Propagation-Model Fidelity for HED Localization in Multilayer Marine Media

Underwater electromagnetic localization can interpret propagation-model error as source displacement. We quantify this effect for single-frequency horizontal electric-dipole localization in vertically stratified marine media. The model hierarchy progresses from unbounded uniform water (H0), through bounded uniform water (W1), to profile-resolved water columns. A fast Fourier transform–Sommerfeld solver and variable-projection matched-field estimator separate boundary and vertical-profile effects while eliminating unknown source coefficients. At 30 dB, adding air and seabed reduces three-dimensional root-mean-square error from 23.079–27.584 m for H0 to 0.495–0.535 m for W1. Resolving the nominal eight-layer profile further lowers error from 0.486–0.575 to 0.094–0.108 m. The improvement is not pointwise monotone and becomes calibration-dependent. Under an independent WOA18 profile extending to 350 m, a seven-layer approximation reduces the circular-layout median from 1.224 to 0.749 m. It reduces the square-layout median from 1.010 to 0.628 m. Adverse pairs and a shared depth ambiguity remain. External boundaries therefore remove gross bias, whereas vertical resolution supplies a conditional correction governed by profile accuracy, frequency, geometry, and calibration.