A Solution to Characteristic Impedance of the Measuring Probe of Soil Water Content

The characteristic impedance of the probe is critical to determine soil water content for the measuring instrument based on the principle of standing wave ratio. In this paper, solution to the characteristic impedance of three-wire and four-wire probes are derived by image method. The results of the image method solution are compared with the reliable data obtained by boundary element method. It was shown that the image method solution can be used in caluclating the probe characteristic impedance when (D/d)≥5.