Field Studies - Dune Worlds: How Windblown Sand Shapes Planetary Landscapes - page 182

Fig. 16.11 Ground penetrating radar survey of a dune in the Victoria
(dry) Valley in Antarctica. The low temperatures minimize the
absorbing effect of any water that may be present in the sand, so this

remarkable observation sees through some 60 m of sand. The dipping
layers are seen in the radargram, and are interpreted in the lower panel.
Image courtesy of Charlie Bristow

diode and phototransistor pair, with a reflective patch or
chopper mounted on the cup shaft)—in both instances, the
data recording system must count pulses. Another approach,
less often used, is to drive a small dynamo or generator (i.e.,
an electrical motor in reverse) whose output voltage will
relate to the rotation speed.
These sensors are relatively inexpensive, and are often
used for measuring the wind gradient in the boundary layer
with, e.g., three anemometers at different heights supple-
mented by a single wind vane for direction. The major issue
with this type of sensor is that the cups have some inertia
which makes it difficult to measure fluctuations in wind

speed of less than a second or so. Cup anemometers were
used by the Russian Venera landers on Venus. Another
approach is to use a propeller, mounted on a horizontal axis.
This in turn is mounted on a swivel with a wind vane, such
that it is free to turn into the wind. Again the shaft rotation
is typically measured optically.

16.3.2 Hot Wire and Hot Film

The electrical resistance of most metals is temperature
dependent. A wire subject to electrical heating will reach a