Resolving CME Characteristics with Polarized PUNCH Data

The Polarimeter to UNify the Corona and Heliosphere (PUNCH) mission will explore the largely unexplored region of the heliosphere from the middle corona out to 1 AU: i.e., the "young solar wind", through direct, global, spatially continuous, and 3D deep-field imaging. This is achieved through Brightness (B) and polarized brightness (pB) measurements, which is analogous to the Stokes system in solar observing coordinates. PUNCH will be able to study the propagation of coronal mass ejections (CMEs) throughout the heliosphere, and in particular the chirality of CMEs, which can be determined directly from physics of Thomson scattering applied to synoptic polarized images. One difficulty in accurately determining the positions of structures lies in the impact of noise, and requires relative photometry accuracy at a few percent precision.

PUNCH will use a symmetric three-polarizer measurement and representation system to derive the Stokes parameters. As part of the PUNCH development project a universal polarization resolver has been built together with tools to characterize noise in polarimetric response (see presentation: "A New Universal Polarization Resolving Software Package for Solar Coronal and Heliospheric Observations" by Walbridge et al.). In this presentation the potential ability to accurately measure the 3D structure of imaged objects in the heliosphere with PUNCH will be assessed. "Clean" synthetic data from the Gamera model, forward modelled to look like PUNCH data using the HAO FORWARD algorithms will be used with the polarization resolver to determine the chirality of synthetic CMEs. Additionally, realistic photometric (poisson) and instrument noise will be applied to the data to assess the impact on the estimated positions of structures, with comparisons made to the clean datasets. The noisy data will be subsequently "noise-gated" to reduce noise and mitigate its impact. The impacts of noise reduction, and how it can improve estimates of 3D position are also assessed.