Low values on edges of mosaic CCD3 labeled as saturated

[djschlegel]

The majority of images from the nights 2017-04-08 through 2017-04-11 show a region of pixels labeled as SATUR (DQ=3) on the left side of the mosaic CCD3 images, and sometimes also on the right side. I’m guessing this has something to do with the code to detect ADC wrap-around getting confused.

This seems to happen when the sky is relatively bright, and then I think this problem is sensitive to the sky both being bright and rolling off in value on the left and right of CCD3 even after flat-fielding.

We won’t do anything about this for DR9, but here are a scattered set of examples spaced throughout the survey for otherwise-good images where the sky is bright and the left part of the CCD3 image gets labeled as SATUR:
mosaic/CP/V4.3/CP20160124/k4m_160125_094047_ood_zd_ls9.fits.fz
mosaic/CP/V4.3/CP20161212/k4m_161213_042915_ood_zd_ls9.fits.fz
mosaic/CP/V4.3/CP20161214/k4m_161215_112604_ood_zd_ls9.fits.fz
mosaic/CP/V4.3/CP20170410/k4m_170411_034232_ood_zd_ls9.fits.fz
mosaic/CP/V4.3/CP20170905/k4m_170906_084928_ood_zd_ls9.fits.fz
mosaic/CP/V4.3/CP20171126/k4m_171127_090519_ood_zd_ls9.fits.fz
mosaic/CP/V4.3/CP20180201/k4m_180202_122318_ood_zd_ls9.fits.fz

Attached image shows the lower-left corner of the OOD image for k4m_170411_034232_ood_zd_ls9.fits.fz, where the DQ values are 3 (saturated) and 4 (bleed mask).