Application of two-dimensional discrete-ordinates methods to multiple scattering of laser radiation

The discrete-ordinates finite element radiation transport code TWOTRAN is applied to describe the multiple scattering of a laser beam from a reflecting target. For a model scenario involving a 99% relative humidity rural aerosol, the authors compute the average intensity of the scattered radiation and correction factors to the Lambert-Beer law arising from multiple scattering. As their results indicate, two-dimensional x-y and r-z geometry modeling can reliably describe a realistic three-dimensional scenario. Specific results are presented for the two visual ranges of 1.52 and 0.76 km which show that for sufficiently high aerosol concentrations (e.g., equivalent to V=0.76 km) the target signature in a distant detector becomes dominated by multiply scattered radiation from interactions of the laser light with the aerosol environment. The merits of the scaling group and the delta M approximation for the transfer equation are also explored.