Flexible Time Domain Reflectometry Probe for Deep Vadose Zone Monitoring Academic Article uri icon


  • into a handle, where it is connected to a coaxial cable; the other end is disconnected so that an open electrical Accurate determination of water content is an important aspect circuit is created. The rods are then inserted into the of most vadose zone monitoring programs. Real-time, continuous, in soil at the point of interest. situ measurements of water content in relatively undisturbed condi- tions are usually limited to shallow soil horizons. We present a new The use of TDR probes for measuring water content methodology using time domain reflectometry (TDR) for water con- in the vadose zone often is limited by the probe installa- tent monitoring in deep vadose zone horizons. The method uses flat, tion technique. In shallow soil horizons, installation of flexible, waveguides pressed against the wall of a borehole. The flexi- standard TDR probes is reasonably straightforward. The ble TDR waveguides are attached to the outer side of a flexible sleeve probes can be inserted into the ground from the surface filled with a liquid resin. The resin (e.g., a two-component urethane) with only minor disturbance of the natural soil proper- generates hydrostatic pressure that forces the flexible waveguides ties. The insertion of TDR waveguides into deep soil against the borehole wall, ensuring a close fit to the irregular shape horizons, however, can be problematic if a natural undis- of the borehole walls. The probe can be used with either a standard turbed soil condition is required. Installation of standard TDR technique, which uses a cable tester (e.g., Tektronix 1520, Tek-

publication date

  • January 1, 2003