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THREE TECHNIQUES FOR MEASUREMENT OF GROUND CONSTANTS IN THE PRESENCE OF VEGETATION
STANFORD RESEARCH INST MENLO PARK CA
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Foliage degrades the usefulness of conventional wave tilt and propagation loss techniques for estimating in situ the RF ground constants in forested regions therefore, an investigation was made of three other techniques that should provide more accurate input data for modeling, mathematically, radio antenna performance in forests. Two of these techniques are RF methods providing complementary information the open-wire transmission-line probe method gives independent measurements of the near-surface conductivity and the dielectric constant the dipole feed-resistance measured as a function of height method allows a coarse estimate of the effective conductivity to the skin depth. The third technique, the dc geophysical resistivity method, yields a measure of the earth conductivity stratification beneath the vegetation. The dc resistivity method is supplementary to the RF methods, but its usefulness may be limited to estimation of stratification since the accuracy with which conductivity can be extrapolated from dc to RF is not known. This special technical report describes the three techniques, giving the theory, instrumentation, and methods of interpretation for each. Results of the tests conducted during this investigation are analyzed briefly.
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