Abstract
Abstract. High-resolution time-lapse ground-penetrating radar (GPR) observations of advancing and retreating water tables can yield a wealth of information about near-surface water content dynamics. In this study, we present and analyze a series of imbibition, drainage and infiltration experiments that have been carried out at our artificial ASSESS test site and observed with surface-based GPR. The test site features a complicated but known subsurface architecture constructed with three different kinds of sand. It allows the study of soil water dynamics with GPR under a wide range of different conditions. Here, we assess in particular (i) the feasibility of monitoring the dynamic shape of the capillary fringe reflection and (ii) the relative precision of monitoring soil water dynamics averaged over the whole vertical extent by evaluating the bottom reflection. The phenomenology of the GPR response of a dynamically changing capillary fringe is developed from a soil physical point of view. We then explain experimentally observed phenomena based on numerical simulations of both the water content dynamics and the expected GPR response.
Highlights
A quantitative description of near-surface soil water dynamics is of paramount interest across a range of disciplines in the Earth sciences, from hydrologic research to irrigation management, encompassing a multitude of applications on various scales, from locally predicting contaminant flow and plot-scale precision agriculture all the way to the application of basin-scale hydrologic models (Vereecken et al, 2008).due to considerable spatial heterogeneity and temporal variability of soil water content, quantitative monitoring of soil water dynamics has remained a challenge, especially at intermediate scales, despite considerable efforts and advances in recent years (Robinson et al, 2008)
We will first discuss the phenomenology of the capillary fringe reflection (CFR) in light of the expectations detailed in the previous paragraphs and will turn to quantitative monitoring of water content changes
We explored several aspects of high-resolution time-lapse ground-penetrating radar (GPR) observations of soil water dynamics with the aim of accessing information about field-scale soil hydraulic properties in a non-invasive manner
Summary
A quantitative description of near-surface soil water dynamics is of paramount interest across a range of disciplines in the Earth sciences, from hydrologic research to irrigation management, encompassing a multitude of applications on various scales, from locally predicting contaminant flow and plot-scale precision agriculture all the way to the application of basin-scale hydrologic models (Vereecken et al, 2008).due to considerable spatial heterogeneity and temporal variability of soil water content, quantitative monitoring of soil water dynamics has remained a challenge, especially at intermediate scales, despite considerable efforts and advances in recent years (Robinson et al, 2008). High-frequency electromagnetic methods such as timedomain reflectometry (TDR) and ground-penetrating radar (GPR) have received considerable attention, due to their high sensitivity to variations in the dielectric permittivity of the subsurface. Such variations are foremost connected to differences in soil water content due to the large permittivity difference between water and air. One standard method for achieving high time resolution monitoring of point-scale soil water dynamics is to install a series of TDR probes in selected soil profiles (Robinson et al, 2003). Wireless soil moisture networks have been established at selected field sites, expanding the scope of such 1-D point-scale measurements for directly addressing field-scale soil water content variability (e.g., Bogena et al, 2010)
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