Frequency-Domain Electromagnetic Forward and Sensitivity Modeling: Practical Aspects of Modeling a Magnetic Dipole in a Multilayered Half-Space

Frequency-domain electromagnetic (FDEM) data are commonly acquired to provide spatially continuous information about subsurface electrical conductivity (EC) and/or magnetic susceptibility. To link the phase-sensitive instrument responses -the quadrature-phase (QP) and in-phase (IP) components of the EM field (i.e., data space) -with the subsurface physical properties (i.e., model space), a forward model is indispensable. In addition, a forward model is essential for calculating the FDEM instrument response theoretically, e.g., during an inversion, and can be used for additional purposes, such as instrument calibration, synthetic data generation, depth of investigation estimation, instrument design, survey design, assessment of the detection limit for a given target within a known host body, apparent EC estimation, and educational purposes.