Permafrost is usually not observable at the surface without measurements. Direct measurements of ground temperature in boreholes are not representative for a larger area to characterize the spatial distribution of permafrost. Hence, geophysical methods that provide quasi-continuous properties of the subsurface have been proposed over the last decades to gain information about the spatial and temporal evolution of permafrost processes. Geophysical methods such as electrical and electromagnetic, seismic and gravimetric techniques have been efficiently used to determine the depth of the active layer and the approximate thickness of the permafrost.
Electrical and electromagnetic methods are particularly relevant taking into account the contrasting electrical properties of ice, water and lithology. However, in many cases the interpretation of the subsurface electrical resistivity is ambiguous, since air and ice and also certain rock types exhibit similarly high electrical resistivity values. Therefore, additional information is needed to improve the quantification of the ice content within the subsurface.
The project focuses on a novel geophysical methodology based on the measurement of electrical resistivity and induced polarization (IP), as ice exhibits a characteristic induced electrical polarization response. Additionally time-domain EM (TEM) induction measurements are used for the extraction of the IP responses. IP measurements are conducted over a broad range of frequencies (in the so-called spectral IP (SIP)), to assess the frequency dependence of the IP.
A combination of field- and laboratory-based studies increase hereby the reliability of the ground ice quantification.