The invest igat ions on Ionosphere developed largely because of the ionospheric communicat ions, the improvement of which depends upon the increased knowledge of the ionospheric behavior and it s characterist ics. The study of radio wave scint illat ions plays an important role in understanding the basic mechanisms of the generat ions of ionospheric irregularit ies as well as planning of atellite based communicat ion systems and developing satellite based radar systems. In this paper we present the digitally recorded ionospheric scint illat ion data of 150.649MHz signal from FLEETSAT satellite at near equatorial station Anantapur, acquired through a PC based real t ime data acquisit ion system and analyze this data to evaluate the S4 index, the auto correlat ion funct ion and power spectra. bhanu1955@37.com, rajamanjula@rediffmail.com
I. INTRODUCTIONWhen a radio wave traverses through the ionosphere containing free electronics, a phase change occurs along the same path. In addition, the ionosphere contains irregularities f plasma density, phase fluctuations build-up across the wave front. As the wave propagates away from the onosphere, phase mixing occurs and fluctuations in amplitude are developed (Amplitude scintillations). The fluctuations in amplitude, phase as well as angle-of-arrival of scintillations have been observed at frequencies ranging from 10 MHz to several GHz. By studying these fluctuations, much information about the characteristics of the ionosphere can be understood [1,11,25,30]. Early observations were made mostly at single frequencies. It is well known that the departure of the relative dielectric permittivity from its background value in the ionosphere is inversely proportional to the square of the signal frequency. Therefore, under these conditions for which fluctuations occur at higher frequencies, signals at lower frequencies will suffer much more severe scintillations. In fact, at times the scintillation will be so intense that the multiple scattering effects will become important [33]. The Radio Beacon Experiments on ATS-6, with the three frequencies at 40, 140 and 360 MHz, provided a good opportunity for simultaneous multi frequency observation of the scintillation phenomenon. Results of the ATS 6 scintillation data are reviewed and the results of the analysis of the FLEETSAT scintillation data are also presented in this paper.
II. WEAK AND STRONG SCINTILLATIONS
A Weak ScintillationFor the analytical study of the scintillation phenomena, it is necessary to solve the inhomogeneous wave equation presented below, for the electric field E.The permittivity å (r) is a random function of position r, and k is the wave number (k = 2ð/ë, ë is the wavelength). First order perturbation techniques provide solutions in the limit of single scatter. For an incident plane waveO O Where E(r) can be written as Where re is classical electron radius, ÄNe (r') is electron density fluctuation (departure from mean) at r'. The Scintillation Index S4 is a very important parameter in characterizing the ...
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