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 A Seven-Rod Dielectric Sensor for Determination of Soil Moisture in Well-Defined Sample Volumes

Sensors ◽  
2019 ◽  
Vol 19 (7) ◽  
pp. 1646 ◽  
Author(s):  
Justyna Szerement ◽  
Aleksandra Woszczyk ◽  
Agnieszka Szypłowska ◽  
Marcin Kafarski ◽  
Arkadiusz Lewandowski ◽  
...  
Keyword(s):  
Dielectric Permittivity ◽  
Water Content ◽  
Sandy Loam ◽  
Sample Volume ◽  
Time Domain Reflectometry ◽  
Complex Dielectric Permittivity ◽  
The Real ◽  
Electromagnetic Simulations ◽  
Different Diameters ◽  
Permittivity Spectrum

This paper presents a novel seven-rod sensor used for time-domain reflectometry (TDR) and frequency-domain reflectometry (FDR) measurements of soil water content in a well-defined sample volume. The probe directly measures the complex dielectric permittivity spectrum and for this purpose requires three calibration media: air, water, and ethanol. Firstly, electromagnetic simulations were used to study the influence of the diameter of a container on the sensitivity zone of the probe with respect to the measured calibration media and isopropanol as a verification liquid. Next, the probe was tested in three soils—sandy loam and two silt loams—with six water contents from air-dry to saturation. The conversion from S 11 parameters to complex dielectric permittivity from vector network analyzer (VNA) measurements was obtained using an open-ended liquid procedure. The simulation and measurement results for the real part of the isopropanol dielectric permittivity obtained from four containers with different diameters were in good agreement with literature data up to 200 MHz. The real part of the dielectric permittivity was extracted and related to the moisture of the tested soil samples. Relations between the volumetric water content and the real part of the dielectric permittivity (by FDR) and apparent dielectric permittivity (by TDR) were compared with Topp’s equation. It was concluded that the best fit to Topp’s equation was observed in the case of a sandy loam. Data calculated according to the equation proposed by Malicki, Plagge, and Roth gave results closer to Topp’s calibration. The obtained results indicated that the seven-rod probe can be used to accurately measure of the dielectric permittivity spectrum in a well-defined sample volume of about 8 cm3 in the frequency range from 20 MHz to 200 MHz.

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.

Water content as a function of apparent dielectric permittivity in a Fibric Limnic Humisol

2008 ◽  
Vol 88 (1) ◽  
pp. 79-84 ◽  
Author(s):  
S F Lange ◽  
S E Allaire ◽  
V. Juneau
Keyword(s):  
Dielectric Permittivity ◽  
Water Content ◽  
Organic Matter Content ◽  
Organic Soil ◽  
Matter Content ◽  
Time Domain Reflectometry ◽  
Volumetric Water Content ◽  
Wide Range ◽  
Intact Soil Cores ◽  
Intact Soil

Volumetric water content (θv) was estimated from time domain reflectometry (TDR) measurementsof apparent dielectric permittivity (Ka) in an organic soil (Humisol). The goals of this study were: (i) to test the accuracy of existing θv-Ka relationships in this soil and if found insufficient (ii) to develop alternative θv-Ka relationships for this organic soil. The Ka values were measured over a wide range of θv in intact soil cores taken from three horizons (Ohp, Of, Oco). Empirical θv-Ka relationships found in the literature for organic porous media could not accurately describe the θv-Ka relationships of any horizon of this Humisol, probably because of the its very large organic matter content (> 75%) of this soil. New θv-Ka relationships for each horizon were consequently developed. Key words: Organic soil, TDR, coprogenic soil, volumetric water content, apparent dielectric permittivity

A modified dielectric probe for increased measurement volume of soil water content

2020 ◽  
Author(s):  
Aleksandra Woszczyk ◽  
Justyna Szerement ◽  
Arkadiusz Lewandowski ◽  
Marcin Kafarski ◽  
Agnieszka Szypłowska ◽  
...  
Keyword(s):  
Dielectric Permittivity ◽  
Water Content ◽  
Electromagnetic Waves ◽  
Mechanical Damage ◽  
Direct Methods ◽  
Soil Disturbance ◽  
Sample Volume ◽  
Time Domain Reflectometry ◽  
Frequency Range ◽  
Probe Calibration

