The overall objective of the project is to improve and harmonize the data products from UV- Visible ground based DOAS spectrometers, in particular MAXDOAS and Pandora, to arrive at Fiducial Reference Measurements (FRMs) for air-quality. DOAS/MAXDOAS instruments provide highly relevant validation data for current, past and future atmospheric chemistry satellite nadir missions such as GOME(-2), SCIAMACHY, OMI, S4 and S5 but also for limb/occultation instruments such as e.g. the ESA Third Party Mission SCISAT/ACE. Moreover, with the launch of S5P scheduled in mid-2016, the project will directly support the preparation of validation activities in view of the future Sentinels 4 and 5 that will provide air quality observations from space in support of the Copernicus programme. 


MAXDOAS systems are currently operated at about 50 sites in the world, some of them being involved in NDACC mainly for stratospheric monitoring. These systems generally have good performance. However in most cases, they are managed in a scientific mode with little or no harmonization on instrument operation, calibration, processing or data formatting. To improve on this situation, the FP7 NORS pilot project has developed procedures for the operational delivery of MAXDOAS data in support of the Copernicus Atmospheric Monitoring Service (CAMS) based on a limited number of NDACC stations with a delay of maximum 1 month. 


The present project aims at further harmonising MAXDOAS systems and data sets, through the specification of best practices for instrument operation, the demonstration of a first centralised NRT processing system for MAXDOAS instruments to be operated within the international NDACC network, and the establishment of links with other UV-Visible instrument networks, e.g., Pandonia. In addition, this project will support the preparation of a major field campaign to intercalibrate UV-Vis DOAS and MAXDOAS systems, organized in Cabauw, The Netherlands in late summer/early Autumn 2016. 


These activities will help and guarantee that homogenous ground-based reference dataset are produced from reference ground-based UV-Vis instruments. Such systems are used both during campaigns and for the long-term monitoring of space-borne instrumentation, and play a crucial role in the validation of atmospheric composition satellite missions. 

The focus of the proposed developments will be on ozone (O3), NO2 and formaldehyde (HCHO) which are operational products from S5P and many of the above mentioned missions.