Issue #2

Flat field

Issue raised Apr 30 2016, 06:25; last modified Jun 21 2017, 06:02

The EDR flat field algorithm is preliminary. It may be wrong by up to 5% in the corners of u- and v-band images. No illumination correction has been applied, although sky gradients are removed from pairs of flat field images rotated by 180 degrees for part of the data set. Whenever the CCD mosaic has been brought to room tempetature, the flat field shape changes by up to 1% from day to day in the u-band due to a spatially inhomogenous condensation process on the CCDs.

The flat field algorithm for DR1 is significantly improved, although no illumination correction is yet applied.