Some aspects of the rapid directional fluctuations of short radio waves reflected at the ionosphere

Measurements have been made of the rapid directional fluctuations observed on single-component first-order ionospheric echoes, at vertical and oblique incidence (range 700km), and on frequencies of 2·5¿10·5 Mc/s. Under quiet ionospheric conditions the r.m.s. angular deviations are of the order of 1° or less, but they are appreciably greater under ionospheric-storm or spread-F conditions. The fluctuations are uncorrelated at an interval of five seconds. It is shown that a layer of irregular ionization-density within region E would account for the quiet-condition F-layer results, and this would require random variations of the phase path through the region of the order of only 3 m at a frequency of 5 Mc/s. The E-layer results appear to be affected by partial reflections at different levels within the region.