Validation of SMOS with Malaspina surface drifter data

During the Spanish Malaspina oceanic expedition, a total of 20 surface drifting buoys, manufactured by the Institut de Ciències del Mar (ICM) of the Spanish Council of Scientific Research (CSIC), were deployed. First developed in 2005, the various prototypes of these drifting buoys have been characterized by: 1) take measurements as close as 40 cm below the sea surface; 2) transmitting in real-time through several satellite networks; 3) long-lasting (about two years) energy source; 4) modular structure designed to host several sensors; 5) low-cost; and 6) small size.

Since the mid 2000s, the deployment of the Argo automatic buoys is providing a quasi-global picture of the subsurface temperature and salinity structure. Currently, more than 3300 automatic profilers gather more than 9000 vertical profiles each month. However, few data just below the surface is being gathered by Argo because, to reduce the risk of sensor fouling, the pumping mechanism is switched off few meters before reaching the surface.

Recently, two satellite missions (the Soil Moisture and Ocean Salinity, SMOS, of the European Space Agency, and Aquarius of National Aeronautics and Space Administration) have become a promising strategy to recover information about the sea surface salinity (SSS). Both instruments exploit the fact that significant information on sea surface dielectric properties (related to salinity) can be retrieved from ocean microwave emissions, particularly on L-band. With them, a new set of data may provide reliable information of the skin-depth surface salinity (Font et al. 2011). Three gridded products are currently being produced by the SMOS Barcelona Expert Centre (SMOS-BEC): i) binned weighted-average, ii) optimal interpolation; iii) Data fusion with OSTIA SST. In the SMOS -BEC, the validation of the SMOS salinity products has been carried out exclusively using Argo data.

To fill the bridge between the skin depth (one cm penetration depth) of the satellite measurements and the uppermost reliable measures (between 5 and 10 meters below the surface) from the Argo floats, a new generation of surface drifters has been designed and deployed in various oceans of the world. Here the drifters deployed during Malaspina Campaign, and their impact in the validation of the various SMOS prodcts, are described.