Differential effective medium schemes for investigating the relationship between high‐frequency relative dielectric permittivity and water content of soils

Differential effective medium (DEM) theory is presented and used to calculate the effective HF dielectric permittivity κ of unsaturated soils considered as mixtures of solid and two fluid phases. In the case of coarse‐grained soils for which dielectric losses are negligible, a good agreement with the empirical equation of Topp et al. [1980] is obtained using only a spherical grain shape. Moreover, results of DEM schemes have shown that ohmic losses induced by salinity modify significantly the relationship between the apparent dielectric permittivity at 120 MHz and the volumetric water content θ, for NaCl concentration greater than 0.045 mol/L. In the case of clayey soils, simulations based on the same theoretical approach show that the available data can not be modeled by considering only the geometrical effect associated with the “platy” units and the ohmic losses associated with the surface conductivity.