Scattering from nonspherical Chebyshev particles I: cross sections, single-scattering albedo, asymmetry factor, and backscattered fraction

Abstract

In this paper, we study the behavior of the scattering efficiency Qsca, the absorption efficiency Qabs, the single-scattering albedo ω, the asymmetry factor g, and the backscattered fraction for isotropically incident radiation β̅ for randomly oriented rotationally symmetric nonspherical particles of radii r = r0[1 + ∊Tn(cosθs)], where Tn is a Chebyshev polynomial of order n. By taking n = 2,3,4,6,8, and 20, and ∊ = −0. 2 to 0.2 in steps of 0.05, twenty-three different shapes have been considered for these Chebyshev particles. The scattering calculations have been carried out using the Extended Boundary Conditions Method for individual particles with refractive index m∼=1.5−0.02i in the equal-volume-sphere size parameter range 1 ≤ x ≤ 25. Unshape-averaged and shape-averaged nonspherical single-scattering quantities have then been compared to corresponding size-averaged (over Δx = 0.1x) spherical results. It is shown that nonsphericity always increases Qabs for size parameters larger than ∼10, while it decreases g—and correspondingly increases β̅—in the size range 8 ≤ x ≤ 15. Qsca seems to be on the average somewhat larger for nonspherical particles, while ω tends to be smaller. Concavity almost always enhances the spherical–nonspherical differences.