High-resolution soil moisture mapping by a proximal ground penetrating radar : a numerical, laboratory and field evaluation

(eng) Soil moisture is an important state variable acting in many environmental, hydrologic and climatic processes. There is thus a pressing scientific demand for revealing the soil moisture dynamics in the biosphere at various temporal and spatial scales. Despite the huge development of remote sensing of soil moisture techniques, there is still a lack of soil moisture measurement techniques available at high spatial resolution (~ m). This thesis aimed to validate and apply advanced proximal ground penetrating radar (GPR) for soil moisture sensing at the field scale. For field acquisition, the GPR system was mounted on a mobile platform that allowed for a fast acquisition rate at high resolution. The impact of shallow soil layering on the GPR backscattered signal was investigated in numerical and laboratory experiments and the best GPR data inversions strategies for dealing with shallow soil layering were determined. Then, coherent two-layered and continuous soil moisture profiles could be characterized in field conditions, owing to the large frequency bandwidth in which the GPR operates. The uncertainties in soil moisture sensing and mapping were comprehensively evaluated in field conditions, and the proposed GPR method appeared to be highly precise and accurate. In that respect, the GPR method showed a high repeatability for soil moisture sensing. This advanced GPR method permitted to characterize the spatiotemporal patterns of soil moisture in an agricultural field and to investigate their temporal stability. Locations showing temporal stability of field-average soil moisture could be revealed. Lastly, the effect of the spatial variability of antecedent soil moisture on the runoff response using a distributed hydrologic model was studied in various field and moisture conditions. Benefiting from an unprecedented spatial resolution, the proposed GPR method bridges the scale gap between large-scale remote sensing instruments and small-scale invasive sensors for an accurate soil moisture determination.