TDR Technologies for Soil Identification and Properties

Recent research indicates that Time Domain Reflectometry (TDR) is becoming capable of identifying soil types in addition to providing water content and density. The process makes use of measured apparent dielectric constant and reflected pulse area, a new concept that captures characteristics of the reflected wave from the embedded probe. The method is relatively calibration free. This paper briefly describes the method and presents a new technique for representing the TDR signature to determine both the apparent dielectric constant and pulse area. The paper also incorporates recent findings with regards to probe geometry on measured electrical conductivity. The fitting is accomplished using the sum of two coupled functions: one is a non-linear hyperbolic function to model the reduction in voltage associated with the reflection from the soil surface and the other is an inverse trigonometric function to model the voltage from the reflection from the end of the probe. The model provides an excellent fit for TDR signals passing through homogeneous materials within the probe.