Dlugach Z. Scattering of electromagnetic radiation by Solar System objects: numerical simulation and analysis of observations.

The dissertation studies the properties of electromagnetic radiation scattered by discrete random medium composed of particles of different morphology and various chemical composition. This study is based on the results of numerical simulation obtained by using numerically exact methods of radiative transfer theory and numerically exact direct solutions of the macroscopic Maxwell equations. Results of numerical simulation are used to interpret a series of observations of atmospheres and surfaces of some Solar System bodies. In the scalar case, a new numerically efficient method for accurate determination of the radiation field in plane-parallel multilayer media has been sugested. An analysis of the illumination measurements in the Venus atmosphere performed by automatic interplanetary stations "Venera-11, -13 and -14" has been made by using this method and a developed package of computer codes. It was shown that the registered variations in illumination on the surface of Venus could be explained by significant rapid changes in the optical thickness of the cloud layer only, for which the quantitative estimations were obtained. Using as an example the atmosphere of Jupiter, the quantitative data have been obtained that indicate a strong effect of particle shape on the values of the refractive index, size and the cloud layer structure retrieved from photometric and polarimetric observations. Quantitative estimations of the dependence of coherent backscattering characteristics on shape, size and refractive index of particles contained in sparse disordered media have been obtained. Coherent backscattering by regolithic layers composed of submicrometer sized grains has been shown to be one of the possible reasons for photometric opposition effects observed for some high-albedo atmoshereless Solar System bodies. By using the T-matrix method, numerically exact solution of the vector radiative transfer equation, and the theory of coherent backscattering, an analysis of radar polarimetric observations of the Saturn's rings at a wavelength of 12.6 cm has been carried out. On the basis of direct numerically exact solutions of the Maxwell equations it has been shown that all backscattering effects predicted by the low-density theory of coherent backscattering can also take place in media with volume packing density typical of particle suspensions and particulate surfaces encountered in natural and man-made conditions. In order to study the possible effect of surface particle irregularities on the light scattering characteristics, a new model in the form of microscopic spherical grains, randomly placed on the surface of spherical particle of larger size, has been proposed and investigated.