Infiltration measurement using a vertical time-domain reflectometry probe and a reflection simulation model

Experimental methods are needed to measure infiltrations at several locations simultaneously during rainfall or irrigation. The objective of this study was to test the feasibility of using a time domain reflectometry (TDR) probe installed vertically into the soil to track the propagation of the wetting front during infiltration. We used a numerical method to simulate wave traces. The dielectric constant above the wetting front and the probe characteristics were known. The trace simulation method was coupled to a nonlinear optimization program to fit the apparent lengths of the TDR probe above and below the wetting front and the dielectric constant of the soil below the wetting front. The optimization program employed a genetic algorithm. The progression of the wetting front into the soil was recorded as a function of the apparent length of the section of the TDR probe above the wetting front. Direct measurements of the wetting front advance were obtained from observations of infiltration in a clear acrylic cylinder packed with soil and ponded with water. The root mean square errors of the predicted wetting front depths did not exceed 0.4 cm. The method shows promise in estimating wetting front depth as a function of time.