A Novel Method to Determine the Volume of Sensitivity for Soil Moisture Sensors

This study presented a novel method to determine the volume of sensitivity (VOS) for dielectric sensors by frozen soil columns radially thawing from outside inward. The method is based on physical equivalence of the dielectric properties between soil drying–wetting and freezing–thawing transitions. We applied this method to determine/compare (i) the VOSs of two types of fringe field probes (one tube type and one cone type) with sandy silt loam samples at a middle level of soil moisture content (θ v = 0.20 cm 3 cm −3 ), (ii) the VOSs of the cone‐type probe with sandy silt loam samples at three levels (θ v = 0.10, 0.20, and 0.28 cm 3 cm −3 ), and (iii) the VOSs of the tube‐type probe with three soil textural samples (sand, sandy silt loam, and silty clay). The determined radii of the cone‐type sensor ranged from 3.0 to 4.1 cm and those of the tube‐type sensor from 5.1 to 8.5 cm. These results could be beneficial for improving the technical design of soil dielectric sensors and understanding the effect of soil physical properties on the VOS.