NUMERICAL MODELING & A FIELD TEST OF GROUND PENETRATING RADAR FOR SOIL MOISTURE CONTENT ESTIMATION (original) (raw)
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Comparison of soil water content estimation equations using ground penetrating radar
Journal of Hydrology
Soil water content has an important impact on many fundamental biophysical processes. The quantification of soil water content is necessary for different applications, ranging from large-scale calibration of global-scale climate models to field and catchment scale monitoring in hydrology and agriculture. Many techniques are available today for measuring soil water content, ranging from point scale soil water content sensors to global scale, active and passive, microwave satellites. Geophysical methods are important methods, used for several decades, to measure soil water content at different scales. Among these methods, ground penetrating radar has been shown to be one of the most reliable and promising ones. Soil water content measurement using ground penetrating radar requires the application of parametric equations that will convert the measured dielectric permittivity to water content. While several studies have been performed to test equations for soil water content sensors such as time domain reflectometry, a few studies have been performed to test different formulae for application to ground penetrating radar. In this study, we compare available formulae for converting dielectric permittivity obtained from detailed laboratory scale measurement of reflected waves using ground penetrating radar. Four soils covering a wide range of textures were used and the measured soil water contents were compared with values obtained from gravimetric measurements. Results showed that the dielectric mixing model of Roth et al. (1990) provided the best fit for individual soil textural classes, except for sandy soils. However, for all data combined the dielectric mixing model performed much better with significant difference in coefficient and determination and root mean square error. Empirical equations developed from calibration of time domain reflectometry performed poorly when applied to estimation of soil water content obtained from ground penetrating radar. Differences in sample volume, frequency of operation and data analysis between ground penetrating radar and time domain reflectometry, suggest to use more flexible and robust electromagnetic mixing formulae, allowing for incorporating the dielectric properties of constituents materials and geometrical features of the media. Sensitivity analysis was then performed to provide detailed information for the most accurate application of the selected dielectric model. Sensitivity analysis showed that the geometric parameter α and the dielectric permittivity of the solid phase ∊ s are the two most sensitive parameters, determining important variations in the estimation of soil water content. Based on these results, these two parameters are suggested as fitting parameters, to be selected if the model is fitted to data. Otherwise, the model can be successfully used without calibration, as presented in this study, by using α = 0.5 (as also suggested by the authors) and ∊ s = 4, which is an average value for soil minerals. methods available for measuring SWC. Among geophysical techniques, Ground Penetrating Radar (GPR) is a powerful and promising one. GPR has the advantage of covering larger areas with respect to point-based measurements typical of soil moisture sensors such as Time Domain Reflectometry (TDR), filling the gap between point scale and large scale satellite-based measurements. SWC can be obtained by performing different types of analysis and
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
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 ...
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.
2013
Monitoring of soil water content (volumetric water content, VWC) is an important process in agricultural and ecological programs, and a vital process in flood and water resource management. There are several methods in estimating VWC but often these are time consuming, invasive and expensive. This paper investigates the applicability of a surface based geophysical technique, Ground-Penetrating Radar (GPR), for estimating the VWC in shallow soil (top 0.30 m of soil subsurface). The guided wave sounding, GWS, technique (an invasive application of the GPR technique) was used on a vegetable garden located at latitude 6.67 and longitude -1.56, south of the College of Engineering, KNUST, Kumasi, Ghana. The MALA ProEx GPR equipment using shielded antennae with a central frequency of 800 MHz was used for the measurements. The result showed that, on the average, the VWC at the top soil (0.065 m) containing humus was high (0.12 m 3 m -3 ) as compared to depth 0.295 m (0.10 m 3 m -3 ). Thus, t...
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.
Small-scale soil-moisture variability estimated using ground penetrating radar
2000
This paper describes development of Ground Penetrating Radar (GPR) techniques for spatially distributed measurement of soil moisture. Traditional measurement techniques are limited; most significantly they are time consuming, invasive and destructive techniques. Measurement with GPR is non-invasive and rapid. This paper investigates the relationship between a number of properties of the GPR signal and Volumetric Moisture Content (VMC). Using a series of controlled laboratory experiments the two most reliable methods were found to be the signal amplitude and amplitude spectra approaches. Significant relationships were found between maximum amplitude and VMC for a variety of earth materials and situations. Quantitative correspondence between the GPR and invasive measurements of moisture is poor due to differences in sampled area, depth of investigation and the impact of rock fragment content on the relationship between soil water and soil volumetric moisture content. In addition GPR specific errors are introduced by coupling of the radar with the ground surface, and the impact of the profile variability on the GPR signal return.
The Use of Ground-Penetrating Radar to Accurately Estimate Soil Depth in Rocky Forest Soils
Forest Science
Ground-penetrating radar (GPR) is a geophysical tool that has the capability, given favorable soil properties, to improve the accuracy of soil depth estimation, compared with other commonly used methods. This study was conducted on three different physiographic regions across the southern Appalachian Mountains: the Ridge and Valley (n = 9), Cumberland Plateau (n = 6), and Allegheny Plateau (n = 6). At each site (n = 21), a 20- × 20-m measurement plot was scanned using both 200- and 400-MHz antennas to estimate average soil depth. Soil depth estimates obtained from both GPR antennas were compared with each other as well as with soil depth estimations obtained with a soil auger using a paired t test (α = 0.05). No significant differences in soil depth were observed for the 200- versus 400-MHz antennas (P = 0.913). Consequently, data recorded from the 400-MHz antenna were used when depth measurements between the GPR and soil auger were compared. This was done because of the smaller and...
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...
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.