Aberrations of VHF-UHF signals traversing the auroral ionosphere

Abstract

This final report summarizes an investigation of radiowave scattering in the auroral ionosphere, based on observations of radio-star and satellite signals. The observations were carried out near solar minimum and are compared with radio-star observations performed near the previous solar maximum. Results show that 223 MHz scintillations of the radio-star Cassiopeia A declined from the start of the current observations in 1962 through the winter of 1964-65. Subsequently, scintillations on 223 MHz have continuously increased. Observations at 137 MHz, begun in 1965, also have shown continuously increasing scintillation. Both radio-star and satellite scintillations have shown a nighttime maximum and a daytime minimum in their diurnal variations, showing little change from the diurnal pattern found near solar maximum. Satellite scintillation at 136 MHz has shown the statistical center of the scattering zone to be north of Fairbanks, Alaska (geomagnetic latitude, 65°N), during 1965-66. A close relation of severe satellite scatter events and radio-star visibility fades, on the one hand, to visible auroral luminosity, on the other, has been found. In addition, strong refraction of satellite signals has been found to occur near auroral arcs, with angular deviations up to at least 7° being observed at 137 MHz. Quantitative predictions are made regarding the severity of scatter effects to be expected during the next solar maximum on VHF and UHF satellite communications links in the auroral zones.