Salinity and temperature gradients drive the thermohaline circulation of the oceans, and play a key role in the ocean-atmosphere coupling. The strong and direct interactions between the ocean and the cryosphere (primarily through sea ice and ice shelves) is also a key ingredient of the thermohaline circulation. The launch of the soil Moisture and Ocean Salinity (SMOS) mission, in 2009, marked the dawn of a new type of space-based microwave observations. Although the mission was originally conceived for hydrological and oceanographic studies [1,2], SMOS is also making inroads in cryospheric science. SMOS carries an L-band (1.4 GHz, or 21-cm wavelength), passive interferometric radiometer (the so-called MIRAS) that measures the electromagnetic radiation emitted by the Earth’s surface, at about 50 km spatial resolution, full polarization, continuous multi-angle viewing, wide swath (1200-km), and with a 3-day revisit time at the equator, but more frequently at the poles. Although the SMOS radiometer operating frequency offers almost the maximum sensitivity of the brightness temperature (TB) to sea surface salinity (SSS) variations, such sensitivity is rather low, even lower at cold waters [3]. 90% of ocean SSS values span a range of brightness temperatures of just 5K. This implies that the SMOS SSS retrieval requires a high performance of the MIRAS interferometric radiometer [4]. Since the SMOS launch, SSS Level 3 maps have been distributed by several expert laboratories including the Barcelona Expert Centre (BEC) team. However, since the TB sensitivity to SSS decreases with decreasing sea surface temperature (SST), no specific attention has been dedicated the retrieval of surface salinity from Arctic regions (i.e., above 50⁰N)). New algorithms, recently developed at BEC to improve the SMOS quality, allow for the first time to derive cold water SSS maps from SMOS data. These algorithms include: i) improvement of the image reconstruction by a reduction of sidelobe levels and ripples caused by abrupt changes of brightness temperatures [5](at level 1); ii) empirical correction of the instrumental systematic biases (land-sea and ice-sea contamination) (at level 2); iii) use of synergistic and multifractal approaches for increasing the spatial and temporal resolution [6] (at levels 3 and 4). The new maps will be presented at the conference together with a thorough assessment of their quality

2016 European Space Agency (ESA) Living Planet Symposium, 9-13 May 2016, Prague, Czech Republic

Peer Reviewed