Comparison of different satellite sensors in detecting cyanobacterial bloom events in the Baltic Sea

Potentially toxic cyanobacterial blooms occur in the Baltic Sea in the middle of summer. Aggregations of cyanobacteria often form dense subsurface blooms or even surface scum, which are spatially extremely patchy. It has been shown by using bio-optical modelling together with the hyperspectral sensor Hyperion image from the western part of the Gulf of Finland that chlorophyll concentration may vary between one and hundreds of mg m− 3 within the 10-m scale during heavy bloom. The SeaWiFS, MODIS/Aqua and MERIS products over heavy bloom region are compared with each other, the modelling results, with the bio-optical modelling data and the available in situ data. In the early stage of bloom, these sensors give consistent results, which are in the same range as in situ data. During the heavy bloom of cyanobacteria, at the time of surface scum formation, results from different sensors are very variable, the values of chlorophyll concentration may exceed the standard processing limits and atmospheric correction often fails. The good capability of the MERIS and MODIS fine resolution bands to detect cyanobacterial bloom quantitatively is shown.