Inversion of airborne tipper and ground-based data for two-dimensional radio-magnetotelluric using the Gauss-Newton method

A two-dimensional inversion algorithm based on the Gauss-Newton optimization has been developed for both ground-based and airborne data of Radio-magnetotelluric (RMT). The Finite Element Method (FEM) has been used in the forward modelling of RMT based on the unstructured mesh. The ground-based responses of a synthetic model including apparent resistivity, phase and tipper have been inverted and the lateral resolution of tipper has been evaluated. Then the effect of observed altitude, topography, and noise level on the airborne RMT tipper response and inverted model has been evaluated. Finally, the simultaneous inversion of ground-based data and airborne tipper has been carried out. The synthetic examples indicate that the inversion incorporating tipper data can more distinctly identify lateral resistivity variation in geological structures. The available anomaly included in the airborne tipper caused by the target structure diminishes as observed altitude increases. And the effect of topography on airborne tipper cannot be ignored, which can be eliminated by inversion with topographic consideration. When adequate airborne tipper data can be acquired, a small number of ground-based impedance data is need to be measured for obtaining resistivity values. The combined strategy of dense airborne tipper with sparse ground-based impedance measurement makes the exploration more effective and keeps great reliability for electrical resistivity imaging.