Daily surface temperature of the Baltic Sea and Finnish lakes (Sentinel-3 SLSTR) 2017–/Daily surface temperature of the Baltic Sea and Finnish lakes (Sentinel-3 SLSTR) 2017—

**[FI]** satellite images monitor the surface temperature of the largest lakes in the Baltic Sea and Finland (79pcs) in ice-free and cloud-free areas. The material also covers nearby lakes, including Ladoga and Peips. The surface temperature is calculated from the data from the EU Copernicus Sentinel-3 satellite series SLSTR (Sea and Land Surface Temperature Radiometer). The temperature has been calculated using two thermal wavelength observations using the Split Window method. Clouds are identified and cloud areas removed by the cloud recognition levels of SLSTR LB1 data and manual verification. Surface temperature observations are made at night, when they correspond well to station observations close to the surface layer. The terrain separation capacity of the images is about 1x1 km. The material consists of daily interpretations made since 2017. Since 2019, material has been produced year-round when ice and cloud conditions allow. The data shall include the days for which correct satellite data is available. The material is part of SYKE’s open data (CC BY 4.0). Purpose: Monitoring the surface temperature of lakes in the Baltic Sea and Finland. *** **[En]** Satellite observations are used to monitor the sea surface temperature (SST) in the Baltic Sea. Sea surface temperature dataset covers daily the non-cloudy ice-free sea areas and many of the largest lakes in Finland (79 lakes). The dataset is based on the observations by Copernicus programme Sentinel-3 satellite series SLSTR (Sea and Land Surface Temperature Radiometer)) instrument. Finnish Environment Institute (SYKE) has produced the dataset by using Split Window method and removed the areas covered by clouds. Clouds are identified by a combination of the basic and probabilistic cloud screening flags in the SLSTR L1B product. The spatial (ground) resolution is ~1 km x 1 km. The dataset covers years from 2017 on and annually the period from April to October. From 2019 on, the dataset covers annually all non-cloudy and ice-free observations throughout the year. *** **WMS server/WMS service endpoint**: https://geoserver2.ymparisto.fi/geoserver/eo/wms **WMS level/WMS layer**: EO_SST *** Surface temperature interpretation resulting from remote sensing monitoring based on Sentinel-3 SLSTR satellite images. Daily surface temperature data from 2017 onwards. Processing history: Surface temperatures have been interpreted from Sentinel-3 SLSTR satellite material. The original satellite data has been downloaded from the European Space Agency (ESA) download services. In the heartbeat, the temperature readings are calculated.