Measurement of relative permittivity in sandy soils using TDR, capacitance and theta probes: comparison, including the effects of bulk soil electrical conductivity

Robinson, David A.; Gardner, C. M. K.; Cooper, J. David

doi:10.1016/s0022-1694(99)00121-3

Cited by 112 publications

(84 citation statements)

References 22 publications

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“…Another plausible explanation for the nonuniform behavior could be the ThetaProbe's rod configuration that significantly concentrates the electromagnetic field around the central electrode, resulting in a small sampling volume (Table 3). This drawback was already raised by Robinson et al (1999) and Vaz et al (2013) who stated that this possibly renders the measurements more sensitive to compaction during the insertion of the instrument, as the effect is most distinct around the probe's center. Additionally, this problem becomes more important as moisture content increases.…”

Section: Comparison Of Fitted Versus the Literature Calibrations For mentioning

confidence: 99%

Soil moisture sensor calibration for organic soil surface layers

Bircher

Andreasen

Vuollet

et al. 2016

Geosci. Instrum. Method. Data Syst.

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Abstract. This paper's objective is to present generic calibration functions for organic surface layers derived for the soil moisture sensors Decagon ECH2O 5TE and Delta-T ThetaProbe ML2x, using material from northern regions, mainly from the Finnish Meteorological Institute's Arctic Research Center in Sodankylä and the study area of the Danish Center for Hydrology (HOBE). For the Decagon 5TE sensor such a function is currently not reported in the literature. Data were compared with measurements from underlying mineral soils including laboratory and field measurements. Shrinkage and charring during drying were considered. For both sensors all field and lab data showed consistent trends. For mineral layers with low soil organic matter (SOM) content the validity of the manufacturer's calibrations was demonstrated. Deviating sensor outputs in organic and mineral horizons were identified. For the Decagon 5TE, apparent relative permittivities at a given moisture content decreased for increased SOM content, which was attributed to an increase of bound water in organic materials with large specific surface areas compared to the studied mineral soils. ThetaProbe measurements from organic horizons showed stronger nonlinearity in the sensor response and signal saturation in the high-level data. The derived calibration fit functions between sensor response and volumetric water content hold for samples spanning a wide range of humus types with differing SOM characteristics. This strengthens confidence in their validity under various conditions, rendering them highly suitable for large-scale applications in remote sensing and land surface modeling studies. Agreement between independent Decagon 5TE and ThetaProbe time series from an organic surface layer at the Sodankylä site was significantly improved when the here-proposed fit functions were used. Decagon 5TE data also well-reflected precipitation events. Thus, Decagon 5TE network data from organic surface layers at the Sodankylä and HOBE sites are based on the hereproposed natural log fit. The newly derived ThetaProbe fit functions should be used for hand-held applications only, but prove to be of value for the acquisition of instantaneous large-scale soil moisture estimates.

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Section: Comparison Of Fitted Versus the Literature Calibrations For mentioning

confidence: 99%

Soil moisture sensor calibration for organic soil surface layers

Bircher

Andreasen

Vuollet

et al. 2016

Geosci. Instrum. Method. Data Syst.

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“…Polar molecules such as water became polarised in the presence of the applied electric field owing to the absorbed energy by its molecules. The real (energy storage) and the imaginary (ionic conduction) parts (Robinson et al 1999) constitute the impedance which can be used in characterising the fluid-fluid-media system. Owing to sharp contrast between the relative permittivity of the porous medium and the surrounding fluids, a change in fluid content causes a change in the bulk relative permittivity, which is seen as a change in probe impedance affecting the shape of the reflected waveform.…”

Section: Bulk Relative Permittivity (ε B ) and Electric Conductivity mentioning

confidence: 99%

Geoelectrical characterization of carbonate and silicate porous media in the presence of supercritical CO₂–water flow

Abidoye

Das

2015

Geophys. J. Int.

