Closing the gap between galvanic and inductive methods: EEMverter, a new 1D/2D/3D inversion tool for Electric and Electromagnetic data with focus on Induced Polarization

The interest on Induced Polarization (IP) in AEM data (AIP) has significantly increased in recent years, both within the research community and in the industry. However, the inversion of AIP data is particularly ill-posed, especially when spectral modelling, such as Cole-Cole modelling, is used. Furthermore, the comparison of AIP and galvanic ground IP inversion models is hindered by the fact that the IP effect is usually modelled differently in the inductive and galvanic computations. In this study we present a new inversion software, EEMverter, which has been developed to model IP in electric and electromagnetic (EM) data within the same inversion framework. In particular, three specific goals have been identified within EEMverter's development: i) to allow multiple inversion cycles that mix, sequentially or simultaneously, 1D, 2D and 3D forward modelling, for diminishing the inversion burden; ii) to allow the joint inversion of AIP, ground EM-IP and ground galvanic IP data; iii) to allow time-lapse inversions of AIP, EM and galvanic IP data. EEMverter has been tested on several AEM and AIP surveys, also in conjunction with ground EM and ground galvanic IP data in joint inversion. In this study, the inversion of the VTEM AIP survey over the Valen Cu-Ni deposit is presented, highlighting the improvements in model resolution when compared to standard inversion approaches.