  Collisionless Boltzmann equation is used to describe the intensity
correlations in partially saturated and fully saturated regimes in terms of
photon distribution function in the phase space. Explicit expression for fourth
moment of the light fields is obtained for the case of moderate and strong
turbulence. Such expression consists of two terms accounting for two regions in
the phase space that independently contribute to the correlation function. It
is shown that present solution agrees with previous results for fully saturated
regime. Additionally it embodies the effect of partially saturated radiation
where the correlations of photon trajectories are important and the magnitude
of the scintillation index is well above the unity. Fourth moment is used to
study the fluctuations of transmittance which consider the effect of finite
detector aperture.
