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Time domain reflectometry (TDR) is commonly used to determine the soil bulk electrical conductivity. To obtain accurate measurements, the three parameters of a series resistor model (probe constant, [K.sub.p]; cable resistance, [R.sub.c]; and remaining resistance, [R.sub.0]) are typically calibrated using liquids with known electrical conductivity. Several studies have reported discrepancies between calibrated and directly measured parameters of the series resistor model. In this study, we examined the possibility that a technical issue with the TDR100 cable tester contributed to part of these inconsistencies. Our results showed that with an increasing level of waveform averaging, the reflection coefficient, as well as [K.sub.p], [R.sub.C], and [R.sub.0], approached a maximum value. A comparison with independently determined values indicated that a high level of waveform averaging provided the physically most plausible results. Based on our results, we propose averaging at least 16 waveforms, each consisting of at least 250 points. An oscilloscope-based signal analysis showed that the increase in the reflection coefficient with increasing waveform averaging in saline media is related to a capacitance associated with electrode polarization in combination with a change in the pulse period of the pulse train when the TDR100 starts collecting data points. This capacitance resulted in a slow change of the average voltage in the TDR pulse train until a stable average voltage was reached. Higher levels of waveform averaging cancel the impact of the first erroneous voltage measurements out. In practical applications, the errors in the determination of the bulk electrical conductivity can be as high as 5% for the low-conductivity range ( Abbreviations: RC, resistor--capacitor; TDR, time domain reflectometry; WavAvg, number of waveform averages. doi:10.2136/sssaj2009.0247

Studying solute transport in soils is hampered by a lack of technology for continuously monitoring ionic concentration of contaminants. The electrical conductivity of pore water is a strong indicator of ionic concentration of contamination in soil. Using the bulk electrical conductivity of a soil measured by lime domain reflectrometry (TDR) to predict the soil pore-water electrical conductivity appears to be a promising technique. This study presents a new method for estimating the pore-water electrical conductivity of saturated sandy soils using a single TDR test. The effects of pore-water electrical conductivity, temperature, porosity, and ionic types on the electrical conductivity of soil were studied. An average value of the exponent in the Archie's Law was found to be 1.457 for the saturated sandy soils used in this study. A laboratory model infiltration test was also conducted with continuous monitoring of the electrical conductivity of the pore water by TDR. The results showed that TDR is able to provide a reasonably accurate estimation of the electrical conductivity of pore water. Consequently, it may be possible to monitor the in situ ionic contamination in saturated sandy soils using TDR technology. Key words: sandy soils, electrical conductivity, time domain reflectometry (TDR), dielectric constant. L'etude du transport des solutes dans les sols est limilee par le manque de technologies pouvant mesurer en continu la concentration ionique des contaminants. La conductivity electrique de l'eau inlerstitielle est tin bon indicateur de la concentration ionique des contaminants dans les sols. L'utilisation de la conductivity electrique globale d'un sol a I'aide de la reflec tome trie en domaine temps (RDT) semble etre une technique prometteuse pour la prediction de la conductivity electrique de l'eau inlerstitielle contenue dans ce sol. Cette etude presente une nouvelle methode pour estimer la conductivity electrique de l'eau inlerstitielle de sols sablonneux satures a I'aide d'un seul essai RDT. Les effets de la conductivity electrique de l'eau interstitielle, de la temperature, de la porosite et des especes ioniques sur la conductivity electrique du sol ont etc etudies. La valeur moyenne de l'exposant de la loi d'Archie a ete evaluee a 1,457 pour les sols sablonneux satures utilises dans cette etude, Un essai en laboratoire d'infiltration, durant lequel la conductivity electrique de l'eau interstitielle a etc mesuree en continu par RDT, a aussi ete effect ue. Les resultats ont demontre qu'il est possible d'oblenir une estimation raisonnablement precise de la conductivity electrique de l'eau interstitielle a I'aide de la RDT, Ainsi, il serail possible de mesurer in situ la contamination ionique dans des sols sablonneux satures avec la technologie RDT. Mots-cies : sols sablonneux, conductivity electrique, reflectometrie en domaine temps (RDT), constante dielectrique. [Traduit par la Redaction], Introduction Determination of ionic concentrations in soils in the field is important for assessment of salinity (Rhoades 1989), study of solute transport (Kachanoski et al. 1992; Ward et al. 1994; [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2009.10.001 Byline: Philippe Grosso (a), Marc Le Menn (b), Jean-Louis De Bougrenet De La Tocnaye (a), Zong Yan Wu (a), Damien Malarde (a) Keywords: Salinity sensor; Absolute salinity; Refractive index; Density Abstract: Optical salinity sensors described here measure directly the seawater refractive index and thus enable a measurement of the seawater density and composition variation. We detail the measurement dependence to environmental parameters (in particular temperature and pressure) compared to conductivity sensors, and demonstrate that it may be advantageous to directly measure refractive index rather than electrical conductivity and so obtain a more direct route to density and absolute salinity. Author Affiliation: (a) Telecom-Bretagne, Departement Optique, UMR CNRS 6082 FOTON, CS 83818, 29238 Brest Cedex 3, France (b) Laboratoire de Metrologie et de Chimie Oceanographique, SHOM, 13 rue du ChAcentstelier, BP 30316, 29603 Brest Cedex, France Article History: Received 17 June 2008; Revised 23 September 2009; Accepted 2 October 2009

