The purpose of this Algorithm Theoretical Basis Document is to describe the procedure that is used in the SMOS CATDS Production Data Center (CPDC) to generate operational sea surface salinity (SSS) maps (also called L3OS/L4OS product, Level 3/4 Ocean Salinity product).

Moreover, this document gives an overview of the different steps of the global processing, from Level 1b to Level 3 and Level 4 products knowing that only L3OS/L4OS products are provided to users by the CATDS (intermediate products are not officially distributed).