Quality control (QC) is performed at the level of the science observations in real-time at night (QC0) and at the level of performance monitoring of the scientific instruments, by means of calibration observations (QC1).
QC0 - OB grading
QC0 is an umbrella term for all actions taken at the telescope to assess (1) the compliance of an observation with the user constraints, and (2) the quality of the scientific signal compared to nominal instrument and telescope performance. The specifications of the QC0 process are evaluated instrument by instrument and detailed here.
QC0 is applied to Service Mode data. The QC0 process evaluates the OB execution according to PI requirements to reach the scientific objective. Its result is an OB quality grade. The quality grade declares an OB execution as fully compliant (A), sufficiently compliant (B), or non-compliant (C or D) with the execution requirements as defined in the OB. A non-compliant execution is a failed execution and the OB can be rescheduled if the objective is considered achievable (grade C). The non-compliant, graded D OB are not rescheduled.
The QC0 assessment is done during the night by the operator, immediately following the OB execution. An OB grade may change in the weeks or months following the observations, depending on the completeness and correctness of associated calibration data or instrumental issues discovered only later.
QC1 - performance monitoring
In the QC1 process, all calibration data are processed by the ESO pipelines to produce data products. The pipeline algorithms compute in addition QC parameters defining the data product which are subsequently extracted to a database and scored with respect to well-defined thresholds. The same data reduction pipelines are used as for the QC0 process. The processing is done in near-real time and its details are described here.