Light-scattering model for aerosol particles with irregular shapes and inhomogeneous compositions using a parallelized pseudo-spectral time-domain technique

Abstract

To improve the modeling accuracy of radiative transfer, the scattering properties of aerosol particles with irregular shapes and inhomogeneous compositions should be simulated accurately. To this end, a light-scattering model for nonspherical particles is established based on the pseudo-spectral time domain (PSTD) technique. In this model, the perfectly matched layer with auxiliary differential equation (ADE-PML), an excellent absorption boundary condition (ABC) in the finite difference time domain generalized for the PSTD, and the weighted total field/scattered field (TF/SF) technique is employed to introduce the incident light into 3D computational domain. To improve computational efficiency, the model is further parallelized using the OpenMP technique. The modeling accuracy of the PSTD scheme is validated against Lorenz-Mie, Aden-Kerker, T -matrix theory and DDA for spheres, inhomogeneous particles and nonspherical particles, and the influence of the spatial resolution and thickness of ADE-PML on the modeling accuracy is discussed as well. Finally, the parallel computational efficiency of the model is also analyzed. The results show that an excellent agreement is achieved between the results of PSTD and well-tested scattering models, where the simulation errors of extinction efficiencies are generally smaller than 1%, indicating the high accuracy of our model. Despite its low spatial resolution, reliable modeling precision can still be achieved by using the PSTD technique, especially for large particles. To suppress the electromagnetic wave reflected by the absorption layers, a six-layer ADE-PML should be set in the computational domain at least.

Design and Validation of the Invariant Imbedded T-Matrix Scattering Model for Atmospheric Particles with Arbitrary Shapes

“…Equations (23), (25), and (26) constitute the basic equation set for the calculation of the T-matrix. By solving these equations, the T-matrix can be obtained directly, and the scattering parameters can also be calculated based on the T-matrix elements.…”

“…In order to solve the equations above, the radial integrals in Equations (25) and (26) should be discretized by Gaussian quadrature, which yields:…”

“…Since the IIM T-Matrix method is derived from the volume integral equation, compared to the T-Matrix method which is based on surface integral principles (i.e., "EBCM" or the "null field method"), it can be applied to the scattering calculations of particle with arbitrary shapes and inhomogeneous compositions, which can greatly expand the application scope of the T-Matrix method. Domain (PSTD) [23][24][25], and Multi-Resolution Time Domain (MRTD) [26,27]. DDA and FDTD can be applied to the light scattering calculation for particles with arbitrary shape; however, due to the limitation of their computational stability and complexity, it is a tough job for them to simulate the light scattering by particles with large sizes [15].…”