  The photon density operator function is used to calculate light beam
propagation through turbulent atmosphere. A kinetic equation for the photon
distribution function is derived and solved using the method of
characteristics. Optical wave correlations are described in terms of photon
trajectories that depend on fluctuations of the refractive index. It is shown
that both linear and quadratic disturbances produce sizable effects for
long-distance propagation. The quadratic terms are shown to suppress the
correlation of waves with different wave vectors. We examine the intensity
fluctuations of partially coherent beams (beams whose initial spatial coherence
is partially destroyed). Our calculations show that it is possible to
significantly reduce the intensity fluctuations by using a partially coherent
beam. The physical mechanism responsible for this pronounced reduction is
similar to that of the Hanbury-Braun, Twiss effect.
