Polarization of the sky

Abstract

Based on full-sky imaging polarimetric measurements, in this chapter we demonstrate that the celestial distribution of the angle of polarization (or E-vector direction) of skylight is a very robust pattern being qualitatively always the same under all possible sky conditions. Practically the only qualitative difference among clear, partly cloudy, overcast, foggy, smoky and tree-canopied skies occurs in the degree of linear polarization d: The higher the optical thickness of the non-clear atmosphere, the lower the d of skylight. We review here how well the Rayleigh model describes the E-vector pattern of clear and cloudy skies. We deal with the polarization patterns of foggy, partly cloudy, overcast, twilight, smoky and total-solar-eclipsed skies. We describe the possible influences of the changed polarization pattern of smoky and eclipsed skies on insect orientation. We consider the polarization of ‘water-skies’ above Arctic open waters and the polarization characteristics of fogbows. Finally, we deal with the change of skylight polarizationdue to the transmission through Snell’s window of the flat water surface.