Fig. 1. Probes of the sensing systems considered in the study are from left to right: Acclima Digital TDT Sensor, three-rod TDR probe used with Tektronix TDR and TDR100 (0.15-m-long 3.20-mm-diam. rods, 12.0-mm rod spacing), CS616, ECH₂O Probe, Hydra Probe, and Theta Probe.