Call Before You Dig: Systematic effects near the noise floor in coronal and solar imaging

Avoidable systematic errors, attributable to lack of caution in data handling, abound in historical and current analyses of coronal image data, affecting a large number of existing photometric and polarimetric analyses in heliophysics. We found, and mitigated, several such “live wires” while digging under the noise floor to develop the PUNCH mission data pipeline.

We present some cautionary tales about non-intuitive interaction between data products, including polarized-brightness (pB) images and even “raw” data, and instrumental and photon-counting noise. These and related effects, arising from nonlinear transformations of original data, affect or invalidate quantitative measurements near or below the noise level of individual single-pixel photometry in aggregate instruments such as imagers.

Fortunately, “forewarned is forearmed”, and the family of effects we describe can be calibrated out of quantitative analyses, provided that researchers are aware of them in advance.