3.5.1 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 cross-match) 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.