Creates and files a flat field derived from dithered frames
It performs debiassing, bad-pixel masking, and dark subtraction before combining normalised frames
pixel by pixel using the median. Details of the flat are filed in the index of flats for future selection and
use of the flat. See the "
NOTES"
for further details.
For best results the field observed should contain few stars and no bright ones. Ideally the
telescope should have been pointed to the "
flat spot"
- usually 5 to 10 degrees away from
the zenith in the anti-solar direction to minimize gradients in the resultant flat.
The bad-pixel mask applied is the binning-appropriate match taken from the
$ORAC_DATA_CAL/index.mask calibration index.
Intermediate frames are deleted.
The created flat fields are of the form
flat_<instrument>_<UT
night>_<flattype>_bin<Xbin>x<Ybin>_<filter>[_c<cycle_number>]
where <instrument>
is the LCOGT instrument identifier,
<flattype>
is the type of flat (either ’
SKYFLAT’
or ’
FAKEFLAT’
(a unity flat),
<filter>
is the common name of the filter (e.g. ’
R’
) and
<Xbin>,
<Ybin>
are the binning factors in X and Y. If a flat of the same name already exists, a
<cycle_number>
will be added, counting from one.
The flats are filed in $ORAC_DATA_OUT/index.flat.
The processing engines are from the Starlink packages: CCDPACK, KAPPA, and FIGARO.
Uses the Starlink NDF format.
History is recorded within the data files.
The title of the data is propagated through the intermediate file to the dark.
Error propagation is controlled by the USEVAR parameter.