Assessing GLISTIN-A to Map Alpine Glacier Surfaces to Estimate Glacier Volume Change

Abstract:

Volume assessments of glaciers and perennial snowfields (G&PS) are important to alpine hydrology, global sea level rise, hazard mitigation, as well as serving as an indicator of climate change. Measurements of glacier volume change are challenging due to the remoteness and a large number of G&PS in any given region. The only practical method to capture changes across a region is remote sensing. Optical remote sending is limited to cloudless daylight conditions, a problem in commonly cloudy alpine environments. Synthetic aperture radar is an attractive alternative for its all-weather, day-night capabilities. To minimize the difficulties in coverage and terrain effects inherent in satellite SAR platforms, we employ a novel approach using NASA’s Airborne Glacier and Ice Surface Topography Interferometer (GLISTIN-A) to map the surface topography of glaciers. To estimate volume change we differenced the elevations derived from GLISTIN-A from historic digital elevation models. Here we evaluate the performance of GLISTIN-A, flown in September 2016, in an alpine environment.

Of the 3389 G&PS surveyed by GLISTIN, 1770 had coverage of ≥ 80%. The missing data is thought to be due to radar shadowing and layover effects in the steep terrain. The magnitude of missing data is reduced when elevations from multiple flights are mosaiced together. About 55% of the glacier coverage was missing for a single flight pass compared to 30% and 10%, for two flight and four flight mosaics, respectively. Comparison of GLISTIN-A elevations (3-meter spatial resolution) collected during a single flight pass, to lidar elevations of non-glaciated control zones near Mount Adams, WA, yielded a root mean square error (RMSE) of 3.12 m. Surfaces facing away from the GLISTIN-A had a higher RMSE (4.54 m) than surfaces facing towards the instrument (1.22 m). Additionally, RMSE increased with surface slope, 1.62 m for slopes between 0° and 10°, and 9.23 m for slopes 60° to 70°. Elevation differencing from historic maps show a volume loss of -6.36 ± 1.41 km³ over the last 40+ years with a total specific volume change of -14.6 ± 6.4 m with a median change of -0.24 ± 0.20 m yr^-1. These results suggest promising potential for using GLISTIN-A for mapping glacier surface topography for glacier change studies.