First regional SMOS Sea Surface Salinity products over the Baltic Sea and its oceanographic added-value

Abstract

The Baltic Sea is one of the most challenging regions for the retrieval of SSS from L-band satellite measurements. Nowadays, available EO-based SSS products are quite limited over this region both in terms of spatio-temporal coverage and quality. This is mainly due to several technical limitations that strongly affect the SMOS TB particularly over semi-enclosed seas, such as the high contamination by Radio-Frequency Interference (RFI) sources and the contamination close to land and ice edges. Besides, the sensitivity of TB to SSS changes is very low in cold waters and much larger errors are expected compared to temperate oceans. Salinity and temperature values are very low in this basin, which implies that dielectric constant models are not fully tested in such conditions. In the recent years, the Barcelona Expert Center (BEC) team has been working on the development of innovative algorithms for improving the quality of SMOS TB and SSS retrievals dealing with the main processing issues. Satellite-based SSS fields as produced by ESA Baltic+ Salinity Dynamics project (https://balticsalinity.argans.co.uk/) can contribute to the monitoring of long-term salinity changes and to the detection of periods with anomalous salinity. These products can also be very useful as initial fields and validation data for improving the existing numerical models. This work aims to present the generation of the first regional SMOS SSS product (2011-2020) that would suit to the needs of the Baltic research community. Very recently, the first version of the Baltic+ SSS product has been produced (2011-2013) and is currently under validation against in-situ measurements. The quality assessment of the SSS product in the Baltic Sea is an issue and its representativeness must be carefully assessed. The basin is strongly stratified and then, the differences between SMOS measurements (first centimetres) and in-situ observations (few meters depth) can be noticeable. Differences are more probable during ice melting and high runoff events in spring where there might be a freshwater layer at the top shallow surface. We will present at the workshop the Baltic+ SSS v1 product and its added-value with respect to other existing EO-based datasets. The potential scientific impact of this satellite SSS product in advancing on-going regional research initiatives like the Baltic Earth Working Group on Salinity dynamics will be discussed. It is expected to adopt all users feedback (i.e. outcomes from the workshop and user survey available in project website) to improve and systematize SSS validation protocols in the Baltic Sea. These outcomes will be accessible to the public as an going effort to delineate the Science Roadmap document to further improve satellite SSS retrievals in the Baltic Sea