Layered Green function Born approximation imaging method for transient electromagnetic virtual wave fields

In this study, the Born approximation imaging method of transient electromagnetic virtual wave fields is used to linearize the transient electromagnetic virtual wavefield equation through the Born approximation, after which the velocity disturbance is obtained, thereby achieving imaging. The Born approximation uses the half-space Green function, which results in low imaging resolution when the background velocity varies greatly. Starting from the virtual wave field, this paper establishes the Helmholtz equation satisfied by the radiation and the scattering fields, then derives the Green function expression of layered media, and applies it to the Born approximation. The calculation formula of Born approximation conductivity based on the Green function of layered medium and the expression of the velocity disturbance of the scattering field are obtained, and finally the velocity disturbance is used to achieve imaging. Through the experimental calculation of the theoretical model, it is verified that the Born approximation imaging algorithm using the Green function of the layered model can reconstruct the resistivity distribution of the stratum, improve the vertical resolution of the inverse scattering inversion of the Born approximation virtual wave equation, and obtain high-quality imaging. The results of the actual data processing in Gansu Province show that the Born approximation of the layered medium Green function is an imaging method that is quite accurate, stable and practical.