The ESA mission SMOS was planned with the aim of obtaining more precise data concerning the global water cycle. The exchange of water between land, ocean and atmosphere is one of the principal factors influencing weather and climate patterns. Constituents of the global hydrological cycle that can be measured with SMOS are a) the soil moisture, b) the ocean surface salinity, and c) the thin (< 50 cm) sea ice thickness.

SMOS is a polar orbiting satellite based passive microwave sensor operating at L-Band (1.4 GHz) (see http://www.smos.zmaw.de/en/). The brightness temperature measured by SMOS at L-Band is dependent on the SST and SSS of the seawater as well as on the sea surface roughness induced by wind and waves. The surface salinity is derived by inverse models on a global basis, taking auxiliary information about the SST and the sea surface roughness into account. SMOS data coverage allows to estimate the global SSS distribution every 3 days.

Data offered here in the second release are based on a re-processed retrieval. The monthly data have been filtered and averaged onto a 1° x 1° grid using reciprocal errors as weights.

This new reprocessing is based on the new level 1 and 2 processors; these have been running operationally since January 2012. Accordingly data until December 2011 are free from any biases when averaging over data from ascending and descending swaths. Problems still exist in coastal regions, in the vicinity of a sea ice cover, in the tropics and in areas of elevated RFI. Data after Feb. 2012 unfortunately again have a bias which cannot simply be averaged out by combing ascending and descending overpasses. The assumption here is that scattering of galactic noise and direct solar radiation, which are also important for the computation of the Ocean Target Transformation (OTT), are not calculated properly (see http://www.argans.co.uk/smos/pages/showcsv.php?name=technotes.csv&path=../docs/technotes/&caption=Technical%20notes).

Another re-processing is planned.