Snow measurement by GPS interferometric reflectometry: An evaluation at Niwot Ridge, Colorado

Snow is a critical storage component in the hydrologic cycle, but current measurement networks are sparse. In addition, the heterogeneity of snow requires surveying larger areas to measure the areal average. We presented snow measurements using GPS interferometric reflectometry (GPS-IR). GPS-IR measures a large area (~100m ²), and existing GPS installations around the world have the potential to expand existing snow measurement networks. GPS-IR uses a standard, geodetic GPS installation to measure the snow surface via the reflected component of the signal. We reported GPS-IR snow depth measurements made at Niwot Ridge, Colorado, from October 2009 through June 2010. This site is in a topographic saddle at 3500m elevation with a peak snow depth of 1.7m near the GPS antenna. GPS-IR measurements are compared with biweekly snow surveys, a continuously operating scanning laser system and an airborne light detection and ranging (LIDAR) measurement. The GPS-IR measurement of peak snowpack (1.36-1.76m) matches manual measurements (0.95-1.7m) and the scanning laser (1.16m). GPS-IR has RMS error of 13cm (bias=10cm) compared with the laser, although differences between the measurement locations make comparison imprecise. Over the melt season, when the snowpack is more homogenous, the difference between the GPS-IR and the laser is reduced (RMS=9cm, bias=6cm). In other locations, the GPS and the LIDAR agree on which areas have more or less snow, but the GPS estimates more snow on the ground on tracks to the west (1.58m) than the LIDAR (1.14m).