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Snow depth is monitored constantly beneath the instrument tower
using a Campbell Scientific UDG01 Ultrasonic Depth Gauge. This
sensor measures the distance from the sensor to the surface; it
is currently mounted at 6.0 above the ground, so during peak
snowpack conditions it is 2-3 m above the snow surface. The
primary components of this sensor are the Polaroid Ultrasonic
transducer and the Polaroid 6500 Sonar Ranging Module. The
instrument bounces an ultrasonic wave off the surface and
listens for the return echo. The time from transmit to return of
the echo is the basis for determining the distance to the
surface. The sensor has a measurement range of 0.1-6 m, and an
accuracy of +/- 1 cm or 0.4% of Distance to Target, whichever is
greatest. The measurement resolution is 0.5 mm. The IFOV of the
sensor is approximately 20 degrees, so at low snow depths (large
distances) echoes are sometimes recorded from the tower itself,
resulting in a multiple signal.
[Source: University of Colorado at Boulder]
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