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Information × Registration Number 0203U008031, 0101U002791 , R & D reports Title Physical, chemical and mineralogical properties of lunar surface from Clementine observation data, laboratory simulation and results of theoretical study of light scattering by regolith-like surfaces popup.stage_title Head Shkuratov Ju., Доктор фізико-математичних наук Registration Date 10-04-2003 Organization Kharkov National University named after V.N.Karazin popup.description2 We present results from simultaneous photometric and polarimetric measurements of laboratory samples that simulate the structure of planetary regoliths. Computer modeling of shadow-hiding and coherent backscattering in regolith-like media are also presented. We studied a range of samples that characterize a variety of mechanical structures and albedo. A strong particle-size dependence of the negative branch of polarization for powdered dielectric surfaces was found. Highly reflective particle-size separates of Al2O3 were studied. For grain sizes larger than 1 mkm the depth of the negative polarization does not exceed 0.2%. It is maximum around 0.8% for the 0.1 and 0.5 mkm fraction. However, the angular widths of the opposition spikes of the separates are very similar. Colored samples such as a powder Fe2O3 exhibit a very prominent wavelength dependence of brightness and polarization opposition effects. Metallic powdered samples usually exhibit a wide branch of the negative polarization independent on size of particles. The negative polarization and brightness opposition effects were not present in fresh and compressed snow samples with particle sizes approximately 50x500 mkm. We measured the brightness and polarization opposition effects for rough solid surfaces that exhibit significant microcrystalline structure to consider the plausibility that surfaces of icy satellites (e.g., Europa) can be covered with rather large icy regolith particlesthat have subtle structure on micron-submicron size-scales. For dielectric powders, both opposition effects become more prominent when the samples were compressed. Decreasing the volume density of smoked MgO coatings shifts the minimum of negative polarization from 1 to 10 grad. making the negative polarization branch regular and symmetric relative to the initially asymmetric one. Our computer modeling shows that shadow-hiding affects the negative polarization only in combination with the coherent backscatter enhancement — it decreases the amplitude of polarization. The computer simulation shows that scattering orders higher than second ones significantly contribute to negative polarization even in case of very dark surfaces. Our measurements and computer simulations show that the degree of polarization for highly reflective dielectric surfaces depends not only on phase angle but also on other illumination/observation geometry parameters related ith surface tilt. Even at exactly zero phase the degree of polarization for tilted surfaces can be non-zero. A tilt of the surface normal in the scattering plane gives a parallel shift of negative polarization branch to large values of IPI. The tilt in the perpendicular plane gives the same shift in the direction of positive polarization. At exactly zero phase angle, a celestial body of irregular shape that is covered by an optically homogeneous surface can exhibit non-zero polarization even in integral polarimetric observations. Product Description popup.authors popup.nrat_date 2020-04-02 Close