Abstract
The pseudo-spectral time domain (PSTD) and the discrete dipole approximation (DDA) are two popular and robust methods for the numerical simulation of dielectric particle light scattering. The present study compares the numerical performances of the two methods in the computation of the single-scattering properties of homogeneous dielectric spheres and spheroids for which the exact solutions can be obtained from the Lorenz-Mie theory and the T-matrix theory. The accuracy criteria for the extinction efficiency and the phase function are prescribed to be the same for the PSTD and DDA in order that the computational time can be compared in a fair manner. The computational efficiency and applicability of the two methods are each shown to depend on both the size parameter and the refractive index of the scattering particle. For a small refractive index, a critical size parameter, which decreases from 80 to 30 as the refractive index increases from 1.2 to 1.4, exists below which the DDA outperforms the PSTD. For large refractive indices (>1.4), the PSTD is more efficient than the DDA for a wide size parameter range and has a larger region of applicability. Furthermore, the accuracy shown by the two methods in the computation of backscatter, linear polarization, and asymmetry factor is comparable. The comparison was extended to include spheroids with typical refractive indices of ice and dust and similar conclusions were drawn.
Highlights
Atmospheric particles, e.g., ice crystals and aerosols, play a significant role in radiative transfer and remote sensing by scattering and absorbing solar radiation and by terrestrial thermal emission
We increase the spatial resolution until the required accuracy criteria are achieved, namely that the relative errors (RE) of Qext are less than 1%, and the root mean square relative errors (RMSRE) of P11(θ) are less than 25%
Indicated within parentheses are the results of cases in which the pseudo-spectral time domain (PSTD) or discrete dipole approximation (DDA) failed to reach the prescribed accuracy even with a very fine spatial resolution
Summary
Atmospheric particles, e.g., ice crystals and aerosols, play a significant role in radiative transfer and remote sensing by scattering and absorbing solar radiation and by terrestrial thermal emission. The discrete dipole approximation (DDA) [6,7,8,9,10,11], the finite-difference time domain (FDTD) method [8,12,13,14,15], and the pseudo-spectral time domain (PSTD) method [16,17] share similar areas of applicability and are numerically rigorous methods based on solving Maxwell’s equations for electromagnetic scattering by arbitrarily shaped particles. The higher order of accuracy means that a errors smaller than a given tolerance level can be achieved by PSTD with coarser spatial resolution in terms of number of grid points per wavelength, than is needed by FDTD [19] This is one way in which PSTD methods can save CPU time.
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