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.