Monitoring algae blooms in the Baltic Sea by using spaceborne optical and microwave sensors

We have analyzed remote sensing data acquired over the Baltic Sea by various sensors flying on different satellites. As an example of our studies we show how different the same (natural) ocean surface films appear on images quasi-simultaneously acquired by the synthetic aperture radar (SAR) aboard the Second European Remote Sensing Satellite (ERS-2), by the Advanced Very High Resolution Radiometer (AVHRR) aboard the NOAA satellites, and by the Thematic Mapper (TM) aboard Landsat. Only areas of high algae accumulation are visible on SAR images because of the sea slicks produced by the algae. The coverage of the sea surface by natural sea slicks is shown to often coincide with enhanced sea surface temperature. We conclude that the combination of images acquired by different sensors allows better monitoring of algae blooms: e.g., the AVHRR has a high coverage in space and time, but under cloudy weather conditions only SAR has the potential of acquiring useful data of the sea surface