Multicolor Polarimetry of the Twilight Sky: The Role of Multiple Light Scattering as a Function of Wavelength

This paper is devoted to the investigation of the role of multiply scattered light of different wavelengths in clear twilight, as well as to the influence of multiple scattering and scattering by atmospheric aerosol particles on the polarization of the twilight sky background during this period. The work is based on wide-angle polarimetric CCD-observations of the twilight sky near zenith in the U, B, V, and R bands, which were carried out in summer 2000 at the South Laboratory of the Moscow Shternberg Astronomical Institute. Based on the data obtained, we have determined the fraction of single-scattered light in clear twilight in the zenith for the U, B, and V bands and have estimated the lower limit of this value for the R band. The analysis of color and polarimetric evolution of the sky background was made taking into account single and multiple scattering properties. The characteristic height of the upper boundary of the tropospheric aerosol layer in the Earth's atmosphere was also obtained.