The base products, for all the CATDS-PDC (Centre Aval de Traitement des Données SMOS - Production & Dissemination Center) processing chains, are the SMOS L1B products - https://doi.org/10.57780/SM1-e20cf57 - from ESA (European Space Agency).

From these, brightness temperatures at various incidence angles are reconstructed. The Sea Surface Salinity (SSS) are retrieved from multi-angular brightness temperatures through a maximum likehood Bayesian approach in which measured Tb and Tb simulated using a forward direct model are compared (see Zine et al. 2008 for a general description of the retrieval method, and pro_con table for a summary of the similarities/differences with respect to ESA level 2 ocean salinity processing).

The L4OS SMOS/SMAP-OI product contains global Level 4 analyses of the of the Sea Surface Salinity (SSS), Sea Surface Density (SSD) and Sea Surface Spiciness (SSSp), along with Sea Surface Absolute Salinity (SSA), Conservative Temperature (SCT), surface thermal expansion coefficient (alpha) and haline contraction coefficient (beta). The SSS product is obtained using an optimal interpolation (OI) algorithm, that combines ISAS in situ SSS OI analyses and satellites image to reduce large scale and temporally varying bias. Two version exists: one with SMOS (Soil Moisture Ocean Salinity) satellite data (since 06/2010), and one with both SMOS and SMAP (Soil Moisture Active and Passive) satellite data (since 04/2015). The SSS L4 product outcome is then combined with satellite SST products to compute thermodynamic sea water parameters using TEOS-10 (Kolodziejczyk et al., 2021).

Products from reprocessing RE07 are available for the period 06/2010 - 05/2021. Products from operational (OPER) processing are available since 06/2021. Reprocessed products and operational products are derived using the same algorithm and configuration, hence ensuring the temporal continuity.

These products are generated with a delay of about 1 month after the end of the period.

File naming :

SM_clas_MIR_CSF4On__startdate_enddate_vvv_ccc_7

- clas: File class (OPER : operational mode, REXX : reprocessing xx)

- n: 1 for SMOS only (since 06/2010), 2 for SMOS+SMAP (since 04/2015)

- startdate: sensing start date/time of the data (format yyyymmddThhmiss)

- enddate: sensing end date/time of the data (format yyyymmddThhmiss)

- vvv: version number of the processor generating the product

- ccc: file counter

File format :

In each archive file (.tgz extension), there are two files

- A Header file (.HDR), which is a text file, in XML Earth Explorer Header format

- A Data file (.DBL.nc), which is a netcdf file, format variant 2 (netcdf 3 with 64 bits offset option)

Simplified version:

This product is also available on Copernicus Marine Service as product MULTIOBS_GLO_PHY_SSS_L4_MY_015_015.

The files are in NetCDF 4, with the alternative file naming:

CATDS_CSF4On_startdate_enddate_vvv_p.nc

- n: 1 for SMOS only (2010-03/2015), 2 for SMOS+SMAP (after 04/2015)

- startdate : sensing start date/time of the data (format yyyymmddThhmiss)

- enddate : sensing end date/time of the data (format yyyymmddThhmiss)

- vvv : version number of the processor generating the product

- p: processing step: 2 for operational processing, 3 for reprocessed.

Reference :

Kolodziejczyk Nicolas, Hamon Michel, Boutin Jacqueline, Vergely Jean-Luc, Reverdin Gilles, Supply Alexandre, Reul Nicolas (2021). Objective analysis of SMOS and SMAP Sea Surface Salinity to reduce large scale and time dependent biases from low to high latitudes. Journal Of Atmospheric And Oceanic Technology, 38(3), 405-421. Publisher's official version : https://doi.org/10.1175/JTECH-D-20-0093.1 , Open Access version : https://archimer.ifremer.fr/doc/00665/77702/