取向比对椭球气溶胶粒子散射特性的影响

利用T矩阵和离散坐标法研究了取向比对椭球粒子散射特性的影响, 计算了小尺度范围内椭球粒子的散射特征参量, 包括消光效率因子、不对称因子、单次散射反照率、散射相矩阵及双向反射函数(BRDF). 结果表明, 椭球粒子的散射特性与取向比密切相关, 粒子取向比会影响散射参量的振荡频率和振幅, 与球形粒子散射参量的相对差异也呈周期振荡趋势. 研究还发现, 某些特殊粒子尺寸的散射参量与粒子取向比基本无关. 在多次散射条件下, 分析不同取向比粒子群的BRDF随反射角和光学厚度的变化特性. 结果显示: 不同取向比粒子群的BRDF随反射角的变化趋势基本一致, 球形粒子群比非球形粒子群的BRDF曲线波动振幅更大; 球形-非球形粒子的BRDF相对差异随光学厚度和取向比的增大而减小, 随入射角的增大而增大.

Influence of aspect ratio on the light scattering properties of spherical aerosol particles

The influence of aspect ratio on the light scattering properties of ellipsoidal particles is studied by using T-matrix method and discrete ordinate method in this paper. The light scattering characteristic quantities including extinction efficiency, asymmetrical parameter, single scattering albedo, scattering phase matrix, and bidirectional reflectance distribution function (BRDF) are computed. It is found that light scattering properties of ellipsoidal particles are sensitive to aspect ratio. The aspect ratio can influence the oscillation frequencies and amplitudes of the scattering parameters except some special size parameters. The value of asymmetrical factor could be as large as 0.3 in wave crest value of size parameter while it is no more than 0.1 at the balance location. As for the multiple scattering, the characteristics of BRDF for different aspect ratios in different incident angles and optical thickness values are analyzed, and for a further study, the relative differences of BRDF influenced by aspect ratio, optical thickness, and incident angle are analyzed. The results show that the variation trends of BRDF for the ellipsoidal particles with various aspect ratios are basically the same. However, the curve of BRDF of spherical particles (i.e., with their aspect ratios being 1) is more variable. With the increasing of aerosol optical thickness and aspect ratio, the curves of BRDF at different aspect ratios for ellipsoidal particles tend to a steady and similar value and the relative difference of BRDF decreases. But with the increasing of aerosol optical depth, the relative difference of BRDF increases with the increasing of incident angles, especially in large optical thickness, the value of the relative difference of BRDF can be as large as 15%.