VHF SCINTILLATIONS AS A DIAGNOSTIC-TOOL FOR THE STUDY OF IONOSPHERIC IRREGULARITIES

In this paper we present the results of observations of the scintillat ions of radio beacon on 250.351 MHz from geostationary satellite FLEET SAT (73 degrees 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 loca l time shows a maxima of 0.589 at 02:55 IST. This scintillation activi ty is linked with the spread F-irregularities, A brief description of the scintillation theories like phase screen theory and theory for wea k scintillations - Rytov solution is given. These theories provide an integral measure of the fluctuations in terms of phase and amplitude f luctuations imposed on VHF signals while traversing through the ionosp here. Power spectrum analysis for the log-amplitude and phase departur e and cross spectrum between them have also been carried out. Using sp ectral index p = 1, we have shown that the scale sizes for the ionosph eric irregularities are greater than 1 km.