Remote sensing studies and climate research require precise knowledge of the single-scattering properties of nonspherical particles. In this study, a three dimensional finite-difference time domain (FDTD) program with a perfectly matched layer (PML) absorbing boundary condition is developed to provide a numerical solution for light scattering by nonspherical dielectric particles. The FDTD model is used to study the single-scattering properties of cirrus ice crystals in the infrared and to investigate the scattering patterns by particles with various morphologies. The FDTD scheme is extended to simulate light scattering and absorption by particles with large complex refractive index. The FDTD scheme is also extended to be applied to simulate light propagation in dielectric media with particles embedded.; The anomalous diffraction theory (ADT) is considered to be suitable for the calculation of the extinction and absorption efficiencies for nonspherical particles with small refractive indices. In this study, an analytical ADT model for light scattering by arbitrarily oriented hexagonal and cylindrical particles is developed. The differences between the analytical ADT model and the simplified ADT model, which is often used in climate and remote sensing studies, are also examined.; Using the FDTD model, we examine a number of commonly used approximate methods including Mie theory, the ADT, and the geometrical optics method (GOM), for the calculation of the scattering and absorption properties of hexagonal ice crystals in cirrus clouds. Some problems in the retrieval of cirrus particle size are addressed.
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