Investigation and development of VHF ground-air propagation computer modeling including the attenuating effects of forested areas for within-line-of-sight propagation paths

The development of a short-range (5-100 nm) air-ground, VHF propagation model is presented. Signal strength estimates are calculated by this model using GTD techniques to determine ground scattering effects in addition to a novel aproach for predicting attenuation due to forested areas. The utility of the model is to enable satisfactory siting of VHF (118-136 MHz) ground-air communications facilities. Confirmation of accurate model performance is obtained via comparisons of model outputs with measured signal strength data that were collected specially for this study. A description of data collection is given, detailing measurement equipment, site conditions, and data reduction. An overview of contemporary propagation modeling techniques is also included which describes theory of operation, deficiencies and accuracy.