50 YEARS OF RADIO-SCINTILLATION OBSERVATIONS

The author attempts a brief summary of the history of ionospheric fadi ng from sources beyond the upper atmosphere. The concentration is on t he early studies of scintillation. The first sources used as transmitt ers were radio stars with varying diameters. With the advent of satell ite transmissions at altitudes varying from 300 km to several earth ra dii, fading was studied as a function of various regions of the globe. In years of high solar flux, trans-ionospheric propagation through po lar and equatorial regions has experienced deep fading at frequencies ranging from 54 MHz to 4 GHz. Fading of radio signals from satellites still plays a role in evaluating operational and proposed system effec tiveness. The relevance of these studies to Global Positioning System reception and users of proposed systems at L band is discussed.