Remote Sensing - Dune Worlds: How Windblown Sand Shapes Planetary Landscapes - page 213

Fig. 18.9 A daytime thermal image of the surface of Mars (a crop of
THEMIS image I25817004) around 70S. The image is 3.2 km from
top to bottom. Illumination is from the top right, and cold shadows are
apparent in the crater walls. The large sand deposit in the center of the

crater, with superposed dune forms is white, indicating a high
temperature due to the low thermal inertia of the sand. Credit ASU/
NASA

Fig. 18.10 Visible wavelengths
have some ability to discriminate
mineral composition. Olivine is
of course greenish (green
corresponds to *0.55 microns),
and hematite red (red light
is *0.65 microns). Pure quartz
is nearly pure white, although is
slightly more yellow (i.e., less
blue) than gypsum

capacity) provides a measure of the ability of a material to
store heat. The higher the heat capacity, the larger the
quantity of heat needed to raise the temperature of a unit
volume; water has a heat capacity 4-5 times that of com-
mon rocks (Table 18.1 ). For most geologic materials, the
product qc can vary by a factor of 2-4, while k can vary by
orders of magnitude. Calculated values for sand and dust on

Mars illustrate how the thin Martian atmosphere greatly
reduces

the thermal conductivity of granular materials

(compare Mars values to those of dry sand).
Usually a model (e.g., Fig. 18.8 , taking into account the
illumination geometry and other factors) is tuned to fit the
observed temperatures, and the free parameter in the model
that is diagnostic of the surface material is the 'thermal