Deriving Soil Hydraulic Properties from Active and Passive Microwave Data
Jonard, François1; Weihermüller, Lutz1; Schwank, Mike2; Jadoon, Khan Zaib3; Vereecken, Harry1; Lambot, Sébastien4
1Research Centre Jülich, GERMANY; 2Swiss Federal Institute (WSL), SWITZERLAND; 3King Abdullah University of Science and Technology (KAUST), SAUDI ARABIA; 4Université catholique de Louvain (UCL), BELGIUM
Soil hydraulic properties are of main interest for estimating water and energy fluxes at the land surface. In general, estimation of the hydraulic properties relies on the measurement of the soil water status within the soil profile usually performed with in-situ sensors such as time-domain reflectometry (TDR) or capacitance probes. Unfortunately, these sensors do not account for the high spatial and temporal variability in the soil, especially over large areas. In that context, we investigated the potential of GPR and L-band radiometer to remotely identify the hydraulic properties of a sandy soil subject to hydrostatic equilibrium with a range of water table depths. At hydrostatic equilibrium, the vertical water content profile exhibits a continuous variation corresponding to the water retention curve of the soil. The GPR and radiometer measurements were performed at the TERENO test site in Selhausen over a 1.00-m deep and 2.00 x 2.00 m2 area wooden box filled with sand. For both GPR and radiometer, all measurements were aggregated in an inversion scheme to reconstruct the vertical water content profiles, which were constrained using the van Genuchten water retention equation. The radar model used to inverse the GPR data consists of a 3D planar layered medium and the inversions were performed using a full-waveform inversion strategie. For the radiometer data, we used a coherent reflectivity model considering the sand box system as a planar layered medium. The results showed that both GPR and radiometer data contain sufficient information to estimate the sand water retention curve and its related hydraulic parameters with a relatively good accuracy compared to TDR estimates.