New SMOS SSS maps in the framework of the Earth Observation data For Science and Innovation in the Black Sea

Status: this preprint was under review for the journal ESSD but the revision was not accepted.-- 40 pages, 18 figures, 7 tables.-- Data availability: The access to the data is provided by the Barcelona Expert Center FTP service, for more details see http://bec.icm.csic.es/bec-ftp-service/. The product is also available in http://www.eo4sibs.uliege.be/. The DOI of the level 2 ascending product is: https://doi.org/10.20350/digitalCSIC/13993 (Olmedo et al., 2021b); the level 2 descending product is: https://doi.org/10.20350/ digitalCSIC/13995 (Olmedo et al., 2021c); the level 3 product is: https://doi.org/10.20350/digitalCSIC/13996 (Olmedo et al., 2021d); and the level 4 product is: https://doi.org/10.20350/digitalCSIC/13997 (Olmedo et al., 2021e)

In the framework of the European Space Agency (ESA) regional initiative called Earth Observation data For Science and Innovation in the Black Sea (EO4SIBS), a new dedicated Soil Moisture and Ocean Salinity (SMOS) Sea Surface Salinity (SSS) product is generated for the Black Sea for the years 2011–2020. Three SMOS SSS fields are retrieved and distributed: a level 2 product consisting of binned SSS in daily maps at 0.25° × 0.25° spatial resolution grid by considering ascending ((Olmedo et al., 2021b), https://doi.org/10.20350/digitalCSIC/13993) and descending ((Olmedo et al., 2021c), https://doi.org/10.20350/digitalCSIC/13995) satellite overpass directions separately; a level 3 product ((Olmedo et al., 2021d), https://doi.org/10.20350/digitalCSIC/13996) consisting of binned SSS in 9-day maps at 0.25° × 0.25° grid by combining as cending and descending satellite overpass directions; and a level 4 product ((Olmedo et al., 2021e), https://doi.org/10.20350/digitalCSIC/13997) consisting of daily maps at 0.05 × 0.0505° that are computed by merging the level 3 SSS product with Sea Surface Temperature (SST) maps. The generation of SMOS SSS fields in the Black Sea requires the use of enhanced data processing algorithms for improving the Brightness Temperatures in the region since this basin is typically strongly affected by Radio Frequency Interference (RFI) sources which hinders the retrieval of salinity. Here, we describe the algorithms introduced to improve the quality of the salinity retrieval in this basin. The validation of the EO4SIBS SMOS SSS products is performed by: i) comparing the EO4SIBS SMOS SSS products with near-to-surface salinity measurements provided by in situ measurements; ii) assessing the geophysical consistency of the products by comparing them with a model and other satellite salinity measurements; iii) computing maps of SSS errors by using Correlated Triple Collocation analysis. The accuracy of the EO4SIBS SMOS SSS products depend on the time period and on the product level. The accuracy in the period 2016–2020 is better than in 2011–2015 and it is as follows for the different products: i) Level 2 ascending: 1.85 / 1.50 psu (in 2011–2015 / 2016–2020); Level 2 descending: 2.95 1.95 psu; ii) Level 3: 0.7 / 0.5 psu; and iii) Level 4: 0.6 / 0.4 psu

This work has been carried out as part of the European Space Agency contract Earth Observation data For Science and Innovation in the Black Sea. This work represents a contribution to CSIC Thematic Interdisciplinary Platform PTI Teledetect, with the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S). Argo data were collected and made freely available by the International Argo Program and the national programs that contribute to it. (https://argo.ucsd.edu, https://www.ocean-ops.org). The Argo Program is part of the Global Ocean Observing System. Romanian Monitoring oceanographic dataset is obtained in the framework of: "The study on the integrated Monitoring Program of the Black Sea marine ecosystem according to the of the MSFD (2008/56/EC) requirements" and funded by Romanian Ministry of Environment, Water and Forests

Peer reviewed