TRASE TDR
References

'A simple empirical method to evaluate the electrical conductivity of soils and waters by TDR'
'Calculation of bulk and solution electrical conductivity of soil using Time Domain Reflectometry measurements'
'Current and potential uses of Time Domain Reflectometry for Geotechnical Monitoring'
'Application of TDR technology to water content monitoring of capillary barriers mead of pulp and paper residues'
'Tillage and crop residue effects on carbon dioxide evolution and carbon storage in a Paleustoll'
'Embankment monitoring with time domain reflectometry'
'Water movement and solute transport through Saprolite'
'Field Calibration and Monitoring of Soil-Water Content with Fiberglass Electrical Resistance Sensors'
'TRASE: A Product History'
'Determination of the Wetting Front in Drip Irrigation Using TDR Multi-wire Probe'
'Elastic wave velocities in partially saturated Ottawa sand: experimental results and modelling'
'The Nerrigundah data set: soil moisture patterns, soil characteristics, and hydrological flux movements'
'Monitoring of water content and electrical conductivity in paddy soil profile by Time Domain Reflectometry'

Aringhieri, R. 2002, 'A simple empirical method to evaluate the electrical conductivity of soils and waters by TDR', 17th World Congress of Soil Science, Bankok, Thailand.

Abstract: A simple empirical method is proposed to evaluate the electrical conductivity of soils and waters by Time Domain Reflectometry (TDR). A preliminary investigation aimed to evaluate the suitablility of employing the TDR for electrical conductivity measurements was carried out on solutions of different electrolyte concentration. An empirical exponential equation correlated well the amplitude of the reflected signal (V_R) to the bridge conductivity (χ) of the solutions. However, the TDR failed when measuring the transit time of the energy pulse in solutions of concentration higher than 40 mmol L^-1 (EC>4 dS m^-1). Within this range of applicability a "one to one" correlation between the bridge conductivity (χ) and the TDR conductivity (σ) of natural waters was observed. For soils, the bulk electrical conductivities were in good agreement with those measured by the Four-electrode Probe technique. Experiments were also carried out to evaluate the effect of salinity on the measured soil volumetric water content (VWC) by TDR. Results showed that at relatively low salinity levels (up to 4 dS m^-1) the bulk electrical conductivity of the soil does not affect the measurement of its volumetric water content.

Bae, B.S., Choi, W.J., Han, G.H., Han, K.H., Yoo, S.H. and Ro, H.M. 2003, 'Calculation of bulk and solution electrical conductivity of soil using Time Domain Reflectometry measurements', Korean Journal of Soil Science and Fertility, vol. 36, no. 1, pp. 1-7.

Abstract: Time domain reflectometry (TDR) is a newly developed method for measuring simultaneously solute concentrations and volumetric water content of soil. Bulk electrical conductivity (EC_a) of soil is obtained from TDR signal using several equations proposed, and electrical conductivity of soil solution (EC_w) can be calculated using the linear relationship [EC_a=EC_wθ(aθ+b)+EC_s] between EC_a and EC_w at constant soil water content. The objectives of this study were to evaluate EC_a proposed by several workers and to obtain the empirical constants (a, b, and EC_s) for EC_w of the soils from A, B1 and B2 horizon of an agricultural field (Coarse loamy, Fluvaquentic Eutrudepts). The EC_a proposed by Yanuka et al. responded most sensitively to the KCl solute concentrations. The empirical constants of a, b and EC_s for EC_w were -0.249, 1.358 and 0.054 for A horizon, -2.518, 2.708 and 0.097 for B1 horizon, and 2.490, -0.250 and 0.103 for B2 horizon, respectively. Therefore, the results of this study showed that Yanuka et al. equation was the most useful one in determining EC_a from TDR signal for agricultural soil with low salinity and that the empirical constants for the calculation of EC_w from EC_a can be obtained through a simple calibration experiment.

Beck, T.J. and Kane, W.F. 1996, 'Current and potential uses of Time Domain Reflectometry for Geotechnical Monitoring', 47th Highway Geology Symposium, Cody, Wyoming, USA. pp. 94-103.

