Split-step Fourier migration of TEM pseudo wavefields via enhanced time-sweep wavefield transformation

Abstract

The ground-airborne transient electromagnetic (GATEM) method is a crucial technique in geophysical exploration. However, conventional imaging methods often struggle to resolve detailed subsurface geological interfaces, limiting their effectiveness in complex environments. To address this limitation, this study implements a migration imaging technique for pseudo wavefields in transient electromagnetic fields of the grounded wire sources, based on the principles of split-step Fourier migration imaging. Additionally, an improved method is proposed for the inverse transformation from the diffusion field to the pseudo wavefield, which leverages the correspondence between diffusion time and virtual time to convert TEM diffusion field data into a pseudo wavefield within the time-sweep wavefield transformation framework. This approach significantly enhances the stability of the inverse transformation by reducing the condition number of the kernel matrix in each time window. The proposed method is validated using synthetic data from uniform half-space, layered, and mining area models. Furthermore, a comparison with conventional one-dimensional inversion using a three-layer model demonstrates our method's superior interface resolution and computational efficiency. Application to field data from a mining area in Gansu Province successfully delineates low-resistivity anomalies consistent with known geological information, confirming the method's practical feasibility for identifying subsurface structures and electrical interfaces.