scholarly journals Characterization of Electromagnetic Properties of In Situ Soils for the Design of Landmine Detection Sensors: Application in Donbass, Ukraine

2019 ◽  
Vol 11 (10) ◽  
pp. 1232 ◽  
Author(s):  
Timothy Bechtel ◽  
Stanislav Truskavetsky ◽  
Gennadiy Pochanin ◽  
Lorenzo Capineri ◽  
Alexander Sherstyuk ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Dielectric Permittivity ◽  
Magnetic Permeability ◽  
Time Domain Reflectometry ◽  
Electromagnetic Properties ◽  
Signal Frequency ◽  
Soil Conditions ◽  
Detector Performance ◽  
Metal Detector

To design holographic and impulse ground penetrating radar (GPR) sensors suitable for humanitarian de-mining in the Donbass (Ukraine) conflict zone, we measured critical electromagnetic parameters of typical local soils using simple methods that could be adapted to any geologic setting. Measurements were recorded along six profiles, each crossing at least two mapped soil types. The parameters selected to evaluate GPR and metal detector sensor performance were magnetic permeability, electrical conductivity, and dielectric permittivity. Magnetic permeability measurements indicated that local soils would be conducive to metal detector performance. Electrical conductivity measurements indicated that local soils would be medium to high loss materials for GPR. Calculation of the expected attenuation as a function of signal frequency suggested that 1 GHz may have optimized the trade-off between resolution and penetration and matched the impulse GPR system power budget. Dielectric permittivity was measured using both time domain reflectometry and impulse GPR. For the latter, a calibration procedure based on an in-situ measurement of reflection coefficient was proposed and the data were analyzed to show that soil conditions were suitable for the reliable use of impulse GPR. A distinct difference between the results of these two suggested a dry (low dielectric) soil surface, grading downward into more moist (higher dielectric) soils. This gradation may provide a matching layer to reduce ground surface reflections that often obscure shallow subsurface targets. In addition, the relatively high dielectric deeper (10 cm–20 cm) subsurface soils should provide a strong contrast with plastic-cased mines.

Measuring transient solute transport through the vadoze zone using time domain reflectometry

Soil Research ◽  
2001 ◽  
Vol 39 (6) ◽  
pp. 1359 ◽  
Author(s):  
I. Vogeler ◽  
S. Green ◽  
A. Nadler ◽  
C. Duwig
Keyword(s):  
Electrical Conductivity ◽  
Solute Transport ◽  
Time Domain ◽  
Deterministic Model ◽  
Soil Surface ◽  
Time Domain Reflectometry ◽  
Richards Equation ◽  
Electrical Conductivities ◽  
Destructive Measurement

Time domain reflectometry (TDR) was used to monitor the transport of conservative tracers in the field under transient water flow in a controlled experiment under a kiwifruit vine. A mixed pulse of chloride and bromide was applied to the soil surface of a 16 m2 plot that had been isolated from the surrounding orchard soil. The movement of this solute pulse was monitored by TDR. A total of 63 TDR probes were installed into the plot for daily measurements of both the volumetric water content (θ) and the bulk soil electrical conductivity (σa). These TDR-measured σa were converted into pore water electrical conductivities (σw) and solute concentrations using various θ–σa–σw relationships that were established in the laboratory on repacked soil. The depth-wise field TDR measurements were compared with destructive measurement of the solute concentrations at the end of the experiment. These results were also compared with predictions using a deterministic model of water and solute transport based on Richards’ equation, and the convection–dispersion equation. TDR was found to give a good indication of the shape of the solute profile with depth, but the concentration of solute was under- or over-estimated by up to 50%, depending on the θ–σa–σw relationships used. Thus TDR can be used to monitor in situ transport of contaminants. However, only rough estimates of the electrical conductivity of the soil solution can so far be obtained by TDR.

Enhancing modelled water content by dielectric permittivity in stony soils

Soil Research ◽  
2016 ◽  
Vol 54 (3) ◽  
pp. 360 ◽  
Author(s):  
M. Pakparvar ◽  
W. Cornelis ◽  
D. Gabriels ◽  
Z. Mansouri ◽  
S. A. Kowsar
Keyword(s):  
Dielectric Permittivity ◽  
Water Content ◽  
Mixture Model ◽  
Model Performance ◽  
Time Domain Reflectometry ◽  
Soil Conditions ◽  
Probe Type ◽  
Regression Equations ◽  
Deep Well ◽  
Reflection Time

Applicability of time domain reflectometry (TDR) under naturally distributed stone fragments in soils has seldom been investigated. A multilayer profile of a 30-m-deep well was sampled and the natural distribution of stone fragments in the soils was replicated in the laboratory. Gravimetric soil water content (SWC) was measured simultaneously with TDR dielectric permittivity (Ka) readings and bulk densities in three subsamples as replications. Two connector and buriable probes and three reflection-time capture windows (10, 20 and 40 ns) were used for the measurements. These were repeated for sieved soil samples <2 mm with fixed, pre-measured bulk densities. Measurements of Ka and observed SWC were repeated for extension-cable lengths of 3–30 m. All measurements were taken in samples saturated from the bottom. A semi-empirical mixture model was applied for different fractions of stony samples in order to convert bulk Ka to bulk volumetric SWC (θv) by the mixture model (θvmx), to be compared with θv by the conventional Topp equation (θvTp). An improvement in model performance was observed with lower root-mean-square error (RMSE, 0.02–0.04 v. 0.07–0.1) and ratio of RMSE to observation standard deviation (0.32–0.87 v. 1.07–3.05) for θvmx compared with θvTp. This approach for converting the in-situ measured dielectric permittivity to the θv of the bulk soil can be applied based on the determined stoniness. The 15-cm, 2-rod (connector) probe type with capture windows 20 ns resulted in a better performance than the 20-cm, 3-rod (buriable) probe type with capture windows 10 and 40 ns. Development of regression equations for the stone-free samples resulted in calibrated equations for converting the measured Ka to θv with better results (RMSE ~0.002 m3 m–3) than those obtained using the Topp equation. In contrast to the traditional equation, new sets of coefficients for the Topp equation were also capable of estimating extremely low θv values of ≤0.02 m3 m–3 where the minimum calculated θv values were adequately similar to the observed ones. Noticeable effects of cable length on measured Ka were found for lengths exceeding 10 m. Accurate Ka values might be obtained in similar soil conditions if the suggested regression equations are employed, provided a correction is made for the extension cables.

