Measuring Soil Water Content, Electrical Conductivity, and Thermal Properties with a Thermo-Time Domain Reflectometry Probe

Ren, Tusheng; Noborio, Kosuke; Horton, Robert

doi:10.2136/sssaj1999.03615995006300030005x

Cited by 174 publications

(137 citation statements)

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“…The length and outer diameter of the stainless tube, and the spacing between the two stainless tubes, are major factors in determining the accuracy of DPHP measurement (Ren et al 1999). In this study, we followed the design of Liu et al (2008) that showed the best accuracy to determine volumetric heat capacity among several combinations of length, diameter, and spacing.…”

Section: Matric Potential Sensor Using Dphpmentioning

confidence: 99%

Matric Potential Sensor Using Dual Probe Heat Pulse Technique

Kojima

Noborio

Mizoguchi

et al. 2017

Agricultural Information Research

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Soil matric potential (ψ m ) is an important property, and its measurement is necessary to determine the availability of soil water for plants. The objectives of this study are to develop a low-cost ψ m sensor using porous media in conjunction with a dual probe heat pulse (DPHP) technique and to evaluate the performance of the developed sensor. The DPHP ψ m sensor measures the volumetric heat capacity and thermal conductivity of the porous media and converts these thermal properties into a ψ m value. The performance was evaluated by comparing the output of the developed DPHP ψ m sensor with that of a commercialized ψ m sensor, and the temperature dependence of the developed sensor was also investigated. The volumetric heat capacity and thermal conductivity of the porous media measured with the DPHP method were converted to their corresponding logarithmic value of ψ m by means of two intersecting linear functions. The use of thermal conductivity to determine ψ m was found to yield more accurate results than the use of volumetric heat capacity, and the accuracy of the determined ψ m value was approximately 10%. The DPHP ψ m sensor was found to be less sensitive to temperature than existing commercialized ψ m sensors. Furthermore, the volumetric heat capacity showed slight temperature dependence regardless of soil water content. The developed DPHP ψ m sensor was found to be versatile because it can use either volumetric heat capacity or thermal conductivity, depending on the magnitude of soil temperature variation and required accuracy. The DPHP ψ m sensor is intended to contribute to expanding the use of information and communications technology (ICT) in agriculture as a low-cost ψ m sensor.

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Section: Matric Potential Sensor Using Dphpmentioning

confidence: 99%

Matric Potential Sensor Using Dual Probe Heat Pulse Technique

Kojima

Noborio

Mizoguchi

et al. 2017

Agricultural Information Research

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“…Noborio et al (1996) combined the functional capabilities of a TDR sensor and a heat pulse sensor into one unit. Ren et al (1999) improved the thermo-TDR sensor design. Thermo-TDR was developed to simultaneously measure the soil water content (q), bulk electrical conductivity (s), thermal conductivity (l), heat capacity (r c ), and thermal diffusivity (a).…”

Section: Jinghui Xumentioning

confidence: 99%

Short, Multineedle Frequency Domain Reflectometry Sensor Suitable for Measuring Soil Water Content

Logsdon

Horton

2012

Soil Science Soc of Amer J

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Time domain reflectometry (TDR) is a well‐established electromagnetic technique used to measure soil water content. Time domain reflectometry sensors have been combined with heat pulse sensors to produce thermo‐TDR sensors. Thermo‐TDR sensors are restricted to having relatively short needles to accurately measure soil thermal properties. Short needle lengths, however, can limit the accuracy of the TDR measurement of soil water content. Frequency domain reflectometry (FDR) sensors are an alternative to TDR sensors that can provide an inexpensive measurement of soil water content. The objective of this study was to determine whether short FDR sensors can accurately measure soil water content. We designed and constructed a short FDR sensor. For four soil types across a range of water contents, temperatures, and salt contents, we measured soil dielectric spectra with the short FDR sensor. A vector network analyzer was used to obtain soil dielectric spectra in the 1‐MHz to 3‐GHz frequency range. The ideal frequency of a short FDR sensor is the frequency at which the permittivity is not altered by changing temperature or salt content. The 47‐ to 200‐MHz range was an ideal frequency range for measuring soil water content, and 70 MHz was the frequency least influenced by temperature and salt content. The short FDR sensor provided quick, continuous, stable, and cheap measurements of soil water content. Because of the promising performance of the short thermo‐FDR sensor in laboratory studies, sensors should be evaluated in future field studies.

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“…In 2001, six three-needle heat pulse sensors based on the design of Ren et al (1999) were installed at the bare soil site. The sensors were installed horizontally at 2, 4, and 6 cm below the soil surface with two sensors at each depth.…”

Section: Heat Pulse Sensorsmentioning

confidence: 99%

Soil Heat Storage Measurements in Energy Balance Studies

Ochsner¹,

Sauer²,

Horton

2007

Agronomy Journal

113

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Energy balance studies require knowledge of the heat flux at the soil surface. This flux is determined by summing the heat flux at a reference depth (z r ) some centimeters below the surface and the rate of change of heat storage in the soil above z r . The rate of change of heat storage, or heat storage for short (DS), is calculated from soil volumetric heat capacity (C) and temperature. The objectives of this study were to determine how choices regarding z r , C measurements, and DS calculations all affect the accuracy of DS data. Heat transfer theory and data from three field sites were used toward these ends. In some studies, shallow reference depths have been used and DS neglected. Our results indicate that when z r is sufficiently deep to permit accurate heat flux measurements, DS is too large to neglect. Three methods for determining C were evaluated: soil sampling, the ThetaProbe soil moisture sensor, and heat pulse sensors. When C was determined using all three methods simultaneously, the estimates agreed to within 6% on average; however, the temporal variability of C was best recorded with the automated heat pulse sensors. Three approaches for calculating DS were also tested. The common approach of letting C vary in time but neglecting its time derivative caused errors when soil water content was changing. These errors exceeded 200 W m 22 in some cases. The simple approach of assuming a constant C performed similarly. We introduce a third approach that accounts for the time derivative of C and yields the most accurate DS data.M EASUREMENTS of the surface energy balance provide valuable scientific information. These measurements contribute greatly to our understanding of the dynamic transfers of water, energy, and trace gases at the Earth's surface. Energy balance studies in terrestrial ecosystems require measurements of soil heat flux. Typically, soil heat flux is measured at a reference depth a few centimeters below the soil surface rather than directly at the surface (Ochsner et al., 2006). The heat flux at the surface is then calculated as the sum of the flux at the reference depth and the rate of change of heat storage above the reference depth (DS).The heat storage is estimated based on the soil volumetric heat capacity, C, and temperature, T. The formal relationship iswhere z r is the reference depth, t is time, and T 0 is an arbitrarily assigned reference temperature. In this study, we chose T 0 5

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Measuring Soil Water Content, Electrical Conductivity, and Thermal Properties with a Thermo-Time Domain Reflectometry Probe

Cited by 174 publications

References 0 publications

Matric Potential Sensor Using Dual Probe Heat Pulse Technique

Matric Potential Sensor Using Dual Probe Heat Pulse Technique

Short, Multineedle Frequency Domain Reflectometry Sensor Suitable for Measuring Soil Water Content

Soil Heat Storage Measurements in Energy Balance Studies

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