Inversion of Airborne IP data with a multi-mesh approach for parameter definition

The interest on Induced Polarization 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. In this study we present a novel approach for model space definition, in which the AIP inversion parameters are defined on model meshes which do not coincide with the forward meshes used for data modelling: the link between model and forward meshes is obtained interpolating the model mesh parameters into the forward mesh discretization. This spatial decoupling allows for defining the AIP model parameters, e.g. the Cole-Cole ones, on different model meshes, for instance one for each inversion parameter. In this way, it is possible to define the spectral parameters, like the time constant and the frequency exponent in the Cole-Cole model, on meshes coarser than the resistivity and chargeability ones, vertically and/or horizontally, with a significant improvement in parameter resolution. However, the novel approach is completely general, and allows for incorporating any kind of prior information through the definition of parameters in problem-tailored meshes. The novel inversion approach is tested on a VTEM AIP survey, highlighting the improvements in model resolution when compared to standard inversion approaches.