Electromagnetic Determination of Soil Water Content Using TDR: I. Applications to Wetting Fronts and Steep Gradients

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Abstract
The time‐domain reflectometry (TDR) technique has been demonstrated to be a viable method for determining soil water content in uniformly wet soils. The TDR response in nonuniformly wet soils was examined herein both theroetically and experimentally. An extensive set of experiments was carried out in a controlled laboratory test facility which permitted synthesis of steep water content gradients and wetting fronts. The water content measured by the TDR technique has been found to be the same as the average water content to within 0.01 cm3cm−3 in extremely nonuniform conditions. This result is quite surprising at first but is readily explained by the nature of the dielectric constant and water content relationship. The TDR technique has also been found useful in detecting and monitoring the progression of wetting front advance through a soil.