Quantifying field-scale surface soil water content from proximal GPR signal inversion in the time domain (original) (raw)
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Water Resources Research, 2006
1] We analyze the common surface reflection and full-wave inversion methods to retrieve the soil surface dielectric permittivity and correlated water content from airlaunched ground-penetrating radar (GPR) measurements. In the full-wave approach, antenna effects are filtered out from the raw radar data in the frequency domain, and fullwave inversion is performed in the time domain, on a time window focused on the surface reflection. Synthetic experiments are performed to investigate the most critical hypotheses on which both techniques rely, namely, the negligible effects of the soil electric conductivity (s) and layering. In the frequency range 1-2 GHz we show that for s > 0.1 Sm À1 , significant errors are made on the estimated parameters, e.g., an absolute error of 0.10 in water content may be observed for s = 1 Sm À1 . This threshold is more stringent with decreasing frequency. Contrasting surface layering may proportionally lead to significant errors when the thickness of the surface layer is close to one fourth the wavelength in the medium, which corresponds to the depth resolution. Absolute errors may be >0.10 in water content for large contrasts. Yet we show that full-wave inversion presents valuable advantages compared to the common surface reflection method. First, filtering antenna effects may prevent absolute errors >0.04 in water content, depending of the antenna height. Second, the critical reference measurements above a perfect electric conductor (PEC) are not required, and the height of the antenna does not need to be known a priori. This averts absolute errors of 0.02-0.09 in water content when antenna height differences of 1-5 cm occur between the soil and the PEC. A laboratory experiment is finally presented to analyze the stability of the estimates with respect to actual measurement and modeling errors. While the conditions were particularly well suited for applying the common reflection method, better results were obtained using fullwave inversion.
Ground-penetrating radar for temporal soil moisture variability analysis along a land slope
Knowledge of temporal surface soil moisture variability is an useful key in agriculture, surface hydrology and meteorology. In that respect, ground-penetrating radar (GPR) is a non-invasive and promising tool for high-resolution and large scale characterization. In the case of quantitative analysis, offground GPR signal modeling and full-waveform inversion has shown a great potential during the last decade. In this research, we applied GPR for time-laps measurements in an agricultural field along a 320 m single transect with a significant landslope for about 3 months. A 200-2000 MHz TEM-horn antenna situated 1.1 m above the ground, connected to a vector network analyzer (VNA) was used as an off-ground frequency-domain GPR. The accurate positioning was done using a differential GPS. All systems were mounted on a 4-wheels vehicle for realtime and automated mapping. The calibration of the antenna and using the GPR signal inversion permitted to the ground surface relative dielectric permittivity. Topp's model was used for transformation of the relative dielectric permittivity to soil moisture. The temporal stability of the field-average soil moisture was computed by indicators based on the relative difference of the soil moisture to the field-average. The results showed an excellent correlation amount of -0.9905 for temporal stability of soil moisture and slope variability.
Ground-penetrating radar for correlation analysis of temporal soil moisture stability and land-slope
2012 14th International Conference on Ground Penetrating Radar (GPR), 2012
Knowledge of temporal surface soil moisture variability is an useful key in agriculture, surface hydrology and meteorology. In that respect, ground-penetrating radar (GPR) is a non-invasive and promising tool for high-resolution and large scale characterization. In the case of quantitative analysis, offground GPR signal modeling and full-waveform inversion has shown a great potential during the last decade. In this research, we applied GPR for time-laps measurements in an agricultural field along a 320 m single transect with a significant landslope for about 3 months. A 200-2000 MHz TEM-horn antenna situated 1.1 m above the ground, connected to a vector network analyzer (VNA) was used as an off-ground frequency-domain GPR. The accurate positioning was done using a differential GPS. All systems were mounted on a 4-wheels vehicle for realtime and automated mapping. The calibration of the antenna and using the GPR signal inversion permitted to the ground surface relative dielectric permittivity. Topp's model was used for transformation of the relative dielectric permittivity to soil moisture. The temporal stability of the field-average soil moisture was computed by indicators based on the relative difference of the soil moisture to the field-average. The results showed an excellent correlation amount of -0.9905 for temporal stability of soil moisture and slope variability.
Journal of Hydrology, 2007
Two ground-penetrating radar (GPR) techniques were used to estimate the shallow soil water 3 content at the field scale. The first technique is based on the ground wave velocity measured 4 with a bistatic impulse radar connected to 450 MHz ground-coupled antennas. The second 5 technique is based on inverse modeling of an off-ground monostatic TEM horn antenna in the 6 0.8 to 1.6 GHz frequency range. Data were collected on a 8 by 9 m partially irrigated 7 intensive research plot and along four 148.5 m transects. Time domain reflectrometry, 8 capacitance sensors, and volumetric soil samples were used as reference measurements. The 9 aim of the study was to test the applicability of the ground wave method and the off-ground 10 inverse modeling approach at the field scale for a soil with a silt loam texture. The results for 11 the ground wave technique were difficult to interpret due to the strong attenuation of the GPR 12 signal, which was related to the silt loam texture at the test site. The root mean square error of 13 the ground wave technique was 0.076 m³m -³ when compared to the TDR measurements and 14 0.102 m³m -³ when compared with the volumetric soil samples. The off-ground monostatic 15 GPR measured less within field soil water content variability than the reference 16 measurements, resulting in a root mean square error of 0.053 m³m -³ when compared with the 17 TDR measurements and an error of 0.051 m³m -³ when compared with the volumetric soil 18
Vadose Zone Journal, 2013
It has been recently demonstrated that the early‐time portion of the ground‐penetrating radar (GPR) signal, consisting of the direct air and ground wave events, is dependent on the shallow subsurface bulk electromagnetic properties of the material; these properties are strongly controlled by the water content in this material. While several controlled experiments have been conducted to study the effects of water content variations on the antenna–material coupling, they considered a limited range of moisture variations and soil textures. Furthermore, those previous experiments did not consider highly dynamic shallow moisture responses that would be encountered under natural field conditions. For these reasons, general acceptance of this method requires that it be tested in real‐life applications. Our paper evaluates the early‐time GPR technique under natural field conditions where surface roughness, lithology, lateral heterogeneities, vegetation and water content dynamics are not con...
