Dependent Scattering Effects in Aggregates with Touching or Overlapping Non-Absorbing Spherical Particles

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 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.