GNSS-based Observation of seasonal acceleration at 79°N Glacier (Greenland) 

The 79° North Glacier (Nioghalvfjerdsbrae, 79NG) is one of three glaciers with a floating tongue in Greenland. Recent investigations indicate an increased subglacial discharge due to a considerably enlarged area of summer surface melt due to the warming of the atmosphere, resulting in increased water input to the base of glaciers. Consequently, ice velocities measured at the surface respond directly to changes in water pressure, revealing detailed insights about the ice dynamics. Global Navigation Satellite System, like GPS and Galileo, can observe ice velocities with high temporal resolution in horizontal and vertical directions. We will present results from the 2022-2023 GNSS measurement campaign where two tinyBlack GNSS receivers were installed at 79NG. Firstly, data quality regarding common indicators like the number of tracked satellites, signal strength, and multipath will be discussed. Secondly, variations in the ice reflection characteristics will be presented based on the GNSS-reflectometry technique. The final processing was carried out as kinematic precise point processing (sampling rate 30s) using GFZ’s processing software EPOS.P8 and GFZ’s operational GNSS products. Thus, thirdly, the derived time series will be discussed with a focus on short-term variations in the surface velocity. We can link speed-up events in July 2022 to rapid lake drainage using optical satellite imagery and interferometrically derived digital elevation models.