In soils with high electrical conductivities, time domain reflectometry (TDR) principles fail to measure the apparent dielectric constant by travel time analysis. This limits the application of water content measurement of existing TDR technologies on those materials. This paper describes a new approach for determining the dielectric constants in highly conductive soils from surface reflections of TDR signals. The multiple reflections at the interfaces of impedance mismatches in the ASTM standard probe were studied. Extension rods were used to avoid the overlap of the reflections along the probe. A relationship between the reflection coefficient at the soil surface and the apparent dielectric constant of the soil was established theoretically and validated by laboratory experiments. Results indicate that the dielectric constant can be determined with reasonable accuracy from the surface reflection coefficient even for soils with high electrical conductivities, where the conventional travel time analysis fails. Compared with alternative approaches, such as based on inversion model, this new method offers high time efficiency in extending TDR applications in highly conductive soils. DOI: 10.1061/(ASCE)GT.1943-5606.0000170 CE Database subject headings: Soil properties; Electrical conductivity; Coefficients; Reflection.

We developed soil-specific calibrations for a time domain reflectometry (TDR) sensor, a water content reflectometer (WCR), and an impedance sensor for 19 soil moisture monitoring sites in Wyoming. The main objective was to calibrate the WCR sensors that form a statewide distributed soil moisture network. A secondary objective was to use the TDR and impedance sensor data to better understand the WCR readings. All calibrations were conducted in the laboratory by mixing different amounts of water in the soils to obtain a range of soil water contents and by packing the soils in a bucket. The observed apparent permittivity as a function of soil water content was relatively high for the WCR and impedance sensors (up to 187 and 150% higher, respectively, than TDR). This was attributed to the relatively low operating frequency (< 175 and 50 MHz, respectively) of the WCR and impedance devices. Soil texture had little impact on sensor readings. Differences between soils for the WCR and impedance sensors were due to differences in bulk soil electrical conductivity (EC) and dielectric relaxation losses. Relaxation losses were found to be significant at 50 MHz for all soils. Regression equations (R2 > 0.643) were developed for the WCR and impedance sensors that relate the slope of the soil water content vs. permittivity relationship to the bulk soil EC (WCR and impedance sensors) or the imaginary permittivity (impedance sensor). Abbreviations: DC, direct current; EC, electrical conductivity; TDR, time domain reflectometry; WCR, water content reflectometer.

