For the mineral exploration in complex terrain areas, the semi-airborne transient electromagnetic (SATEM) technology is one of the most powerful methods due to its high efficiency and low cost. However, since the mainstream SATEM systems only observe the component dBz/dt and the data are usually processed by simple interpretation or one-dimensional (1D) inversion, their resolutions are too low to accurately decipher the fine underground structures. To overcome these problems, we proposed a novel 3D forward and inversion method for the multi-component SATEM system. We applied unstructured tetrahedron grids to finely discretize the model with complex terrain, subsequently we used the vector finite element method to calculate the SATEM responses and sensitivity information, and finally we used the quasi-Newton method to achieve high-resolution underground structures. Numerical experiments showed that the 3D inversion could accurately recover the location and resistivities of the underground anomalous bodies under the complex terrain. Compared to a single component data, the inversion of the multi-component data was more accurate in describing the vertical boundary of the electrical structures, and preferable for high-resolution imaging of underground minerals.

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Electrical anisotropy, manifested as varying resistivities of a medium with the direction of current flow, exists widely in nature. The electrical anisotropy can be divided into microanisotropy and macroanisotropy. The microanisotropy belongs to the attribute characteristics of media that shows anisotropic characteristics in very small scale. The anisotropy studied in geophysics is generally macroanisotropy, which is caused by the tiny isotropic structures that have same orientations, such as layering. Due to the limited resolution of electromagnetic (EM) methods, these tiny structures are generally treated as a whole and replaced by the parameter of anisotropy. These are typical macroanisotropy in EM geophysics. In the past decades, more and more long-period magnetotelluric (MT) signal shows that the electrical anisotropy exists widely in the deep crust and mantle (