Dependence of profile probe sensitivity zone on probe diameters

Monitoring volumetric water content (VWC) at several depths in the soil profile can be performed using either a few soil moisture sensors placed at various depths or a profile probe. The use of a profile probe is less disturbing to the soil, less laborious more convenient, and more cost-effective. The objective of the paper is to estimate the dependence of the depth of the sensitivity zone of a single section of a profile probe working in the time-domain transmission mode (P-TDT probe) on the probe's diameters. This issue was assessed with the use of the finite element method (FEM) simulations in the frequency domain. The scattering parameters matrices obtained in the simulations were transformed to the time domain. Based on the results, the depth of the sensitivity zone was estimated for different probe diameters. It was concluded that the effective soil volume measured by the profile probe of a given geometries is in range 14.3 to 30.9 mm around the tested probe.