Accurate computation of radiomagnetotelluric fields on 3D topography with surface integral equation methods

摘要

The radiomagnetotelluric (RMT) method is an electromagnetic technique that is particularly well suited for hydrogeological investigations of the shallow subsurface. Its frequency range extends from 10 kHz to 300 kHz, which allows a depth range from 10m to 500m to be imaged. We present a new edge-based boundary element method designed to model efficiently effects of 3D topography and displacement currents on RMT data. Surface charges, magnetic surface currents and electrical surface currents are introduced to grant the stability at a wide rage of frequencies. Using a Galerkin approach, a system of three double surface integral equations is assembled. A dense system of complex valued linear equations is then obtained by discretizing the distribution of surface charges using constant triangular elements. Surface magnetic and electrical currents are discretized with edge-based linear triangular elements. A special singularity extraction technique is applied to the Green's functions to evaluate the singular integrals. The performance of this singularity removal technique is demonstrated with two simple numerical tests.