The size of low-latitude ionospheric irregularities determined from observations of discrete sources of different angular diameters

Several methods have been used to measure the horizontal dimensions of ionospheric irregularities that cause the scintillation of radio signals propagating through the terrestrial ionosphere. A frequently used technique is to measure the size of the shadow pattern on the ground with spaced receivers using a very strong radio source (usually Cassiopeia A or Cygnus A) or a satellite as the source of radio frequency energy. The technique described in this paper is to utilize the differences in the angular diameter of various discrete radio sources to determine irregularity size. The phenomenon, by which a radio source of small angular diameter scintillates while one of large angular diameter does not, is directly analogous to the optical portion of the electromagnetic spectrum where stars scintillate but planets do not.