HR: 16:15h
AN: NS14A-02 INVITED    [Abstracts]
TI: Monitoring and Quantifying Subsurface Ice and Water Content in Permafrost Regions Based on Geophysical Data Sets
AU: * Hauck, C
EM: hauck@imk.fzk.de
AF: Institute for Meteorology and Climate Research, University of Karlsruhe/Forschungszentrum Karlsruhe, Postfach 3640, Karlsruhe, 76021, Germany
AU: Bach, M
EM: bach@imk.fzk.de
AF: Institute for Meteorology and Climate Research, University of Karlsruhe/Forschungszentrum Karlsruhe, Postfach 3640, Karlsruhe, 76021, Germany
AU: Hilbich, C
EM: c7hich@uni-jena.de
AF: Geographical Institute, University of Jena, Loebdergraben 32, Jena, 07743, Germany
AB: Based on recent observational evidence of climate change in permafrost regions, it is now recognised that a detailed knowledge of the material composition of the subsurface in permafrost regions is required for modelling of the future evolution of the ground thermal regime and an assessment of the hazard potential due to degrading permafrost. However, due to the remote location of permafrost areas and the corresponding difficulties in obtaining high-quality data sets of the subsurface, knowledge about the material composition in permafrost areas is scarce. In frozen ground subsurface material may consist of four different phases: rock/soil matrix, unfrozen pore water, ice and air-filled pore space. Applications of geophysical techniques for determining the subsurface composition are comparatively cheap and logistically feasible alternatives to the single point information from boreholes. Due to the complexity of the subsurface a combination of complementary geophysical methods (e.g. electrical resistivity tomography (ERT) and refraction seismic tomography) is often favoured to avoid ambiguities in the interpretation of the results. The indirect nature of geophysical soundings requires a relation between the measured variable (electrical resistivity, seismic velocity) and the rock-, water-, ice- and air content. In this contribution we will present a model which determines the volumetric fractions of these four phases from tomographic electrical and seismic data sets. The so-called 4-phase model is based on two well-known geophysical mixing rules using observed resistivity and velocity data as input data on a 2-dimensional grid. Material properties such as resistivity and P- wave velocity of the host rock material and the pore water have to be known beforehand. The remaining free model parameters can be determined by a Monte-Carlo approach, the results of which are used additionally as indicator for the reliability of the model results. First results confirm the good model performance for various field cases in permafrost research. Especially the 2- dimensional monitoring and detection of ground ice and air cavities in the blocky surface layer was substantially improved. Validation of the model results was obtained using borehole and energy balance data from different permafrost sites.
DE: 0702 Permafrost (0475)
DE: 0770 Properties
DE: 0925 Magnetic and electrical methods (5109)
DE: 1621 Cryospheric change (0776)
DE: 1835 Hydrogeophysics
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting