Probe for Measuring Soil Specific Heat Using A Heat‐Pulse Method

Campbell, Gaylon S.; Calissendorff, C.; Williams, J. H.

doi:10.2136/sssaj1991.03615995005500010052x

Cited by 382 publications

(360 citation statements)

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“…Each needle contained a Type E thermocouple for measuring temperature; the central needle also contained a resistance heater for generating a heat-pulse. The sensors were calibrated in agar stabilized water to determine the apparent distance between the needles (Campbell et al, 1991). The sensors were installed on DOY 140 via a 10 cm deep access trench by pushing the needles from the trench into undisturbed soil.…”

Section: Heat Flux Measurementsmentioning

confidence: 99%

Latent heat in soil heat flux measurements

Heitman

Horton

Sauer

et al. 2010

Agricultural and Forest Meteorology

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The surface energy balance includes a term for soil heat flux. Soil heat flux is difficult to measure because it includes conduction and convection heat transfer processes. Accurate representation of soil heat flux is an important consideration in many modeling and measurement applications. Yet, there remains uncertainty about what comprises soil heat flux and how surface and subsurface heat fluxes are linked in energy balance closure. The objective of this study is to demonstrate the presence of a subsurface latent heat sink, which must be considered in order to accurately link subsurface heat fluxes between depths near and at the soil surface. Measurements were performed under effectively bare surface conditions in a silty clay loam soil near Ames, IA. Soil heat flux was measured with heat-pulse sensors using the gradient heat flux approach at 1-, 3-, and 6-cm soil depths. Independent estimates of the daily latent heat sink were obtained by measuring the change of mass of microlysimeters. Heat flux measurements at the 1-cm depth deviated from heat flux measurements at other depths, even after calorimetric adjustment was made. This deviation was most pronounced shortly after rainfall, where the 1-cm soil heat flux measurement exceeded 400 W m−2. Cumulative soil heat flux measurements at the 1-cm depth exceeded measurements at the 3-cm depth by >75% over a 7-day rain-free period, whereas calorimetric adjustment allowed 3-and 6-cm depth measurements to converge. Latent heat sink estimates from the microlysimeters accounted for nearly all of the differences between the 1-and 3-cm depth heat flux measurements, indicating that the latent heat sink was distributed between the 1-and 3-cm depths shortly after the rainfall event. Results demonstrate the importance of including latent heat when attempts are made to link or extrapolate subsurface soil heat flux measurements to the surface soil heat flux. The surface energy balance includes a term for soil heat flux. Soil heat flux is difficult to measure because it includes conduction and convection heat transfer processes. Accurate representation of soil heat flux is an important consideration in many modeling and measurement applications. Yet, there remains uncertainty about what comprises soil heat flux and how surface and subsurface heat fluxes are linked in energy balance closure. The objective of this study is to demonstrate the presence of a subsurface latent heat sink, which must be considered in order to accurately link subsurface heat fluxes between depths near and at the soil surface. Measurements were performed under effectively bare surface conditions in a silty clay loam soil near Ames, IA. Soil heat flux was measured with heat-pulse sensors using the gradient heat flux approach at 1-, 3-, and 6-cm soil depths. Independent estimates of the daily latent heat sink were obtained by measuring the change of mass of microlysimeters. Heat flux measurements at the 1-cm depth deviated from heat flux measurements at other depths, even after calorimetric adjust...

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Section: Heat Flux Measurementsmentioning

confidence: 99%

Latent heat in soil heat flux measurements

Heitman

Horton

Sauer

et al. 2010

Agricultural and Forest Meteorology

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“…and the resulting temperature increase 6 mm away at the sensing needle is measured and recorded. The maximum temperature increase is inversely proportional to the heat capacity (Campbell et al, 1991).…”

Section: Heat Pulse Sensorsmentioning

confidence: 99%

“…The center needle was the heating needle and was positioned at the desired depth with temperature sensing needles 6 mm above and below. In 2002, eight two-needle heat pulse sensors (Thermal Logic, Pullman, WA) based on the design of Campbell et al (1991) were installed at both the soybean site and the corn site. These sensors were installed horizontally at 1.5 and 4.5 cm below the soil surface, with four 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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“…Jones (1988), following van der Held and van Drunen and Batty, worked on obtaining thermal conductivity results from Δθ/ln(t) at early times, before linearity had necessarily been reached, by finite element analysis. Campbell et al (1991) used two parallel probes to measure thermal diffusivity in various soils, in a similar method to that used by Drury (1988) and Morabito (1989). Davies et al (2004), used dual thermal probes to measure relative and fluctuating moisture content of building envelopes, assuming that the volumetric heat capacity of soil could be measured within 1% of accepted values when using typical probe geometries and heating times.…”

Section: Introduction To the Thermal Probe Techniquementioning

confidence: 99%

Validation of data analysis routines for a thermal probe apparatus using numerical data sets

2008

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Most thermal properties of construction materials used in the analysis of building performance have been measured under laboratory conditions, using a guarded hot box or hot plate apparatus. As a consequence, these properties seldom reflect the impact of actual conditions (especially moisture content) on the values of conductivity and diffusivity. Hence there is a need to develop techniques that allow to take into account local conditions, and measure building material properties in situ. One option available is the use of a thermal probe. The thermal probe technique is based on creating a line source in a material sample, and measuring the temperature rise in the sample in reaction to heat being applied. Obviously the data analysis routines used to calculate thermal conductivity and thermal diffusivity based on the temperature rise observed are crucial to the success of the technique.

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Probe for Measuring Soil Specific Heat Using A Heat‐Pulse Method

Cited by 382 publications

References 0 publications

Latent heat in soil heat flux measurements

Latent heat in soil heat flux measurements

Soil Heat Storage Measurements in Energy Balance Studies

Validation of data analysis routines for a thermal probe apparatus using numerical data sets

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