High-Accuracy 3-D TEM Forward Modeling Using Adaptive Finite Element Method

The accurate and efficient forward modeling of the transient electromagnetic (TEM) method requires proper mesh generation, which influences both calculation speed and response accuracy. This article presents a 3-D TEM forward modeling method that achieves high accuracy by using a frequency-to-time domain transformation strategy and adaptive mesh refinements in the frequency domain. Specifically, an interpolation-based Fourier transform method is employed to reduce the number of computed frequencies in the frequency domain, resulting in significant efficiency improvement without compromising accuracy. Furthermore, the method incorporates unstructured tetrahedral meshes and an adaptive finite element (FE) algorithm based on posterior error estimators to enhance the accuracy of the frequency-domain response calculation. The proposed method is applied to the widely used long-offset TEM (LOTEM) system. The accuracy of the method is verified by comparing the simulated response of a layered model with the analytical solution. In addition, the effectiveness of the algorithm is tested using three 3-D models. Cross-validation results with other popular open-source codes demonstrate that the proposed method can achieve high accuracy and efficiency for both simple and complex models.