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It is now well established that a relatively simple Mie theory does not reproduce correctly the single-scattering properties of nonspherical particles, such as ice crystals (for example, Baran AJ 2004) and other atmospheric aerosols (for example, Liou and Takano 1994), as well as other particles (for example, Gordon and Du 2001) although Mie theory does provide the first-order-of-magnitude approximation, especially for unpolarized light scattering (for example, Kahnert FM et al 2002). Hence, the computations of single-scattering properties of nonspherical particles encountered in nature remain difficult for several reasons.
First, the ranges of the relative size, x, representative for atmospheric aerosols (~0.1 < x < 1000), and natural waters' dispersions (~0.1 < x < ~10,000) are rather large. In the visible, as represented by a wavelength of 0.5 µm, this corresponds to an absolute particle size range of ~0.016 to ~160 µm (atmosphere) and up to ~2 mm (natural waters). To date there is no single method that can compute all the single-scattering properties of nonspherical and/or inhomogeneous particles in such a wide range of x.
Second, the particle shape, internal structure, and orientation, three other particle characteristics that may significantly affect light scattering, may also vary considerably for naturally occuring dispersions. Hence, computations of light scattering by using "exact" methods must take into account probability distributions of not only the particle size but also of the particle shape, structure, and composition (the latter as represented in optics by the refractive index). Relatively few studies using "exact" methods that have been undertaken to examine light scattering properties of particle size-shape-structure distributions were not only computationally difficult and time consuming (for example, Vilaplana RI et al 2006, see also Scattering matrix of nonspherical particles: Sensitivity to particle characteristics; Gordon and Du 2001), but also limited to a moderate range of the relative particle size (x < ~10). Given these problems regarding the use of "exact" electromagnetic methods, various approximations are still required in order to address the full range of particle characteristics encountered in nature, albeit "exact" methods have been sucessfully used in limited ranges of the particle characteristics.
See also Scattering calculations for nonspherical/inhomogeneous particles: "Exact" methods and Scattering calculations for nonspherical/inhomogeneous particles: Approximate methods.
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| CITATION: Baran A. J. 2007. Scattering calculations methods for nonspherical/inhomogeneous particles: Introduction (www.tpdsci.com/Tpc/ScaCalcMetNspIntro.php). In: Top. Part. Disp. Sci. (www.tpdsci.com). |
HISTORY: Published: 02-Jun-2007 Modified: 02-Jun-2007 Reviewed: PENDING |
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