Can SMOS observe mesoscale eddies in the Algerian basin?

The circulation in the Algerian Basin is characterized by the presence of fresh-core eddies that  propagate along the coast or at distances between 100-200 km from the coast. Significant improvement in the  processing of the Soil Moisture and Ocean Salinity (SMOS) data have allowed to produce, for the first time, satellite Sea Surface Salinity (SSS) maps in the Mediterranean Sea that capture the signature of Algerian eddies. SMOS data can be used to track them for long periods of time, especially during winter. SMOS SSS maps are well correlated with in situ measurements although the former has a smaller dynamical range. Despite this limitation, SMOS SSS maps capture the key dynamics of Algerian eddies allowing to retrieve velocities from SSS with the correct sign of vorticity. These results have been recently published in Geophysical Research Letters (Isern-Fontanet et al. 2016).

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New operational SSS products: version 2.00

L4 SSS product. The new binned debiased SSS product is fused with OSTIA SST daily, The animation corresponds to the full year 2015.

L4 SSS product. To product it, the new OA debiased SSS product is fused with OSTIA SST daily. The animation corresponds to a period from February to July 2015.

 

In a continuous effort to bring the higher quality products to our users, BEC is happy to announce that a new version of BEC SSS products (v2.00) has been put into operations.

In the new operational version, Land Sea Contamination has been mitigated by means of the empirical salinity debiasing method proposed in [Olmedo et al., 2016]. This leads to higher quality products that can be used for many different purposes. This new dataset is available at BEC products – Available variables – Sea Surface Salinity – Operational V2.0 section or by clicking here.

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New Research: Ocean Currents at BEC

Ocean currents are a key element for the understanding of many oceanic and climatic phenomena and their knowledge is crucial for navigation and operational applications. Following the official broadening of its scope, BEC has extended its research activity towards the diagnosis of ocean surface currents from satellite observations. This new research line, led by Dr. Jordi Isern-Fontanet, is being funded through the ComFuturo program (http://comfuturo.es/proyectos/) granted by the Fundación General del CSIC (http://www.fgcsic.es/) and through the GlobCurrent project (http://www.globcurrent.org/) funded by ESA.
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BEC officially broadens its scope

The SMOS-BEC (SMOS-BARCELONA EXPERT CENTER ON RADIOMETRIC CALIBRATION AND OCEAN SALINITY) was created in July 2007 by agreement between CSIC (Spanish Research Council) and UPC (Technical University of Catalonia) to enhance coordination and visibility of both institutions in their joint work in processing data from the SMOS mission. It was installed in the Centre Mediterrani d’Investigacions Marines i Ambientals (CMIMA) building, belonging to CSIC and that also hosts the Institut de Ciències del Mar (ICM) and the Unitat de Tecnologia Marina (UTM), in the Barcelona sea front. The UPC participation is made through the Passive Remote Sensing Group / Remote Sensing Lab from the Department of Signal Theory and Communications. The main CSIC actor in SMOS is the Physical and Technological Oceanography Department from ICM, together with the Earth Observation Group from the Institut de Ciències de l’Espai (ICE).

BEC scientists play a key role in the mission: Jordi Font (ICM) is the SMOS Co-Lead Investigator for ocean salinity, Ignasi Corbella (UPC) and Antonio Turiel (ICM) are members of the SMOS Quality Working Group, the BEC-UPC team is an Expert Support Laboratory to ESA for the SMOS level 1 processor definition and development, and the BEC-ICM team is an ESL for the level 2 ocean salinity processor. The BEC proposed, designed and validated the level 3 and level 4 SMOS products generated in CP34, Centro de Producción de datos SMOS de niveles 3 y 4, an additional Spanish contribution to the mission to build and operationally distribute SMOS added value products beyond the level 2 official ESA data. CP34 was operated at ESAC, the ESA establishment near Madrid that hosts the SMOS Data Processing Ground Segment, until July 2013. Then it was moved to BEC facilities, where an improved web site allows now an easy access to operational and experimental SMOS level 3 and 4 products, with user friendly format plus additional information to the international users community. …read more

Preliminary validation of 8-day SMAP L3 Salinity product V1.0

Atlantic discharges. April 25-May 2, 2015

Amazon, Niger and Congo discharges over the Atlantic Ocean as measured by SMAP

Scientists at Remote Sensing Systems (RSS, http://www.remss.com), using the experience acquired with the Aquarius mission are developing the necessary algorithms to retrieve sea surface salinity from brightness temperature provided by the SMAP radiometer team.

Recently, RSS has released version 1.0 (BETA) SMAP Level 3 Ocean Surface Salinities. The data can be accessed through the RSS web site or FTP server and it is described in [Meissner et al., 2015]. Their Level 3 salinity product has worldwide coverage and correspond to  8-day and monthly averages. The 8-day average field, centered on each day, starts on April 4, 2015 and ends at November 15, 2015.

A preliminary comparison of the 8-day L3 product with ARGO profiles and the World Ocean Atlas (WOA13) climatology has been performed by BEC team over the zones indicated on the map below.

