Remove DIT/NDIT from the matched keywords?

[hugobuddel]

I added DIT/NDIT to the matched keywords and to the description in 4.7. However, this might be a mistake as I cannot find much evidence in the other documents that this is necessary.

We did match on DIT/NDIT in MICADO, and since most of our detectors are also HxRG, it seemed natural to do it here too.

I've asked Roy for clarification. For now I think we should assume that DIT/NDIT should not have to match.

What I wrote to Roy:

A related question about DIT and NDIT is about how to select the right calibration data to reduce a science observation.

The general procedure is as follows:

• During the night, the science observations are taken with several instrument settings,
• Then during the day (or monthly, or whatever), the calibration data is taken with 'the same' instrument settings.
• Finally, the processing software selects the right calibration data for a specific observation by comparing the instrument settings.

It depends on the calibration step which instrument settings need to be equal between the science data and the calibration data. For example, the filter is not necessary to find the right dark, but it is necessary to find the right flat. (There are other selection criteria possible than equality, but I don't think we need that for METIS.)

Up till now, I assumed that in many cases we need NDIT and DIT to be the same for the calibration data and the science data. One of the results of this requirement would be to restrict the set of allowed NDIT + DIT combinations, in order to limit the amount of calibration data that has to be taken.

But now I'm not so sure whether that assumption is actually true, because I cannot find much evidence in our documents that DIT+NDIT should match between science data and calibration data, except for what I wrote myself (e.g. in 4.7 of the DRLD). The only thing I could find is this line in 3.3.1 of the Calibration Plan for the internal flats:

select DIT and NDIT such that about half the detector full well capacity is reached (select from list of allowed exposure times

For example, the data rates document only assumes "filter" as possible instrument setting, but not DIT/NDIT or exposure time. So it seems I was mistaken.

Could you help clear this up Roy; will we need to have calibration data taken with the same DIT / NDIT as the science data?

I'm going to assume that the answer is "no", but I won't update the DRLD to reflect that yet.

[hugobuddel]

See also #245, about interpolation of DIT/NDIT