Three-Dimensional Multi-Scale and Multi-Method Inversion to Determine the Electrical Conductivity Distribution of the Subsurface (Multi-EM)

Combining different electromagnetic (EM) methods in joint inversion approaches can enhance the overall resolution power. Every method is associated with a particular sensitivity pattern. By assembling complementary patterns, subsurface imaging becomes more complete and reliable. We describe different paths to obtain multi-EM inversions. First, a joint inversion approach using finite difference forward operators is outlined that formulates the problem of minimizing the objective function using different weights for each individual method. Then we address a sequential approach using finite element methods on unstructured grids to cycle through the different EM methods iteratively. Both methods are based on a traditional parametrization using piecewise constant model parameters which may be inefficient when describing the usually rather coarse models. Therefore, we investigate wavelet-based model representations as an alternative.