Mutual coherence function of the field in a regular waveguide filled with an inhomogeneous medium

The mean field is calculated and radiative transfer equations are formulated for the mode expansion of the mutual coherence function of a regular waveguide filled with a medium the refractive index of which fluctuates randomly. Attenuation of the mean field due to scattering on inhomogeneities resembles mean-field attenuation in an unbounded inhomogeneous medium. As an illustration, attention is given to a waveguide with two plane boundaries and filled with an inhomogeneous medium, under the assumption that the inhomogeneity scale is small in comparison with waveguide width. A possible application of the theory is the tropospheric waveguide.