Fig. 6. Time domain reflectometry traces recorded in air, water, and sand–water mixtures of different volumetric water contents, with single rod probes (SRP) of different lengths L. Top: SRP300 (300 mm); middle: SRP200 (200 mm); bottom: SRP150 (150 mm). The start of the probe section embedded in the sand–water mixture is the point after which the traces diverge and have travel times proportional to .