TROPOMI validation will be carried out in two ways, using a routine validation approach and with campaign-based efforts. Routine validation includes use of data from core measurement stations and networks for rapid, semi-automated validation. Routine implies that the validation dataset will be consistent relying upon so-called Fiducial Reference Measurements (FRM) which will help build long-term validation sets to evaluate trends measured in TROPOMI data with respect to the core ground stations. FRM consists of data from balloon-borne sondes and ground-based measurement networks. Use of data from satellite instruments with similar global coverage, overpass time, and data product characteristics like those from OMI and OMPS will be also be important for both initial verification and long-term assessment of the TROPOMI Level 2 data products.
The routine validation will take place in two phases. A rapid, but thorough first check of the Level 1 and 2 products will take place during the E1 Commissioning Phase occurring in the first six months after launch. In this phase, the data user community will be able to see how the earliest data stream from TROPOMI is used to create the suite of TROPOMI data products and how they each compare with select validation datasets. In the following E2 Operational Phase, validation will be carried out to systematically evaluate the quality of TROPOMI data products.
The campaign-based approach is equally important for evaluating TROPOMI performance for select regions with targeted measurement campaigns tailored to address TROPOMI objectives. Validation activities will be taking place on several scales: at the broad ESA level aimed at all products and on a slightly smaller, more focused institutional level. That is, the institutes which are responsible for the production of various Level 2 data products including KNMI, BIRA, and SRON will also be coordinating their own campaign-based validation activities. The work of the Sentinel-5 Precursor Validation Team will be used create a rich and varied set of measurements to validate TROPOMI data products.