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Airborne EM Modelling for an Anisotropic Earth Using Spectral Element Method
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 79th EAGE Conference and Exhibition 2017, Jun 2017, Volume 2017, p.1 - 5
Abstract
Though the anisotropy exists popularly in the earth, it is frequently neglected both in geophysical data interpretation and in modelling. However, negligence of the electrical anisotropy can have a serious influence on near-surface prospecting, like airborne electromagnetic (AEM), especially in areas where the underground bears well-developed stratification. In this paper, we first put forward a modelling algorithm, named spectral element method (SEM), for airborne EM modelling for a three-axis anisotropic earth. SEM is a technique based on weighted residual method. The latter uses a polynomial basis function for SEM, which can achieve a high accuracy when increasing the polynomial order. We take as example a horizontal coplanar coil (HCP) of an AEM system to check the accuracy of our algorithm for anisotropic models and we compare the 3rd and 4th order SEM modelling results with 1-D semi-analytical solution for a half-space or layered-earth model. To study the anisotropic effect on AEM responses, we calculate and compare the responses for both isotropic and anisotropic abnormal bodies using 3rd to 5th order SEM. Finally, we analyse the influence of the order of SEM interpolation functions on the AEM responses.