Investigations of using the 1st group when saturation happens in a pixel between the 2nd and 3rd group. Generally, the 1st group is always flagged as DO_NOT_USE in all MIRI observations due to a known transient seen in the 1st group.
These investigation found that in the case of saturation between the 2nd and 3rd group, the 1st and 2nd groups can be used to get a slope measurement that is around 1% accurate. This is because the 1st group transient is small compared to the number of DN measured between the 1st and 2nd group. The analysis is given in Test_use_group1_if_bright.ipynb.
This work was written up in a JWST report (ref TBA) and the PR to the jwst pipeline that added the bright_use_group1 flag to the firstframe CALWEBB_DETECTOR1 step.
In addition, there is a 2nd notebook Test_use_only_group1_if_bright.ipynb that has done a preliminary analysis of using just the 1st group along to estimate the slope. This analysis assumes the ramp stars at 0 DN, something that is not correct, but may be a reasonable approximate for such bright pixels. This prelminary analysis shows that such a slope estimate is likely at least 10% incorrect. More analysis is needed on using the 1st group alone.
Active development.
Karl Gordon
This code is licensed under a 3-clause BSD style license (see the
LICENSE file).