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Browsing Publications by Author "Fuller, Kirk A., author"

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    Progress in visibility modeling
    (Colorado State University. Libraries, 1992-12) Fuller, Kirk A., author; O'Brien, Dennis M., author; Stephens, Graeme L., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
    The cross section for total scattering by a cluster of spheres is derived from an integration, over a closed spherical surface, of the scattered Poynting flux associated with the different pairs of spheres in the ensemble. With the use of the addition theorem for vector spherical harmonics, the integral can be evaluated analytically. The pair-wise cross sections can be rearranged into an expression for the scattering cross section of sphere aggregates which is analogous to that obtained from Lorenz-Mie theory for a single sphere. This latter formulation, however, is more difficult to treat numerically than is the summation over pair-wise cross sections. The cross section for total scattering by a cluster of spheres thus derived is applied to a study of the effects of scavenging and aggregation on the specific absorption of carbon. Results are presented for polarization- and orientation-dependent absorption cross sections of sulfate haze elements and cloud droplets with small carbon grains (spheres) attached to their surfaces. Soot typically occurs as aggregates of carbon spherules. In order to address the validity of certain assumptions that are made in the analysis of such structures by fractal theory, comparisons between the absorption cross sections of free carbon, linear chains, and tightly clumped carbon spheres are also provided. Monte Carlo integration of the radiative transfer equation is the technique most easily adapted to complex scattering geometries. It is demonstrated that the multidimensional integrals can be evaluated more accurately and more efficiently with quasi Monte Carlo integration and that the convergence of the multiple scattering series can be accelerated by estimating the rate of decay of the tail of the series. Each of these techniques has been found to be robust and applicable to scattering with any geometry.