Controlled Source Radiomagnetotelluric Method Applications in Near Surface Geophysics

This thesis deals with the application of the newly developed controlled source radiomagnetotelluric (CSRMT) method in near-surface geophysics. There are three field experiments discussed in this thesis with different objectives and challenges. The CSRMT method with a horizontal electric dipole as a source is a new and innovative method of near-surface geophysics which development started at around 2010. The transmitter in the CSRMT system generates rectangular signals operating in frequency band 1 - 150 kHz and is then connected to a grounded horizontal electric dipole with a length between 100 - 1000 m. The advantages of the rectangular signals produced by the transmitter that their odd harmonics can be received along the main frequencies. Therefore, by only using 3 - 4 main frequencies, all the CSRMT frequency ranges can be fulfilled on one sounding. Furthermore, the new developed 5 channel CSRMT receivers enable us to estimate the impedance data (apparent resistivity and impedance phase) in tensor form and also to extract the tipper data. During this project, a new processing algorithm was also developed to process the data in both scalar and tensor (apparent resistivity and impedance phase) and also to estimate the tipper data. The first measurement was carried out in Vuoksa Region around 100 km north of St. Petersburg, Russia in May 2015. The main aim of the survey was the detection of buried faults with the CSRMT method in the far-field zone. The 2D conductivity structures in the far field profile of the survey area are known from geology and mainly consist of crystalline bedrock covered by thin (5 - 10 m) sediments. The profile was also extended to the source, where the plane wave approximation fails. The data from all the field zones were successfully modelled and interpreted using 2D conductivity model including the source. The second measurement was carried out in Krauthausen (near Aachen), Germany in June 2016. The objective of the survey is to study the conductivity distribution in the hydro-geological test area with CSRMT method. The survey area (on the receiver site) has been studied intensively by many geophysical methods. From the previous DC and RMT measurements, it is assumed that the survey area has 1D conductivity structure down to 20 m. However, both on transmitter and receivers site are contaminated heavily by cultural noises such as pipelines, powerlines, and railways. It is important to understand the effect of cultural noise on CSRMT data to know the limitations of the CSRMT method since it is now hard to find a place without any cultural noises except for very remote areas. One of the effects of cultural noise (pipeline) is current channelling, where the current density flows in one particular direction since the pipeline is much more conductive than the surrounding regardless the polarizations of the injected currents. This current channelling results in shifted zones (or transmitter), from far-field zone to near-field and transition zone. In this case, the measured data can only be interpreted by considering the buried pipeline as the source. The third measurement was carried out in Radevormwald (near Wuppertal), Germany in May 2017. The objective of the survey is to investigate probable hydrocarbon contamination in Luftsportverein (LSV) Radevormwald Germany around the simple filling station. The system of the filling station in the LSV Radevormwald is a simple one. The fuel dispensers are placed above the ground. In the past, there was no concrete on the top of the filling stations to cover the ground from possible spill to the ground when the plane was refuelled. After analysing the data, the hydrocarbon contamination was not found