Estimation of field-scale soil hydraulic and dielectric parameters through joint inversion of GPR and hydrological data

A method is described for jointly using time-lapse multiple-offset cross-borehole ground-penetrating radar (GPR) travel time measurements and hydrological measurements to estimate field-scale soil hydraulic parameters and parameters of the petrophysical function, which relates soil porosity and water saturation to the effective dielectric constant. We build upon previous work to take advantage of a wide range of GPR data acquisition configurations and to accommodate uncertainty in the petrophysical function. Within the context of water injection experiments in the vadose zone, we test our inversion methodology with synthetic examples and apply it to field data. The synthetic examples show that while realistic errors in the petrophysical function cause substantial errors in the soil hydraulic parameter estimates, simultaneously estimating petrophysical parameters allows for these errors to be minimized. Additionally, we observe in some cases that inaccuracy in the GPR simulator causes systematic error in simulated travel times, making necessary the simultaneous estimation of a correction parameter. We also apply the method to a three-dimensional field setting using time-lapse GPR and neutron probe (NP) data sets collected during an infiltration experiment at the U.S. Department of Energy (DOE) Hanford site in Washington. We find that inclusion of GPR data in the inversion procedure allows for improved predictions of water content, compared to predictions made using NP data alone