Grynko Y. Modelling of light scattering by planetary regoliths

In this thesis we use computer simulations to study light scattering by particles, large compared with the wavelength, and media consististing of such particles. Our model exploits a ray tracing method and it can be applied for calculations of scattering poperties of particles of arbitrary shape. A new algorithm for generating media consisting of random irregular particles is presented. The main mechanisms of scattering in particulate media are studied: the shadowing effect, single and multiple scattering. The investigation of shadowing effect showed that the contributions of scattering orders rapidly diminish as the order grows. Only the first scattering order shows the opposition effect and is rather sensitive to packing density. The shape of particles plays a small role. The calculations of single scattering by particles of different shapes showed that strongly irregular particles of all the studied classes reveal much more resemblance, than the perfect representatives of their classes. By the ray-tracing in media, consisting of the particles with different shapes, the analytical model of spectral albedo of powder-like media of Shkuratov et al. (1999) has been verified. Neither backscattering enchancement nor negative polarization branch is observed for media consisting of irregular semitransparent particles in at normal incidence. Randomly shaped particles appear to show smoother phase angle behavior as distinct from the particles of regular shapes that reveal well-detected features characteristic for single particle scattering. This demonstrates that modeling of light scattering of regolith-like surfaces with spherical (or cubical) particles is not adequate, at least in the geometric optics approximation. At grazing incident angles second maximum of positive polarization at large phase angles is found.