Microwave Dielectric Spectrum of Vegetation-Part I: Experimental Observations

This is the first paper in a two-part sequence that evaluates the microwave dielectric behavior of vegetation material as a function of water content, microwave frequency, and temperature. Part I presents experimental measurements of the dielectric spectrum from 0.2 to 20 GHz for various types of vegetation material including leaves, stalks, and trunks at various moisture conditions. The measurements were acquired using a coaxial probe technique suitable for measuring the dielectric constant of both thick materials, such as tree trunks, and thin materials, such as leaves. In Part II, the experimental data are used to guide the development of a dual-dispersion dielectric model that incorporates the dielectric properties of water in both "free" and "bound" forms.