Abstract

We developed a model for the two-point joint probability density function for irradiance fluctuations in the atmosphere. Light was assumed to propagate some distance through refractive turbulence to two points located in a plane perpendicular to the propagation direction. Scattered light from turbulent eddies smaller than the Fresnel zone size is diffracted and assumed to produce a complex field whose real and imaginary parts are jointly Gaussian. This field adds coherently to the unscattered field to produce jointly Rician irradiance fluctuations. The light is also refracted by the larger eddies to produce an additional random modulation factor. The logarithm of this modulation factor was assumed to be jointly Gaussian. In weak turbulence, the result is nearly lognormal and has a single scale size. In strong turbulence, the scattered field has a jointly exponential density function with a small-scale size. The lognormal modulation has a larger scale size, which gives rise to the two-scale covariance function observed in strong turbulence. This model for the probability density function agrees well with recent experimental data.

© 1988 Optical Society of America