Revelations on Heliospheric Imaging of Polarized Light

We report on recent developments on the theory of observing the inner heliosphere with heliospheric imagers. We have extended the theory of Thomson scattering, which governs the appearance of features observed by heliospheric imagers, to polarized light observations, and consider potential benefits to the analysis of features observed with a polarizing heliospheric imager. We find that when observing in unpolarized light (as do the current generation of heliospheric imagers), it is difficult to identify the 3-D location of observed features because of the broad nature of the scattering function (causing the Thomson surface to be a Thomson plateau). The broadening does not occur in polarized light observations, enabling the accurate 3-D location of features to be determined. Our theory is validated by recent unpolarized light observations from the STEREO/HI-2 heliospheric imager, and with polarized light simulations of coronal mass ejection simulations using the ENLIL model.