Kevin: The community does not know what to qualify as "saturation"
Could each team make recommendations to the community here?
Marcia: We can look it up quickly. But it should be ~80% full well
-- that is well into non-linearity, but NL can be correct to high precision.
Tom: Could you recommend what level is desireable?
Kevin: We are looking for ~1% after correction
Loic: Each team for TSOs has its own saturation levels that converge to magnitude limits.
-- i.e. NIRSpec 65k for saturation; NIRISS has 72k, etc
Kevin: what is your definition for saturation
Loic: I think it is 90% full well
Kevin: and what about non-linearity?
Loic: the NL grows linearly with %FW, so at 90% FW, it should be about 9% non-linear
Kevin: What about the error on the correction?
Loic: That is a fair question, but not necessarily trivial. We need to look into second order effects.
Kevin: We don't want the community to push towards the 90% saturation limit without knowing the caveats.
-- we want the community to be able to estimate their level of risk.
-- there has already been confusion in planning obs
Loic: Okay. The error on the NL correction results in an error on the PPM of the final spectrum.
-- a 1% error on NL is a 1% error on the ppm
-- it is probably a second order thing
-- the bigger question is how is your results effect by saturation
Kevin: That is more reason to advise people to stay away from saturation.
-- should people avoid saturation completely
Jonathan: do you mean saturation at the first group or anywhere up the ramp?
Loic: it matters depending on the error (i.e. persistence). if we saturate at group=10, can we use groups 1-9?
Jarron: If we use groups 1-9, then we are making assumptions about the errors. any time we make assumptions about the persistence, we are added error into the results.
Loic: will any proposal be rejected if there is any saturation anywhere?
Kevin: They will definitely not reject saturated proposals, some peoples' science depends on it.
Kevin: Sarah gave slides that suggest MIRI might recommend saturation because if you have less than 5 groups, then there is difficulty in stability (1st/last frame effects).
-- if we run through 6 frames (saturated), then the last frame effect is on the saturated frame, instead of the last science frame.
Marcia: We should also inform people that the throughputs may be off by as much as 10%, which will affect these limits as well.
Marcia: one last thing: the JDox page says "check saturation limits with ETC"; so we (IDTs) need to make sure that the ETC is giving the right saturation limits.
Tom: The JDox pages give a more favorable result. The ETC may be using a static Gain for each instrument
Jarron: Everett, did you compare our simulations with the ETC?
Everett: Yes. a few months ago.
Maria: Tom, could you have the student you mentioned send us the notebook? We would like to check these numbers with our ETC
Loic: For NIRISS, the agreement is well below 5%
Marcia: For NIRCam, it depends on which SCA you are on. The values on the screen (exoctk.stsci.edu) are not what we expect for NIRCam.
-- the LW detectors should say max pos. sat. ~80k
-- the SW detectors should say max pos. sat. ~100k
Loic: For NIRISS, we have it at 90%
Maria: For NIRSpec, 65k counts already include bias
Kevin: [ACTION ITEM] Could each team rep send me those numbers in an email, with caveats for how we got these numbers -- to add to JDox
Pierre: These values are delivered to the ETC, if we send it in an email, then the ETC gets new numbers and we don't send new numbers to JDox, then there could be inconsistencies.
Kevin: We want to make recommendations to people that are aligned with the ETC; so please send us the ETC numbers.
Jarron: I am looking at JDox now and see that the numbers match, but in ADU instead of electrons.
-- Is it possible that the units on the ExoCTK page are in ADU instead of e-?
-- the numbers on ExoCTK match the ADU from JDox
-- the numbers on the Jdox for e- is correct
Marcia: for (..?) SCAs, we can basically digitized full well above the bias level