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DIVISION S-1—SOIL PHYSICS

Calibration and Temperature Correction of Heat Dissipation Matric Potential Sensors

^a U.S. Geological Survey, Placer Hall, 6000 J Street, Sacramento, CA 95189
^b Decagon, Inc., 950 NE Nelson Ct., Pullman, WA 99163
^c 1111 Myrtle Dr., Burlington, WA 98233

* Corresponding author (aflint{at}usgs.gov)

This paper describes how heat dissipation sensors, used to measure soil water matric potential, were analyzed to develop a normalized calibration equation and a temperature correction method. Inference of soil matric potential depends on a correlation between the variable thermal conductance of the sensor's porous ceramic and matric potential. Although this correlation varies among sensors, we demonstrate a normalizing procedure that produces a single calibration relationship. Using sensors from three sources and different calibration methods, the normalized calibration resulted in a mean absolute error of 23% over a matric potential range of -0.01 to -35 MPa. Because the thermal conductivity of variably saturated porous media is temperature dependent, a temperature correction is required for application of heat dissipation sensors in field soils. A temperature correction procedure is outlined that reduces temperature dependent errors by 10 times, which reduces the matric potential measurement errors by more than 30%. The temperature dependence is well described by a thermal conductivity model that allows for the correction of measurements at any temperature to measurements at the calibration temperature.

Abbreviations: CSI, Campbell Scientific, Inc. • USGS, United States Geological Survey • WSU, Washington State University

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