scholarly journals Time domain reflectrometry measurements using a movable obstacle for the determination of dielectric profiles

2008 ◽  
Vol 6 ◽  
pp. 1-4
Author(s):  
B. Will ◽  
M. Gerding ◽  
S. Schultz ◽  
B. Schiek
Keyword(s):  
Dielectric Constant ◽  
Water Content ◽  
Time Domain ◽  
Measurement Techniques ◽  
Measurement Data ◽  
Time Domain Reflectometry ◽  
Dielectric Measurement ◽  
Effective Dielectric Constant ◽  
Pulse Delay

Abstract. Microwave techniques for the measurement of the permittivity of soils including the water content of soils and other materials, especially TDR (time domain reflectometry), have become accepted as routine measurement techniques. This summary deals with an advanced use of the TDR principle for the determination of the water content of soil along a probe. The basis of the advanced TDR technique is a waveguide, which is inserted into the soil for obtaining measurements of the effective soil permittivity, from which the water content is estimated, and an obstacle, which can mechanically be moved along the probe and which acts as a reference reflection for the TDR system with an exactly known position. Based on the known mechanical position of the reference reflection, the measured electrical position can be used as a measure for the effective dielectric constant of the environment. Thus, it is possible to determine the effective dielectric constant with a spatial resolution given by the step size of the obstacle displacement. A conventional industrial TDR-system, operating in the baseband, is used for the signal generation and for the evaluation of the pulse delay time of the obstacle reflection. Thus, a cost effective method for the acquisition of the dielectric measurement data is available.

scholarly journals Determination of the permittivity of soils by use of double transmission measurements

2009 ◽  
Vol 7 ◽  
pp. 1-4 ◽  
Author(s):  
B. Will ◽  
M. Gerding
Keyword(s):  
Dielectric Constant ◽  
Water Content ◽  
Delay Time ◽  
Effective Permittivity ◽  
Time Domain Reflectometry ◽  
Effective Dielectric Constant ◽  
Step Size ◽  
Transmission Method ◽  
Average Value

Abstract. Delay time measurements, e.g. time domain reflectometry (TDR), are a well-established method for the measurement of permittivity of various materials, especially soils. However, common measurement systems only provide one average value of the dielectric constant along the length of the TDR probe. This contribution deals with an advanced application of the TDR principle, the so-called double transmission method, for the determination of the water content of soil along a probe. To apply the advanced TDR technique, a probe, realized by a combination of a transmission line and a dielectric obstacle, which can mechanically be moved along the probe, is used. The probe is inserted into the soil to measure the effective soil permittivity. Thus, the water content along the probe can be estimated by means of the effective permittivity. Based on the known mechanical position of the reflection at the end of the probe and the position of the obstacle, the measured delay time can be used as a measure for the effective dielectric constant of the environment surrounding the obstacle. Thus, it is possible to determine the effective dielectric constant with a spatial resolution given by the step size of the obstacle displacement.

Impact of density on the hydraulic properties of peat and the time domain reflectometry (TDR) moisture calibration curve

2005 ◽  
Vol 42 (1) ◽  
pp. 279-286 ◽  
Author(s):  
Anushka Shibchurn ◽  
Paul J Van Geel ◽  
Paula L Kennedy
Keyword(s):  
Dielectric Constant ◽  
Soil Moisture ◽  
Water Content ◽  
Time Domain ◽  
Calibration Curve ◽  
Hydraulic Properties ◽  
Time Domain Reflectometry ◽  
Organic Soils ◽  
Dry Density ◽  
Water Contents

