In this study, we experimentally analyze the feasibility of esti-mating the soil hydraulic properties from L-band radiometer and ground-penetrating radar (GPR) data. L-band radiome-ter and ultrawideband off-ground GPR measurements were performed above a sand box in hydrostatic equilibrium with a water table located at different depths. The results of the inversions showed that the radar and radiometer signals con-tain sufficient information to estimate the soil water retention curve and its related hydraulic parameters with a relatively good accuracy compared to time-domain reflectometry esti-mates. However, an accurate estimation of the hydraulic pa-rameters was only obtained by considering the saturated water content parameter as known during the inversion.