Detecting a Large-Scale Upper-Atmospheric Plasma Inhomogeneity Using the Method of Multifrequency Radio Sounding in the Decametric Wavelength Range

We examine the problem of transionospheric sounding with satellite radio signals at frequencies that are close to the edge of the radio transparency frequency range of the ionosphere. We derive asymptotic formulas for the group delay time of the transionospheric radio signal and present an example of how they are implemented if there is a localized large-scale electron density inhomogeneity in the ionosphere. Finally, we suggest techniques for detecting large-scale ionospheric inhomogeneities, which are based on numerical-asymptotic synthesis of disturbed distance-frequency characteristics of decametric signals radiated from a low-orbiting or geostationary satellite.