Remote Sensing - Dune Worlds: How Windblown Sand Shapes Planetary Landscapes - page 216

Fig. 18.14 a Profiles across the DEM in Fig. 18.13 . Note the overall
slope, dropping about one dune-height every five dune wavelengths
towards the Atlantic to the west (left). b Zoom-in on parts of the profile

to make individual postings visible (at 30 m intervals), with a linear
trend removed—the regularity of the profiles is seen. Compare these
profiles with GPS profiles

is some indication of diurnal temperature change. These
findings are consistent with overall dry, porous sands with a
low albedo, although Titan's thick atmosphere will proba-
bly preclude the more quantitative analysis of thermal
inertia that has been possible at Mars. On Venus, sadly, the
atmosphere is so thick and hot that thermal observations
from orbit are impossible.

narrow wavelengths across a wide range of wavelengths
into the infrared, rather than just the three wide bands of
primary color our eyes have evolved to exploit (which after
all serve principally to discriminate what is good to eat).
A plethora of instrumental techniques exist to develop
this sort of information. One possibility is narrowband
imaging through a number of filters—usually giving a high-
quality image (high spatial resolution, but poor spectral
resolution). Another approach is a point spectrometer
wherein the light (or emitted thermal radiation in some
cases) from a patch of terrain is passed through a grating or
scanned with an interferometer, giving a high-quality
spectrum. In between there are many variants: imaging
spectrometers, hyperspectral imagers, with all kinds of
variations of scanning and sweeping. A common approach
for orbiters has a slit with a grating projected onto a 2D
detector, with one dimension corresponding to a spatial
position along the slit (and thus along the ground) and the
other dimension corresponding to wavelength. If the slit is

18.4 Hyperspectral Imaging

The reflectivity of a mineral can be a complex function of
wavelength (Figs. 18.10 and 18.11 ); this is after all why
some minerals—especially ores of transition metals—are
pretty colors. Thus color imaging can give insights into the
composition of surface minerals, including those segregated
into dunes. The ability to discriminate different composi-
tions can be enhanced by looking at a large number of