Monday, November 13, 2006
84-2
The Spatial Sensitivity of Multi-Probe Heat-Pulse Sensors for Measuring Soil Thermal Properties.
Gerard J. Kluitenberg1, John H. Knight2, Wei Jin1, and Jan W. Hopmans3. (1) Kansas State University, Department of Agronomy, 2004 Throckmorton Hall, Manhattan, KS 66506, (2) CSIRO Land and Water, 120 Meiers Road, Indooroopilly, QLD 4068, Australia, (3) University of California, Davis, Dept. of Land, Air and Water Resources, 123 Veihmeyer Hall, Davis, CA 95616
Methods for measuring soil thermal properties implicitly assume that these properties are spatially uniform over some volume of soil around the sensor. If thermal properties are not uniform it is important to know the “volume of influence” of the sensor. In multi-probe heat-pulse methods, a pulse of heat is released from a single heater probe and the temperature signals are received by a number of probes surrounding the heater probe. We analyze the sensitivity of this class of methods to small spatial variations in volumetric heat capacity, thermal conductivity, and thermal diffusivity. We assume that each of these thermal properties is approximately uniform, with departures from uniformity being expressed as small perturbations. In previous work we performed a perturbation expansion of the heat equation to derive exact analytical expressions for the spatial sensitivity of thermal properties as measured using a sensor with a single temperature probe. Here we use the principle of superposition to extend our previous results to apply for the case of two or more temperature probes.