Some FORS2 calibration data are presently monitored to extract information about their quality and the instrument performance. The quality information is extracted into so-called QC parameters.
FORS2 calibration data are pipeline-processed to create calibration products. The quality of the products is measured by QC1 parameters. Most QC1 parameters are obtained by pipeline procedures; some are measured by post-pipeline recipes.
All measured QC1 parameters are stored in a database. Their evolution with time is evaluated by the trending process.
All FORS2 calibration products are quality-checked. While details of
this process vary from case to case, some features are generally valid:
- Raw frames and master frames are displayed and visually checked for
- When applicable, raw frames are checked for over-exposure (e.g. flats).
- The distribution of pixel values is controlled in histograms. E.g.,
the distribution of pixel values in BIAS frames is checked to be consistent
with statistical noise.
- The product tables from format check and wavelength calibration frames
are checked for number and distribution of fitted lines.
A calibration product is certified when experience shows that it measures
the instrumental status in the proper way. This may mean that it complies
with the expected result within certain limits. But it may also be true
that it represents a valid outlier. E.g., after a realignment of a grating
its X and Y shift against a reference frame will differ from the previous
values, but this is a valid deviation.