1 ABSTRACT. Absorption of solar radiation by snow grains in the near-infrared part of the solar spectrum can not be neglected when computing radiative properties of snow. Thus, a geometrical optics method is developed to compute scattering and absorption cross section of particles of arbitrary complex refractive index assuming large snow meltclusters (1 cm-order), observed ubiquitously in the snow cover during summer, can be characterized as spheres, one may compute absorption and scattering efficiencies, and the scattering phase function on the basis of this geometrical optics method. The number of internal reflections and transmissions are truncated based on the ratio of incident irradiance at the n-th interface to the initial incident irradiance within a specific optical ray. Phase functions for both near- and far-field are directly calculated at a specific scattering angle using a hybrid algorithm based on the bisection and Newton-Raphson methods. With these methods the absorption and scattering properties of a single particle can be calculated for any wavelength in the solar spectrum or microwave region. This “Geometrical Optics Method for SPHEREs ” code (GOMsphere) is tested against Wiscombe’s Mie scattering code (MIE0) for a range of size parameters. It can be combined with MIE0 to calculate the single scattering properties of snow grains of any size.
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