The focus of this thesis is the derivation of an independent multidimensional resistivity model utilising land based controlled source electromagnetics (CSEM) with resolution to conductive structures down to 1 km depth. Data is evaluated in both, time and frequency domain. Since the resistivity distribution is strongly multidimensional, besides conventional 1D inversion methods, 2D inversion techniques are applied to the dataset.
The objective of the BMBF funded DESMEX (Deep Electromagnetic Sounding for Mineral Exploration)
project is the development of an electromagnetic exploration system which can be used for the detection and
assessment of deep mineral resources. In order to obtain a high data coverage as well
as a high spatial and depth resolution, airborne and ground based methods are combined in a semi-airborne concept. In the framework of the DESMEX
project, the University of Cologne conducted large scale ground based long offset transient electromagnetic (LOTEM)
measurements along an 8.5 km long transect in a former mining area in eastern Thuringia, Germany. Within the LOTEM validation study, an independent multidimensional resistivity model of the survey area was derived, which serves as a reference
model for the semi-airborne concept developed within DESMEX and is eventually integrated into a
final mineral deposition model. Utilising in total 6 transmitters in broadside configuration, data at 170 electric field stations were recorded during two large scale
LOTEM surveys. In addition, a full component magnetic field dataset was acquired with SQUID
sensors using a dense station spacing along the transect. For a preliminary evaluation, conventional 1D techniques are applied to the dataset. The individual switch on transients of the electric field can be explained by a 1D approach, the obtained models however indicate a strong multidimensional subsurface with rather large variations in resistivity. For further interpretation, the LOTEM data is analysed in frequency domain. Obtained 1D and 2D inversion models
of the electric field component in frequency domain are in a good agreement with the time domain results. Subsequently, a joint multidimensional inversion of the full dataset in frequency domain was carried out, including electric and
magnetic field data. Derived 2D inversion models are discussed in terms of sensitivities and resolution capabilities. Shallow high conductive structures are well comparable to inversion results from other conducted reconnaissance surveys and the semi-airborne CSEM model. The dominant conductivity structures can be linked to the occurrence of Silurian graptolite shales
