Light depolarization by non-uniform polarization distribution over a beam cross section

We study the depolarization effects caused by a non-uniform distribution of the polarization over the cross section of a light beam. Stokes' parameters of a natural light beam are averaged over its cross section. By introducing the correlation function between two points of the cross section we found that the degree of polarization of the light beam depends on both the correlation function and the number of uncorrelated polarization states. Our description is valid also for a cross section resulting from the incoherent overlap of light beams having different intensities and polarizations