VOLUME CHANGE ESTIMATES FOR GLACIERS IN THE WESTERN UNITED STATES USING AIRBORNE RADAR

Glaciers are important to alpine hydrology, ecology, and serve as an important indicator of climate. Whereas field measurement of glacier mass balance may be the most useful for understanding the connection between climate and glacier change, this approach is not feasible for assessing such changes over broad regions. An alternative approach is to measure glacier volume change from differences in glacier topography over time. We utilize a novel instrument to rapidly map surface topography, NASA’s Airborne Glacier and Ice Surface Topography Interferometer (GLISTIN-A), a Ka-band synthetic aperture radar (SAR). Advantages of SAR, compared to other remote methods, are its all-weather capability and rapid survey of large areas. To estimate volume change digital elevation models (DEMs) derived from GLISTIN-A are differenced from historical DEMs.

In September 2016 GLISTIN-A was flown over the glacier-populated regions in six states of the western US, exclusive of Alaska. Due to complex terrain, the entire surface of a glacier could not always be mapped and about half of the surveyed glaciers had > 80% coverage. The root mean square error (RMSE) between GLISTIN-A and independently flown lidar was 0.89 m for glacial surfaces on Mt. Adams, WA. Preliminary results for glaciers >80% showed a volume change of -4.45 ± 1.12 km³ over the last 40+ years. The total specific volume change was -15.0 ± 3.8 m. Thickness change per year ranged from -1.53 ± 0.19 m yr^-1 to +0.22 ± 0.04 m yr^-1 with a median change of -0.28 ± 0.07 m yr^-1. Glaciers in the Beartooth-Absaroka experienced the greatest average loss, -0.58 m yr^-1. Initial results highlight the promising potential for using GLISTIN as a tool to monitor changes of alpine glaciers.