We explore the possibility of measuring a continuously variable soil moisture profile by inversion of a ground penetrating radar (GPR) signal. Synthetic experiments were conducted to demonstrate the well-posedness of the inverse problem for the specific case of identifying a soil moisture profile in hydrostatic equilibrium with a water table. In this case, the profile agrees with the water retention curve of the soil. The analysis subsequently extends to an actual case study in controlled outdoor conditions on a large tank filled with sand. Due to the presence of a discontinuity in the actual dielectric profile, inversion of the continuous model (Model 1) led to poor results. Only the surface soil moisture was well estimated. Including the observed discontinuity in the model (Model 2) led to a good estimation of the water content profile. Finally, we observed that the surface water content can be accurately estimated using a simplified three-layer model (Model 3). Generally, the observed confidence intervals on the estimated parameters are large, which denotes a lack of model sensitivity to the soil parameters. We attributed the low sensitivity to the high operating frequency range. Lower frequencies would have been required to obtain more information from the larger depths. Nevertheless, high frequencies allowed for an accurate estimation of the surface soil moisture, which offers particularly promising perspectives in humanitarian demining and agricultural applications.

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