In the context of the ESA Baltic+ Salinity Dynamics project, the first SMOS (Soil Moisture and Ocean Salinity) sea surface salinity (SSS) dedicated products over the Baltic Sea have been developed. A first prototype of these SSS products evidenced the sea surface temperature (SST) as one important driver of the SSS errors. Considering the low sensitivity of brightness temperatures to SSS changes in cold waters (with a mean value below 3 degrees C in winter in the Baltic Sea), it is crucial to use the most accurate SST product for the salinity retrieval. Besides, SST is used as a template when using multifractal fusion techniques to increase the spatial resolution of these SSS products. In order to identify the most suitable SST product over the Baltic Sea, we have analysed the state-ofthe- art EO-based SST products (OSTIA, CMC, REMSS, CCI) [Woo and Park, 2020], by comparing them with the collocated in-situ temperature measurements provided by SeaDataNet. This analysis has revealed that the best quality salinity product over the Baltic Sea is the CCI SST, with a standard deviation of the difference with in-situ of 0.62 degrees C, , which is still large compared to open ocean regions. Therefore, EO SSS products would benefit from improvements in SST products over the Baltic Sea

This work has been carried out as part of the Baltic+ Salinity Dynamics project (4000126102/18/I-BG), funded by the European Space Agency. It has been also supported in part by the Spanish R&D project INTERACT (PID2020-114623RB-C31), which is funded by MCIN/AEI/10.13039/501100011033. We also received funding from the Spanish government through the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S)

23rd International Group for High Resolution Sea Surface Temperature (GHRSST) Science Team Meeting, 27 June -1 July 2022, Barcelona.-- This work is a contribution to the CSIC Thematic Interdisciplinary Platform Teledetect

Peer reviewed