Sharp spatially constrained inversion of 3D FD-EMI datasets with structural prior information from GPR data: application to peat soil evaluation

3D frequency domain electromagnetic induction (FD-EMI) surveying consists in using a profile spacing, which is smaller than the cross-line footprint of the measurements. Using portable multi-configuration loop-loop sensors, this approach can image the spatial distribution of electrical conductivity in the shallow subsurface with a relatively high lateral resolution. A pseudo-3D sharp inversion procedure (spatially constrained 1D inversion) can be improved by using further constraints like structural prior information obtained from 3D ground-penetrating radar (GPR) surveying. Two field examples show how both structural and model sharpness constraints yield to improved pseudo-3D models compared to models as obtained from more classical approaches (e.g., non-structurally constrained and based on smoothness constraints). These results also highlight the non-uniqueness of the resulting FD-EMI conductivity models, which can critically influence the following interpretation in terms of geological units and petrophysical properties.