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The Copernicus mission from the European Space Agency (ESA) consist of a system of several new satellites. The mission will operational and provide a data service of Earth Observation not seen before with several satellites in orbit at the same time, providing both high temporal and spatial data. ESA’s new Ocean and Land Colour Instrument (OLCI) will be launched on the satellite platform Sentinel-3A in early 2016. Validation of OLCI will be crucial for describing the reliability and uncertainties of the derived water products. In order to validate the satellite data, high quality in situ data measured in the field from ships at the same time as a satellite overpass, are required. Validation is also needed for the development and validation of new algorithms. In order to make sure that the data retrieved from satellite are correct, the field radiometers from the various research groups measuring reflectance and contributing to mission validation must be intercalibrated. This is to assure that there are no systematic differences between the validation groups. But before performing a field intercalibration all instruments should first be calibrated against the same traceable light source (e.g. NIST lamp). In 2010, our group at Stockholm University participate in Arc2000, an intercalibration workshop that was performed by the Joint Research Council (JRC, Ispra, Italy) at Venice Tower. This workshop was proceeded by a joint lab calibration at JRC prior field measurements. The results of the intercalibration workshop were published in Zibordi et al. (2012) and showed the errors of our reflectance measurements during rather good conditions (relatively clear water and clear skies). It is important to evaluate the errors in less ideal conditions such as the highly absorbing waters of the Baltic Sea. We are therefore planning an intercalibration workshop of field radiometers at Askö during 9-13 May 2016. The workshop will be conducted by the leading European ESA ocean colour validation groups and coordinated by our group at Stockholm University. The inter-calibration exercise is aimed at securing the data quality of remote sensing reflectance over the Baltic Sea. The results will be reported to the European Space Agency and published in a peer-review journal and will contribute to the PhD theses of several PhD students.

Participants: Susanne Kratzer (project leader), Elina Kari (PhD student), Dmytro Kyryliuk (PhD student), Department of Ecology, Environment and Plant Sciences, Stockholm University, Sweden Martin Ligi (PhD student), Ilmar Ansko (PhD student), Tartu Observatory, Estonia; Instrument inter-calibration in Tartu Observatory; Miroslav Darecki, IOPAN, Poland (participating with research vessel Oceania); several PhD students from IOPAN Kevin Ruddick and Bouchra Nechad (researchers) , Royal Belgian Institute for Natural Sciences, Belgium, responsible for turbidity inter-calibration; Kai Sørensen and Pierre Jaccard (researchers), NIVA, Oslo, Norway; Gerald Moore (researcher) Bio-Optika, UK.