Abstract
Abstract. The vertical profile of shallow unsaturated zone soil moisture plays a key role in many hydro-meteorological and agricultural applications. We propose a closed-loop data assimilation procedure based on the maximum likelihood ensemble filter algorithm to update the vertical soil moisture profile from time-lapse ground-penetrating radar (GPR) data. A hydrodynamic model is used to propagate the system state in time and a radar electromagnetic model and petrophysical relationships to link the state variable with the observation data, which enables us to directly assimilate the GPR data. Instead of using the surface soil moisture only, the approach allows to use the information of the whole soil moisture profile for the assimilation. We validated our approach through a synthetic study. We constructed a synthetic soil column with a depth of 80 cm and analyzed the effects of the soil type on the data assimilation by considering 3 soil types, namely, loamy sand, silt and clay. The assimilation of GPR data was performed to solve the problem of unknown initial conditions. The numerical soil moisture profiles generated by the Hydrus-1D model were used by the GPR model to produce the "observed" GPR data. The results show that the soil moisture profile obtained by assimilating the GPR data is much better than that of an open-loop forecast. Compared to the loamy sand and silt, the updated soil moisture profile of the clay soil converges to the true state much more slowly. Decreasing the update interval from 60 down to 10 h only slightly improves the effectiveness of the GPR data assimilation for the loamy sand but significantly for the clay soil. The proposed approach appears to be promising to improve real-time prediction of the soil moisture profiles as well as to provide effective estimates of the unsaturated hydraulic properties at the field scale from time-lapse GPR measurements.
Highlights
Understanding the dynamics of soil moisture at the shallow unsaturated zone is essential for hydrological, meteorological and agricultural research
We propose a new sequential assimilation procedure to raise the accuracy of the soil moisture profile prediction using time-lapse ground-penetrating radar (GPR) data
We explored the potentials of assimilating UWB GPR data based on the maximum likelihood ensemble filter (MLEF) technique
Summary
Understanding the dynamics of soil moisture at the shallow unsaturated zone is essential for hydrological, meteorological and agricultural research. The water content at this zone influences the most important processes of the hydrological cycle as well as partitioning of energy at the land surface into a sensible and latent exchange with the atmosphere (Vereecken et al, 2008; Lambot et al, 2009). The availability of the unsaturated zone water is the main factor that controls the separation of the rainfall into runoff and infiltration. Information on the unsaturated zone soil moisture is crucial for optimal management and irrigation practices toward a tangible impact on the crop production (Vereecken et al, 2008). Development and integration of measurement techniques for quantitative characterization of the shallow unsaturated zone soil moisture is an urgent need
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