The Soil Moisture and Ocean Salinity (SMOS) mission was launched by European Space Agency (ESA) in November 2009 to measure soil moisture and ocean surface salinity. SMOS is a synthetic aperture L-band radiometer and provides global coverage in 3 days. The level 2 soil moisture products are distributed by ESA’s DPGS (European Space Agency’s Data Processing Ground Segment) for each half orbit since January 2010. The Centre National d’Etudes Spatiales (CNES) has developed the CATDS (Centre Aval de Traitement des Donnees SMOS) ground segment that now provides spatial and temporal synthesis products (referred to as Level 3 products) of soil moisture, ocean salinity and brightness temperatures at multiple incidence angles over the entire operational of SMOS. The AMSR –E sensor on board NASA’s AQUA satellite and its successor, JAXA’s AMSR-2, has been providing soil moisture estimates since 2002 either through the NASA DAAC at the National Snow and Ice Data Center (NSIDC) or through the Vrije Universiteit of Amsterdam. Similarly, the ERS-1 and -2 scatterometers, followed by ASCAT on board METOP have been delivering soil wetness indices through the Eumetsat H-SAF project with a very long climatological record since 1991. Also available now the new Aquarius SM retrievals which are now available and will soon be distributed through NSIDC. The goal of this presentation is three folds: 1 - provide an estimate of the SMOS retrieval accuracy using a large set of ground data 2 - intercompare the different products to assess the pros and cons of each mission and their relative merits as a function of land cover, season etc.. 3 - establish how one could build up a long term environmental data record of soil moisture from these data sets in order to study the impact of climate change on the global water cycle.< Réduire