A new sequential procedure for hydraulic tomographic inversion

We present a novel hydraulic tomography procedure, which is based on a travel-time based inversion and application of pilot points. The travel-time based inversion allows for the reconstruction of a diffusivity distribution, which displays the dominant structural elements of a heterogeneous aquifer. This information is used to guide pilot point based inversion of hydraulic conductivity distribution. We utilize the diffusivity distribution to optimize the spatial positions of the pilot points and the relationships among them. For the implementation of the relationships, graph theory is applied. The associated high-computational effort was encountered with subspace regularization and parallel computing. The developed inverse methodology was successfully applied to a three-dimensional sedimentary aquifer analogue. The validation shows that the sequential procedure strongly improves the misfit between predicted and true pressure response in comparison to the results, only when travel-time inversion is employed