A. A. Suvorov

Joint moments of the wave beam amplitude and inverse power in an absorbing random medium with lens properties

Abstract This paper presents a derivation of a system of closed equations for joint moments of the amplitude and inverse power of a wave beam propagating in a regularly inhomogeneous dissipative random medium. The radiation transfer in the medium is characterized by non-conservation of the total radiation energy flux and by the existence of power fluctuations. The statistics of the wave beam power fluctuations have been studied. Information on the power statistical characteristics is applied to close the system of equations for joint moments. For task parameters which are not very strict (an effective radius of the wave beam should be considerably less than the outer scale of the turbulence) a system of independent equations for arbitrary joint moments has been obtained. The equations for the first two lower joint moments of the beam intensity and inverse power have been solved analytically. With the solutions obtained the effective wave beam parameters were calculated, i.e. the beam mean displacement, ef...

Wave beam tremble within an absorbing random medium with lens properties

Abstract The present paper investigates the joint influence of fluctuations of the complex dielectric constant, ϵ, of a medium and its lens properties on random displacements of a radiation beam. Based on a non-traditional approach, an expression is obtained for the variance of the beam energy centre tremble, σ2 ρ, taking into account the contribution of fluctuations of the real and imaginary parts of ϵ, as well as that of their correlations. It was shown that the influence of fluctuations of the imaginary part of ϵ is particularly pronounced in the initial section of the path, as well as in paths of great length. Due to regular refraction, a considerable enhancement of the dependence of σ2 ρ upon the path length occurs, with the greatest contribution being made by fluctuations of the imaginary part of the dielectric constant. A positive correlation of random changes of the real and imaginary parts of ϵ was shown to result in a partial compensation of the beam tremble.

Saturation of Irradiance Fluctuations in a Weakly Absorbing Turbulent Atmosphere

Statistical characteristics of the irradiance of an electromagnetic wave propagating in a dissipative random medium are studied. For the propagation regime of strong irradiance fluctuations, asymptotic expressions are obtained for the second statistical moment of the irradiance. The behavior of the relative variance of irradiance fluctuations is analyzed for different propagation conditions. It is shown that, if the outer scale of turbulence exceeds the maximum correlation length of irradiance fluctuations because of random attenuation, no saturation of the relative variance of irradiance fluctuations to unity occurs. Depending on the ratio between the structure characteristics of the real and imaginary parts of the permittivity and on the degree of their correlation, the relative variance of irradiance fluctuations in this case may be either an increasing, or a decreasing, or a nonmonotonic function of the path length, deviating from the level corresponding to a transparent turbulent medium. It is found that the saturation of the relative variance of irradiance fluctuations to unity in a randomly absorbing medium occurs in the region of strong fluctuations if the correlation length of irradiance fluctuations is greater than the outer scale of turbulence.

The “cumulant” method for solution of problems of wave propagation in random media

The “cumulant” method for solving problems of radiation propagation in randomly inhomogeneous media is described. Integral expressions for statistical moments of the wave complex amplitude in general form with the Feynman representation of Green’s function of the quasioptics parabolic equation have been obtained in the framework of the “cumulant” method. It was shown that taking into account some approximation of the processes of radiation multiple scattering in the “cumulant” method allows us to obtain expressions for statistical moments of intensity to an accuracy sufficient to restore the lognormal distribution function.