romancal assumes that read noise reflects how far an individual read is from truth, while stcal's ramp fitting assumes that read noise is the typical difference between two reads of the same quantity (CDS read noise). These two quantities are conceptually different by the square root of two; stcal converts the CDS read noise to the ordinary read noise here:
https://github.com/spacetelescope/stcal/blob/main/src/stcal/ramp_fitting/likely_fit.py#L74
romancal currently sends the ordinary read noise instead of the CDS read noise, meaning that this conversion leads us to use too little read noise.
We should fix this by sending stcal the CDS read noise rather than the ordinary read noise.
romancal assumes that read noise reflects how far an individual read is from truth, while stcal's ramp fitting assumes that read noise is the typical difference between two reads of the same quantity (CDS read noise). These two quantities are conceptually different by the square root of two; stcal converts the CDS read noise to the ordinary read noise here:
https://github.com/spacetelescope/stcal/blob/main/src/stcal/ramp_fitting/likely_fit.py#L74
romancal currently sends the ordinary read noise instead of the CDS read noise, meaning that this conversion leads us to use too little read noise.
We should fix this by sending stcal the CDS read noise rather than the ordinary read noise.