-pixel anisothermality effects (e.g. lateral mixing of multiple
thermophysically distinct materials).