Radio refractive index investigations over Bass Strait, Southern Australia

Radio refractive index profile measurements between 500 and 5000 feet were made over Bass Strait (Australia) during January and March 1966, using a microwave refractometer car-tied in a light aircraft. During these flights continuous radio propagation measurements at 173 MHz and 1.9 GHz were made over paths at points along which the profiles were measured. Supporting meteorological observations were also made. The measured refractive index profiles and associated weather conditions are described, and possible mechanisms to account for the observed relations between propagation behavior, refractive index, and meteorological data are discussed. The measurements show the progressive development of a strong superrefractive layer near 3000 feet, resulting from a subsidence inversion. This layer produced enhanced signals on the 173-MHz over-horizon radio path, due mostly to partial reflection at the layer and at some times possibly to trapping. Fading on the 1.9 GHz optical path probably resulted from trapping.