A novel technique is developed based on the piezoresistivity of electrically filled polymers to measure the tensile strain in modified geosynthetics without the need for conventional instrumentation (e.g., strain gauges). This paper reports the development of the technique and the results obtained on high-density polyethylene and polypropylene (PP) geogrid specimens filled with carbon black and carbon nanotubes (NTs). It was found that except for NT-filled PP specimens all other composites exhibited significant strain sensitivity in their conductivity. The proof-of-concept study reported in this paper has two important features: (1) strain sensitivity of electrical conductivity was demonstrated in polyolefins used to manufacture geosynthetics; and (2) this strain sensitivity was obtained and demonstrated over the range of strain values that are important in geosynthetic engineering applications. DOI: 10.1061/(ASCE)GT.1943-5606.0000062 CE Database subject headings: Geosynthetics; Instrumentation; Sensors; Strain.

Lime kiln dust (LKD) is used for modifying pavement subgrades to expedite construction on wet clayey soils. This paper describes the short-term development (typically, over the first 3 to 7 days) of electrical conductivity and penetration resistance of LKD-modified soils. The normalized net change of electrical conductivity is solely related to the LKD dosage. The decrease of electrical conductivity with time coincides with the increase of penetration resistance with time. The correlations of electrical conductivity with strength gain in LKD and lime-modified soils suggest that electrical conductivity measurements can potentially be useful for quality control in field applications. CE Database subject headings: Dust; Electrical conductivity; Penetration resistance; Clays.

Time domain reflectometry (TDR) is a technique that allows simultaneous estimates of apparent permittivity ([epsilon].sub.a]) and hence volumetric water content ([theta]) and bulk electrical conductivity ([[sigma].sub.a]). Difficulties arise for [theta] and [[sigma].sub.a] determination, however, when uncoated TDR probes (UP) are used in highly conductive media. This work shows that [[sigma].sub.a] can be estimated in highly conductive media using a TDR probe coated with a high-dielectric insulator (CP). To this end, the Dalton method for [[sigma].sub.a] estimations was applied to a 10-cm-long three-rod TDR probe insulated with a 0.2-mm-thick epoxy-ceramic composite coating with a relative permittivity, [[epsilon].sub.r], of 32.3. This method was calibrated on different NaCl--water solutions (0-15 dS [m.sup.-1]) and compared with the standard long-time TDR method for ([[sigma].sub.a] estimations using an UP. The method was subsequently used for determining [[sigma].sub.a] in four different soils with different values of [theta] and [[sigma].sub.a] (0-6 dS [m.sup.-1]) and again compared with the standard TDR procedure. The low error (RMSE = 1.5) for the comparison between the [[epsilon].sub.a] measured with the CP and that calculated with the analytical solution for coaxial probes indicates that the CP is accurate enough for [[epsilon].sub.a] estimations. For [[sigma].sub.a] values Abbreviations: CP, high-dielectric coated time domain reflectometry probe; DC, direct current; TDR, time domain reflectometry; UP, uncoated time domain reflectometry probe.

Measurement of electrical conductivity by time domain reflectometry (TDR) requires knowledge of the source step voltage, which is often implicitly accounted for in the measured reflection coefficient. Errors may arise, however, from imperfect amplitude calibration when transforming the voltage signal into the reflection coefficient signal. This instrument error was identified as a considerable source of error in addition to cable resistance for TDR electrical conductivity measurements. The effect of the instrument error due to imperfect amplitude calibration was theoretically examined by the direct current circuit model and experimentally verified. The instrument error resulted in an overestimation of electrical conductivity while the cable resistance led to an underestimation. We clarified that the series resistors model for correction of cable resistance is accurate if the measured reflection coefficient is corrected for the instrument error. A calibration (correction) method for the measured reflection coefficient was proposed to account for both the instrument error and the effect of cable resistance, leading to a simple, accurate, and theoretically sound procedure for TDR electrical conductivity measurements. Abbreviations: EC, electrical conductivity; TDR, time domain reflectometry.

