One of the problems facing the Baltic Sea is eutrophication. Large fluxes of carbon, nutrients and other material enter the Baltic Sea from the drainage area through rivers, and change the functions of the Baltic Sea ecosystem. While a lot of data about the fluxes is available from in situ measurements and models, there still are large information gaps that prevent us from fully characterising and understanding the biogeochemical processes taking place in different parts of the Baltic Sea. Thus, better observations of carbon dynamics are needed.

Earth Observation (EO) can provide information about the state of surface waters with good spatial and temporal resolution. An especially interesting new satellite sensor is the MSI on-board Sentinel-2 satellites since its spatial resolution is sufficient for coastal areas. Chlorophyll-a (Chl-a) and Coloured Dissolved Organic Matter (CDOM) are important parameters for characterizing carbon flux. However, due to the high absorption by CDOM in the Baltic Sea, the estimation accuracy of the current EO methods is not sufficient and the algorithms have to be improved before satellite data can be fully integrated with models and in situ data.

Due to its better band combination Sentinel 3 OLCI can provide thematically more accurate concentration estimates but with a lower spatial resolution. Thus, the synergistic use of Sentinel-2 and Sentinel-3 may enhance the capabilities of EO for observing and characterising the carbon cycle in the Baltic Sea.