Full waveform inversion of transient electromagnetic data in the time domain

Abstract

Quasi-seismic imaging is a popular form of electromagnetic imaging technology. In most cases, it is considered that it will yield more obvious layered characteristics if the electromagnetic response is transformed into the virtual wave domain. However, the time profile of virtual wave cannot effectively show the underground electromagnetic structure before migration. In this paper, we make an improvement to process the virtual wave, by applying the full waveform inversion method, with the steps detailed as follows: (1) we use the truncated singular value decomposition method to transform the transient electromagnetic response to the virtual wave field. (2) Using the FDTD method, we calculate the virtual wave field according to the resistivity model, then use the shearlet transform to remove the direct wave. (3) We use a least square equation between the virtual wave and transformed virtual wave to express the problem of full waveform inversion. Next, we apply one of steepest descent methods—the Marquardt approach—to obtain the optimal underground conductivity information. Finally, we use the synthetic and field data to show the accuracy and rationality of the method proposed in this paper.