Soil water flux density measurements near 1 cm d−1 using an improved heat pulse probe design

The heat pulse probe (HPP) technique has been successfully applied for estimating water flux density (WFD). Estimates of WFD have been limited to values greater than 10 cm d−1, except for two recent studies with lower detection limits of 2.4 and 5.6 cm d−1. Although satisfactory for saturated soils, it is recognized that current HPP capabilities are limited for applications in the vadose zone, where WFD values are generally below 1 cm d−1. Since numerical sensitivity analysis has shown that large heater needle diameters may increase HPP capabilities in the lower flux density range, a HPP with a 4‐mm‐diameter heater needle was developed and tested. WFD values were obtained by fitting temperature data to the analytical solution for a pulsed cylindrical heat source of infinite length. Effective heater‐thermistor distance and soil thermal diffusivity values were determined for specific heat input scenarios with zero WFD, prior to imposing water flow across the HPP needles. We showed excellent results in the range of 1–10 cm d−1 and satisfactory results in the range of 10–1000 cm d−1.

[1]  J. Bear.  Dynamics of Fluids in Porous Media , 1975 .

[2]  J. Hopmans,et al.  Multi‐Functional Heat Pulse Probe for the Simultaneous Measurement of Soil Water Content, Solute Concentration, and Heat Transport Parameters , 2003 .

[3]  Robert Horton,et al.  Determining Soil Water Flux and Pore Water Velocity by a Heat Pulse Technique , 2000 .

[4]  J. Hopmans,et al.  Estimation of Vadose Zone Water Flux from Multi-Functional Heat Pulse Probe Measurements , 2005 .

[5]  A. Demond,et al.  Packing of Sands for the Production of Homogeneous Porous Media , 1996 .

[6]  J. Tarara,et al.  Measuring Soil Water Content in the Laboratory and Field with Dual‐Probe Heat‐Capacity Sensors , 1997 .

[7]  G. Byrne,et al.  A sensor for water flux in soil. “Point source” instrument , 1967 .

[8]  Jirka Simunek,et al.  Indirect estimation of soil thermal properties and water flux using heat pulse probe measurements: Geometry and dispersion effects , 2002 .

[9]  T. Ochsner,et al.  Evaluation of the Heat Pulse Ratio Method for Measuring Soil Water Flux , 2005 .

[10]  J. Ham,et al.  On the Construction and Calibration of Dual-Probe Heat Capacity Sensors , 2004 .

[11]  J. Šimůnek,et al.  Multi-functional heat pulse probe measurements of coupled vadose zone flow and transport , 2006 .

[12]  B. Das,et al.  Error Analysis of Heat Pulse Method for Measuring Soil Heat Capacity, Diffusivity, and Conductivity , 1995 .

[13]  T. Ochsner,et al.  Improved analysis of heat pulse signals for soil water flux determination , 2007 .

[14]  D. D. Vries.  A NONSTATIONARY METHOD FOR DETERMINING THERMAL CONDUCTIVITY OF SOIL IN SITU , 1952 .

[15]  D. R. Nielsen,et al.  Spatial variability of field-measured soil-water properties , 1973 .

[16]  E. Bresler,et al.  Simultaneous transport of solutes and water under transient unsaturated flow conditions , 1973 .

[17]  Keith L. Bristow,et al.  Error Analysis of the Heat Pulse Method for Measuring Soil Volumetric Heat Capacity , 1993 .

[18]  G. Campbell,et al.  Probe for Measuring Soil Specific Heat Using A Heat-Pulse Method , 1991 .

[19]  Tyson Ochsner,et al.  Mathematical analysis of heat pulse signals for soil water flux determination , 2002 .

[20]  G. Campbell,et al.  TEST OF A HEAT-PULSE PROBE FOR MEASURING CHANGES IN SOIL WATER CONTENT , 1993 .

[21]  Numerical evaluation of alternative heat pulse probe designs and analyses , 2007 .

[22]  R. Horton,et al.  Measurement of Soil Thermal Properties with a Dual‐Probe Heat‐Pulse Technique , 1994 .