Stray Light Removal

Stray light is light in an optical system, which does not follow the designed path for detection. The light may be from the intended source, but follows paths other than that intended, or it may be from a source other than the intended source. This light can limit the signal-to-noise ratio or contrast ratio, by limiting how dark the system can be.

We estimate and remove the instrumental stray light within each PUNCH instrument. This is a subtraction of the current additive stray light model, which is developed from a time series of L1 data that is bootstrapped with validation data acquired during on-orbit commissioning. These are regenerated periodically to capture instrument changes.

Concept

Separating instrumental stray light from the F-corona has been demonstrated with Solar and Heliospheric Observatory (SOHO) Large Angle Spectrometric Coronagraph (LASCO) and with STEREO/COR2 coronagraph data. It requires an instrumental roll to hold the stray light pattern fixed while the F-corona rotates in the Field of View (FOV). PUNCH rolls once per orbit and the same techniques previously used for stray light measurement with intermittent rolls on SOHO and STEREO are used routinely for PUNCH.

Applying correction

This correction is carried out by simply subtracting the stray light model using the punchbowl.level1.stray_light.remove_stray_light_task.

punchbowl.level1.stray_light.remove_stray_light_task(data_object: ~ndcube.ndcube.NDCube, stray_light_path: <module 'pathlib' from '/home/docs/.asdf/installs/python/3.12.10/lib/python3.12/pathlib.py'>) → NDCube

Prefect task to remove stray light from an image.

Stray light is light in an optical system which was not intended in the design.

The PUNCH instrument stray light will be mapped periodically as part of the ongoing in-flight calibration effort. The stray light maps will be generated directly from the L0 and L1 science data. Separating instrumental stray light from the F-corona. This has been demonstrated with SOHO/LASCO and with STEREO/COR2 observations. It requires an instrumental roll to hold the stray light pattern fixed while the F-corona rotates in the field of view. PUNCH orbital rolls will be used to create similar effects.

Uncertainty across the image plane is calculated using a known stray light model and the difference between the calculated stray light and the ground truth. The uncertainty is convolved with the input uncertainty layer to produce the output uncertainty layer.

Parameters:

• data_object (NDCube) – data to operate on

• stray_light_path (pathlib) – path to stray light model to apply to data

Returns:

modified version of the input with the stray light removed

Return type:

NDCube

Deriving stray light model

Stray light parameters will be derived from spacecraft observations on orbit.