There will be transition zones of electric current near the electrodes, if the electric conductive area of electrodes is smaller than that of soil. Electroosmosis tests show that the electric current in the transition zones follows a complicated two-dimensional path, while the electric current outside these zones is approximately one dimension. The thickness of transition zones is potty compared to the whole thickness of soil between anodes and cathodes. Conception of interface resistance on zero thickness interfaces, which is a simplified expression for finite thickness transition zones, is presented in this paper to simplify the two-dimensional problem within the transition zones into one dimension. Studies show that the interface electric resistance is inversely proportional to the ratio of electric conductive areas between electrodes and soil. A brief formula is deduced to predict the in situ interface electrical resistance, which presents a more accurate estimation of electric current and energy consumption to the design of electroosmotic consolidation engineering. CE Database subject headings: Interfaces; Electrical resistivity; Electric transmission; Soil consolidation; Fine-grained soils.

This paper presents a model-based approach to determine dielectric constants from time domain reflectometry (TDR) measurement in highly conductive soils. It makes use of information contained in the TDR signal from the reflection at the surface of the soil rather than the reflection from the end of the probe. The TDR method is widely used to determine the volumetric water content of soils. Commonly used information from the TDR signals includes the apparent dielectric constant and the electrical conductivity. The apparent dielectric constant is generally measured by analyzing the travel time of electromagnetic waves reflected from the end of the soil probe. In soils with high electrical conductivities, the attenuation of the signal can eliminate the reflection from the end of the probe, which limits the application of TDR to these materials. A simplified frequency-independent dielectric model is utilized to invert the dielectric constant from the reflected signals at the soil surface. Results indicate that the dielectric constant can be determined with reasonable accuracy by the proposed approach for soils with high electrical conductivity, where the conventional travel time analysis fails due to significant signal attenuation. CE Database subject headings: Dielectric constant; Electrical conductivity; Electrical resistivity; Soil properties; Travel time.

Detailed information on soil textural heterogeneity is essential for land management and conservation, h is well blown that in individual fields, measurement of the soil's apparent electrical conductivity ([EC.sub.a]) offers an opportunity to map the clay content of soils with Free drainage under a humid climate. At the catchment scale, however, units of different land management and differing sampling dates add variation to [EC.sub.a] and constrain the mapping across field boundaries. We analyzed their influence and compared three approaches For applying electromagnetic induction ([EM.sub.v]) to clay-content mapping at the landscape scale across the boundaries of individual fields and different sampling dates. In the study region, a separate calibration of the relation between clay and [EC.sub.a] For each field and sampling date (fieldwise calibration) yielded satisfactory clay-content predictions only if the costly precondition of sufficient calibration points for each field was fulfilled. We propose a method (nearest-neighbors [EC.sub.a] correction) For unifying [EC.sub.a] across boundaries based only on the [EC.sub.a] data themselves, and the assumption of continuity of textural properties at field boundaries, which was fulfilled in the landscape studied. Prediction is calibrated once for the entire landscape, which allows a reduced set of calibration points. The coefficient of determination for predicting clay content (here, including silt Abbreviations: [C.sub.org] organic carbon content: [EC.sub.a], apparent electrical conductivity: [EM.sub.v], electromagnetic induction.

The EM-38 is a noninvasive instrument, commonly used for monitoring salinity, mapping bulk soil properties, and evaluating soil nutrient status. Users in the Southwest USA have observed as much as 20% 'drift' in the measurement of bulk soil electrical conductivity (E[C.sub.a]) with this instrument. This drift has usually been ignored or compensated for by statistical procedures. We performed laboratory and field experiments to determine if the drift is doe to calibration instability of the instrument or to heating of the instrument by the sun. In laboratory experiments, after a warm-up period, the instrument provided constant readings in the range 25 to 40[degrees]C; above 40[degrees]C the response of the instrument was unpredictable. In field experiments, where we placed the EM-38 in a fixed location we observed an unexpected response at air temperatures below 40[degrees]C. Temperature sensors in different locations on the instrument demonstrated that temperature differences between the instrument's transmitting and receiving coils and the control panel (CP) were as great as 20[degrees]C. As the instrument is temperature compensated from this CP, erroneous compensation occurred when the instrument was placed in direct sunlight. In this study, we demonstrate that differential heating of the EM-38is one cause of drift and erroneous bulk electrical conductivity measurement; shading the instrument substantially reduced this problem, effectively extending the reliable working temperature range by minimizing drift.

