Joint application of ground-based transient electromagnetics and airborne electromagnetics

Abstract

The focus of this thesis lies on the joint application of ground-based and airborne electromagnetic methods for the investigation of a glacial valley. For the first time two different airborne electromagnetic (AEM) surveying methods were employed to determine the resistivity structure of a single geological target: the frequency-domain helicopter-borne electromagnetic (HEM) system operated by the Federal Institute for Geosciences and Natural Resources (BGR), Germany, and the time-domain SkyTEM system developed at the University of Aarhus, Denmark. For verification of the airborne results, ground-based transient electromagnetics (TEM) and 2D resistivity surveying were also performed. The target survey area was the Cuxhaven valley in northern Germany, a significant local groundwater reservoir. The course of this buried valley was revealed by drillings, and the shape determined by reflection seismics along several transects across the valley. Electrical and electromagnetic methods were applied to investigate the structure of the valley fill, consisting of gravel, sand, silt and clay. Here, the extension and the thickness of clay layers are of particular interest. They have a low hydraulic permeability and often serve as protection for underlying aquifers against pollution from the surface ...