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legacysurvey / legacypipe

Image reduction pipeline for the DESI Legacy Imaging Surveys, using the Tractor framework
BSD 3-Clause "New" or "Revised" License
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DECam S30 amplifier unstable calibrations #510

Open djschlegel opened 4 years ago

djschlegel commented 4 years ago

The DECam S30 amplifier (which one?) is unstable, leading to both discontinuities in the sky+fringe correction, but also photometric offsets. This is a ~0.7% effect. The CP fits out the discontinuities in the sky models. The fringe image discontinuities will not be properly modeled, but this is only a ~1% effect on a small correction. The photometric calibration differences probably will be noticed. Presumably, we're currently computing the average zero-point for both amplifiers.

djschlegel commented 4 years ago

Note this same CCD S30 was dead until 29 Dec 2016 when it started working again.

schlafly commented 4 years ago

We did nothing to address this in DR9. In DR10, we could do something. In the PS1 region, this would require separate zero points for the two amps; that would require a data model change in the CCDs file. Outside the PS1 region, we could treat this amplifier like S7, more aggressively clipping the CCD and fitting separate zero points. Ubercal doesn't know about separate amplifiers yet, though, so that would be a major effort.