A method for computing ionospheric focusing of radio waves, using vertical incidence ionograms

The dependence of the signal strength of radio waves upon ionospheric focusing and spatial attenuation is calculated for a spherical ionosphere in terms of parameters obtainable from the appropriate vertical incidence ionogram. The signal strength at any given distance can be presented as a function of these ionospheric parameters in the form of a contour chart from which the unabsorbed field strength can be obtained easily as a function of frequency. The geometrical optics approximation is used. The limits of the region at the skip distance for which this method fails are estimated by comparing the results of a ray- and a wave-type calculation.