Investigating firn structures in the Aletch glacier’s accumulation area using Ground Penetrating Radar

The role of firn structure and density in glacier mass balance estimation has been constrained, with studies in alpine conditions primarily limited to models. Our research focuses on understanding firn structures and firn density-depth profiles in the Aletsch Glacier's accumulation area. This is achieved through field methods, Ground-Penetrating Radar (GPR) as a geophysical tool, glaciological methods, and firn compaction models.

We aimed to characterize the firn structure and determine the spatial firn density-depth profiles by estimating electromagnetic wave velocities by identifying reflection hyperbolae via semblance analysis, using data collected with the common midpoint (CMP) method. Three density-depth profiles were obtained at various locations within the accumulation area, providing firn density profiles up to 35 meters deep. Firn compaction models Ligtenberg (LIG) and Kuipers Munnekee (KM), were selected from the community firn models (CFM), to evaluate how well the model results match the observations. These models were adjusted to fit the estimated 1-D firn density profiles from CMP gathered by tuning model parameter coefficients based on regional climatic conditions.

We developed a method to estimate accumulation history by chronologically identifying GPR-derived internal reflection horizons (IRHs) as annual firn layers. This method was validated against estimated snow water equivalent (SWE) from long-term stake measurements. Our findings emphasize the importance of direct measurements, such as snow cores, firn cores, and isotope samples, in identifying the previous summer horizon. We demonstrated the spatial firn density distribution and the glacier's accumulation history over the past 12 years using a 1.8 km GPR transect, supported by CMP-derived density-depth profiles. Our study underscores the potential of integrating GPR, direct measurements, and firn compaction models in monitoring firn structures and density, ultimately enhancing glacier mass balance estimation in future research.