Snow depth measurement using ultrasonic sensors and temperature correction

Snow depth is commonly measured by visual observation, thus limiting the availability and frequency of observations in remote areas. Ultrasonic depth sensors can overcome this limitation by allowing automated snow depth measurement at remote, unstaffed sites. An ultrasonic sensor determines the distance between a surface and itself by measuring the transmission time of a sound pulse reflected off the surface. The sensors are used in industry and water resources management for a variety of purposes. Measurement errors arise both from temperature-based changes in the speed of sound and from the effect of temperature on the electronics of the sensor. These problems may be reasons that the instrujments have not seen widespread use in snow hydrology. We installed two sensors, one with on-board temperature compensation and one without, to follow changes in snowpack depth during the winter of 1993in California's Sierra Nevada. Sensor depths agreed well with daily visual observationjs, but depth flucuations, measured quarter-hourly, were evident with both sensors and correlated to changing air temperature. Air temperature waw measured independently at the site, and two algorithms were designed that used air temperature or air and instrument temperature to remove the spurious depth flucuations.