Abstract
In order to compare EXSCA measurements with light-scattering calculations, numerical studies characterizing the optical properties of soot aggregates were compared by using different approaches: [1] the Rayleigh-Debye-Gans theory for the fractal aggregate model (RDG-FA), studied by Faeth and Koylu, [2] the rigorous solution model (RS) proposed by Xu, and [3] the discrete dipole approximation model (DDA), developed by Draine and Flatau. The extinction, absorption and scattering cross-sections, C, C and C, and matrix scattering coefficients, |S1|2, |S2|2, |S3|2 and |S4|2, were studied, emphasizing the extinction coefficient C and the scattering coefficient |S1(90°)|2. First, these coefficients for a panel of six aggregates with 64 or 128 primary spheres were compared using the three models. For the absorption and extinction cross-sections, the results are close and RDG-FA may be adequate to determine these parameters. For the total scattering cross-section, the DDA model is close to RS whereas the RDG-FA model shows limitations with strong relative differences. For the scattering coefficients, we focused on |S1|2 and |S2|2, |S3|2 and |S4|2 being negligible. For the 64-sphere aggregates, the relative differences between DDA and RDG-FA are generally great and higher for RDA-FA than for DDA. These deviations are especially significant for backscattering. If, on the contrary, we focus on |S1(90°)|2, all of the models give a good prediction. To complete this study, computation times for DDA and RS are indicated and cross-section distributions for a panel of 28 aggregates obtained using RDG-FA and DDA are presented.
Published Version
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