Evaluation of Lichtenecker’s Mixing Model for Predicting Effective Permittivitty of Soils at 50 MHz

Abstract

Mixing models help describe the contribution of liquid, gas, and solid phases to the bulk dielectric permittivity of porous materials. They are particularly useful when studying the electromagnetic properties of the vadose zone using TDR or GPR techniques. The objective of this research was to evaluate the Lichtenecker Mixing Model applied to undisturbed and repacked soil data collected with a 50 MHz impedance sensor. These data along with four different applications of the Lichtenecker Mixing Model were used to predict the α parameter and/or solid phase permittivity. The four models employed were: (1) the Complex Refractive Index Model, α = 0.5 (CRIM); (2) dual varying of both α and solid phase permittivity (LI); (3) the direct-weighted average model, α = 1 (DW); and (4) a two-phase simplification of the Lichtenecker model (TM). Overall, the CRIM, LI, and TM models estimated the solid phase permittivity, α, and soil bulk permittivity within the ranges previously reported in the scientific literature, while the other model proved to be of little practical value. Further validation with glass beads showed that the simple CRIM model was the best predictor for soil bulk permittivity when compared to the two-parameter LI model. A regression model was also developed that accurately predicted the volumetric water content of glass beads from soil bulk permittivity, solid phase permittivity, and porosity.