Field Studies - Dune Worlds: How Windblown Sand Shapes Planetary Landscapes - page 178

Fig. 16.5 Images a couple of days apart of the same spot (an
anemometer and several reference stakes 20 cm apart are fixed in the
ground). Not only have the ripples coarsened and thinned, but they

have become somewhat steeper and more sinuous. These images were
taken by a timelapse camera on a fencepost, the shadow of which is
visible at left. Photo R. Lorenz

Fig. 16.6 An image taken from a kite at about 200 m altitude,
showing Sand Mountain, Nevada at right (a few dark spots are
vehicles). A maze of narrow linear dunes snake away from it to the
edge of the sand field; the profiles of these dunes are somewhat

rounded due to recreational vehicle activity (see also Fig. 7.2 ) . Four
persons (including the kite 'pilot') are just visible on the dune crest at
bottom left. Photo R. Lorenz

16.2.4 Laser Scanning

surface from depths of a few centimeters, where (depending
on the time of day) it may be warmer or cooler than the
undisturbed surface. Thus even when the optical contrast
between undisturbed and avalanching sand is tiny, their
temperatures are quite different and so avalanching lobes
show up well in thermal images (e.g., Fig. 16.7 ).

Shape measurements of dunes and ripples can be made with
field laser scanners (Fig. 16.8 ) which measure the distance
(to *mm precision) to the ground over a specified range of
angles from a fixed point. For cm-scale measurements