The hydraulic properties of a peat used in a commercial peat biofilter were evaluated to determine their relationship with density and to establish a time domain reflectometry (TDR) calibration curve for water content as a function of the measured dielectric constant. The peat studied was a milled Sphagnum peat with a high organic content (99%). The dry densities evaluated in this study ranged from 90 to 180 kg/m3. The saturated hydraulic conductivity (Ks) decreased with an increase in dry density (ρdry) and was found to follow a log-linear relationship (Ks = 0.2462 exp(–0.0438ρdry), correlation coefficient R2 = 0.9789). As expected, the soil moisture curve was impacted by density, with a higher density resulting in higher water contents for a given suction. The data were fit to the van Genuchten relationship. A TDR calibration curve was generated at five different densities. A comparison of the curves indicates that the water content as a function of dielectric constant was not dependent on density because of the significantly larger dielectric constant (Ka) of water compared with those of peat solids and air-filled voids. The TDR calibration curve for the peat evaluated in this study (volumetric water content Θv = 0.2667 ln(Ka) – 0.1405, R2 = 0.9564) predicted higher water contents for a given dielectric constant compared with those from similar calibration curves for peat published in the literature. The data were compared with those from six other studies and indicated that the TDR calibration varied for different organic soils. The density-dependent hydraulic parameters and TDR calibration curve are important parameters needed to study the hydraulics of peat biofilters.Key words: peat, TDR, time domain reflectometry, density, hydraulics, soil moisture.

scholarly journals Experimental Determination of TDR Calibration Relationship for Pyroclastic Ashes of Campania (Italy)

Sensors ◽  
2018 ◽  
Vol 18 (11) ◽  
pp. 3727 ◽  
Author(s):  
Giovanna Capparelli ◽  
Gennaro Spolverino ◽  
Roberto Greco
Keyword(s):  
Dielectric Constant ◽  
Water Content ◽  
Organic Matter Content ◽  
Free Water ◽  
Time Domain Reflectometry ◽  
Dielectric Constants ◽  
Phase System ◽  
Three Phase ◽  
The Relationship

Time domain reflectometry (TDR) is one of the most widely used techniques for indirect determination of soil volumetric water content (θ). TDR measures the relative dielectric constant (εr) which, in a three-phase system like the soil, depends on water, air, and solid matrix dielectric constants. Since dielectric constant of water is much larger than the other two, εr of bulk soil mainly depends on water content. In many cases, the application of TDR requires a specific calibration of the relationship θ(εr) to get quantitatively accurate estimates of soil water content. In fact, the relationship θ(εr) is influenced by various soil properties, such as clay content, organic matter content, bulk density, and aggregation. Numerous studies have shown that pyroclastic soils often exhibit a peculiar dielectric behavior. In Campania (Southern Italy) wide mountainous areas are covered by layered pyroclastic deposits of ashes (loamy sands) and pumices (sandy gravels), often involved in the triggering of landslides induced by rainwater infiltration. Reliable field measurements of water content of such soils are therefore important for the assessment of landslide risk. Hence, in this paper, the θ(εr) relationship has been experimentally determined on samples of typical pyroclastic soil of Campania, collected around Sarno, reconstituted with different porosities. The aim of the study is to identify specific calibration relationships for such soils based not only on empirical approaches. In this respect, a three-phase dielectric mixing model with a variable exponent is introduced, and the variable value of the exponent is related to the different dielectric properties of bond and free water within the soil pores.

CORRECTING SOIL VOLUMETRIC WATER CONTENTS FROM A DIRECT-READING TIME DOMAIN REFLECTOMETRY INSTRUMENT (IRAMS)

1989 ◽  
Vol 69 (3) ◽  
pp. 701-704 ◽  
Author(s):  
G. C. TOPP ◽  
J. L. B. CULLEY
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Time Domain ◽  
Computer Software ◽  
Time Domain Reflectometry ◽  
Direct Reading ◽  
Volumetric Soil Water Content ◽  
Linear Correction

Determination of volumetric soil water content (θ) using time domain reflectometry (TDR) is well established. A commercially available instrument (IRAMS) (the IRAMS (Instrument for Reflectometry Analysis of Moisture in Soils) is a trademark registered by Foundation Instruments Inc. of Ottawa) is now available which incorporates computer software, thus providing direct readouts of θ. A field study of the operation of the IRAMS showed that it operates consistently and repeatedly. The IRAMS values were higher but related linearly to those obtained using a TDR cable tester and manual calculations of travel times. A linear correction of the IRAMS readings is proposed and possible causes are suggested for the observed deviations from expected values. Key words: Time domain, reflectometry, soil water content, field

Time domain reflectometry for water content and density of soils: study of soil-dependent calibration constants

