9.2 Data interpretation
Although not common, the SnowVUE 10 can output invalid-reading indicators if unable to obtain
a measurement. For invalid distance-to-target values, 0 is returned to indicate an error. For snow
depth outputs and temperature reading outputs, the error indicator value is –999. Invalid
readings can easily be filtered out when analyzing the data. Invalid readings should be detected
and discarded in control-type applications.
9.3 Data filtering
The following scenarios can produce values with higher than expected errors:
1. Low-density snow, which results in weak echos returned to the sensor.
2. Weak signal, as indicated by an increased number of echo-quality numbers returned to the
sensor.
Under these circumstances, a SnowVUE 10 can underestimate or overestimate snow depth. If the
signal is too weak, the sensor will output a value of 0 for the distance to target. When the echoes
are weak, the sensor automatically increases sensitivity, which makes the sensor prone to
erroneous readings from flying debris, drifting snow, or obstruction near the beam angle.
Averaging the values is discouraged because high-error values can skew the average. The
recommended method is to take the median value, so as to minimize errors and filter out high-
error readings. This technique also helps to automatically filter out readings of 0.
(p. 26) shows a station that reads the SnowVUE 10 every 5 seconds for 1 minute and
takes the median value from the readings.
SnowVUE 10 Sonic Ranging Sensor
25
