FREQUENCY-DOMAIN ANALYSIS OF TIME-DOMAIN REFLECTOMETRY WAVE-FORMS .2.A 4-COMPONENT COMPLEX DIELECTRIC MIXING MODEL FOR SOILS

Although time domain reflectometry (TDR) is becoming accepted as an im portant tool for the measurement of soil water content and bulk soil e lectrical conductivity, a major part of the method is based on empiric al relationships. An improved understanding of dielectric measurements on soils mat give more insight into soil properties other than soil w ater content and bulk soil electrical conductivity. Frequency domain a nalysis of TDR waveforms enables the measurement of the frequency depe ndent complex dielectric permittivity of soils. The frequency dependen t complex dielectric permittivity of soils can be described with a fou r-component complex dielectric mixing model based on the volumetric mi xing of the refractive indices of the soil components. The four soil c omponents in the model are air, solids, bound water, and free water. R esults indicate that the apparent dielectric permittivity obtained fro m the travel time of the TDR pulse in the soil is the dielectric permi ttivity at the highest measurement frequency of the cable tester, prob e, arid soil system. The model based on the volumetric mixing of real permittivities underestimates the measurements in situations with high values of the imaginary part of the dielectric permittivity. Because the model based on the mixing of the complex dielectric permittivities can describe the data, we conclude that the apparent dielectric permi ttivity is influenced by the imaginary parts in the dielectric permitt ivities of the soil components. Combination of the four-component comp lex dielectric mixing model with the complex dielectric permittivity o btained from the frequency domain analysis of TDR waveforms gives a to ol for modeling the bulk soil electrical conductivity by separating th e conductivity of the soil water into a bound water conductivity and a free water conductivity.