METHOD FOR COMPUTING OF SCINTILLATION INDEX UNDER ANISOTROPIC IRREGULARITIES IN PERTURBED IONOSPHERE
Electron density fluctuations in ionosphere leads to scintillation effect, which means random variations of amplitude and phase of received signal. According to known method for scintillation index evaluation, at first this index is computed for conditions of wave weak scattering, and then an empirical correction of obtained results is used for multiple scattering without strong focusing. This method supposes the using of expressions been derived by utilizing of approximation of power low with spectral index at most 5 under condition that radius of the first Fresnel zone is substantially smaller than outer scale of irregularities. This condition is fail, when the maximal ionization altitude is much more then thickness of irregularity layer or scintillation index becomes moderate intensive and Gaussian law or power law with spectral index above 5 should be applied for spectral density description. This work presents method for computing of scintillation index for conditions of weak scattering, which takes into account all mentioned above. Proposed method provides evaluation of high spectral index scintillation influence over full value range of first Fresnel zone radius to irregularity outer scale ratio. Method is based on reduction of quadric form of electronic concentration and phase fluctuations in the arguments of autocorrelation function to scalar value, which is further taken into account during Radon and Fourier transformations. Expressions for calculation of scintillation index written in the form of integral of the product of phase fluctuation spectral density and filtering functions were derived by proposed method. Arguments of these expressions takes into account anisotropy of irregularities and oblique wave propagation. Obtained expressions are specified for spectral density of electronic density fluctuations described by both Gaussian law and power law with spectral index ranging from 4 to 6 of that provides more comfortable computing.