Anisotropic Inversion of Induced Polarization (IP) Data

The induced polarization (IP) method is a multi-frequency AC geoelectrical measurement technique that utilizes the phase difference between transmitted and recorded current alongside with the conventional complex electrical conductivity. This information is used to derive the subsurface complex electrical conductivities, usually by means of an inversion algorithm. Presently, these algorithms are based on isotropic complex electrical conductivities. However, it was shown for DC conductivity that assuming this isotropy can yield misleading or unnecessary complex results. We propose an IP inversion algorithm supporting anisotropic complex conductivities. For this purpose, we implemented a numerical forward operator and extended the sensitivity calculation to support these anisotropic complex conductivities. We incorporated a penalty function for the anisotropy as a factor for the individual model cells, which is minimized alongside with the non-smoothness penalty of the original algorithm. We successfully verified the code with synthetic examples targeting the detectability of anisotropy. As a false test, we successfully inverted a synthetic example with isotropic conductivities. First results of the synthetic study indicate that the algorithm is able to resolve anisotropic conductivities while underestimating the original anisotropy factor.