Fig. 4. Response models fit to the NR-NC media data for the (a) higher frequency broadband sensing systems (model is Eq. [1] fit to the data using an electrical length, L_e, of 0.15 m and where the travel times measured with the Acclima TDT are divided by a factor of four to account for 0.60-m waveguide length), (b) CS616, (c) Hydra Probe (response model was not derived for the Hydra Probe because it uses three output voltage values to derive permittivity and the details concerning how this is accomplished were not available from the manufacturer), (d) Theta Probe and ECH₂O Probe. The models for the CS616, Theta Probe, and ECH₂O Probe are empirical equations fit to the data with TableCurve (Jandel Scientific, San Rafael, CA).