2005 ◽  
Vol 42 (4) ◽  
pp. 1053-1065 ◽  
Author(s):  
V P Drnevich ◽  
A K Ashmawy ◽  
X Yu ◽  
A M Sallam
Keyword(s):  
Dielectric Constant ◽  
Water Content ◽  
Time Domain ◽  
Field Experiments ◽  
Engineering Application ◽  
Time Domain Reflectometry ◽  
Sensitivity Analyses ◽  
Dry Density ◽  
Theoretical Predictions ◽  
Apparent Dielectric Constant

The paper studies the soil-dependent calibration constants used for determining water content and density of soil using time domain reflectometry (TDR), specifically, to establish the typical soil calibration values and study the extent of the uncertainty in calibration factors on measurement accuracy. The TDR method described here makes use of a calibration equation normalized by soil dry density, which involves two soil-dependent constants, a and b. Both a and b have physical significance, with the value of a related to the apparent dielectric constant of the dry density – normalized dry soil solids and the value of b related to the apparent dielectric constant of the pore fluid. From theoretical predictions, typical values of a are around 1.0, and typical values of b are around 9. Practically, the constants a and b are obtained through calibration tests performed in conjunction with standard compaction tests. Experimental study shows that calibration constants fall within the ranges from theoretical predictions. Tests on five soil mixtures provided average values of a = 0.945 and b = 8.76, while 11 clean sands resulted in average values of a = 1.0 and b = 8.5. The study also shows that there are no significant effects of compaction energy on the measured values of a and b. Sensitivity analyses indicate that variations in a and b both cause variations in TDR-determined water content and density, but the variations are typically within acceptable limits for engineering application purpose. Results from TDR tests on simulated field experiments are consistent with the sensitivity analyses.Key words: time domain reflectometry, TDR, calibration constants, water content, dry density, sensitivity.

scholarly journals Models for moisture estimation in different horizons of yellow argisol using TDR

2017 ◽  
Vol 38 (4) ◽  
pp. 1727
Author(s):  
Karla Silva Santos Alvares de Almeida ◽  
Luciano Da Silva Souza ◽  
Vital Pedro Da Silva Paz ◽  
Maurício Antônio Coelho Filho ◽  
Eduardo Holzapfel Hoces
Keyword(s):  
Dielectric Constant ◽  
Water Content ◽  
Time Domain Reflectometry ◽  
Volumetric Water Content ◽  
Advantages And Disadvantages ◽  
Disturbed Soil ◽  
Cubic Polynomial ◽  
Indirect Technique ◽  
Moisture Estimation

The determination of soil moisture is very important because it is the property with the most influence on the dielectric constant of the medium. Time-domain reflectometry (TDR) is an indirect technique used to estimate the water content of the soil (?) based on its dielectric constant (Ka). Like any other technique, it has advantages and disadvantages. Among the major disadvantages is the need for calibration, which requires consideration of the soil characteristics. This study aimed to perform the calibration of a TDR100 device to estimate the volumetric water content of four horizons of a Yellow Argisol. Calibration was performed under laboratory conditions using disturbed soil samples contained in PVC columns. The three rods of the handcrafted probes were vertically installed in the soil columns. Weight measurements with digital scales and daily readings of the dielectric constant with the TDR device were taken. For all soil horizons evaluated, the best fits between the dielectric constant and the volumetric water content were related to the cubic polynomial model. The Ledieu model overestimated by approximately 68 % the volumetric water content in the A and AB horizons, and underestimating by 69 % in Bt2, in relation to volumetric water content obtained by gravimetry. The underestimation by linear, Topp, Roth, and Malicki models ranged from 50 % to 85 % for all horizons.

Factors Affecting Determination of Subgrade Water Content from Multisegment Time Domain Reflectometry Probes

2002 ◽  
Vol 1808 (1) ◽  
pp. 3-10
Author(s):  
Gang Zuo ◽  
Wesley C. Wright ◽  
N. Randy Rainwater ◽  
Eric C. Drumm ◽  
Ronald E. Yoder
Keyword(s):  
Water Content ◽  
Time Domain ◽  
Time Domain Reflectometry ◽  
Factors Affecting
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