Fig. 2. Scaled frequency as a function of volumetric water content as measured in the field (dots) and as calculated by combining the circuit model for nonlossy media with five models that describe the relative permittivity as a function of soil water content (lines). The model of Birchak et al. (1974) is given for phases in series and for phases in parallel. The model of Friedman (1998) is given for the solids, water, air configuration, and the air, solids, water configuration.