Assessing Airborne Radar to Map Glacier Elevations in Alpine Terrain Including Estimated Glacier Volume Change

Alpine glaciers and perennial snowfields (G&PS) are important hydrologically and ecologically, providing meltwater during the hottest and driest summer periods. Climate warming shrinks these natural reservoirs while temporarily providing increased streamflow. To assess regional changes in glacier volume, from which contribution to streamflow can be estimated, I used NASA\u27s Airborne Glacier and Ice Surface Topography Interferometer (GLISTIN). This instrument mapped the surface topography of alpine glaciers; differencing these elevations from historic elevations derived from topographic maps, volume change is calculated. GLISTIN was flown over the glacier-populated mountain ranges of the western U.S. Of the 3289 glaciers and perennial snowfields with at least 1 pixel of GLISTIN coverage, 1770 had coverage ≥ 80%. Modeling shows that about half of the missing data is due to terrain shadowing of the radar and the remainder is likely caused by layover effects due to the steep terrain. Data coverage is increased with more passes of the GLISTIN aircraft. For a single pass about 55% of the data (all terrain) was missing, and for two and four pass mosaics, it was reduced to 30% and 11%, respectively. GLISTIN elevations (3-meter resolution) were compared to lidar elevations over non-glaciated control zones for four regions in the Cascade Range. The mean GLISTIN height-precision, a self-reported value from data processing, over bedrock control zones was between 0.69 ± 0.57 m (standard deviation) and 1.34 ± 1.23 m. The mean elevation difference (GLISTIN minus lidar) for control zones ranged from -0.14 ± 1.78 m to +0.38 ± 1.83 m. Differencing GLISTIN elevations from elevations of the historical National Elevation Dataset for glaciers shows a thinning (and volume loss) over the last ~60 years. The thinning for individual G&PS ranged from -1.28 ± 0.25 m yr-1 to +0.80 ± 0.33 m yr-1 with a median of -0.24 ± 0.20 m yr-1. Results show GLISTIN potential to be a valuable tool for rapidly mapping ice surfaces in the alpine environment