Summary The semi-airborne transient electromagnetic (TEM) method enables rapid subsurface exploration in regions with complex terrain. However, topographic effects often degrade the accuracy of inversion and imaging results, making it essential to incorporate terrain information into the forward modeling process. Conventional modeling approaches typically rely on fine discretization near terrain interfaces, which leads to high computational costs. To improve computational efficiency, we propose a novel TEM forward modeling method for undulating terrain based on equivalent parameters defined on regular grids. The proposed method eliminates the need for mesh refinement at terrain interfaces, thereby substantially reducing computational resource consumption while preserving the accuracy of three-dimensional topographic modeling. An equivalent parameters formulation for anisotropic media is derived. Furthermore, when the transmitter current is predominantly confined to the horizontal plane, the anisotropic representation reduces to an isotropic form. Numerical experiments demonstrate that the proposed method significantly reduces computational requirements while maintaining an acceptable level of accuracy.
Zhong et al. (Thu,) studied this question.