Characterization of Soil Water Content Variability and Soil Texture using GPR Groundwave Techniques

Abstract

Accurate characterization of near-surface soil water content is vital for guiding agricultural management decisions and for reducing the potential negative environmental impacts of agriculture. Characterizing the near-surface soil water content can be difficult, as this parameter is often both spatially and temporally variable, and obtaining sufficient measurements to describe the heterogeneity can be prohibitively expensive. Understanding the spatial correlation of near-surface soil water content can help optimize data acquisition and improve understanding of the processes controlling soil water content at the field scale. In this study, ground penetrating radar (GPR) methods were used to characterize the spatial correlation of water content in a three acre field as a function of sampling depth, season, vegetation, and soil texture. GPR data were acquired with 450 MHz and 900 MHz antennas, and measurements of the GPR groundwave were used to estimate soil water content at four different times. Additional water content estimates were obtained using time domain reflectometry measurements, and soil texture measurements were also acquired. Variograms were calculated for each set of measurements, and comparison of these variograms showed that the horizontal spatial correlation was greater for deeper water content measurements than for shallower measurements. Precipitation and irrigation were both shown to increase the spatial variability of water content, while shallowly-rooted vegetation decreased the variability. Comparison of the variograms of water content and soil texture showed that soil texture generally had greater small-scale spatial correlation than water content, and that the variability of water content in deeper soil layers was more closely correlated to soil texture than were shallower water content measurements. Lastly, cross-variograms of soil texture and water content were calculated, and co-kriging of water content estimates and soil texture measurements showed that geophysically-derived estimates of soil water content could be used to improve spatial estimation of soil texture.

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

“…Significant advances have recently been made using groundpenetrating radar (GPR) to study near-surface water content in both static (Greaves et al, 1996;Grote et al, 2010;Huisman et al, 2001;Vellidis et al, 1990) and dynamic conditions (Haarder et al, 2011;Mangel et al, 2012;Moysey 2010;Truss et al, 2007;van Overmeeren et al, 1997). In time-lapse studies, it is common to see large increases in water content at the surface associated with infiltration events which create a high permittivity region of the soil column.…”

Validation of ground penetrating radar full-waveform inversion for field scale soil moisture mapping

“…A review about recent GPR developments can be found in Slob et al (2010) while a complete review of GPR applications for soil moisture sensing was given in . Numerous studies used the now well-established GPR ground-wave techniques for soil moisture determination (e.g., Huisman et al, 2002;Grote et al, 2003;Galagedara et al, 2005;Lunt et al, 2005;Grote et al, 2010). Recently, some authors proposed innovative soil moisture retrieval techniques using the same GPR sensors.…”

Estimating field-scale soil water dynamics at a heterogeneous site using multi-channel GPR

“…This is in particular the case for all hydrologic applications. Borehole GPR can be used to map temporal soil water content variation with high resolution at larger depths (Galagedara et al, 2003;Kowalsky et al, 2005;Grote et al, 2010;Wijewardana and Galagedara, 2010), but limited at plot scale. For characterizing soil water flow at larger scale, the GPR reflection method has big advantages.…”

“…Huisman et al, Grote et al, 2003;Galagedara et al, 2003Galagedara et al, , 2005Grote et al, 2010). The field study by Huisman et al (2003b) showed that the temporal development of spatial soil water content variation could be observed with the ground wave method at an accuracy comparable to TDR.…”