Daily surface algae blooms of the Baltic Sea (Sentinel-3 OLCI) 2017– / Daily surface algae blooms of the Baltic Sea (Sentinel-3 OLCI) 2017–

**[FI]** A four-class interpretation map describing the surface algae platforms in the Baltic Sea region and especially in the sea areas surrounding Finland. An interpretation map describes the probability of surface algae occurring in a given area. The categories on the map are 1) no surface algae, 2) possible, 3) likely and 4) certain surface algae. It is not possible to observe surface algae through clouds with optical satellite instrumen, so the surface algae map is missing in cloudy areas. Interpretations will be made from the end of June to the beginning of September, and longer if necessary. Most algae ferries occur in July-August, so the number of surface algae observations during this period is the highest. The method of interpretation is based on the strength of the reflection observed by the satellite in different wavelength ranges, which is different in cyanobacterial areas than in restless waters. The surface algae interpretation of individual pixels will be generalised to make the algae areas visible on the map clearer. Cloudy areas are removed from the map area using an automatic cloud detection method, which is supplemented manually if necessary before publication. The interpretation method has been developed in Syke and utilizes the observations of a different satellite instrument. This dataset consists of observations from ESA’s Copernicus Sentinel-3 satellite series OLCI instrument since 2017. OLCI observes with 300 m off-road resolution. The data are made into an annual aggregate map for algae information needs (separate meta). The data is included in SYKE's open data (CC BY 4.0). *** **[EN]** A four-class interpretation map maintained surface floating algae blooms in the Baltic Sea region and especially in the sea areas surrounding Finland. The interpretation map describes the probability that surface algae will occur in a particular area. The map categories are 1) No, 2) Potential, 3) Likely, and 4) Evident surface algae. Surface algae cannot be detected by optical satellite instruments through clouds, so a map of surface algae is missing from cloudy areas. Interpretations will be made from late June to early September, and longer if necessary. Algae bloom principals occur most in July-August, so the number of surface algae observations is the highest during that period. The interpretation method is based on the intensity of the reflection detected by the different wavelength ranges of the satellite, which is different in cyanobacterial areas than in restless waters. A surface algae interpretation made from the area of individual pixels is generalized to a rougher one so that the areas of algae displayed on the map are clearer. Cloudy areas are removed from the map area by an automatic cloud detection method, which is also completed before publication, if necessary. The interpretation method has been developed at Syke and utilizes the observations of various satellite instruments. This data is based on the OLCI instrument (OLCI) of the Sentinel-3 satellite series of ESA's Copernicus program starting from year 2017. OLCI observes in 300 m terrain resolution. An annual summary map of the data is made for the needs of Syke's algae bloom monitoring (separate metadata). *** **WMS server/WMS service endpoint**: https://geoserver2.ympäristö.fi/geoserver/eo/wms **WMS layer/WMS layer**: EO_MR_OLCI_ALGAE *** **[FI]** Algal ferry interpretation resulting from remote sensing monitoring based on Sentinel-3 OLCI satellite observations. Daily algal ferry data from 2017 onwards. Processing history:  Algae rafts have been interpreted from the Sentinel-3 OLCI satellite instrument data. The original satellite data has been downloaded from the European Space Agency's (ESA) charging services. In the heartbeat, the resting interpretations have been calculated.