2D Finite difference modelling of diffusion of electromagnetic fields from a line source of current

Abstract

Time domain electromagnetic (TDEM) method uses a grounded current wire as a controlled source. Owing to this artificial source, we can investigate the underground up to the depth of several kilometers efficiently. The signal to noise ratio of TDEM data is usually higher than Magnetotelluric (MT) data. However, most of the interpretation of practical TDEM data is limited to horizontally layered earth, although 2-D analysis is already popular in commercial MT surveys. Therefore, the understanding of the diffusion process of electromagnetic fields in time domain is essential for the 2-D interpretation of TDEM data. The author has developed an implicit time domain 2-D modeling algorithm to model the diffusion of electromagnetic fields from a line source of current. A 2-D earth whose resistivity is invariant in y-direction is considered, and the line source is oriented to the strike direction. The derivation of linear equations is based on an integral form finite-difference method, and we obtain the nine-point finite-difference equation. By using the Crank-Nicolson approach, the solution of the linear equations is obtained in an implicit manner.