Presented at the 2018 Ocean Sciences MeetingAn ESA project was set up in October 2016 aimed at assessing the impact of satellite sea surface salinity (SSS) data assimilation on analyses/forecasts of the 2015/16 El Niño event. To improve the uptake and use of SSS data for ocean forecasting this project is designing and performing Observing System Experiments (OSEs) of SSS using ocean modelling and assimilation systems. The project is a direct ESA support to the GODAE OSEval-TT and will develop an Observation Impact Statement for satellite SSS. Two different global ocean forecasting systems are used in the project. The Met Office FOAM system consists ofthe ocean NEMO model and a variational approach (3D-Var) with a 1-day data assimilation window. The Mercator Ocean systems consists of the ocean NEMO model and a SEEK filter with a 7-day data assimilation window. Work is going on to develop assimilation of satellite SSS data (SMOS, Aquarius and SMAP), with particular attention on observation bias correction. Coordinated experiments are planned so that assessments of the impact of the satellite SSS data can be made from more than one system. Salinity in situ observations are quite sparse and the atmospheric forcing error do not allow a precise constraint of the smaller scale of the SSS. The focus is on the information brought by satellite SSS during the Niño 15 event. The project will be described and the latest results shown.