462 research outputs found
Light scattering by Gaussian particles: Rayleigh-ellipsoid approximation
No full textWe study absorption and scattering by irregularly shaped Gaussian random particles in the Rayleigh-ellipsoid approximation. For a given sample shape, we determine the best-fitting ellipsoid as the equal-volume ellipsoid with the largest volume overlapping the sample shape. We present an efficient method for calculating such ellipsoids for Gaussian particles and characterize the goodness of the approximation with the complementary volume. We study the scattering properties of Gaussian particles much smaller than the wavelength with different complex refractive indices, comparing the Rayleigh-ellipsoid approximation to the Rayleigh-volume, discrete-dipole, and second-order perturbation approximations, and to the computations using the variational volume integral equation method. Our new method can prove valuable in microwave remote sensing of terrestrial ice clouds: crystalline structures are often elongated with dimensions in the Rayleigh domain for typical radar frequencies
Simulations of Effects of Nanophase Iron Space Weather Products on Lunar Regolith Reflectance Spectra
No full textLunar soil spectra differ from pulverized lunar rocks spectra by reddening and darkening effects, and shallower absorption bands. These effects have been described in the past as a consequence of space weathering. In this work, we focus on the effects of nanophase iron (npFe) inclusions on the experimental reflectance spectra of lunar regolith particles. The reflectance spectra are computed using SIRIS3, a code that combines ray optics with radiative-transfer modeling to simulate light scattering by different types of scatterers. The imaginary part of the refractive index as a function of wavelength of immature lunar soil is derived by comparison with the measured spectra of the corresponding material. Furthermore, the effect of adding nanophase iron inclusions on the reflectance spectra is studied. The computed spectra qualitatively reproduce the observed effects of space weathered lunar regolith. © 2018. The American Astronomical Society. AllThis work has been supported by the Plan Nacional de Astronomia y Astrofisica contracts AYA2015-67152-R and AYA2015-71975-REDT. Jesus Escobar-Cerezo, Antti Penttila, and Karri Muinonen acknowledge the support from the ERC project No. 320773 >SAEMPL.> Tomas Kohout is supported by the Academy of Finland project No. 285432, and by the Institute of Geology (Czech Academy of Sciences), supported by Ministry of Education, Youth and Sports project No. RVO67985831. Computational resources were provided by CSC-IT Centre for Science Ltd, Finland
Disk-integrated brightness of a Lommel-Seeliger scattering ellipsoidal asteroid
No full textContext. The scattering of light by an asteroid’s surface depends on the properties of its particles, volume density, and roughness. It is described by the reflection coefficient which, upon integration over the illuminated and observed part of the surface, yields the disk-integrated photometric brightness of the asteroid. The Lommel-Seeliger reflection coefficient is applicable to dark, low-albedo C-class asteroids, with prospects for moderate-albedo S-class and M-class asteroids.
Aims. We calculate the disk-integrated brightness for an ellipsoidal asteroid with a Lommel-Seeliger reflection coefficient (LS ellipsoid). Furthermore, we calculate the photocenter for the LS ellipsoid, that is, the distance of the center of light from the barycenter.
Methods. Because of their analytical nature, the closed-form expressions can be readily utilized in numerical simulations.
Results. We show lightcurves and photocenter variations for realistic examples of ellipsoidal shapes for a number of pole orientations. The results highlight the reciprocity principle of the radiative-transfer theory and suggest a nontrivial dependence of the photocenter on the pole orientation and viewing geometry.
Conclusions. Finally, we outline a number of applications and future prospects
Light scattering by horizontally oriented particles: Symmetry properties of the phase matrix
No full textUsing elementary symmetry considerations, we present seven symmetry relations for the phase matrix of horizontally oriented particles. These relations have a wide range of validity and hold for all directions of incident and scattered electromagnetic radiation
Light scattering by horizontally oriented particles: Symmetry properties of the phase matrix
No full textUsing elementary symmetry considerations, we present seven symmetry relations for the phase matrix of horizontally oriented particles. These relations have a wide range of validity and hold for all directions of incident and scattered electromagnetic radiation
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