Do Grenzgletscher's Dynamics Shift? Insights from Terrestrial Radar Interferometry and Comparative Analyses

We present surface velocity maps of Grenzgletscher (Swiss Alps) obtained by terrestrial radar interferometry and compare them to velocity maps derived in earlier field campaigns to examine changes over time. To obtain recent velocity maps, we installed a Gamma Portable Radar Interferometer (GPRI) near Rotenboden Station facing the Grenzgletscher and collected data for five days in October 2023 with a three-minute sampling interval. From the resulting interferograms, the line-of-sight velocities can be calculated for various time intervals after averaging, which corrects for atmospheric noise. We find high line-of-sight velocities in the area of a steep ice fall, which suggests that the glacier is sliding in this area. We validate with concurrent GPS measurements and compare our velocity maps with those obtained in previous field campaigns, including a similar GPRI survey in 2008 and a survey utilizing unmanned aerial vehicles in 2017. This comparative analysis aims to identify temporal dynamic changes in areas where the various surveys overlap, ranging from sub-daily, to seasonal and yearly time intervals. This work will provide important observational boundary conditions to better understand mechanisms for the onset of basal sliding beneath glaciers in alpine and polar environments.