3D forward modelling of time domain electromagnetic data

We develop a forward modelling algorithm for computing time domain electromagnetic responses for conductive, permeable bodies in the low frequency regime. Both physical properties can be highly discontinuous. The parameter regimes considered give rise to highly stiff problems in the time domain and an implicit method, backward Euler, is used for time-stepping. At each time step the electromagnetic equations are solved in a stable manner by using a Helmholtz decomposition of the electric field to convert to potentials, and then discretizing in space by using a finite volume formulation. The final system is solved using a biconjugate gradient solver with preconditioning. Numerical comparisons are made against a 1d semi-analytic solution for a conductive permeable half-space, and a 3d integral equation solution for a block in a halfspace.