A New Snow Depth Measurement Technique using ICESat-2 SlideRule in the Western U.S.

Thesis (Master's)--University of Washington, 2022Snow depth is highly variable across watersheds, yet most snow depth data in the Western U.S. come from sparse point measurements. The water resources community is in need of more spatially representative snow depth data for improved basin-wide snow depth estimates. The NASA ICESat-2 mission is a polar-orbiting laser altimetry satellite launched in October 2018 with the primary goal of measuring ice sheet mass changes at the poles. Previous studies have shown that standard ICESat-2 data products have the potential to provide snow depth measurements of varying accuracy depending on factors such as surface slope and canopy cover. In this study we show that snow depth measurements can be improved using a new on-demand data processing and customization tool named ICESat-2 SlideRule, through which user-specified processing parameters can be used to produce a custom data product optimized for specific scientific aims outside the original goals of the mission. When combined with snow-off Digital Terrain Models (DTMs) from airborne lidar observations, snow-on ICESat-2 SlideRule observations have the potential to provide a new snow depth dataset across the Western US and the globe. Here we investigate the accuracy of ICESat-2 SlideRule snow depths compared to reference in situ snow telemetry and aerial lidar snow depth observations at two locations with varying terrain characteristics: the upper Tuolumne River watershed, CA and the Methow Valley, WA. We observe strong agreement between the ICESat-2 SlideRule and reference snow depth measurements at both sites, with median residuals of about 0.2 m and 0.4 m in the upper Tuolumne River watershed and the Methow Valley, respectively. Basin-wide aggregation is found to be a better method for ICESat-2 SlideRule calculations than is individual point comparison. Differences in accuracy between sites are attributed to differences in terrain characteristics and the spatial distribution of these characteristics. The ICESat-2 SlideRule data used in this study produced more accurate snow depth results than those found by previous studies using standard ICESat-2 data products in mid-latitude mountainous regions. Therefore, we strongly recommend the use of SlideRule to process ICESat-2 data in such regions and conclude that these data can provide valuable snow depth measurements for areas where high-resolution DTMs are available