Ultrasonic Snow Depth Sensor Accuracy, Reliability, and Performance

The Natural Resources Conservation Service Snow Survey Data Collection Office (DCO) in Boise, Idaho began installing Judd Communications Snow Depth Sensors in the late-1990s. Since that time the number of SNOTEL sites in the DCO with snow depth sensors has increased to 76 out of a total of 117 sites. Over the years 348 depth sensor ground truth measurements have been made each time snow water equivalence was measured at a site. Telemetered SNOTEL snow depths compare very well with manually sampled depths with a high degree of accuracy (R2 = 0.98). To test the reliability of the sensor during the accumulation phase of winter, hourly data between 12/1/2007 - 3/20/2008 were analyzed to determine the number of missed measurements (full-scale readings). Results showed that out of 228,798 hourly readings, 14% were full-scale. No clear relationship was found between the age of the depth sensor and its reliability. In 1999 the Idaho DCO began editing daily snow depth data. This editing process has provided an opportunity to observe the performance of depth sensors. Performance related to damaged transducers, transducer obstruction, wind effects, sensor misalignment and storm effects are discussed.