Three-dimensional scalar controlled-source audio-frequency magnetotelluric inversion using tipper data

The configuration of the common scalar controlled-source audio-frequency magnetotelluric (CSAMT) method is a solo finite grounded wire and its measuring data are only a set of orthogonal electric and magnetic field data. The receiving electric field for scalar CSAMT is parallel with the grounded wire, which makes the resolution of the direction perpendicular to the grounded wire unsatisfactory, especially for a complex zone. With the increasing demand of complex geological target exploration, the drawback of scalar CSAMT has gradually aroused people's attention. A well-known solution is adopting tensor CSAMT, which is multi-source and measures more data. However, tensor CSAMT needs a much larger workload and is less efficient than scalar CSAMT. This paper researches the tipper data generated from a scalar CSAMT finite grounded wire. Measuring the vertical magnetic field is the only extra workload. The numerical simulation method is a three-dimensional (3D) staggered-grid finite difference. Then we use tipper data with apparent resistivity and phase data to invert two theoretical models. The inversion method is the limited-memory Broyden-Fletcher-Goldfarb-Shanno (LBFGS). Through forward modeling and synthetic data inversion tests, we prove that adopting an apparent resistivity and phase with tipper data can enhance the resolution of scalar CSAMT. Our research shows that using tipper data in scalar CSAMT is useful for electromagnetic exploration.