Three-dimensional inversion of semi-airborne electromagnetic data with a second-order finite-element forward solver

SUMMARY The analysis of controlled-source electromagnetic (EM) data recorded with semi-airborne exploration systems requires advanced simulation and inversion tools that are capable handling realistic survey geometries. Semi-airborne EM setups elongated transmitters deployed in mountainous terrain prohibit the exploitation secondary-field formulations numerical approximations without producing hardly quantifiable errors. Building upon open-source software custEM for forward modeling pyGIMLi geophysical inversion, we present an inverse procedure based on highly accurate second-order finite-element solutions irregular grids fast-converging Gauss–Newton minimization. Using total-field formulation electric field approach combination a direct solver enables calculating explicit sensitivities comparatively cheap back-substitutions thousands ground airborne receiver stations multiple flight areas. Second-order basis functions show general superiority over first-order basis-functions regarding accuracy performance problem. Beyond that, synthetic real studies related to geometries indicate help particularly avoid high errors weakest components artifacts vicinity or at surface. This leads generally better convergence final results higher robustness quality. presented freely available such as underlying software.