A Fast Two-Stream-Like Multiple-Scattering Method for Atmospheric Characterization and Radiative Transfer

Multiple-scattering effects can significantly impact radiative transfer calculations for remote sensing and directed-energy applications. This study describes the development and implementation of a fast-calculating two-stream-like multiple-scattering algorithm that captures azimuthal and elevation variations into the Air Force Institute of Technology Center for Directed Energy's Laser Environmental Effects Definition and Reference ( LEEDR) atmospheric characterization and radiative transfer code. LEEDR is a fast-calculating, first-principles, worldwide surface-to-100-km, atmospheric characterization package for the creation of vertical profiles of temperature, pressure, water vapor content, optical turbulence, atmospheric particulates, and hydrometeors as they relate to line-by-line layer transmission and radiance from the ultraviolet to radio frequencies. The newly implemented multiple-scattering algorithm fully solves for molecular, aerosol, cloud, and precipitation single-scatter layer effects with a Mie algorithm at every atmospheric layer. A unique set of asymmetry and backscattering phase-function parameter calculations accounts for radiance loss due to the molecular and aerosol constituent reflectivity within a layer and accurately characterize diffuse layers that contribute to multiple-scattered radiances in inhomogeneous atmospheres. LEEDR is valid for spectral bands between 200-nm and radio wavelengths. Accuracy is demonstrated by comparing LEEDR results with published sky radiance observations and experimental data. Determining accurate aerosol loading via an iterative visibility/particle-count calculation method is ultimately essential to achieve agreement between observations and model results for realistic atmospheres.