A profiling TDR probe for water content and electrical conductivity measurements of soils

Abstract

Measurements of water content profiles are of great interest in hydrology and soil science. Time domain reflectometry (TDR) is a well‐established method for water content measurements; however, most TDR probe designs are suitable for measurements in only a small soil volume. In this article, a 1‐m long TDR profiling probe with five measurement sections is described. Unlike most other previous profiling probes, our probe allows for both dielectric permittivity (ε) and electrical conductivity (σa) measurements. The accuracy of the ε and σa measurements was excellent; the precision of the measurements was, however, significantly poorer than with a 0.20‐m long standard three rod TDR probe. The new probe was installed in a field and successfully measured water content profiles during the growing season of 2009. During an infiltration experiment it was shown that because of its geometry, the profiling probe over‐estimated the wetting‐front velocity. At a 0.10‐m depth, the over‐estimation was almost 30%. The over‐estimate will be less significant at greater depths.