Topics in Particle and Dispersion Science

Scattering calculations for nonspherical/inhomogeneous particles: "Exact" methods

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"Exact" computational methods of calculating electromagnetic scattering by nonspherical and/or inhomogeneous particles have been reviewed, for example, by Kahnert FM 2003, Mishchenko MI et al 2000, and Wriedt T 1998. The work edited by Mishchenko et al in particular concentrates on three key computational methods: finite-difference time-domain (FDTD) method, T-matrix method, and separation-of-variables method (SVM).

The FDTD method (for example, Taflove A and Hagness 2005, Taflove A and Umashankar 1989) has been applied to calculate the single-scattering properties of nonspherical particles as diverse as ice crystal aggregates up to relative particle size, x ~20 (Yang P et al 2000) and concave red blood cells (Lu JQ et al 2005). The T-matrix method (for example, Mischenko MI et al 2004c, Mischenko MI et al 1994a, Barber and Hill 1990) has been applied to the finite pristine hexagonal ice column (Fig. 1) for x up to ~40 by Havemann S et al 2003. It has also been applied to more general particle shapes (polyhedral prisms) by Kahnert FM et al 2001a. The SVM was applied to the infinitely extended hexagonal ice column by Rother T et al 2001 for x (corresponding to the column diameter) of up to about 60.

The FDTD and T-matrix methods have been shown to agree very well with respect to calculations of the integrated optical properties, such as the attenuation coefficient and single-scattering albedo and some elements of the scattering phase matrix for hexagonal ice column with x of up to ~20 (Baran AJ et al 2001). The FDTD method has been applied by Baum BA et al 2000 to bullet-rosettes (Fig. 2), Gaussian random particles (Sun W et al 2003), and to the droxtals (Yang P et al 2003). However, it is computationally difficult even for a relative particle size, x, as moderate as ~20 (Yang P et al 2000).

The discrete dipole approximation (DDA) (for example, Draine BT and Flatau 1994) has been used to model light scattering by complex regular particle shapes, such as coccoliths of marine phytoplankton Emiliania huxleyi (for example, Gordon HR and Du 2001), as well as irregular, porous particles (for example, Vilaplana RI et al 2006, see also Scattering matrix of nonspherical particles: Sensitivity to particle characteristics). More recently, the discrete dipole method of moments (DDMM) (Mackowski DW 2002), a derivative of DDA, also shows promise for application to ice crystals with relative particle size, x, of up to ~40. The boundary-element method has also been applied to the finite hexagonal ice column up to x ~50 (referred to the largest dimension) for certain particle orientations by Mano Y 2000.

See also Scattering calculations for nonspherical/inhomogeneous particles: Approximate methods.

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CITATION: Baran A. J. 2007. Scattering calculations for nonspherical/inhomogeneous particles: "Exact" methods (www.tpdsci.com/Tpc/ScaCalcMetNspExct.php). In: Top. Part. Disp. Sci. (www.tpdsci.com).

HISTORY: Published: 02-Jun-2007 Modified: 02-Jun-2007 Peer-reviewed: PENDING

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