Fig. 1. Relative permittivity as a function of volumetric water content for the empirical models of Topp et al. (1980) and Malicki et al. (1996), and the dielectric mixing models of Dobson et al. (1985), Birchak et al. (1974) (phases in series and in parallel), and Friedman (1998) (solids, water, air configuration and air, solids, water configuration).