The SMOS mission (European Space Agency – ESA, and French Space Agency – CNES), as well as the subsequent NASA Aquarius and SMAP missions, have demonstrated the value of L-band passive radiometry (1.4 GHz, 21 cm) for measuring soil moisture and ocean surface salinity, the primary applications of these missions. SMOS provides the longest time series of L-band measurements (since 2009) and it plays a central role in the Soil Moisture and Sea Surface Salinity programmes of the ESA Climate Change Initiative (CCI) and contribute to the CCI Biomass. Since SMOS’ launch, many new research and operational applications have emerged. SMOS soil moisture is operationally assimilated at the European Centre for Medium-Range Weather Forecasts. SMOS data are also used to monitor the thickness of sea ice (thin) or to monitor the freeze-thaw cycle at high latitudes, which affects methane emissions. However, the resolution of SMOS and SMAP (~ 40 km) is a limiting factor for several applications, particularly in agriculture or hydrology, as well as for the study of mesoscale phenomena in the ocean or the monitoring of processes in coastal regions such as ice cap melting and river plumes. Those requirements have been recently documented in an ESA study on the continuity of L-band observations that concludes that many applications can make significant progress if measurements were available at a native spatial resolution of 10 km or less. This is the goal of the SMOS-HR (High Resolution) mission: ensuring the continuity of L-band observations with a resolution increased by at least a factor of 4 compared to SMAP/SMOS .

Nemesio Rodriguez-Fernandez, Yann H. Kerr; François Cabot & Eric Anterrieu