Quality Control and
Data Processing

The main goals of ESO data quality control (QC) are:

• to know the current instrument status (health checks),
• to monitor it over time (trending),
• to deliver data products of known and defined quality (certification), to be used for science reduction.

The QC process is focussed on calibration and instrument quality. Most calibration data are taken as daytime calibrations. Twilight calibrations (sky flats) and night calibrations (standard stars) are also processed and QC checked.

After the calibration data have been acquired, they are transferred from Paranal into the archive at ESO headquarters within minutes. The archive is the source of data for the QC process.

The calibration data are then processed incrementally at ESO Headquarters (once per hour). The quality information is extracted into QC1 parameters. The most important parameters are displayed graphically on the Health Check monitor. Also, their values are scored against configured thresholds, to discover anomalies. The quality scores are also displayed graphically and are evaluated both by the QC scientists and the Paranal staff astronomers.

The complete trending history of each VLT instrument is maintained on the Health Check monitor.

QUALITY CONTROL LEVEL 0

The QC0 process is an entirely different process. It runs on the science data in real-time and is maintained by the science operations staff. It aims at assuring that

• the acquired science data have the exposure level requested by the PI,
• that the user-defined observational constraints have been matched during the observation.

QUALITY CONTROL LEVEL 1

Quality Control Level 1 consists of quality checks on pipeline-processed calibration data. Quality is measured by numbers, the QC1 parameters. Main goals of the QC1 process are to monitor instrument stability and performance.

The checks are done on calibration data.

The QC1 parameters are used

• to assess the quality of master calibration files (e.g. noise properties, gradients),
• to compare with expected performance values (e.g. gain, resolving power),
• 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).

The result of the QC1 process is used to

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

The QC1 parameters are archived. They are directly available for studies through the QC1 database interface.

TRENDING and SCORING

Trending is monitoring QC1 parameters over time (e.g. effective resolution as function of time). A core task of QC Garching is to create trending pages (also called Health Check monitor) which are used to monitor the instrument evolution and performance.

The most recent values of important QC1 parameters are scored against configured thresholds, to discover anomalies. The quality scores are also displayed graphically and are evaluated both by the QC scientists and the Paranal staff astronomers.