VHF scintillations as a diagnostic tool for the study of ionospheric irregularities

Abstract

In this paper we present the results of observations of the scintillations of radio beacon on 250.351 MHz from geostationary satellite FLEETSAT (73° E) recorded at Bombay on April 9–10, 1992 during night hours. The scintillation index,S 4, is used to describe the strength of the scintillations. The variation of scintillation index with local time shows a maxima of 0.589 at 02:55 IST. This scintillation activity is linked with the spreadF-irregularities. A brief description of the scintillation theories like phase screen theory and theory for weak scintillations - Rytov solution is given. These theories provide an integral measure of the fluctuations in terms of phase and amplitude fluctuations imposed on VHF signals while traversing through the ionosphere. Power spectrum analysis for the log-amplitude and phase departure and cross spectrum between them have also been carried out. Using spectral indexp = 1, we have shown that the scale sizes for the ionospheric irregularities are greater than 1 km.