J. Gal et al., Polarization patterns of the summer sky and its neutral points measured byfull-sky imaging polarimetry in Finnish Lapland north of the Arctic Circle, P ROY SOC A, 457(2010), 2001, pp. 1385-1399
Citations number
31
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON SERIES A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
Using 180 degrees field-of-view (full-sky) imaging polarimetry: the pattern
s of the degree and angle of polarization of the entire summer sky were mea
sured on 25 June 1999 at a location north of tire Arctic Circle in Finnish
Lapland as a function of the angular solar zenith distance. A detailed desc
ription of the used full-sky imaging polarimeter and its calibration is giv
en. A series of the degree and angle of polarization pattern of the full sk
y is presented in the form of high-resolution circular maps measured in the
blue (450 nm) spectral range as a function of the solar zenith distance. G
raphs of the spectral dependence of the degree and angle of polarization of
skylight at 90 degrees from the Sun along the antisolar meridian are shown
. The celestial regions of negative polarization and the consequence of the
existence of this anomalous polarization, the neutral points, are visualiz
ed. The measured values of the angular zenith distance of the Arago and Bab
inet neutral points art: presented as a function of the zenith distance of
the Sun for the red (650 nm), green (550 nm) and blue (450 nm) ranges of th
e spectrum. The major aim of this work is to give a clear and comprehensive
picture, with the help of full-sky imaging polarimetry, of what is going o
n in the entire polarized skydome. We demonstrate how variable the degree o
f polarization of skylight and the position of the neutral points can be wi
thin 24 h on a sunny, almost cloudless, visually clear day.