Progress of the pseudoseismic imaging technology for transient electromagnetic method

The transient electromagnetic method (TEM) has been widely applied in metal mineral detection and engineering geology investigation. While mapping the resistivity distribution through the inversion of the TEM data, the subsurface structure of conductivity can be revealed by converting TEM data to the pseudo wavefield. The wavefield transform method is consequently an effective way to highlight the geoelectric structure. However, this field inversion belongs to a first-class Fredholm integral, which is a typical ill-posed problem. So, the key problem of wavefield transform is how to get a pseudo wavefield with proper resolution and stability. This paper first analyzes some traditional TEM imaging algorithms, including aspects such as time-frequency equivalent conversion, wavefield transform, and the Kirchhoff integral imaging and swept time transformation algorithms. Then, this paper concludes with some methods that can improve the inversion results resolution of wavefield transform. To obtain high-quality electromagnetic pseudo wavefield profiles, additional technical methods, such as Born approximation imaging, pulse spectrum inversion and full waveform inversion, are used in the inversion interpretation of electromagnetic field.