Zones under study

Zones under study (click to enlarge image)

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Effective SMOS PSF and Antenna Correlations

Given the interferometric characteristics of SMOS, SMOS snapshots are full-polarization brightness temperatures rendered on a hexagonal grid (the so-called synthetic antenna). In fact, what the instrument actually measures are the cross-correlations of all pairs of receivers, from which a visibility function can be derived. The vector of visibilities is linearly related to brightness temperatures TB by means of a reconstruction matrix G. Due to the imperfect knowledge of the matrix G, the difficulties to invert such a big matrix together with some aliasing effects, spurious spatial correlations on brightness temperature snapshots are induced. BEC team is investigating the scope of such correlations. The shape of the found correlations reveals a clear geometrical pattern.

X polarization correlation pattern

a) X polarization correlation pattern. Correlation of the central point with the rest of the synthesized scene

X polarization correlation pattern

b) Real part of XY polarization correlation pattern. Correlation of the central point with the rest of the synthesized scene

X polarization correlation pattern

c) X polarization correlation pattern. Correlation of a point located in the edge of AF-FOV with the rest of the synthesized scene

X polarization correlation pattern

d) X polarization correlation pattern. Correlation of a point beyond the horizon with the rest of the synthesized scene

Figure 1.- Correlation patterns for different polarizations and antenna points. Patterns corresponding to polarization Y and to the imaginary part of cross polarization are similar to those corresponding to X polarization (figures 1.a, 1.c and 1.d) and real part of cross polarization respectively (figure 1.b).

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BEC L4 soil moisture product is now “all-weather”

Soil moisture at fine-scale (BEC L4 soil moisture product) can now be estimated under all-weather conditions. A delayed 5-year (2010-2015) data set covering the Iberian Peninsula is already available, and maps from 2015 onwards are provided in near real-time. This is BIG news! The L4 product is obtained by combining SMOS brightness temperatures with higher spatial resolution MODIS information into fine-scale soil moisture estimates [1,2]. In all previous releases, the presence of clouds masked the information from MODIS and therefore the fine-scale soil moisture. In the new L4 version 3.0 or “all-weather” product, we are including additional information in the downscaling algorithm, which allows fine-scale soil moisture mapping from space independently of cloud cover.

With the L4 all-weather product, we plan to extend the downscaling approach to other climatic regions. See Fig. 1 for an example of its application over Europe on July 1, 2014 (ascending passes). The version 2.0 is also provided (Fig. 2) to illustrate the differences between the two versions.

BEC L4 soil moisture map at 1 km spatial resolution, from 1/07/2014 (AM).

Fig.1. Soil moisture map at 1 km spatial resolution (with version 3.0 downscaling), from 1/07/2014 (AM).

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5+ years of fine-scale soil moisture estimates available!!

At Barcelona Expert Center (BEC) we are able to provide a Level 4 (L4) Surface Soil Moisture (SSM) product with 1 km spatial resolution that meets the requirements of land hydrology applications. To do so, we use a downscaling method that combines highly-accurate, but low-resolution, SMOS radiometric information with high resolution, but low sensitivity, visible-to-infrared imagery to SSM across spatial scales. A sample L4 SSM map from September 1, 2014 (6 AM) is shown in Figure 1.

Fig. 1. SMOS-BEC L4 product from September 1, 2014 (6 AM).

This downscaling approach was first presented in [1] along with results of its application to a set of SMOS images acquired during the commissioning phase over the Oznet network, South-East Australia. Using reprocessed SMOS data obtained with the latest L1 and L2 processors, we have further developed and validated this technique; we now use SMOS polarimetric and multi-angular information in the downscaling method, which results in improved fine-scale soil moisture estimates [2].
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New study on the detection of cold-core rings in the Gulf Stream area using remote sensing platforms

The Gulf Stream plays a major role in the meridional transport of heat and salt across the North Atlantic Ocean. The Gulf Stream acts as a barrier between the cold (10-18 °C) and relatively fresh (salinity around 30-32 in the practical salinity scale) waters of the Labrador Current and the warm (23 °C), salty (36), clear, and unproductive waters of the Sargasso Sea. After leaving Cape Hatteras, the Gulf Stream forms large-amplitude meanders that may loop back onto themselves and break off the stream forming detached rings. Warm-core anti-cyclonic rings bring significant amounts of warm tropical water to the continental slope and shelf seas north of the Gulf Stream. Similarly, cold-core cyclonic rings bring cold, nutrient-rich shelf water, to the biologically barren Sargasso Sea waters. Detection of cold-core rings from satellite data has been quite elusive so far as the surface temperature signature rapidly disappears.

Figure 1

Sea Surface salinity on August 23, 2015 according to various SSS products with superimposed OSCAR velocities. The plot on (a) correspond to the one-degree binned Aquarius L3 map. The other three maps show the fusion of the map shown in (s) with: AVISO SSH (b); SMOS SSS (c); and AVHRR SST (d).

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