In time domain reflectometry (TDR), the ohmic resistance of the sample medium is related to the amplitude of the reflected signal at long time, once all the multiple reflections have taken place and steady state is achieved. Such a relationship, which permits measuring the sample electrical conductivity, is exact when no signal dissipation occurs other than in the sample. To account for signal attenuation along the coaxial cable, sample and cable are generally modeled as two resistors in series. In this work we review the fundamentals of the transmission line theory and demonstrate, both theoretically and experimentally, that such a formulation is incorrect. We propose a new simple procedure for the analysis of TDR signals based on a difference reflection method, by scaling the reflection coefficients with respect to one or more standards of known conductivity. The procedure was tested on 16 Ca[Cl.sup.2] solutions, using two different TDR probes and two cable lengths. The experimental results are in excellent agreement with the theory.

A noninvasive approach for measurements of near-surface water content ([Theta]) and bulk electrical conductivity ([[Sigma].sub.a]) using time domain reflectometry (TDR) is presented. In this approach, an ordinary three-rod TDR probe is used together with a polyvinyl chloride (PVC) surface block that surrounds half the measurement volume. Theoretical and experimental results show that an analytical solution of the apparent dielectric constant [K.sub.a] and the [[Sigma].sub.a] of the soil is possible. Thus, the suggested technique does not require a separate calibration of the relationship between the measured effective [K.sub.a] and [K.sub.a] of the soil. The variability of the measurements was shown to be slightly higher than using the traditional approach. The spatial sensitivity of the suggested technique was also investigated. it was shown that using a three-rod TDR probe with a rod spacing of 0.05 m allows the [Theta] and [[Sigma].sub.a] to be measured in the uppermost 2 cm of the soil.

Time domain reflectometry (TDR) based electrical conductivity (EC) measurements underestimate solution conductivity ([Sigma]) as salinity increases unless a correction parameter, [R.sub.cable], is incorporated into the EC calculation. The parameter [R.sub.cable] accounts for series resistance of cable, connectors, and cable tester. The main objective of this study was to propose and verify a simple method of directly measuring [R.sub.cable] from the load resistance on waveguides that are shorted together. Also, the dependence of [R.sub.cable] on cable length vs. other resistances was investigated. The parameter [R.sub.cable] was found to be a function of cable length and a constant probe resistance. Errors caused by ignoring [R.sub.cable] in EC determinations increased with both salinity and series resistance. Although there may be cases where [R.sub.cable] has a negligible effect on EC determinations, there are also situations where it is important. This study shows that the measurement of [R.sub.cable] is so simple that there is little reason not to routinely incorporate it in all TDR-based EC determinations.

The measurements of soil water content and bulk soil electrical conductivity is conducted using Time Domain Reflectometry. Estimating specific refraction characteristics of various soils is absolutely essential for this process. The estimation of refraction characteristics on the basis of physico-chemical properties of soils, requires further experimentation and analysis to understand the effect of bulk density and bound water on the refraction process.

An economical balun that transforms the electrical field from unbalanced to balanced without causing impedance transformation overcomes the difficulties in time domain reflectometry (TDR) when it is used for simultaneous identification of soil moisture content and electrical conductivity (EC). Coaxial probes, when compared to parallel probes, imply signal losses in the antenna wire leading to the probe, the need for a costly balun and weakening of signals in the balun that impeded precise EC estimation.

A high pressure, high temperature cell has been constructed and used to determine the temperature dependence of the electrical conductivity of various geological materials at a frequency of 60 Hz. Test conditions in the cell approximate an in situ environment by means of a variable uniaxial confining pressure and a separately variable pore pressure. A wide array of constituents of typical oil bearing formations have been examined at temperatures up to 240 degress C.

