A newly designed TDR probe for soils with high electrical conductivities

Time domain reflectometry (TDR) is a fast, accurate, and safe technology for field monitoring of soil moisture. Commonly used information in TDR signals includes the apparent dielectric constant and electrical conductivity. Because general TDR principles are not available for apparent dielectric constant measurements by travel time methods in soils with high electrical conductivities caused by the significant signal attenuation, the conventional commercial probes lose their purposes. For this reason, a new probe has been designed for measuring dielectric constants in highly conductive soils on the basis of the surface reflection coefficients method. This new probe can make the reflection at the soil surface more distinct. Experiments were conducted to verify the accuracy of measuring dielectric constants in different soils using this new probe. Finally, the probe was used to measure water content and dry density in the field. The results show that the probe has good integrity and high strength. This probe is capable of obtaining the dielectric constant in soils with high electrical conductivities using surface reflection coefficients methods with reasonable accuracy. In addition, it indicates that the dielectric constant measured by this approach matches well with that determined by travel time methods in the relative error range of 10 % in lowly conductive soils. Compared to oven-dry methods, the relative errors of water content and dry density determined using this new probe are less than 10 % and 3 %, respectively.