Mapping Spatial Moisture Content of Unsaturated Agricultural Soils with Ground-Penetrating Radar
ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, 2016
Soil subsurface moisture content, especially in the root zone, is important for evaluation the influence of soil moisture to agricultural crops. Conservative monitoring by point-measurement methods is time-consuming and expensive. In this paper we represent an active remote-sensing tool for subsurface spatial imaging and analysis of electromagnetic physical properties, mostly water content, by ground-penetrating radar (GPR) reflection. Combined with laboratory methods, this technique enables real-time and highly accurate evaluations of soils' physical qualities in the field. To calculate subsurface moisture content, a model based on the soil texture, porosity, saturation, organic matter and effective electrical conductivity is required. We developed an innovative method that make it possible measures spatial subsurface moisture content up to a depth of 1.5 m in agricultural soils and applied it to two different unsaturated soil types from agricultural fields in Israel: loess soi...
Measuring Soil Water Content with Ground Penetrating Radar: A Decade of Progress
Vadoze Zone Journal, 2018
Tremendous progress has been made with respect to ground penetrating radar (GPR) equipment, data acquisition, and processing since the establishment of GPR as a tool for soil water content determination in vadose zone hydrology about 25 yr ago. In this update, we aim to provide a critical overview of recent advances in vadose zone applications of GPR with a particular focus on new possibilities for multi-offset and borehole GPR measurements, the development of quantitative off-ground GPR methods, full-waveform inversion of GPR measurements, the potential of time-lapse GPR measurements for process investigations and hydrological parameter estimation, and recent improvements in GPR instrumentation. We hope that this update encourages the soil hydrology, groundwater, and critical zone community to embrace GPR as a viable tool for soil water content determination and the elucidation of subsurface hydrological processes.
Vadose Zone Journal, 2004
properties of the subsurface. In that respect, GPR constitutes a promising high resolution characterization We explore the possibility of measuring a continuously variable tool. However, despite considerable research devoted to soil moisture profile by inversion of a ground penetrating radar (GPR) signal. Synthetic experiments were conducted to demonstrate the well-GPR, its use for assessing quantitatively the subsurface posedness of the inverse problem for the specific case of identifying properties has been constrained by a lack of appropriate a soil moisture profile in hydrostatic equilibrium with a water table. GPR systems and signal analysis methods. Ground pen-In this case, the profile agrees with the water retention curve of the etrating radar has been used to identify soil stratigraphy soil. The analysis subsequently extends to an actual case study in con-(Davis and Annan, 1989; Kung and Lu, 1993; Boll et al., trolled outdoor conditions on a large tank filled with sand. Due to 1996), to locate the water table (Nakashima et al., 2001), the presence of a discontinuity in the actual dielectric profile, inversion to follow wetting front movement (Vellidis et al., 1990), of the continuous model (Model 1) led to poor results. Only the to measure soil water content (Greaves et al., 1996; surface soil moisture was well estimated. Including the observed dis
Remote Sensing
Soil moisture content (SMC) down to the root zone is a major factor for the efficient cultivation of agricultural crops, especially in arid and semi-arid regions. Precise SMC can maximize crop yields (both quality and quantity), prevent crop damage, and decrease irrigation expenses and water waste, among other benefits. This study focuses on the subsurface spatial electromagnetic mapping of physical properties, mainly moisture content, using a ground-penetrating radar (GPR). In the laboratory, GPR measurements were carried out using an 800 MHz central-frequency antenna and conducted in soil boxes with loess soil type (calcic haploxeralf) from the northern Negev, hamra soil type (typic rhodoxeralf) from the Sharon coastal plain, and grumusol soil type (typic chromoxerets) from the Jezreel valley, Israel. These measurements enabled highly accurate, close-to-real-time evaluations of physical soil qualities (i.e., wave velocity and dielectric constant) connected to SMC. A mixture model ...
Journal of Hydrology, 2005
Knowledge of ground wave penetration depth and methods for facilitating ground wave velocity analysis are important practical aspects to consider when measuring soil water content with surface ground penetrating radar. A field study was conducted to optimize the wide angle reflection and refraction and fixed offset methods of measuring the ground wave velocity and to find the effective ground wave sampling depth under irrigation and drainage conditions. In this study, a PulseEkko 1000 GPR system with 450 MHz antennas was used at a sandy loam soil site. Water contents measured with time domain reflectometry (TDR) were used to determine the sampling depth of GPR based water content estimates. Cumulative irrigation and drainage calculated with GPR were found to be more closely related with cumulative irrigation and drainage measured with shorter TDR probes, suggesting that the ground wave sampling depth was in the 0.2-0.5 m range. During the infiltration phase the depth of the ground wave penetration was found to be in the 0-0.56 m range, assuming a sharp boundary between wet and dry sand. Comparison of water contents measured with the WARR and FO methods revealed that an antenna separation distance of 1.5-2.0 m for the FO method was required to obtain similar results between the two methods. q