Abstract: The California Department of Transportation successfully used Time Domain Reflectometry (TDR) in a number of case studies to monitor the movement of landslides and embankment failures. This application of TDR technology uses a cable tester and a coaxial cable grouted in a borehole. TDR measures changes in cable impedance to determing the location of shearing, tension, or a break in the cable. The authors also deployed a remotely accessed TDR system (cellular phone, modem, datalogger, and cable tester) to monitor landslide movement. There are several advantages to TDR over the standard inclinometer technology. There is a cost advantage: $0.16/foot ($0.52/meter) for certain cables versus up to $5.50/foot ($18/meter) for inclimometer casing (the cost of the cable tester is comparable to the inclinometer probe and readout unit). The TDR reading is taken at the surface end of the cable, whereas the inclinometer probe is lowered down the casing and is occasionally lost. A TDR reading only takes a few minutes, regardless of length, compared to inclinometer readings which can be time consuming. If the monitoring location is inconvenient or unsafe, such as in a roadway, the cable end can be extended to a more convenient and safe "reading" location off the roadway, preferably behind a guardrail or other barrier. This also eliminates the traffic control which would be required for a inclinometer reading. Cables can be installed in smaller diameter boreholes, or in inclinometer casings that have deflected so much that the probe is blocked and readings can no longer be taken. Finally, readings can be taken on cables installed in borings at any inclination, horizontal through vertical. The authors' research and experience suggest a number of additional geotechnical monitoring applications for TDR. For example, foam or air-filled coaxial cables can be used to monitor groundwater levels. The presence of water in the dielectric produces a characteristic change in cable impedance. Horizontal cables buried in shallow trenches cne be used to monitor potentially unstable slopes and embankments. With the addition of some computer software, the remotely accessed TDR equipment could be used as a landslide warning system. Finally, rockfall barriers could be remotely monitored with TDR for rock impacts and damage.

Cabral, A.L., Burnotte, F. and Lefebvre, G. 1999, 'Application of TDR technology to water content monitoring of capillary barriers mead of pulp and paper residues', Geotechnical Testing Journal, vol. 22, no. 1, pp. 39-43.

Abstract: Acid mine drainage (AMD) can be curbed by covering tailings with capillary barriers. The purposes of these barriers is to prevent O₂ from interacting with mine residues. This control can be made by keeping a high degree of moisture inside the cover material. Saturation is thus a key parameter to be monitored. The purpose of this paper is to present how the time domain reflectometry (TDR) technique can be used in order to monitor the volumetric water content (θ) for pulp and paper residues that have been used as capillary barriers. Calibration curves for deinking residues are presented and compared to literature data relating to mineral and organic soils.

Dao, T.H. 1998, 'Tillage and crop residue effects on carbon dioxide evolution and carbon storage in a Paleustoll', Soil Science Society of America Journal, vol. 62, pp. 250-256.

Abstract: Cultivation, high temperatures, and a semiarid climate accelerate organic carbon (OC) loss and weaken soil structure in the Southern Plains. Our hypothesis was that differences in soil C storage attributable to tillage method are related to differences in soil respiration and microbial biomass dynamics. Carbon dioxide fluxes following wheat (Triticum aestivum L.) harvest were determined in Bethany silt loam (fine, mixed, thermic Pachic Paleustoll). Treatments were moldboard plowing (MP) and no-till (NT) at two residue rates (0 and 4 Mg ha^-1). Soil respiration was measured from 1 August to 30 September using closed chambers. Peak CO₂-C flux densities reached 1.3 g m^-1 d^-1 in NT for 2 d and stabilized at 0.4 g m^-1 d^-1. The CO₂-C evolution peaked at 4.1 and 2.9 g m^-1 d^-1 in MP with and without buried residues, respectively. After 3 d, they decreased to a steady state of 0.4 g m^-1 d^-1. Daily average temperatures in the 0- to 0.2-m depth were 0.5 to 3.4^oC higher under MP than NT, increasing microbial adenosine triphosphate (ATP), biomass C, and CO₂-C fluxes. The proportion of soil OC respired in the 60-d period was twice as great under MP than NT, accounting for 0.42 to 0.58% and 0.19 to 0.22%, respectively. After 11 yr, NT soil OC showed increases of 65,17, and 7% over the MP for the 0- to 0.05-m, 0.05- to 0.1-m, and 0.1- to 0.2-m depths, respectively. Tillage and residue incorporation enhanced C mineralization and atmospheric fluxes, suggesting that tillage intensity should be decreased to reduce C loss.

Kane, W.F. 1998, 'Embankment monitoring with time domain reflectometry', Tailings and Mine Waste '98, Balkema, Rotterdam. pp. 223-230.

