Coupled hydrogeophysical inversion of time-lapse surface GPR data to estimate hydraulic properties of a layered subsurface

摘要

A major challenge in vadose zone hydrology is to obtain accurate information on thetemporal changes of the vertical soil water distribution and its feedback with theatmosphere and groundwater. A state of the art coupled hydrogeophysical inversion schemeis applied to evaluate soil hydraulic properties of a synthetic model and a field soil insouthern Ontario based on time-lapse monitoring of soil dynamics with surface groundpenetratingradar (GPR). Film flow was included in the hydrological model to account fornoncapillary water flow in a sandy medium during dry conditions. The synthetic studyillustrated that GPR data contain sufficient information to accurately constrain soilhydraulic parameters within a coupled inversion framework and led to an accurateestimation of the soil hydraulic properties. When film flow was not accounted for within theinversion, an equally good fit could still be achieved. In this case, errors introduced byneglecting film flow were compensated by different hydraulic parameters. For the field data,the coupled inversion reduced the overall misfit compared to an uncalibrated model usinghydraulic parameters obtained from laboratory data. Although the data fit improvedsignificantly for water content in the deeper soil layers, accounting for film flow in theuppermost subsurface layer did not lead to a better fit of the GPR data. Further research isneeded to describe the processes controlling water content in the dry range, in particularcoupled heat and vapor transport. This study illustrates the suitability of surface GPRmeasurements combined with coupled inversion for near-surface characterization of soilhydraulic parameters.