Sky Wave Propagation at Low Frequencies

Abstract

Although LF sky waves have been used since the earliest days of radio science, vigorous study of these waves occurred mainly between 1950 and 1970. This research was in large measure a consequence of the development of precision pulsed ground‐wave radio navigation and positioning systems. Although the ground wave is very stable with time of day, season, and so on, the ionospheric waves vary with time, and if such waves were not somehow sidestepped, the accuracy and precision of the navigation or positioning system would deteriorate. Thus, from an engineering point of view, LF sky waves were a problem in developing navigation systems such as Loran‐C or Loran‐D. One direct consequence of this research was the development of the wave hop theory of LF sky wave propagation, which will be introduced here.