Abstract
The Algerian Basin is a key area for the general circulation in the western Mediterranean Sea. The basin has an intense inflow/outflow regime with complex circulation patterns, involving both fresh Atlantic water and more saline Mediterranean water. Several studies have demonstrated the advantages of the combined use of autonomous underwater vehicles, such as gliders, with remotely sensed products (e.g., altimetry, MUR SST) to observe meso- and submesoscale structures and their properties. An important contribution could come from a new generation of enhanced satellite sea surface salinity (SSS) products, e.g., those provided by the Soil Moisture and Ocean Salinity (SMOS) mission. In this paper, we assess the advantages of using Barcelona Expert Center (BEC) SMOS SSS products, obtained through a combination of debiased non-Bayesian retrieval, DINEOF (data interpolating empirical orthogonal functions) and multifractal fusion with high resolution sea surface temperature (OSTIA SST) maps. Such an aim was reached by comparing SMOS Level-3 (L3) and Level-4 (L4) SSS products with in situ high resolution glider measurements collected in the framework of the Algerian Basin Circulation Unmanned Survey (ABACUS) observational program conducted in the Algerian Basin during falls 2014–2016. Results show that different levels of confidence between in situ and satellite measurements can be achieved according to the spatial scales of variability. Although SMOS values slightly underestimate in situ observations (mean difference is −0.14 (−0.11)), with a standard deviation of 0.25 (0.26) for L3 (L4) products), at basin scale, the enhanced SMOS products well represent the salinity patterns described by the ABACUS data.
Highlights
The Algerian Basin is a wide and deep transit region located in the western Mediterranean Sea, of which it constitutes the southern part
The results obtained from the L4 products indicate that the simplified scheme of multifractal fusion is not enough to fully describe the fast, small-scale dynamics present in this region, and that more complex schemes are needed
Since the large scale salinity patterns are well described, future releases of these products should be focused on using different interpolation/fusion schemes to improve the effective spatial and temporal resolutions of the soil moisture and ocean salinity (SMOS) sea surface salinity (SSS) products
Summary
The Algerian Basin (hereafter AB) is a wide and deep transit region located in the western Mediterranean Sea, of which it constitutes the southern part. AW carried by the Algerian Current (AC) generates several fresh-core coastal eddies that propagate downstream [9,10] and promote water mass mixing, affecting the spatial distribution of salinity, and, the Mediterranean Sea surface circulation These mesoscale energetic structures have marked repercussions on nutrient injection (removal) into (out of) the euphotic layer. 2019, 11, 1361 upcoming satellite missions, such as the Surface Water and Ocean Topography (SWOT) wide-swath radar interferometer [45,46] In such a context, this study compares ABACUS (Algerian Basin Circulation Unmanned Survey) in situ high resolution glider measurements collected in the AB during fall 2014–2016 with co-located SMOS enhanced SSS L3 and L4 products, provided by BEC, in order to confirm that retrieving reliable SMOS SSS in the Mediterranean region is possible.
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