ESA Arctic+ Salinity Product v4: Enhanced Retrievals Near the Ice-Edge

In the framework of the extension of the European Space Agency (ESA) regional initiative Arctic+ Salinity, a new Sea Surface Salinity (SSS) product (version 4.0) was developed from the Soil Moisture and Ocean Salinity (SMOS) measurements. The data was generated starting from the SMOS Level 0 (L0) data, and specific algorithms for reducing the contamination close to the ice edge were applied to enhance the quality of the salinity retrieval. This includes an improvement in the Nodal Sampling technique at Level 1 (L1) at the level of the Brightness Temperature, and at Level 2 (L2) in the correction of biases that in the Arctic depend on the distance to the ice in the salinity Debiased Non-Bayesian retrieval. In this paper, we explain these algorithms and present the results of the quality assessment of this new 12-year temporal series of SMOS SSS Arctic+ v4.0 maps. We also compare it with the previous version of the product (SMOS SSS Arctic+ v3.1). The new algorithm can retrieve salinities closer to the coast and the ice edges, increasing the coverage by 25% with respect to its previous version. Furthermore, version v4.0 presents a reduction of the Root Mean Square (RMS) difference values with respect to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> measurements in the range from 24% to 43% with respect to v3.1, which demonstrates a very significant improvement in the accuracy of the v4.0 product.