The influence of thermal, hydrologic, and snow deformation mechanisms on snow water equivalent pressure sensor accuracy

Abstract

AbstractA 5 year field study was conducted to determine the mechanisms that cause snow water equivalent (SWE) pressure sensor measurement errors. The objective is to establish design and installation criteria to develop an accurate electronic SWE pressure sensor that minimizes errors. We monitored a 3 m snow pillow and installed three prototype electronic SWE sensors of our own design to examine how SWE errors occur. We also measured the heat flux through the prototype sensors and the soil, snow temperature, soil moisture content, and soil thermal conductivity. The SWEs of snow cores were used to assess the accuracy of the snow pillow and prototype sensors. Experimental results indicate that SWE measurement errors occur only when the snow–SWE sensor and/or the snow–soil interfaces are at the melting temperature. The magnitude of SWE errors is related to the diameter of the sensor and the difference in heat flux through the sensor and the surrounding soil. SWE over‐measurement errors occur when the heat flux through the sensor is less than through the surrounding soil, producing a snowmelt rate on the sensor that is less than on the adjacent soil. SWE under‐measurement errors occur when the heat flux through the sensor is greater than through the surrounding soil. The most severe SWE measurement errors occur during the transition from winter to spring, when the snow cover first reaches an isothermal condition causing a maximum difference in snowmelt rate between an SWE sensor and the surrounding soil. SWE measurement errors are reduced by increasing the SWE sensor diameter, matching the thermal properties of the soil and SWE sensor, allowing water to flow through the sensor, and using a surface cover to diffuse heat into the adjacent soil. SWE measurement errors relax through snow creep mechanisms that redistribute the snow load equally between the sensor and surrounding soil. Published in 2002 by John Wiley & Sons Ltd.