Registration Number
0213U001493,
0111U001455
, R & D reports
Title
Theoretical, computer and laboratory modelling of light scattering by particles and mediums for interpretations of astrophysical observations
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Head
Shkuratov Yuriy,
Registration Date
25-02-2013
Organization
Kharkov National University named after V.N. Karazin
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Object of research - powdery surfaces and their computer models. The purpose of the research - investigation of lightscattering by particles of arbitrary shapes. Method of research - modeling of lightscattering with discrete dipole approximation (DDA) and T-matrix techniques, and measurements of phase dependences of intensity and linear polarization degree for powdery surfaces. We use the discrete dipole approximation (DDA) method to model the lightscattering by agglomerated debris particles with hierarchical structure. Such structures are important, e.g., for cometary and interplanetary dust particles. Calculations for three combinations of refractive index were made, which correspond to regions of water ice, organic matter, and silicates. We examine the photometric and polarization properties of agglomerated particles with prefractal (Whitten-Sander model) and nonfractal porous structures of particle fragments formed by dipoles. We find that the aggregated particles can produce significant negative polarization at small phase angles. Increasing the packing density of dipoles and/or refractive index makes the negative polarization more prominent. The depth of the negative polarization branch depends on the type of internal structure: the negative polarization branch of particles having nonfractal structure is noticeably shallower in comparison with that of those having a prefractal structure. The negative polarization branch depth strongly depends on the imaginary part of the refractive index and increases with decreasing absorption. Polarization phase curves for agglomerated debris particles become smoother as the number of hierarchical levels increases. We present measurements of backscattering by surfaces consisting of small transparent spherical particles. At small phase angles, powdery samples consisting of spherical particles having very high albedo showed prominent features that corresponded to single-particle scattering. All the samples demonstrate spectrally dependent negative polarization branches that become more prominent with sample compression. We anticipate that since the particles composing the substrates are well-characterized spheres these results may be useful in modeling applications. We present measurements of the complete scattering matrix as a function of the scattering angle of randomly oriented irregular hematite and rutile particles. Apart from their astronomical interest (hematite is believed to be the component of Mars surface and aerosol component in the Earth's atmosphere) these two samples are extremely interesting from a theoretical point of view, because they both have high real parts of the refractive index. According to our experimental and theoretical results, the scattering behavior of particles with high real parts of the refractive index does not strongly depend on the shape of the particles. Furthermore, we have shown by means of T-matrix calculations for spheroids and cylinders that the scattering matrix as a function of the scattering angle of an ensemble of particles with high real parts is not very dependent on the shape of the particles. Thus, the use of the Mie theory to reproduce the scattering behavior of samples with high real (as well as imaginary) parts of the refractive index may be considered a reasonably good approach.
Product Description
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Акімов Л.
Ахметов В.
Бєлкіна І.
Велікодський Ю.
Кайдаш В.
Корохін В.
Марченко Г.
Опанасенко М.
Петров Д.
Псарьов В.
Шкуратов Ю.
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2020-04-02
