Using Argo to validate remote sensing missions

With its more than 3500 automatic profilers, the Argo array is one of the most important component of the Global in-situ Ocean Observing System. The array provides measurements of temperature and salinity profiles down to 2000 m. These data are rapidly expanding the historical database of the ocean sub-surface (specially in the case of ocean salinity) and are providing novel information about the ocean’s vertical structure and its variability. Moreover, these data allow real-time monitoring, model-constraining and contribute to calibration and verification efforts.

Number of available profiles from January 2005 to December 2014: Shown are the total number of profiles, the delayed mode profiles as for Apri 27, 2015 and the number of delayed mode profiles with salinity.

Figure 1: Number of Argo profiles from January 2005 to December 2014: Shown are the total number of profiles, the delayed mode profiles as for April 27, and the number of delayed mode profiles with salinity.

The Euro-Argo ( research infrastructure, designed to coordinate the European contribution to Argo, is part of the European Strategy Forum on Research Infrastructures (ESFRI). Euro-Argo is expected to provide additional 50 floats per year and support about the 25% of
the Argo array.

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Barcelona World Race 2014-2015

The 2014-15 edition of the Barcelona World Race (BWR) has had an active ocean observation contribution that will provide new data about the ocean water dynamics and its environmental quality.

In addition to contribute to the build-up of the Argo system by deploying eight Argo profilers during January 2015, the One Planet, One Ocean & Pharmaton ship carried a Sea Bird SBE37-SI MicroCAT instrument to collect continuous (every minute) sea surface temperature and salinity measurements.

Photography by Mireia Perelló from

The One Planet, One Ocean & Pharmaton. Photography by Mireia Perelló from

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A blending algorithm using SST data to improve SMOS SSS maps

Data fusion is a process for combining two, or more, sources of information to improve the representation of a given system. In a recent paper, data fusion has been used to remove noise from SMOS sea surface salinity (SSS) products, by fusing SMOS data with sea surface temperature (SST) fields.

Our approach is justified by the correspondence between the singularity exponents of SSS and SST. The singularity exponent is a non-dimensional measure of the regularity or irregularity of a field in a given point. The value of the singularity exponent increases with the smoothness of a field. The correspondence between the singularity exponents of SST and SSS implies the existence of a local functional dependence between these two variables. This correspondence can be illustrated using data of a numerical simulation (OFES, Ocean General Circulation Model for the Earth Simulator).

Figure 1 shows two conditioned histograms. The one in the top illustrates the histogram of SSS conditioned by each given value of SST. The conditioned histogram looks like a superposition of narrow lines. It indicates that, while strong local SSS-SST correlations exist, these relations do change from one region to the other. On the contrary, the conditioned histogram of SSS singularity exponents conditioned by the value of the singularity exponents of SST indicates that a unique correlation exists all over the world ocean. In fact, the slope of the maximum probability line is close to one, indicating an almost perfect identity between the singularity exponents of SST and SSS.


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Data assimilation of SMOS SSS data to create Level 4 salinity maps. A case study

Many approaches can be used to reduce the amount of noise present in a given set of data (observed or retrieved). In the SMOS processing chain, weighted averages are used to reduce the noise present in the sea surface salinity (SSS) data retrieved from brightness temperature measurements. This is the rationale of the existence of the higher production levels (Levels 3 and 4) of sea surface salinity and soil moisture.

Differences between SMOS level 3 (right) or FREE-run(left) and Argo data (2011). All 2011 match ups are shown in these plots.

Figure 1: Differences between SMOS level 3 (right) or FREE-run(left) and Argo data (2011). All 2011 match ups are shown in these plots.

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Glancing over RFI sources

The Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) instrument onboard SMOS is a Y-shaped antenna with a total of 72 receivers distributed along its three arms and central body. Each receiver captures the thermal radiation in the microwave L-band, more specifically in the protected passive band comprised between 1400 and 1427 MHz. Since the emission within this band is prohibited by the International Telecommunications Union (ITU), no relevant external interferences were expected before SMOS launch (2009). Nevertheless, the real situation is that the Radio Frequency Interferences (RFI) are present in large areas of Europe and Asia leading to low quality measurements. Moreover, due to the MIRAS interferometric processing, RFI sources located far away, even beyond the MIRAS Field of View (FOV), can contaminate large portions of the MIRAS image.

Retrieved L2 values. Ascending passes. Year 2012

Figure 1. Map of the number of retrieved L2 SSS values during 2012 for ascending passes. White areas have no valid L2 SSS values along 2012.

For a given zone, RFI signals can be classified in terms of the mean life time of the interference as transient emissions or permanent emissions. The former have a limited temporal influence and are mainly produced by mobile sources (for instance ships in open ocean). The latter have a strong effect and may even systematically prevent  the retrieval of salinity or soil moisture.

