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Ellipsoids have also been applied to investigate the radiative effects of atmospheric dust by Yi et al. (2011). The application of ellipsoids to mineral dust is facilitated by the pre-computed lookup tables in the form of an optical database made available by Meng et al. (2010). The close similarity of spheroids and ellipsoids suggests that ellipsoids probably suffer from the same flaws. Even though no studies apparently exist to test the applicability of ellipsoids for predicting the spectral dependence of dust particle single-scattering properties, Merikallio et al.

8d), defined by two shape parameters: the aspect ratio and the number of corners in the polygonal cross-section. The number of corners was varied from four to seven, while the aspect ratios were varied roughly within a factor of two, with different sets for polyhedra with different cross-sections. A T -matrix code specifically tailored for different types of polyhedra was used for light-scattering computations; recently, this code has been made publicly available (Kahnert, 2013). To test the performance of polyhedra as model particles for mineral dust, the simulations were compared against a scattering matrix for a feldspar sample measured by Volten et al.

The size parameter is also an important parameter when considering the suitability and applicability of different light-scattering methods. The composition specifies the complex refractive index m(λ) of a particle, or, in the case of anisotropic materials, the dielectric tensor. These describe how the material responds to the time-harmonic electric and magnetic fields of the incident radiation. The imaginary part of m is related to the absorptivity of the material. 2 Models with simple homogeneous particles For light-scattering purposes, dust particles are often modeled using simple geometries, assuming internal homogeneity, even though real dust particles are very complex targets.