C. E. DeForest, T. A. Howard, S. J. Tappin
The solar corona and heliosphere are visible via sunlight that is Thomson-scattered off of free electrons, yielding a radiance against the celestial sphere. In this second part of a three-article series, we discuss linear polarization of this scattered light parallel and perpendicular to the plane of scatter in the context of heliopheric imaging. The difference between these two radiances, (\emph{pB}), varies quite differently with scattering angle, compared to the sum that would be detected by a nonpolarizing instrument (\emph{B}). In particular, the Thomson surface defined by 90\degr{} scattering angle is a local minimum in scattering efficiency for \emph{B} measurements, but a local maximum in scattering efficiency for \emph{pB} measurements. We describe the polarization properties of heliospheric Thomson scattered light and their applications, covering basic scattering physics, signal-to-noise considerations, measurement of 3-D object location, background subtraction, and modeled \emph{pB} instrument response to particular classes of solar feature. We conclude that \emph{pB} measurements of heliospheric material are much more localized to the Thomson surface than are \emph{B} measurements, that the ratio \emph{pB/B} of polarized to unpolarized feature brightness can be used to track solar wind features in three dimensions for scientific and space weather applications; and that, by providing an independent measurement of background signal, \emph{pB} measurements may be used to reduce the effect of background radiances including the stably polarized zodiacal light.
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http://arxiv.org/abs/1207.5894
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