Gravimetric Investigations at Vernagtferner

摘要

The globally observed melting of mountain glaciers is an indicator of local and regional effects of climate change. From the observational point of view, two research questions need to be answered for individual glaciers, namely how much mass is lost or gained from year to year and how much mass is there in total, i.e., how thick is the glacier. There exist various geophysical/glaciological methods for estimation of mass balance and thickness of mountain glaciers. Most of these methods are geometric in nature and not directly sensitive to mass. In contrast, gravimetry provides a direct measure for mass distribution and mass transport. Satellite gravimetry has proven to provide valuable information on regional to global scales. However, the limited spatial resolution does not allow to infer mass balance or ice thickness of individual mountain glaciers. Therefore, the Bavarian Academy of Sciences and Humanities has set up an observational program at Vernagtferner in the Austrian Alps, to test terrestrial gravimetry for small scale glaciological applications. The work reported in the present paper is conducted in collaboration with the Technical University Munich and the German Federal Agency for Cartography and Geodesy. The results are based on 5 years of repeated relative gravimetry and a first absolute gravity campaign conducted with an A10 instrument. We show, that gravimetric observations can be used to constrain glacier thickness as well as temporal mass variations along various profiles over the glacier. Thereby, reaching the target accuracy of 5-10μ Gal seems to be feasible, at least what the internal accuracy of individual relative gravimetry sessions is concerned. The results also underline the importance of carefully checking instrumental parameters in order to reach such a demanding accuracy in absolute sense and to guarantee stability of long-term time series.