Comparison between the extended-medium and the phase-screen scintillation theories

By numerically solving the fourth moment equation, comparisons are made between (i) situations in which fluctuations of refractive index extend uniformly from the transmitter to the receiver and (ii) situations in which the fluctuations are confined to a phase screen. The comparisons are made for inverse power-law phase spectra having a total mean square fluctuation of phase (ΔΦ) 2 , an outer scale L 0 and an inner scale 0.01 L 0. Four values of the spectral index are investigated, including the Kolmogoroff value. The comparisons are made for a wavelength such that the Fresnel scale is intermediate between the outer scale and the inner scale, so that both refractive and diffractive scattering are involved. The study extends from situations dominated by weak diffractive scattering up to ones dominated by multiple refractive scattering. It is found that, provided that the equivalent screen (i) is centrally located, (ii) has the same type of fluctuation spectrum and (iii) generates the same value of (ΔΦ) 2 as the extended medium, then the scintillation index and the intensity autocorrelation function in the reception plane are approximately the same in the two cases. Results are very dependent on how many refractive scatterings occur between the transmitter and the receiver, but they are not very dependent on how these refractive scatterings are distributed along the path.