VIRCAM
Quality Control

The Quality Control Group in Garching provides quality checks of the VIRCAM 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

QC0 involves checks whether the user-defined observational constraints have been respected during the observation. The QC0 checks are done on Paranal and are based on the inspection of some raw data but primarily on the QC logs that are coming from the online pipeline that reduces the data and creates the pawprint level stacks in parallel with the observations for every OB. Note that in this processing it is not possible to have the best possible master calibration frames.

The data are checked for the following constraints:

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

Quality Control Level 1 consists of quality checks on pipeline-processed data. The calibration date are fully processed by the offline pipeline in Garching and QC1 level checks are performed.

Most of t he QC1 parameters are provided by the VIRCAM pipeline in the header of the pipeline product files, others are measured by post-pipeline procedures, on master calibration files and raw files. The purpose of measuring QC1 parameters is:

• to assess the quality of calibration products (e.g. noise properties),
• to compare with expected/nominal values (e.g. image quality),
• to assess the performance of the instrument (e.g. photometric zeropoint),
• to monitor efficiency of master creation process (e.g. reduction of random noise).

The result of the QC1 process is used to

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

All master calibration data created by QC Garching are quality-checked. Apart from measuring QC1 parameters, these files are also checked for "unusual" effects like overexposure and vignetting.

The QC1 data are internally used for decision making. They are also provided in a public QC1 database as part of the ESO Science Archive Facility.

Trending is monitoring QC1 parameters over time (e.g. detector ron as function of time).

Main results are:

• monitor instrument health,
• detect long-term trends,
• detect sudden changes.