Abstract: Time domain reflectometry (TDR) is used to determine embankment slope movements and piezometric levels easily, safely, and economically. The digital nature of the data allows remote monitoring by telemetry. A cable tester sends a waveform down a coaxial cable embedded in a vertical hole. If the pulse encounters a deformation or the presence of water, it is reflected. The distance to the point of reflection is determined by the cable tester. This is used to locate shear failure in the embankment. The amplitudes of the reflections in a TDR signiture indicate the severity of damage to the cable. Changes in amplitude with time correspond qualitatively to the rate of ground movement. Piezometric lebels are determined by using a hollow coaxial cable as a standpipe. Water levels are measured by noting the location where the cable displays an electrical fault.

Li, K., Amoozegar, A., Robarge, W.P. and Buol, S.W. 1997, 'Water movement and solute transport through Saprolite', Soil Science Society of America Journal, vol. 61, pp. 1738-1745.

Abstract: Many soils are underlain by saprolite. The purpose of this study was to assess the potential for preferential movement of pollutants through one soil and two saprolites in the Piedmont region of North Carolina. At one site (Site 1), two 100 by 100 by 100 cm intact blocks were isolated in situ in the Bt horizon and underlying saprolite, and a solution containing KBr, NH₄NO₃, a blue dye, and a red dye was applied to the top of each block. At a second location (Site 2), a 120 by 120 by 100 cm intact block of saprolite was similarly prepared. Acid red dye powder (5 g) was placed in four small holes (3 cm deep) bored into the surface of the block, and the block was leached with a solution containing only KBr and NH₄NO₃. After drainage, each block was dissected layer by layer (5 or 10 cm thick), and the middle 80 by 80 by 100 cm volume was divided into 768 samples and analyzed for K⁺, Br^-, NH⁺₄, and NO^-₃, as well as dye content. The visible patterns of the dyes, and extracted solute concentrations, at Site 1 indicated that preferential movement was more pronounced in the Bt horizon than in the saprolite. At Site 2, the red dye and solutes moved vertically with little lateral deviation. Our results suggest that vertical water movement in the two saprolites occurs mainly through matrix pores with little preferential movement via the visible features inherited from respective parent rocks.

Seyfried, M.S. 1993, 'Field Calibration and Monitoring of Soil-Water Content with Fiberglass Electrical Resistance Sensors', Soil Science Society of America Journal, vol. 57, pp. 1432-1436.

Abstract: Electrical resistance sensors, combined with data acquisition systems, offer a relatively inexpensive means of continuously monitoring soil-water content (θ) at barely accessible remote sites. Fiberglass resistance sensors respond across the range of θ but require calibration. With field calibration, site-specific soil conditions are implicitly accounted for, but calibration results have not been presented in the literature. The objectives of this study were to determine the accuracy and precision of field-calibrated fiberglass resistance sensors and to demonstrate their application to monitoring at remote sites. Time domain reflectometry (TDR) was used for calibration. Sixteen individual sensor-TDR calibrations and one overall calibration combining all measurements showed a strong log-linear relationship between TDR measured ? and sensor-measured resistance. Individual calibration 80% confidence intervals ranged from 0.02 to 0.045 m³ m^-3. Calibration statistics did not appreciably drift during the study. These results, and subsequent measurements, were unaffected by soil freezing, indicating that the sensors respond to liquid water content. The overall calibration 80% confidence interval was 0.065 m³ m^-3, due largely to high variability among sensors. However, changes in θ could be estimated with reasonably accuracy. Most (73%) of the resistance measurements made the year after calibration were within ̴�0.05 m³ m^-3 of the TDR-measured value. Sensor response time was shown to be within the 1-h measurement interval. In this study, field-calibrated fiberglass resistance sensors provided reasonably accurate estimates of θ at a high level of spatial and temporal resolution.

Skaling, W. 1992, 'TRASE: A Product History', in Advances in Measurement of Soil Physical Properties: Bring Theory Into Practice, eds G.C. Topp, W.D. Reynolds and R.E. Green, Soil Science Society of America, pp. 169-185.

Souza, C.F., E., M.E. and Testezlaf, R. 2001, 'Determination of the Wetting Front in Drip Irrigation Using TDR Multi-wire Probe', TDR 2001 Symposium, Evanston, Illinois, USA. 5-7 September.

