RAPID LABORATORY CALIBRATION OF TIME-DOMAIN REFLECTOMETRY USING UPWARD INFILTRATION

We propose an upward infiltration method to calibrate a time domain re flectometry (TDR) system. The method is rapid, allows the soil to rema in unchanged during the experiment, and provides hundreds of data poin ts. Three experiments were conducted using 18.7-cm-long probes in soil s of three textures (nine experiments total). Calibrations also were p erformed by packing soil cores with soil at progressively higher water contents. The data from the two methods were fitted using regression techniques to two published models of the dielectric constant-water co ntent relationship. The results show that the calibration curves of al l three soils, fitted simultaneously to replicate experiments, mere si milar in shape and statistically the same. A single calibration curve, fitted simultaneously to the replicate experiments of the three soils , was compared with Topps equation and was statistically the same. The results support the conclusion that the upward infiltration method pr ovides a fast and repeatable calibration method, consistent with conve ntional calibration.