The single scattering properties of atmospheric particles are fundamental to
radiative simulations and remote sensing applications. In this study, an efficient
technique, namely, the pseudo-spectral time-domain (PSTD) method which was first
developed to study acoustic wave propagation, is applied to the scattering of light by
nonspherical particles with small and moderate size. Five different methods are used to
discretize Maxwell’s equations in the time domain. The perfectly matched layer (PML)
absorbing boundary condition is employed in the present simulation for eliminating
spurious wave propagations caused by the spectral method.
A 3-D PSTD code has been developed on the basis of the five aforementioned
discretization methods. These methods provide essentially the same solutions in both
absorptive and nonabsorptive cases. In this study, the applicability of the PSTD method
is investigated in comparison with the Mie theory and the T-matrix method. The effects
of size parameter and refractive index on simulation accuracy are discussed. It is shown
that the PSTD method is quite accurate when it is applied to the scattering of light by spherical and nonspherical particles, if the spatial resolution is properly selected.
Accurate solutions can also be obtained from the PSTD method for size parameter of 80
or refractive index of 2.0+j0.
Six ice crystal habits are defined for the PSTD computational code. The PSTD
results are compared with the results acquired from the finite difference time domain
(FDTD) method at size parameter 20. The PSTD method is about 8-10 times more
efficient than the conventional FDTD method with similar accuracy. In this study, the
PSTD is also applied to the computation of the phase functions of ice crystals with a size
parameter of 50.
Furthermore, the PSTD, the FDTD, and T-matrix methods are applied to the study
of the optical properties of horizontally oriented ice crystals. Three numerical schemes
for averaging horizontal orientations are developed in this study. The feasibility of using
equivalent circular cylinders as surrogates of hexagonal prisms is discussed. The
horizontally oriented hexagonal plates and the equivalent circular cylinders have similar
optical properties when the size parameter is in the region about from 10 to 40.
Otherwise, the results of the two geometries are substantially different.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1418 |
| Date | 15 May 2009 |
| Creators | Chen, Guang |
| Contributors | Yang, Ping |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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