Three-Dimensional Transient Electromagnetic Modelling and Inversion Using the Octree-Based Vector Finite Element Method

Summary 3D transient electromagnetic (TEM) modelling and inversion has been continuously developed in the last decade, together with the undergoing rapid developments in computational resources. In this work we present an efficient and practical finite element 3D implementation, applicable to both airborne and ground-based TEM, developed with an octree-based hexahedral meshing that implements topography through a mesh deformation. This new implementation is compared to both 1D modelling and 3D finite-element tetrahedral modelling, in terms of accuracy, speed and memory requirement and inversion results on synthetic modelling. Furthermore, a verification of the topography implementation obtained comparing results with and without deformation is presented. Overall, the octree-based implementation is ~5x faster than tetrahedral simulation, while the memory cost in the forward modelling process is ~6x smaller.