Multiple scattering effects in spatial frequency filtering

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Abstract
The existing theory of imaging through an aerosol medium based on the small-angle approximation to radiative transfer is extended to the general case of multiple scattering with an arbitrary degree of anisotropy. By applying the discrete-ordinates finite-element radiation transport code twotran, we compute the modulation transfer function for a medium characterized by optical depth, single-scattering albedo, and asymmetry parameter. To partially suppress the ray effect in the discrete-ordinates solution to the transfer equation, the first-collision source approach is employed. The results of our modeling which apply to the case of incoherent imaging indicate a strong dependence on the angular divergence of an isotropic source of radiation. Distinctions between the coherent and incoherent illumination cases are stressed, and the earlier small-angle approximation results are rederived.