&lt;p&gt;The information of water amount in soil is essential in many fields (e.g. agriculture, forestry, hydrology). Methods to determine water content (WC) can be classified as direct and indirect. Direct methods are connected with the destruction of a sample, are time-consuming and impractical for the measurements in the crop fields. Indirect methods ensure non-destructive and in situ measurements and depend on monitoring a dielectric soil property which is a function of WC. The soil dielectric permittivity is one of the used properties which may be determined by time domain reflectometry (TDR) or frequency domain reflectometry (FDR) techniques. TDR probes are expensive and can be easily damaged at multiple insertions to soil. The open-ended (OE) probes, well-known for their application in the measurements of the complex dielectric permittivity of materials in broadband frequency range, are more resistant to mechanical damage but they are characterized by low penetration depth of electromagnetic waves. Therefore, there is a need to develop sensors able to measure bigger volumes and at the same time sufficiently durable for multiple insertions in soil. &amp;#160;&amp;#160;&amp;#160;&amp;#160;&lt;/p&gt;&lt;p&gt;The objective of this work was to test the performance of an open-ended dielectric probe with an antenna (OE-A) in the frequency range 1 MHz &amp;#8211; 6 GHz for two mineral soils using vector network analyzer (VNA) one port (reflective) measurements. Firstly, numerical simulations of the probe using Ansys HFSS software were performed. Secondly, the probe calibration was done on the reference materials (air, distilled water and ethanol). Thirdly, the soils measurements were done to check the possibility to determine soil moisture. &amp;#160;&amp;#160;&lt;/p&gt;&lt;p&gt;The obtained results show that the tested probe can be applied for fast moisture measurement with minimal soil disturbance. The real part of dielectric permittivity (&amp;#949;&amp;#8217;) obtained for the tested soils was connected with their moisture and the relation between &amp;#949;&amp;#8217; and volumetric water content was determined. Additionally, the effect of the sample volume was considered and the relation between the high-frequency limit and diameter of the sample was determined. &amp;#160;&amp;#160;&amp;#160;&amp;#160;&lt;/p&gt;&lt;p&gt;Acknowledgement:&lt;/p&gt;&lt;p&gt;This research was supported by the National Centre for Research and Development (BIOSTRATEG/343547/8/NCBR/2017).&lt;/p&gt;

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.

scholarly journals On the Accuracy of Factory-Calibrated Low-Cost Soil Water Content Sensors

Sensors ◽  
2019 ◽  
Vol 19 (14) ◽  
pp. 3101 ◽  
Author(s):  
Jesús María Domínguez-Niño ◽  
Heye Reemt Bogena ◽  
Johan Alexander Huisman ◽  
Bernd Schilling ◽  
Jaume Casadesús
Keyword(s):  
Dielectric Permittivity ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Solid Phase ◽  
Low Cost ◽  
Time Domain Reflectometry ◽  
Sensor Calibration ◽  
Undisturbed Soil ◽  
Calibration Approach

Soil water content (SWC) monitoring is often used to optimize agricultural irrigation. Commonly, capacitance sensors are used for this task. However, the factory calibrations have been often criticized for their limited accuracy. The aim of this paper is to test the degree of improvement of various sensor- and soil-specific calibration options compared to factory calibrations by taking the 10HS sensor as an example. To this end, a two-step sensor calibration was carried out. In the first step, the sensor response was related to dielectric permittivity using calibration in media with well-defined permittivity. The second step involved the establishment of a site-specific relationship between permittivity and soil water content using undisturbed soil samples and time domain reflectometry (TDR) measurements. Our results showed that a model, which considered the mean porosity and a fitted dielectric permittivity of the solid phase for each soil and depth, provided the best fit between bulk permittivity and SWC. Most importantly, it was found that the two-step calibration approach (RMSE: 1.03 vol.%) provided more accurate SWC estimates compared to the factory calibration (RMSE: 5.33 vol.%). Finally, we used these calibrations on data from drip-irrigated almond and apple orchards and compared the factory calibration with our two-step calibration approach.

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