The effect of fading on the accuracy of measurement of ionospheric absorption

The rapid and slow components of a fading signal are separated by a semi-empirical process in which each component is, in turn, assumed to consist of a steady or specularly reflected component with a random component added. The process is applied to some measurements of the amplitude of first-order reflections from the E-region at vertical and oblique incidence on equivalent frequencies. The standard deviation of the amplitude variation due to rapid fading was found to be greater at vertical than at oblique incidence, but insufficient evidence is yet available to determine whether the variation due to slow fading was also greater. The accuracy of measurement of the smoothed value of field strength is defined as the range of values having a 99% chance of containing the correct value. On this basis, the accuracy of noon absorption, as calculated from a single day´s observations at one frequency, has been estimated to be about +4, ¿12dB at vertical incidence and +4, ¿11 dB at oblique incidence. These limits are not symmetrically disposed about the mean value, as is conventional in normal statistics, partly because of the effect of the decibel scale, and partly owing to the characteristics of deep fading.