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Noninvasive Water Content and Electrical Conductivity Laboratory Measurements using Time Domain Reflectometry

Dep. of Water Resources Engineering, Lund Univ., Box 118, 221 00 Lund, Sweden

Ronny Berndtsson

*Corresponding author (magnus.persson{at}tvrl.lth.se).

ABSTRACT

A noninvasive approach for measurements of near-surface water content () and bulk electrical conductivity (_a) using time domain reflectometry (TDR) is presented. In this approach, an ordinary three-rod TDR probe is used together with a polyvinyl chloride (PVC) surface block that surrounds half the measurement volume. Theoretical and experimental results show that an analytical solution of the apparent dielectric constant K_a and the _a of the soil is possible. Thus, the suggested technique does not require a separate calibration of the relationship between the measured effective K_a and K_a of the soil. The variability of the measurements was shown to be slightly higher than using the traditional approach. The spatial sensitivity of the suggested technique was also investigated. It was shown that using a three-rod TDR probe with a rod spacing of 0.05 m allows the and _a to be measured in the uppermost 2 cm of the soil.

Received for publication December 8, 1997.