It has been assumed, but not proved, that the spatial weighting and sample volume of Time domain reflectometry (TDR) regarding bulk soil electrical conductivity ([EC.sub.b]) equal those determined for the relative dielectric permittivity (K). In this study, two types of experiments were carried out: (i) sensitivity experiments where the cumulative vertical weighting as a function of distance between the probe rods and the soil surface were determined for both K and [EC.sub.b] at two different soil water contents and (ii) solute diffusion experiments to evaluate the discrepancies between actual and TDR-measured relative [EC.sub.b] in the case where a steep gradient in [EC.sub.b] passes the probe. Three-rod TDR probes and a sandy loam soil were used in both experiments. The sensitivity experiments confirmed that TDR weights K and [EC.sub.b] equally in the transverse plane. Hence, previously established relationships to calculate the weighting function and sample area of a given TDR-probe geometry apply for both K and [EC.sub.b]. The diffusion experiments showed that if a steep vertical solute gradient passes a horizontally inserted TDR probe, the TDR-measured [EC.sub.b] profile will be more spread than the actual profile passing the probe. This phenomenon of artificial (TDR-induced) diffusion is caused by (i) TDR probes not representing a point measurement, and (ii) the nonlinear weighting of K and [EC.sub.b] in the transverse plane. As the steepness of the solute concentration profile diminishes the TDR-induced diffusion decreases rapidly and becomes negligible for most applications. The effect of TDR-probe geometry on the discrepancy between actual and TDR-measured relative concentration was examined theoretically for selected two- and three-rod probe configurations.

The success of time domain reflectometry (TDR) has !ed to the development of other instruments that use the soil dielectric constant as the basis for determining volumetric soil water content. An example is the Water Content Reflectometer (WCR; Campbell Scientific, Logan, UT), which is much less expensive than TDR and is used widely, although little has been published concerning its applicability to soil water content monitoring. The primary objectives of this study were to determine the WCR soil water calibration for different soils and to investigate how it is affected by changing temperature. We found the individual sensors to be very precise (CV [is less than or equal to] 0.05) under the controlled laboratory conditions of this study. Variability among sensors, determined in air and ethanol, indicated significant ([Alpha] = 0.05) sensor differences that were largely accounted for with a simple additive correction. Sensor soil water calibration was investigated in four soils under varying water contents across a 40 [degrees] C temperature range. We found that (i) soil water calibration was significantly ([Alpha] = 0.05) different for each soil tested, (ii) there was a significant ([Alpha] = 0.05) temperature response for all soils, and (iii) the effect of temperature varied with soil water content and soil type. Both the soil type and temperature sensitivities we observed were probably due to the relatively high electrical conductivity (EC) of the soils tested.

The electrical permittivity and conductivity of the bulk soil are a function of the permittivity and conductivity of the pore water. For soil water contents higher than 0.10 both functions are equal, facilitating in situ conductivity measurements of the pore water. A novel method is described, based on simultaneous measurements of permittivity and conductivity of the bulk soil from which the conductivity of the pore water can be calculated. A prototype of a pore water conductivity sensor based on this method is presented. Validation results show that the method can be used for a broad range of soils and is valid for water contents between 0.10 and saturation and for the conductivity of the pore water up to 0.3 S [m.sup.-1].

Cross-well induction logging as known in the oil industry is a method for determining the electrical conductivity distribution between boreholes from the low-frequency electromagnetic field measurements in the boreholes. In this paper, we discuss the reconstructions of the three-dimensional (3-D) conductivity distribution using the contrast source inversion (CSI) method. In order to improve the reconstruction results, the concept of the extended Born approximation has been used to arrive at a preconditioning operator. Results of a number of numerical examples show that by using this preconditioning operator, a large conductivity contrast of the unknown objects (factor of 100) can be reconstructed up to an acceptable degree of accuracy. Moreover, in each iteration, the computational effort to generate the preconditioning operator is negligible. Index Terms--Cross-well, induction logging, nonlinear inversion, three-dimensional.

Estimation of bulk electrical conductivity using time domain reflectometry, has been proposed by Topp even before Nadler. Nadler's method also involves an extra level of equation which is not necessary. Nadler, Dasberg and Lapid, when questioned by Heimovaara, did not produce satisfactory reply and never cleared the doubts of Heimovaara. Although Nadler claimed that the method does not use the Giese-Tiemann (G-T) equation, the results reveal a misapplication of the G-T equation.