FEASIBILITY STUDY ON THE USE OF OPEN-WIRE TRANSMISSION LINES, CAPACITORS, AND CAVITIES TO MEASURE THE ELECTRICAL PROPERTIES OF VEGETATION

Abstract
Theory, design, and usefulness of experiments to measure effective complex dielectric constants in foliage and vegetation by means of rigid open- wire transmission lines are described. The frequency ranges 30 to 75 MHz (VHF) and 4 to 30 MHz (HF) are covered by using a 5/8-inch-diameter, 3-inch spacing line and a 4-inch diameter, 40-inch spacing line, respectively. Use of these instruments allows one to place bounds on the macroscopic electrical parameters of foliage. Results are presented of measurements with these equipments in October 1965 in the Hoh Rain Forest, Olympic National Park, Washington. There, in the most dense growth available, representative values of effective relative permittivity and effective conductivity were estimated to average about 1.2 and 8 x 10 to the minus five power mhos/meter, respectively. An experiment relating the density of freshly cut willow boughs to the properties of the sample measured by the VHF transmission line is described in detail. From this, it is estimated that vegetation intrinsic conductivities are of the order of 0.03 mhos/meter, or greater, in living willows during mid-October. The relative permittivity is linearly related to 'biodensity' as indicated by the theory of the complex dielectric constant of mixtures. Other methods of measurement, such as the use of large capacitors or resonant cavities, are discussed.

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