Ground Penetrating Radar for Measuring Snow Water Equivalent in Wet Snow

Thursday, 18 December 2014
Mark Robertson and Hans-Peter Marshall, Boise State University, Boise, ID, United States
Accurate estimates of snow water equivalent (SWE) are important for mountainous areas where snow accounts for the majority of the annual precipitation. Radar has been proven to be an effective tool for estimating SWE in dry snow but can be challenging in wet snow packs. Liquid water rapidly attenuates the radar signal and decreases the velocity, leading to large errors in SWE estimates if not accounted for. Pulsed radar in the 1-6 GHz range has been relatively unexplored for studying snow due to only recently being available commercially, and offers ~6 cm vertical resolution while using frequencies that are low enough to effectively penetrate wet snow. Field observations from a fixed post were performed continuously through a range of liquid water content values during melt in spring 2014. Since liquid water causes frequency-dependent attenuation in the 1-6 GHz range, the difference in frequency content of the source signal and ground surface reflection can be used to estimate the complex permittivity of the snow through empirical relationships. The snow depth is known from the snow surface reflection from the fixed post and is used to estimate radar velocity. Snow density is estimated from empirical relationships with permittivity, and SWE estimates are made that account for liquid water in the snow. The field data are compared to in-situ wetness measurements in a nearby snow pit. A 1D reflectivity model is used to characterize the theoretical ability of the 1-6 GHz pulsed system to estimate SWE in a mountain snow pack for ranges of snow depth and signal loss due to liquid water content and reflections from internal layers.