Abstract: The adequate estimation of wetting front is fundamental to determinate the number of drippers per plant and its location below the plant canopy in drip irrigation. Measurements of wetting front dimensions are usually made by opening trenches, which is a time consuming method and sometimes imprecise. The recent scientific developments create the possibility to monitor the soil moisture content using electronics sensors. The objective of this research is to study the possibility to use TDR Multi-wire probes (Time Domain Reflectometry) with electrical impedance discontinuities in the determination of the wetting front dimensions in drip irrigation application. The experiment was divided in two parts. In the first one, it was studied the laboratory performance of two Multi-wire probe configurations and evaluated the probes reliability to monitor the water content variation in a porous media profile. The second part was conducted in a 250 L bucket and the water dynamic process was monitored during 48 h, after 5 mm of water application using a drip system. The results showed the viability to estimate the wetting front using TDR equipment coupled the Multi-wire probes with electrical impedance discontinuities.

Velea, D., Shields, F.D. and Sabatier, J.M. 2000, 'Elastic wave velocities in partially saturated Ottawa sand: experimental results and modelling', Soil Science Society of America Journal, vol. 64, pp. 1226-1234.

Abstract: A theoretical model is needed to predict the macroscopic mechanical properties of soil from the size, shape, and elastic properties of its constituent particles. To test one such model, we compared measured and calculated values of compressional and shear wave velocities in Ottawa sand. The sand was packed in a cylindrical tank -0.9 m in diameter and 0.9 m deep. The velocities were measured in the horizontal direction as a function of depth as the zero tension level of the water in the sand was slowly raised. In the air-dry sand the velocities varied nonuniformly with depth, reaching a maximum value about two-thirds of the way to the bottom of the tank. When water was introduced into the bottom of the sand, the nonuniform depth dependence was removed. At higher saturations, the velocities gradually decreased until the zero tension level was at the top of the sand. The nonuniform depth dependence in the dry sand has been attributed to the tank wall supporting part of the gravitational stress in the material. A modified Digby (1981) model was found to adequately account for the results in the wet material. A lumped parameter combining the contacts per grain, size, and the grain roughness was used to fit the data. In terms of the model, it is concluded that the water in the contacts between the grains had little effect on the normal contact stiffness, but reduced the tangential contact stiffness to zero.

Walker, J.P., Willgoose, G.R. and Kalma, J.D. 2001, 'The Nerrigundah data set: soil moisture patterns, soil characteristics, and hydrological flux movements', Water Resources Research, vol. 37, no. 11, pp. 2653-2658.

Abstract: This paper presents a data set that describes the spatial and temporal variability of soil moisture within the 6 ha Nerrigundah catchment, located in a temperate region of eastern Australia. The data set includes high-resolution elevation data; high-resolution (20 m) near-surface soil moisture maps; soil moisture profile measurements at 13 locations, with one being applicable for one-dimensional modeling; soil moisture measurements from four different measurement devices at a single location; soil temperature profile measurements; soil heat flux and supporting meteorological measurements, including data obtained with two pluviometers and four collecting rain gauges; surface roughness measurements; soil information for 19 locations, including field measurements of saturated hydraulic conductivity; and catchment runoff measurements. These data are available on the World Wide Web at http://www.civag.unimelb.edu.au/~jwalker/data/nerrigundah.

Yoo, S.H., Han, G.H., Bae, B.S. and Park, M.E. 1999, 'Monitoring of water content and electrical conductivity in paddy soil profile by Time Domain Reflectometry', Journal of the Korean Society of Soil Science and Fertility, vol. 32, no. 4, pp. 365-374.

Abstract: To obtain information on vertical movements of water and solute in rice paddy field during the growing season, soil water contents and bulk electrical conductivity (σ_a) were monitored using Time Domain Reflectometry. Soil water contents with depth showed ε-shaped profiles constituting of partly saturated zones at top and bottom layers and unsaturated zones (20-100cm) between them. Analysis by fitting with a van Genuchten-type model showed that soil water contents at 60 cm were affected by both water supplied from surface water and groundwater, but at 80 cm mainly affected by groundwater. Water percolation at the rate of 2 cm day-1 were, but large fluctuation from 10 to 38 cm day^-1 in C1 layer (60-90 cm). Therefore, it can be said that any water or solute entering C1 layer is very rapidly transported to C2 layer, especially during the period of high groundwater table staying and retarded to a relatively constant percolation rate in C2 layer. This can be manifested by the fact that rapid decrease and steady increase of electrical conductivities at 50 and 110 cm depth respectively, were found around that period.

TRASE TDRReferences

TRASE TDR
References