With the increasing use of polarization as an added dimension in imagery for a variety of scientific, defense, and civilian
applications comes a need for better understanding of how the natural environment affects polarization signatures. In the
visible and near-infrared spectral range, the most important environmental component is polarized skylight. To provide
data to help improve understanding of how atmospheric polarization varies with aerosols, clouds, and surface
reflectance, an all-sky polarization imager has been designed, built, calibrated, and operated in a variety of field
experiments. This paper describes modifications made to that instrument to enable continuous, unattended outdoor
operation. The primary modifications were development of a weather-proof housing and an automated sun occulter
incorporating an on-board microcontroller that continually calculates solar position and moves an occulting disk on a
thin metal band to prevent direct sunlight from falling on the polarimeter lens. This occulter is designed to not obstruct
the principal scattering plane, defined as the plane containing the zenith, the Sun, and the observer.
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