Interpretation of controlled source radiomagnetotelluric data in the frequency range 1 kHz - 1 MHz using multidimensional conductivity models

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Controlled Source Radiomagnetotellurics (CSRMT) is a new and innovative electromagnetic method for shallow subsurface investigations down to roughly 100 m depth depending on the subsurface resistivity. In this project, tensor CSRMT measurements will be realized for the first time in the extended frequency range from 1 kHz to 1 MHz using a prolonged electric dipole source. Two survey will be conducted on two selected test areas in Russia. CSRMT far field data using such an extended frequency range and dipole source will also be interpreted for the first time by a 3D inversion. A rectangular signal with base frequencies between 0.1 kHz and 150 kHz will be injected through two approximately 700 m long grounded electric dipoles located perpendicular to each other. Time series of the electric and magnetic fields in the far and near field of the transmitter at spatially distributed receiver-locations will be observed. Full impedance and tipper transfer functions will be derived using a bivariate time series analysis. The spatially distributed far field CSRMT data will be interpreted by 2D and 3D inversion calculations. Conventional RMT measurements will be carried out during the time the transmitter is not active to increase data coverage. The derived conductivity 3D CSRMT model of the far field and the model derived from the RMT data will then be used to interpret the transfer functions of the near field by using the trial and error approach and 3D forward calculations. The investigated area close to St. Petersburg is a landfill area where the aquifer contamination will be investigated, whereas the survey area close to Moscow is a paleo-valley in which local high resistive sand lenses are embedded. These paleo-valleys are associated with deposits of mineral resources. Previous geophysical measurements and modellings (DC, RMT & Seismic) on these survey areas will be used as constraints in the multidimensional CSRMT modeling. Both targets are in a depth of about 15m and can be ideally detected by the CSRMT method.