DIELECTRIC-PROPERTIES OF SOILS IN THE 0.3-1.3-GHZ RANGE

In 1985, we reported the development of a semiempirical dielectric model for soils, covering the frequency range between 1.4 and 18 GHz. The model provides expressions for the real and imaginary parts of the relative dielectric constant of a soil medium in terms of the soil's textural composition (sand, silt, and clay fractions), the bulk density and volumetric moisture content of the soil, and the dielectric constant of water at the specified microwave frequency and physical temperature. This communication provides similar expressions for the 0.3-1.3-GHz range. Upon comparing experimental results measured in this study with predictions based on the semiempirical model, it was found that the model underpredicts the real part of the dielectric constant for high-moisture cases and underestimates the imaginary part for all soils and moisture conditions. A small linear adjustment has been introduced to correct the expression for the real part and a new equation was generated for the effective conductivity to correct the expression for the imaginary part. In addition, dielectric measurements were made to evaluate the dependence of the dielectric constant on clay type. The results show significant variations for the real part and large variations for the imaginary part among soils with the same clay fractions but with clays of different specific surface areas.