2.5.1 Overview

Author(s): Uli Bastian

An extensive, continuous assessment and validation has been performed on all astrometric and photometric pre-processing products, as well as on the telemetry input data entering the pre-processing steps.

In this section, the highest emphasis is given to the monitoring of the daily pre-processing (IDT) and to the monitoring of the sole cyclic pre-processing step (namely the IDU crossmatch) for Gaia DR2. These two processes produced output which directly entered the generation of the astronomical contents of Gaia DR2. The other three relevant quality assessment and validation processes – namely the First Look (FL), the AVU Astrometric Instrument Model (AIM) and the AVU treatment of the Basic-Angle Monitoring data (AVU–BAM) – are described briefly, just for completeness. They contributed to the quality of Gaia DR2, e.g., by finding on-ground processing defects and disturbing on-board phenomena, so that those defects and problems could be mitigated as far as possible. No data products from FL, AIM, and/or AVU–BAM directly contribute to the input data generating the astrometric and photometric source parameters in Gaia DR2.