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

Three-dimensional frequency-domain electromagnetic induction (FD-EMI) surveying involves using a profile spacing that is smaller than the crossline footprint of the measurements. Using portable multiconfiguration 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, such as structural prior information obtained from 3D ground-penetrating radar surveys. Two field examples indicate how structural and model sharpness constraints yield improved pseudo-3D models compared with models obtained from more classical approaches (e.g., nonstructurally constrained and based on smoothness constraints). These results also highlight the nonuniqueness of the resulting FD-EMI conductivity models, which can critically influence subsequent interpretations in terms of geologic units and petrophysical properties.