FDFD: A 3D finite-difference frequency-domain code for electromagnetic induction tomography

A new 3D code for electromagnetic induction tomography with intended applic ations to environmental imaging problems has been developed. The approach c onsists of calculating the fields within a volume using an implicit finite- difference frequency-domain formulation. The volume is terminated by an ani sotropic perfectly matched layer region that simulates an infinite domain b y absorbing outgoing waves. Extensive validation of this code has been done using analytical and semianalytical results from other codes. and some of those results are presented in this paper. The new code is written in Fortr an 90 and is designed to be easily parallelized. Finally. an adjoint held m ethod of data inversion. developed in parallel for solving the fully nonlin ear inverse problem for electrical conductivity imaging (e.g.. for mapping underground conducting plumes). uses this code to provide solvers for both forward and adjoint fields. Results obtained from this inversion method for high-contrast media are encouraging and provide a significant improvement over those obtained from linearized inversion methods. (C) 2001 Academic Pr ess.