scholarly journals Indirect measurements of water content using TDR-inferred dielectric permittivity and electrical resistivity

2019 ◽  
Vol 92 ◽  
pp. 02005
Author(s):  
Bruna de Carvalho Faria Lima Lopes ◽  
Laís de Carvalho Faria Lima Lopes ◽  
Alessandro Tarantino
Keyword(s):  
Electrical Conductivity ◽  
Dielectric Permittivity ◽  
Moisture Content ◽  
Water Content ◽  
Time Domain Reflectometry ◽  
Moisture Distribution ◽  
Salt Mines ◽  
Destructive Measurement ◽  
Non Destructive

The measurement of moisture distribution in Engineered Barrier Systems (EBS) in salt mines and deep geological disposals is essential in order to monitor fluid ingress and record data for long-term security analyses. Additionally, soil moisture content has influence over the mechanical properties of the soil as well as plant growth, soil stability and contaminant transport to cite some. Therefore, finding affordable and reliable ways to determine moisture content, quickly and in the field without sampling, is of great interested among people in different subject areas. Time-domain reflectometry (TDR) has become a recognized electromagnetic method for non-destructive measurement of dielectric permittivity and electrical conductivity of moist porous materials. It turns out that both these measurements depend on the material moisture content, among other things. This paper presents a series of calibration tests performed on soil samples. TDR probes were used to obtain the dielectric permittivity and electrical conductivity of the samples. As a consequence, relationships between these measurements and the samples' volumetric water content were later established. These relationships can then be used to indirectly determine that important information of water content on similar soil material using cheap, quick and non-destructive TDR probes.

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.

scholarly journals Field scale effective hydraulic parameterisation obtained from TDR time series and inverse modelling

2009 ◽  
Vol 6 (2) ◽  
pp. 1489-1522 ◽  
Author(s):  
U. Wollschläger ◽  
T. Pfaff ◽  
K. Roth
Keyword(s):  
Time Series ◽  
Hydraulic Properties ◽  
Preferential Flow ◽  
Time Domain Reflectometry ◽  
Inverse Modelling ◽  
Soil Conditions ◽  
Small Scale ◽  
Field Scale ◽  
Time Period

Abstract. Due to the large heterogeneity in the hydraulic properties of natural soils, estimation of field scale effective hydraulic parameters is difficult. Past research revealed that data from accurate but small scale laboratory measurements could hardly ever be transferred to the field scale. In this study, we explore an alternative approach where hydraulic properties of a layered soil profile are directly estimated from hydraulic inverse modelling using a time series of in situ measured soil water contents obtained from time domain reflectometry. Simulations were conducted for natural boundary conditions and run for a one-year time period including both wet and dry soil conditions. For the time period used for inversion, the model is able to reproduce the general evolution of water content in the different soil layers reasonably well. However, distinct drying and wetting events could not be reproduced in detail which we explain by the complex natural processes that are not included in the rather simple model, e.g. an accurate site-specific representation of the evapotranspiration process and, potentially, preferential flow. The study emphasizes the importance of a correct representation of the various processes occuring in the soil-plant-atmosphere continuum. Still, we conclude that – for time periods where measured data for calibration are available – this simple estimation of effective hydraulic properties from in situ data is a good approach to obtain effective parameters for describing unsaturated water movement in field soils which are not dominated by complex processes like preferential flow.

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.

scholarly journals Electromagnetic Properties of Carbon Gels

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4143 ◽  
Author(s):  
Jimena Castro-Gutiérrez ◽  
Edita Palaimiene ◽  
Jan Macutkevic ◽  
Juras Banys ◽  
Polina Kuzhir ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Dielectric Permittivity ◽  
Low Frequency ◽  
Microwave Frequency ◽  
Power Laws ◽  
Wide Frequency Range ◽  
Electromagnetic Properties ◽  
Frequency Range ◽  
Carbon Gels ◽  
Electrical Conductivities

The electromagnetic properties of various carbon gels, produced with different bulk densities, were investigated in a wide frequency range (20 Hz–36 GHz). The values of dielectric permittivity and electrical conductivity at 129 Hz were found to be very high, i.e., more than 105 and close to 100 S/m, respectively. Both strongly decreased with frequency but remained high in the microwave frequency range (close to 10 and about 0.1 S/m, respectively, at 30 GHz). Moreover, the dielectric permittivity and the electrical conductivity strongly increased with the bulk density of the materials, according to power laws at low frequency. However, the maximum of microwave absorption was observed at lower densities. The DC conductivity slightly decreased on cooling, according to the Arrhenius law. The lower activation energies are typical of carbon gels presenting lower DC electrical conductivities, due to a higher number of defects. High and thermally stable electromagnetic properties of carbon gels, together with other unique properties of these materials, such as lightness and chemical inertness, open possibilities for producing new electromagnetic coatings.

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