Estimating snow-water equivalent (SWE) over long mountain transects with snowmobile-mounted GPR

Abstract:

The hydrologic balance in most alpine watersheds is dominated by snowmelt, which provides peak spring runoff and recharges mountain aquifers, contributing to baseflow throughout the year. Measurement of snow-water equivalent (SWE) is necessary for accurate modeling of alpine hydrology but is challenging due to the variability in snow accumulation, ablation and redistribution at scales from microtopography to hillslopes to mountainsides. Here we present a method for imaging snow stratigraphy and estimating SWE over large distances from a ground-penetrating radar system mounted on a snowmobile. We mount commercial GPR systems (500 and 800 MHz) to the front of the snowmobile to provide maximum mobility and ensure that measurements are taken on pristine snow. High-quality images show detailed snow stratigraphy down to the ground surface over snow depths up to at least 8 m, enabling elucidation of snow accumulation and redistribution processes. We estimate snow density (and thus SWE, assuming no liquid water) by measuring radar velocity of the snowpack through migration focusing analysis. Results from the Medicine Bow Mountains, Wyoming, show that estimates of snow density from GPR (0.40±0.15 gm/cm³) are in good agreement with those from coincident snow cores (0.35±0.08 gm/cm³). Using this method, snow thickness, snow density, and therefore SWE can be measured over large areas solely from rapidly acquired common-offset GPR profiles, without the need for common-midpoint acquisition or snow cores.