Dual thermal probes near plane interfaces

The dual probe estimates the thermal properties of soils. Because it is strongly dependent on water content, volumetric heat capacity is useful for moisture estimation. A previous study of probe errors due to soil heterogeneity is taken further with the aid of a new solution for instantaneous line sources near a plane interface between two regions. The solution allows for different conductivities and heat capacities in the regions, but requires uniform diffusivities. This condition holds reasonably well near wetting fronts in a range of soils. Previous error bounds are confirmed and sharpened. The conclusion in the previous study that errors are small when the heterogeneity is no closer to the probes than the probe separation (typically 0.006 m) is reinforced. The expectation that the dual probe gives good resolution of water content close to fronts and interfaces is strengthened.