General The Quality Control Group in Garching provides quality checks of the FORS1 data. These checks are part of the Quality Control (QC) process. They are executed on raw data as well as on pipeline-processed data.

The QC checks consist of
 

• Quality Control Level 0 (QC0),
• Quality Control Level 1 (QC1),
• trending.

QC level 0

The SM observer receives a QC0 report which lists all the programme-specific science files, their user-defined constraints (as read from the OB Repository which was filled from P2PP), and the actual QC0 parameters during observation (as read from the Ambient Database which is fed from the Ambient Site Monitor).

The data are checked for the following constraints:
 

• airmass,
• moon distance,
• fractional lunar ilumination (FLI),
• seeing.

Quality Control Level 1 consists of quality checks on pipeline-processed data.

The QC1 parameters are in practice measured by post-pipeline procedures, on master calibration files and reduced files. The purpose of measuring QC1 parameters is:
 

• to assess the quality of master calibration files (e.g. noise properties, gradients),
• to compare with expected values (e.g. gain value),
• to assess the performance of the instrument (e.g. throughput from photometric zeropoints),
• to monitor efficiency of master creation process (e.g. reduction of random noise).

• decide whether master creation data are certified or rejected,
• assess the quality of the reduction process.

For reduction of SCIENCE data master calibration data are chosen which are as close in time as possible.

Right now the QC1 data are internally used for decision making. It is planned to provide them as part of the SM package, as well as store them in the Science Archive.

Find more details about QC1 parameters and trending here.
 

Trending

Trending involves monitoring QC1 parameters over time (e.g. bias level as function of time). Investigating the mutual relations of QC1 parameters is also part of trending. E.g., plotting photon noise vs. median level checks for true random nature of this QC1 parameter since a square-root law is expected.

Main results are:
 

• monitor instrument stability,
• detect long-term trends,
• detect sudden changes (e.g. change of a broken lamp, baking of CCD).