MULTIPLE-SCATTERING OF NARROW LIGHT-BEAMS IN AEROSOLS

A multiple scattering propagation model of narrow light beams in aeros ol media is described. It is based on a paraxial approximation of the radiative transfer equation in which the flux normal to the incident b eam direction is modeled by a diffusion process. The model solutions a re the forward- and backscattered intensity profiles for the specified geometry and receiver aperture and field of view. The required inputs are the system parameters, and the aerosol single scattering angular phase function and extinction and scattering coefficients which are al lowed to vary along the beam axis. Good agreement is shown with measur ements performed in the laboratory over scales ranging from a few tens of mm to a few m, and in the atmosphere over a scale of the order of 1 km. The solutions are valid for optical depths smaller than approxim ate to 10, for phase functions corresponding to average size parameter s of order one or greater, and for off-axis positions not exceeding ap proximate to 25% of the reciprocal of the scattering coefficient.