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S U M M A R YThe relative permittivity (ε r ) and the electrical conductivity (σ ) of porous media are known to be functions of water saturation (S). As such, their measurements can be useful in effective characterisations and monitoring of geological carbon sequestration using geoelectrical measurement techniques. In this work, the effects of pressure, temperature and salt concentration on bulk ε r -S and σ -S relationships were investigated for carbonate (limestone) and silicate porous media (both unconsolidated domains) under dynamic and quasi-static supercritical CO 2 (scCO 2 )-brine/water flow. In the silica sand sample, the bulk ε r (ε b ) for scCO 2 -water decreases as the temperature increases. On the contrary, slight increase was seen in the ε b with temperature in the carbonate sample for the scCO 2 -water system. These trends are more conspicuous at high water saturation. The ε b -S curves for the scCO 2 -water flow in the silica sand also show clear dependency on the domain pressure, where ε b increases as the domain pressure increases. Furthermore, the bulk σ (σ b ), at any particular saturation for the scCO 2 -brine system rises as the temperature increases with more significant increase found at very high water saturation. Both ε b and σ b values are found to be greater in the limestone than silica sand porous samples for similar porosity values. Based on different injection rates investigated, we do not find significant dynamic effects in the ε b -S and σ b -S relationships for the scCO 2 -brine/water system. As such, geoelectrical characteristics can be taken as reliable in the monitoring of two-phase flow system in the porous media. It can be inferred from the results that the geoelectrical techniques are highly dependent on water saturation. This dependence is more conspicuous at higher water saturation. Different mathematical models examined show their reliability at different water saturation ranges. The polynomial fit developed in this work takes into consideration the fluid pressure in the system as well as the initial bulk relative permittivity prior to the injection of CO 2 . The polynomial fit shows a good reliability in the prediction of the geo-electrical properties of the CO 2 -water-porous media system, especially at higher water saturation. In comparison, the mixing model from the literature shows more reliability in the prediction of similar property at lower water saturation.

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“…That confirms the validity of the sensor on one hand and that of the experimental procedure applied on the other hand. Actually, the performance of the ThetaProbe sensors in field conditions was confirmed in various works (Lukangu et al, 1999;Robinson et al, 1999;Verhoef et al, 2006;Smethurst et al, 2006;Zhan et al, 2007). The results obtained in this study show that the compaction procedure used allowed the sensors to be installed with negligible effect on soil density.…”

Section: Discussionmentioning

confidence: 81%

Development of a Large-Scale Infiltration Tank for Determination of the Hydraulic Properties of Expansive Clays

Tang

Cui

et al. 2009

Geotechnical Testing Journal

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A large-scale infiltration tank was developed to study the water transfer in compacted expansive clay. Volumetric water content sensors were buried in a soil column for water content monitoring during infiltration. In addition to water content, soil suction and temperature at various locations and the heave at the soil surface were also monitored. Emphasis was put in minimizing the effect of sensors installation on water transfer and soil deformation. The results obtained for 338 days of infiltration were presented in terms of changes in suction, volumetric water content, temperature, and the soil heave. Based on the recorded data, the performance and limitation of different suction and volumetric water content sensors and the adopted test procedure were analyzed. The recorded data on soil suction and volumetric water content were finally analyzed for determining the unsaturated hydraulic properties of soil, such as the water retention curve and the unsaturated hydraulic conductivity. Note also that the results constitute useful data for further physical analysis or numerical models’ calibration.

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Measurement of relative permittivity in sandy soils using TDR, capacitance and theta probes: comparison, including the effects of bulk soil electrical conductivity

Cited by 112 publications

References 22 publications

Soil moisture sensor calibration for organic soil surface layers

Soil moisture sensor calibration for organic soil surface layers

Geoelectrical characterization of carbonate and silicate porous media in the presence of supercritical CO₂–water flow

Development of a Large-Scale Infiltration Tank for Determination of the Hydraulic Properties of Expansive Clays

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Measurement of relative permittivity in sandy soils using TDR, capacitance and theta probes: comparison, including the effects of bulk soil electrical conductivity

Cited by 112 publications

References 22 publications

Soil moisture sensor calibration for organic soil surface layers

Soil moisture sensor calibration for organic soil surface layers

Geoelectrical characterization of carbonate and silicate porous media in the presence of supercritical CO2–water flow

Development of a Large-Scale Infiltration Tank for Determination of the Hydraulic Properties of Expansive Clays

Contact Info

Product

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Geoelectrical characterization of carbonate and silicate porous media in the presence of supercritical CO₂–water flow