Off-axis propagation of a laser beam in low visibility weather conditions

The role of non-small-angle scattering is examined for off-axis laser beam propagation under low visibility weather conditions. The near-axis radiance distribution function is obtained from a radiative transfer equation with the aid of the small-angle approximation. The contribution of the non-small-angle scattering is described via another transfer equation with the on-axis radiance as an external source, and this equation is solved in the diffusion approximation. Numerical results for radiational and advective fogs are presented to show the importance of non-small-angle scattering in the case of off-axis detection.