The optical flatfield is measured through all optics of the MATISSE instrument. This calibration is necessary in order to compensate all space-variant gain table variations caused by the different optical paths (photometric and interferometric channels).
They are recorded each day when data on sky are taken.
An observation FLATFIELD and Bias maps are created for each scientific setup (geometry and exposure time).
The input data consist in one file containing 50 dark frames and one file containing 50 flatfield frames.
In addition, the static bad pixel map, the static
nonlinearity map and the static flatfield map are needed.
The static bad pixel map (PRO.CATG = BADPIX)
is needed to ignore the bad pixels during normalization of the optical flat. The static
nonlinearity map is needed to separate the optical (large scale) variations from the fix pattern noise
and the nonlinearity (small scale) variations.
The static flatfield map (PRO.CATG = FLATFIELD)
is used to get the conversion factor for converting ADU into electrons and copy it into
the optical flatfield.
The static non linearity map is needed to separate the optical (large scale) variations from teh fix pattern noise and the nonlinearity (small scale) variations.