Spatiotemporal Variations in Liquid Water Content in a Continental Seasonal Snowpack Measured by Ground-penetrating Radar

Seasonal snow provides water resources for an estimated 1.2 billion people globally, yet no current satellite remote sensing method can measure snow water equivalent (SWE) on global scales. L-band (1-2 GHz) Synthetic Aperture Radar (SAR) is a promising approach for measuring SWE at high spatial resolution in complex topography, yet key details remain unresolved, particularly related to wet snow. The planned 2021 launch of the NASA-ISRO NISAR satellite mission provides further motivation for an improved understanding of the application of L-band SAR to measure SWE. Here, we use 1 GHz ground-penetrating radar (GPR) to study the spatiotemporal variability of liquid water content (LWC) development in a continental snow regime and examine the influence of slope, aspect, and canopy cover on LWC development. To meet our objectives, we collected weekly to biweekly GPR surveys from May to June 2019 at Cameron Pass, CO, a high-elevation site (>3500 m). Transects (~1 km distance) contained 0-70% canopy cover on south, flat, and north facing aspects and were surveyed three times per survey date with ~2 hours separating each survey. GPS locations of GPR traces were post-processed (0.5-2 m accuracy) to ensure high quality comparisons between repeated surveys. We derive radar velocities from GPR travel times and coincident snow depth measurements from snow probes and repeat terrestrial LiDAR scans. Radar velocities are used to invert for LWC, which are subsequently compared to pit-observed LWC observations using a SLF Snow Sensor.