Electromagnetic Prospecting for Underground Structure by a 2.5-D Frequency-Domain Algorithm

In this work, we present a novel 2.5-D frequency-domain algorithm using mixed spectral element method with the divergence-free constraint to solve the EM prospecting problem, and show its application to the marine controlled-source electromagnetic (MCSEM) systems. Because the divergence-free constraint is explicitly enforced (unlike the conventional spectral element method), the charge conservation is honored in the governing equation. The stability of the solution is ensured, making the system matrix well-conditioned even at low frequencies. Numerical experiments show that the proposed method is well suited for solving low-frequency MCSEM problems by an iterative method.