Our Web Map Server service (based on ncWMS and Godiva2 developed by Reading e-Science Centre at the University of Reading) can be used to reveal the spatial distribution of persistent RFI over ocean. The presence of a RFI source reduces the number of valid measures in the zone. Thus, affected zones can be detected by mapping the L2 used measures parameter.

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SPURS cruise ends

Research vessel Sarmiento de Gamboa

Research vessel Sarmiento de Gamboa

The R/V Sarmiento de Gamboa arrived to Ponta Delgada, Azores, on April 12, and R/V Endeavor is expected to be at Narragansett a few days later. The SPURS spring 2013 cruise is finished and both vessels have achieved the collection of an impressive amount of high resolution oceanographic data, as well as the deployment of several autonomous sampling devices. The SPURS blog (Cruises, SPURS-March 2013) has reported several aspects of the work done. It has been one month of intensive sampling of the high salinity region in the central convergence of the North Atlantic subtropical gyre. The data we have recorded will contribute understanding how this maximum is formed and sustained.

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The SPURS-MIDAS cruise

The Spanish in-situ contribution to the international SPURS (Salinity Processes in the Upper ocean Regional Study) experiment is taking place on board the R/V Sarmiento de Gamboa from March 16, 2013. A team of scientists from SMOS-BEC, plus other researchers and technicians from ICM and UTM-CSIC Barcelona, NUI Galway, LOCEAN Paris, LDEO-U. Columbia New York and U. Vigo are performing a wide range of mesoscale and submesoscale measurements to contribute understanding the mechanisms of formation and permanence of the largest ocean salinity maximum in the centre of the North Atlantic subtropical gyre. Several standard and prototype instruments are used in measuring sea surface salinity and other ocean variables.

Underway near-surface salinity along Sarmiento de Gamboa track from the Canary Islands to the SPURS site (figure: O. Hernandez, LOCEAN)

Underway near-surface salinity along Sarmiento de Gamboa track from the Canary Islands to the SPURS site (figure: O. Hernandez, LOCEAN)

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SMOS in the SPURS experiment


SPURS field experiment. Click on image to enlarge

The SPURS-MIDAS cruise (Las Palmas de Gran Canaria 16 March 2013 – Ponta Delgada, Açores 17 April) on board the Spanish R/V Sarmiento de Gamboa is a contribution to the SPURS experiment (Salinity Processes in the Upper ocean Regional Study) aimed at understanding the processes that drive the upper ocean dynamics and the role that salinity plays on them in the area of maximum salinity in the center of the North Atlantic subtropical gyre. The experiment is coordinated by WHOI (R. Schmitt) and sponsored by NASA (E. Lindstrom), and includes intensive field work with a large variety of state-of-the-art instrumentation, the use of satellite remotely sensed salinity information (Aquarius and SMOS), as well as dedicated numerical modeling. The SMOS BEC team is one of the participants in SPURS where it will contribute with in situ data acquisition, processing and mapping SMOS salinity data, and a regional implementation of the NEMO model with assimilative and process-based simulations to complement and analyze the processes suggested by the observations.

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Christmas, El Niño, and SMOS

Christmas is surely an appropriate moment to talk about the “El Niño / Southern Oscillation” (ENSO). Today there is no doubt that ENSO is the largest source of inter-annual climate variability at regional and planetary scales. Although its ocean-atmosphere coupled nature was postulated in 1969, the quasi-periodic oceanic and atmospheric anomalous behavior has been observed for centuries. For more than five hundred years, Peruvian fishermen and farmers have been aware that a periodic warm surface counter-current off the Peruvian Coast reduces the anchovy catch, while, at the same time, increased rainfalls transform barren lands onto fertile ones. This counter-current was termed as the current of the “El Niño” (the Child Jesus) because it usually appears around Christmas. On the other hand, several tens of thousands of kilometers to the west, over the Asian continent, other climate events also have a strong impact on society. For example, the failure of monsoons resulted in the Great Drought (1876-1877) that contributed to cause more than seven million deaths in the British-controlled India. Since then, various efforts were made to predict the interannual variability of the Indian monsoons. In 1904 Sir Gilbert Walker was appointed as the director-general of Observatories in India to lead such task. Although Walker was not aware of the El Niño current, he did know about the existence of synchronized interannual pressure fluctuations over the Indian Ocean and eastern tropical Pacific (fluctuations that Walker called the “Southern Oscillation”). His research team evidenced that monsoons are part of a global phenomenon, and that the Southern Oscillation is correlated with major changes in the rainfall patterns and wind vents over the tropical Pacific and Indian Oceans.

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