scholarly journals Estimating Pore Water Electrical Conductivity of Sandy Soil from Time Domain Reflectometry Records Using a Time-Varying Dynamic Linear Model

Sensors ◽  
2018 ◽  
Vol 18 (12) ◽  
pp. 4403 ◽  
Author(s):  
Basem Aljoumani ◽  
Jose Sanchez-Espigares ◽  
Gerd Wessolek
Keyword(s):  
Electrical Conductivity ◽  
Dielectric Permittivity ◽  
Linear Relationship ◽  
Linear Model ◽  
Pore Water ◽  
Sandy Soil ◽  
Time Domain ◽  
Time Domain Reflectometry ◽  
Relative Dielectric Permittivity ◽  
Time Varying

Despite the importance of computing soil pore water electrical conductivity (σp) from soil bulk electrical conductivity (σb) in ecological and hydrological applications, a good method of doing so remains elusive. The Hilhorst concept offers a theoretical model describing a linear relationship between σb, and relative dielectric permittivity (εb) in moist soil. The reciprocal of pore water electrical conductivity (1/σp) appears as a slope of the Hilhorst model and the ordinary least squares (OLS) of this linear relationship yields a single estimate ( 1 / σ p ^ ) of the regression parameter vector (σp) for the entire data. This study was carried out on a sandy soil under laboratory conditions. We used a time-varying dynamic linear model (DLM) and the Kalman filter (Kf) to estimate the evolution of σp over time. A time series of the relative dielectric permittivity (εb) and σb of the soil were measured using time domain reflectometry (TDR) at different depths in a soil column to transform the deterministic Hilhorst model into a stochastic model and evaluate the linear relationship between εb and σb in order to capture deterministic changes to (1/σp). Applying the Hilhorst model, strong positive autocorrelations between the residuals could be found. By using and modifying them to DLM, the observed and modeled data of εb obtain a much better match and the estimated evolution of σp converged to its true value. Moreover, the offset of this linear relation varies for each soil depth.

Measurement of electrical conductivity of pore water in saturated sandy soils using time domain reflectometry (TDR) measurements

2010 ◽  
Vol 47 (2) ◽  
pp. 197-206 ◽  
Author(s):  
R. P. Chen ◽  
Y. M. Chen ◽  
W. Xu ◽  
X. Yu
Keyword(s):  
Electrical Conductivity ◽  
Pore Water ◽  
Time Domain ◽  
Sandy Soils ◽  
Ionic Concentration ◽  
Time Domain Reflectometry ◽  
Laboratory Model ◽  
Accurate Estimation ◽  
Archie’S Law ◽  
Average Value

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 time 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.

Time-domain reflectometry — parametric study for the evaluation of physical properties in soils

2009 ◽  
Vol 46 (7) ◽  
pp. 753-767 ◽  
Author(s):  
Jeffrey M. Schneider ◽  
Dante Fratta
Keyword(s):  
Dielectric Permittivity ◽  
Time Domain ◽  
Parametric Study ◽  
Capillary Rise ◽  
Time Domain Reflectometry ◽  
Relative Dielectric Permittivity ◽  
Proper Understanding ◽  
Abrupt Changes ◽  
Sand And Gravel

Time-domain reflectometry (TDR) has become a commonly used method in geotechnical engineering to measure the volumetric water content and electrical conductivity in soils. The ability of TDR to accurately determine soil properties depends on the proper understanding of the parameters that affect the propagation of an electromagnetic pulse along the TDR waveguide. The purpose of this paper is to document a parametric study and analyses aimed at gaining a better understanding of TDR measurements and to evaluate the limits in the measurement technique. A parametric study on TDR signals was performed by determining the effects of heterogeneities in the dielectric permittivity, conductivity, and magnetic permeability in sand and gravel specimens. Impedance differences in the probe head were found to contribute to inaccurate travel-time measurements that affect material dielectric permittivity calculations. The calculated relative dielectric permittivity may also be dependent on local changes in porosity near the probes. Tests performed in layered materials indicate that TDR can be used to find abrupt changes in material permittivity, such as the depth to saturation. However, problems in the determination of capillary rise may contribute to uncertainties in the proper determination of permittivity and thicknesses of layers. The presence of ferromagnetic materials was found to change the measured electromagnetic wave velocity. However, the properties of materials outside the radius defined by the probes and beneath the probes minimally affected the TDR results in the two-rod probe used.

scholarly journals Factors affecting soil permittivity and proposals to obtain gravimetric water content from time domain reflectometry measurements

2014 ◽  
Vol 51 (11) ◽  
pp. 1303-1317 ◽  
Author(s):  
L.M. Thring ◽  
D. Boddice ◽  
N. Metje ◽  
G. Curioni ◽  
D.N. Chapman ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Water Content ◽  
Time Domain ◽  
Time Domain Reflectometry ◽  
Silty Sand ◽  
Dry Density ◽  
Relative Dielectric Permittivity ◽  
Swell Potential ◽  
Custom Made ◽  
Gravimetric Water Content

