EGU25-19541, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-19541
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
3D Inversion and resolution study of different CS-/RMT transfer functions for different source configurations
Stefan Schöttle1, Maxim Smirnov2, Alexander Grayver1, Maria Smirnova1, Pritam Yogeshwar1, Wiebke Mörbe1, and Bülent Tezkan1
Stefan Schöttle et al.
  • 1University of Cologne, Institute of Geophysics and Meteorology , Geosciences, Germany (stefan.schoettle@uni-koeln.de)
  • 2Luleå University of Technology, Division: Geosciences and Environmental Engineering, Sweden

Over the last two decades, controlled source (CS) electromagnetic (EM) methods using an extended frequency range from 1-1000 kHz have been developed. Controlled sources complement the Radio-magnetotellurics (RMT) method by providing a wider frequency range, a greater depth of investigation and more stable responses. In addition, they remain operational even without radio antennas in the vicinity of the measurement area. While initially CS-/RMT was originally considered only in far-field conditions, it has recently been extended to include data from the intermediate zone, closer to the transmitter. This approach has several advantages over the solemn far-field consideration: (i) beneficial logistics, as there is no need to ensure sufficient source-receiver offsets; (ii) improved signal-to-noise ratio; (iii) combination of the unique resolution properties of CSEM and RMT, among others. Since EM fields in the intermediate zone depend on the source geometry, it is crucial to model the source geometry accurately.

We present a 3D inversion and resolution study for different inductively and galvanically coupled sources for synthetic data. We use (i) conventional CSEM single source configurations and (ii) CS/RMT source configurations with two orthogonal transmitters to provide two polarisations. Due to the lack of sufficiently accurate current measurements in the RMT frequency range, we invert: (i) impedance and tipper, (ii) admittance and (iii) interstationary transfer functions instead of univariate transfer functions. For modelling we use our newly in-house developed software package MR3DMod. The inversion package of MR3DMod follows the recipes of well established codes such as MODEM. The CS 3D forward modelling is based on a secondary field approach including quasi analytical modelling of the primary field. We have extensively tested the stability of the primary field solution for high frequency stability including displacement currents.

Based on our analysis, we are able to make further recommendations regarding high frequency CSEM and CS/RMT survey design. This includes the identification of favourable source configurations for specific shallow targets, such as waste deposits.

How to cite: Schöttle, S., Smirnov, M., Grayver, A., Smirnova, M., Yogeshwar, P., Mörbe, W., and Tezkan, B.: 3D Inversion and resolution study of different CS-/RMT transfer functions for different source configurations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19541, https://doi.org/10.5194/egusphere-egu25-19541, 2025.