Glacier Flow Dynamics from Terrestrial Radar Interferometry: Grenzgletscher, Switzerland

Alpine glaciers are analogues to remote polar ice streams and serve as accessible natural 
laboratories for understanding the key processes driving ice flow. Here, we capture temporal 
variability of surface velocities as a proxy for processes at the glacier bed using a terrestrial radar 
interferometer (GPRI, GAMMA Portable Radar Interferometer). We conducted two field 
campaigns in October 2023 and June 2024 to measure velocity variability over several days at a 
temporal resolution of three minutes. We focus on a steep icefall zone in which the onset of basal 
sliding is hypothesized. A common challenge in processing terrestrial radar data is the 
contribution of atmospheric turbulence to the measured interferometric phase. To reduce this 
effect, we stack 2653 (1420) one-hour interferograms for each of the two field campaigns. After 
stacking, displacement on fixed rock walls is minimal compared to the mean ice velocity. Across 
both time series, we captured velocity variability on daily as well as seasonal time scales. On the 
steep ice fall, mean velocity differences between the fall and spring campaigns show ~30% faster 
flow in the spring season, when more surface meltwater may lubricate the glacier bed leading to 
seasonally accelerated glacier flow. This research highlights the effectiveness and challenges of 
terrestrial radar interferometry and provides valuable information for understanding glacier 
dynamics in alpine environments.