Time domain reflectometry (TDR) measures the apparent relative dielectric permittivity (ARDP) of a soil and is commonly used to determine the volumetric water content (VWC) of the soil. ARDP is affected by several factors in addition to water content, such as the soil’s electrical conductivity, temperature, and density. These relationships vary with soil type and are very soil-dependent, and despite previous research, they are still not fully understood. A multivariate statistical approach (principal component analysis, PCA) is used to describe a range of soils from two separate sites in the UK (clay and silty sand – sandy silt). The advantage of a PCA is that it considers several variables at a time, giving an immediate picture of their underlying relationships. It was found that for the studied soils, ARDP was positively correlated with VWC and bulk electrical conductivity, but did not show any dependence on some other geotechnical parameters. TDR has recently been used in geotechnical engineering for measuring the gravimetric water content (GWC) and dry density. However, the current approaches require a custom-made TDR probe and an extensive site specific empirical laboratory calibration. To extend the potential use of TDR in the geotechnical industry, three relatively simple methods are proposed to estimate the GWC from VWC (derived from the measured ARDP values) and dry density depending on the amount of information known about the soil. Examples of possible applications of these methods include continuous monitoring of consolidation adjacent to a structure, the effect of seasonal weather and climate change on ageing earthwork assets, and the shrink–swell potential adjacent to trees. All three methods performed well, with between 83% and 98% of the data lying within a ±5% GWC envelope, with the data for clay soils performing better than those for silty sands – sandy silts. This is partly due to the fact that the applied relationship converting ARDP to VWC performs better for clays than silty sands – sandy silts, as well as less variation of the estimated bulk density that is needed to derive the dry density.

scholarly journals Time-Domain Reflectometry (TDR) Monitoring at a Lab Scale of Aerobic Biological Processes in a Soil Contaminated by Diesel Oil

2019 ◽  
Vol 9 (24) ◽  
pp. 5487 ◽  
Author(s):  
Andrea Vergnano ◽  
Alberto Godio ◽  
Carla Maria Raffa ◽  
Fulvia Chiampo ◽  
Francesca Bosco ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Dielectric Permittivity ◽  
Time Domain ◽  
Diesel Oil ◽  
Time Domain Reflectometry ◽  
Biological Processes ◽  
Sem Images ◽  
Soil Matrix ◽  
Biological Phenomena ◽  
Salt Depletion

This study aims to monitor the biological processes ongoing in a hydrocarbon polluted soil. The experiments were carried out at a laboratory scale by measuring the evolution of its geophysical electromagnetic parameters. Time-domain reflectometry (TDR) probes were used to measure dielectric permittivity and electrical conductivity in columns of sandy soil artificially contaminated with diesel oil (Voil/Vtot = 0.19). To provide aerobic conditions suitable for the growth of microorganisms, they were hydrated with Mineral Salt Medium for Bacteria. One mesocosm was aerated by injecting air from the bottom of the column, while the other had only natural aeration due to diffusion of air through the soil itself. The monitoring lasted 105 days. Geophysical measurements were supported by microbiological, gas chromatographic analyses, and scanning electron microscope (SEM) images. Air injection heavily influenced the TDR monitoring, probably due to the generation of air bubbles around the probe that interfered with the probe–soil coupling. Therefore, the measurement accuracy of geophysical properties was dramatically reduced in the aerated system, although biological analyses showed that aeration strongly supports microbial activity. In the non-aerated system, a slight (2%) linear decrease of dielectric permittivity was observed over time. Meanwhile, the electrical conductivity initially decreased, then increased from day 20 to day 45, then decreased again by about 30%. We compared these results with other researches in recent literature to explain the complex biological phenomena that can induce variations in electrical parameters in a contaminated soil matrix, from salt depletion to pore clogging.

Time domain reflectrometry measurements of water content in coarse waste rock

2003 ◽  
Vol 40 (1) ◽  
pp. 137-148 ◽  
Author(s):  
Craig Nichol ◽  
Leslie Smith ◽  
Roger Beckie
Keyword(s):  
Electrical Conductivity ◽  
Dielectric Permittivity ◽  
Ambient Temperature ◽  
Water Content ◽  
Travel Time ◽  
Pore Water ◽  
Time Domain ◽  
Waste Rock ◽  
High Electrical Conductivity ◽  
Laboratory Calibration

Methods are presented to calibrate and implement a time domain reflectrometry (TDR) system to estimate the water content of coarse mine waste rock containing high solute concentrations in the pore water. High electrical conductivity of the pore water reduces the quality of TDR waveforms through the loss of signal amplitude. Zegelin-type probes with a resistive coating on the center conductor were used to obtain higher signal-to-noise waveforms. These probes must be calibrated prior to use. The TDR pulse travel-time measured in soils containing pore water with high solute concentrations increases systematically with solute concentration. Empirical calibrations are derived for waste rock with low and high electrical conductivity pore water. An ambient temperature correction is derived from observed diurnal fluctuations in the measured travel time to determine whether or not a detailed laboratory calibration for temperature effects is required. The variation of apparent dielectric permittivity with temperature is positively correlated with temperature at low water content and negatively correlated at high water content. This trend indicates the influence of water bound to mineral surfaces on the variation of apparent dielectric permittivity with temperature. Examination of our field data indicates that the effect of dissolved ions on the TDR calibration was great enough to justify a calibration that accounts for pore-water composition. The effect of ambient temperature was found to be small enough that an intensive laboratory calibration was not required.Key words: time domain reflectrometry, water content, mining.

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