3D time-domain airborne EM forward modeling with topography

• Published in: Journal of applied geophysics Vol. 134; pp. 11 - 22
• Main Authors: Yin, Changchun, Qi, Yanfu, Liu, Yunhe, Cai, Jing
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2016
• Subjects: Airborne EM, time-domain; Edge finite-element method; Local mesh; Topography; Unstructured mesh; Unstructured mesh; Local mesh; Edge finite-element method; Airborne EM, time-domain; Topography
• ISSN: 0926-9851; 1879-1859
• DOI: 10.1016/j.jappgeo.2016.08.002

The time-domain finite-difference method has been widely used in simulation of the electromagnetic field diffusion. However, this method is severely restricted by the mesh size and time step. To overcome the defect, we adopted edge finite-element method for unstructured grid with Backward Euler method to conduct 3D airborne electromagnetic forward modeling directly in time-domain. The tetrahedral meshes provide the flexibility required for representing the rugged topography and complex-shape anomalous bodies. We simulated the practical shape, size and attitude of transmitting source by directly setting the loop into the well-generated grids. The characteristic properties of vector basic functions guarantee automatic satisfaction of divergence-free property of electric fields. The Galerkin's method is used to discretize the governing equations and a direct solver is adopted to solve the large sparse linear system. We adopted an algorithm with constant step in each time segment to speed up the forward modeling. Further we introduced the local mesh strategy to reduce the calculations, in which an optimized grid is designed for each sounding station. We check the accuracy of our 3D modeling results against the solution for a homogenous half-space and those for a buried vertical plate model using integral equation. The numerical experiments for a hill, a valley or undulating topography model with buried anomalous bodies were further studied that show that the topography has a serious effect on airborne EM data. [Display omitted] •Edge finite-element method using unstructured grids•Backward Euler scheme for airborne time-domain EM modeling•Local mesh strategy for unstructured grid•Modeling for 3D topographic earth•Handling of EM transmitters of arbitrary shape and attitude