Dependent scattering effects in aggregates with touching or overlapping non-absorbing spherical particles. (February 2022)

• Record Type: Journal Article
• Authors: Galy, Tiphaine; Pilon, Laurent
• Is Part Of: Journal of quantitative spectroscopy & radiative transfer. Volume 278(2022)
• Publication Date: 2022-02
• Subjects: Electromagnetic scattering -- Light scattering -- Dependent scattering -- Equivalent sphere approximations -- Aerogels atmospheric dust; Spectrum analysis -- Periodicals; Radiation -- Periodicals; Analyse spectrale -- Périodiques; Rayonnement -- Périodiques; Radiation; Spectrum analysis; Periodicals; 543.0858
• DOI: 10.1016/j.jqsrt.2021.108018
• Languages: English
• ISSNs: 0022-4073

Abstract

Highlights: Scattering by aggregates with non-absorbing spheres was studied systematically. A very wide range of particle x s and aggregate X s size parameters was explored. Dependent scattering effects increased with decreasing particle size parameter x s . Particle overlapping did not notably affect the aggregates integral radiation characteristics. The equivalent effective property approximation was valid for aggregates with particles size x s ≤ 1 . Abstract: This study evaluates the effect of dependent scattering and particle overlapping on the integral radiation characteristics of fractal aggregates of monodisperse and non-absorbing spherical particles for a wide range of particle and aggregate sizes. It also aims to identify a scattering approximation capable of rapidly predicting these radiation characteristics. The scattering cross-section and asymmetry factor of fractal aggregates with touching or overlapping spherical particles were computed using the T -matrix method or the discrete-dipole approximation, respectively. The simulated aggregates were composed of up to 30, 000 spherical particles with size parameter x s varying from 0.03 to 5 for an aggregate size parameter χ s of up to 23. The results established that dependent effects (i) were more significant in the scattering cross-section and asymmetry factor than in the absorption cross-sections and (ii) increased with decreasing particle size parameter x s . In addition, overlapping of particles was found to have a negligible effect on the integral radiation characteristics of the aggregates. Finally, the scattering cross section and asymmetry factor of any aggregates consisting of particles such that x s ≤ 1 could be predicted by the so-called equivalent effective property (EEP) approximation treating the aggregates as equivalent homogeneous spheres with the same diameter and with effective refractive index given by the Maxwell–Garnett effective medium approximation.