The Minnesota Road Research Project (Mn/ROAD) has completed time domain reflectometry measurements of soil moisture since 1993. But questions about interpretation about the data remain, because of soil characteristics at the site, the unusual design of waveguides, and long transmission lines that are known to degrade TOR system performance. This study's objectives included developing a procedure to recover moisture content data measured in situ with TOR since 1993 at the Mn/ROAD site.
Researchers calibrated the relationship between TOR system response and soil water content and characterized the influences of unusual waveguide design, high soil bulk density, high soil clay content, cable length, and soil temperature. Cable lengths greater than 33 m caused errors in the TOR calibration relationship. In addition, soil temperature had a small effect on TDR measurements. Researchers developed correction equations to correct TOR measurements of water content for long cable lengths and soil temperature.
Past TDR moisture measurements taken at the Mn/ROAD site must be interpreted using this report's calibration equation and cable length/soil temperature corrections. Additionally, present and future interpretations of soil moisture using the existing TDR system at the Mn/ROAD site must use these equations.
This report is unpublished. 15 copies were produced and distributed.
