Dr Christin Hilbich (Department of Geosciences, University of Fribourg)
22nd February 2012, 11 h
Faculty of Sciences, University of Lisbon, room C8-2-11
In high mountain regions, climate change does not only affect the glaciers or the duration and thickness of the snow cover, but also the temperature and ice content of the permanently frozen ground, called permafrost. Within the Swiss Permafrost Monitoring network PERMOS the thermal and kinematic monitoring activities of mountain permafrost are therefore complemented by geophysical monitoring in order to observe long-term changes in the ice content of different landforms.
The application of geophysical techniques has a long tradition in the research of frozen ground. Especially electrical and seismic methods are employed to detect, monitor and characterize ground ice occurrences. Electrical resistivity tomography (ERT) monitoring started already in 1999 in the Alps and has become operational since 2006. Until now, at more than 10 permafrost sites in the Swiss Alps regular ERT measurements are carried out, at one site even with daily resolution. Further, since 2007 annual refraction seismic measurements are conducted in parallel to the ERT monitoring at some of the sites, providing valuable complementary information regarding changes in ice and water content in the ground.
In addition, the so-called 4-phase model (4PM) provides estimates of the volumetric fractions of the subsurface constituents (ice, water, and air content) from tomographic electrical and seismic images. Major drawbacks of the current 4PM comprise the unsatisfactory discrimination between rock and ice and its under-determinedness, requiring the prescription of the porosity and further parameters. The model will be presented and results and its reliability will be discussed. Current work is related to the validation of the model results with ground truth data and with the improvement of the model performance by combining the 4PM with a similar but complementary approach developed at the Instituto Dom Luiz for an improved determination of ice and water contents in permafrost regions.