The EOSAEL92 large area screening systems applications (LASS) module is an adaptation of a similar model originally developed through the support of the Joint Technical Coordinating Group/Munitions Expenditures Smoke and Aerosol Working Group for use in research on the effectiveness of smoke screens deployed at large fixed and semi-fixed military installations. The original impetus for the work was to develop a tool for the assessment of smoke screens, employed with other techniques of camouflage, concealment, and deception, as an electro-optical countermeasure against low-level nap-of-the-earth attack by high-performance aircraft. The outputs of the model are symbolic maps displaying the direct and diffuse components of scene transmission as affected by a large-area smoke screen. In principle, the digital maps can be used with appropriately scaled maps of any given fixed installation to asses the effectiveness of a smoke screen under various ambient meteorological an illumination conditions for various attack scenarios. The model is logically divided into two distinct parts: One that applies the Gaussian diffusion approximation to compute obscurant concentration path length, or CL product, and another that applies the plane parallel approximation to compute target-background contrast. The transport and diffusion algorithms are similar to those employed in other EOSAEL92 obscuration models, differing only in minor detail. The radiative transfer algorithms, however, are unique in the use of the extensive radiative transfer tables originally published by Van de Hulst, which are used together with novel scaling algorithms to account for effects of single and multiple scattering along arbitrary slant path and horizontal lines of sight. The model as thus far developed treats scattering processes only and is thus restricted to wavelength regions where absorption and thermal emission are negligible. The obscurant phase function is taken to be of the Henyey-Greenstein form and can account for various degrees of anisotropic scattering as well as isotropic scattering. The model accounts for scattering of the direct solar beam, uniform diffuse sky light, and diffuse reflection from the underlying (earth) surface.

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