Microwave Dielectric Behavior of Wet Soil-Part 1: Empirical Models and Experimental Observations

TLDR

The study evaluates microwave dielectric behavior of soil‑water mixtures across water content, temperature, and soil texture, and proposes two mixing models to explain the observations. Dielectric constant measurements were conducted on five soil types over 1.4–18 GHz, and two mixing models—a semiempirical refractive model and a theoretical four‑component model—are presented to account for the data. Soil texture markedly affects dielectric behavior, especially below 5 GHz, and frozen soils retain liquid water even at –24 °C; room‑temperature measurements are summarized by polynomial expressions in moisture and sand/clay content for both real and imaginary dielectric constants.

Abstract

This is the first paper in a two-part sequence that evaluates the microwave dielectric behavior of soil-water mixtures as a function of water content, temperature, and soil textural composition. Part I presents the results of dielectric constant measurements conducted for five different soil types at frequencies between 1.4 and 18 GHz. Soil texture is shown to have an effect on dielectric behavior over the entire frequency range and is most pronounced at frequencies below 5 GHz. In addition, the dielectric properties of frozen soils suggest that a fraction of the soil water component remains liquid even at temperatures of -24° C. The dielectric data as measured at room temperature are summarized at each frequency by polynomial expressions dependent upon both the volumetric moisture content m and the percentage of sand and clay contained in the soil; separate polynomial expressions are given for the real and imaginary parts of the dielectric constant. In Part II, two dielectric mixing models will be presented to account for the observed behavior: 1) a semiempirical refractive mixing model that accurately describes the data and requires only volumetric moisture and soil texture as inputs, and 2) a theoretical four-component mixing model that explicitly accounts for the presence of bound water.