Revealing the Recent Height Changes of the Great Altesch Glacier Using TanDEM-X DEM Series

Monitoring glacier mass balance is essential for understanding glacier-climate interactions and predicting water resources management. As the largest glacier in the Alps, the Great Aletsch Glacier has a length of 22 km and covers about of 78 km2. It contains 20% of the entire Swiss ice mass, and thus plays significent role in understanding the dynamics of glacier mass change in this region. Because of its significance, the TanDEM-X satellite mission has selected the Great Aletsch Glacier as a super-testsite and has collected abundant single-pass bistatic Synthtetic Aperture Radar (SAR) data over the glacier since 2011. Leveraging these TanDEM-X satellite data, we generated 124 digital elevation models (DEMs) from the Coregistered Single-look Slant Range Complex (CoSSC) data product, calculated glacier elevation changes between 2011 and 2022, and quantified the temporal dynamics of the mass balance of the Great Aletsch Glacier. The DEMs were generated using an iterative approach. We initially used an external DEM (swissALTI3D) as the reference for geocoding and interferogram simulation. The simulated interferogram was subtracted from the interferogram between the CoSSC data pairs to generated a differential interferogram. The unwrapped phase in the differential interferogram corresponds to the height difference between the TanDEM-X measurements and the reference DEM, and thus we converted the phase into differential height to update the reference DEM. At this point, the updated reference DEM was accepted as the final product if the mean and standard deviation of the differential height met with the convergence criteria, otherwise it was used as the new reference in the subsequent iteration. Following the DEM generation, we used xDEM python package to analyze the DEM series. We first measured the elevation change by differencing two DEMs, then used a local hypsometric interpolation method to fill the dDEM voids within the glacier outline, and finally integrated the elevation difference over the glacier to calculate the ice volume and mass change. Our results revealed a consistent glacier-wide height loss of 1 ma−1 on average between 2011 and 2022, corresponding to a cumulative volumetric ice loss of 79×106 m3 a−1 and mass loss of 68 Mt a−1 (assuming a mean ice density of 850 kgm3). Notably, the Konkordiaplatz region, situated at elevations between 2600 and 2800 meters, exhibited an average elevation loss of 2.3 ma−1, whereas the Glacier tongue region, ranging in elevation between 1900 and 2100 meters, witnessed an average elevation loss of 5.2 ma−1. In summary, our results have provided valuable insights into the dynamic changes of the Great Aletsch Glacier by analyzing the abundant TanDEM-X data. The detailed spatiotemporal of our work advanced our understanding of glacier recession in the Alps under the climate change