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

Abstract

A major challenge in vadose zone hydrology is to obtain accurate information on the temporal changes of the vertical soil water distribution and its feedback with the atmosphere and groundwater. A state of the art coupled hydrogeophysical inversion scheme is applied to evaluate soil hydraulic properties of a synthetic model and a field soil in southern Ontario based on time‐lapse monitoring of soil dynamics with surface ground‐penetrating radar (GPR). Film flow was included in the hydrological model to account for noncapillary water flow in a sandy medium during dry conditions. The synthetic study illustrated that GPR data contain sufficient information to accurately constrain soil hydraulic parameters within a coupled inversion framework and led to an accurate estimation of the soil hydraulic properties. When film flow was not accounted for within the inversion, an equally good fit could still be achieved. In this case, errors introduced by neglecting film flow were compensated by different hydraulic parameters. For the field data, the coupled inversion reduced the overall misfit compared to an uncalibrated model using hydraulic parameters obtained from laboratory data. Although the data fit improved significantly for water content in the deeper soil layers, accounting for film flow in the uppermost subsurface layer did not lead to a better fit of the GPR data. Further research is needed to describe the processes controlling water content in the dry range, in particular coupled heat and vapor transport. This study illustrates the suitability of surface GPR measurements combined with coupled inversion for near‐surface characterization of soil hydraulic parameters.

Recent Developments and Applications of the HYDRUS Computer Software Packages

“…For example, electrical resistivity surveys and HYDRUS modeling were used by Batlle‐Aguilar et al (2009) to investigate axisymmetrical infiltration patterns and by Lehmann et al (2013) to observe the evolution of soil wetting patterns preceding a hydrologically induced landslide. A large number of studies involved the complementary use of HYDRUS modeling and GPR data (e.g., Laloy et al, 2012; Jadoon et al, 2012; Scholer et al, 2013; Moghadas et al, 2013; Busch et al, 2013; Léger et al, 2014; Tran et al, 2014) or cosmic‐ray neutron probes (e.g., Franz et al, 2012; Bogena et al, 2013; Lv et al, 2014; Villarreyes et al, 2014). While the depth of penetration for GPR may be up to 10 to 15 m, its spatial extent is quite limited.…”

Resolving precipitation induced water content profiles by inversion of dispersive GPR data: A numerical study

“…Shuffled complex evolution (SCE) (Duan et al 1993) is a well-established optimization algorithm that has been used in multi-parameter hydrologic and geophysical problems (Yapo et al, 1998;Mertens et al, 2004;Busch et al, 2013;von Hebel et al, 2014) as well as other optimization research. The SCE algorithm uses a combination of probabilistic and deterministic approaches to move clusters of points spanning the parameter space toward a global minimum using competitive evolution between the clusters (see Duan et al (1993) for details).…”

Does textural heterogeneity matter? Quantifying transformation of hydrological signals in soils

“…Resulting structural information has been included to inverse soil hydrological modeling (e.g. Busch et al, 2013;Hinnell et al, 2010;Kowalsky et al, 2004). Vogel et al (2006) performed a dye tracer experiment in a structured soil and reconstructed geometry of observed structural components in a three dimensional model domain.…”