Préparation de l'étalonnage et de la validation des mesures de salinité SMOS : De l'influence de la stratification verticale de la salinité

The objective of European satellite SMOS (Soil Moisture and Ocean Salinity),, deployed on 2nd November 2009, is to measure sea surface salinity (SSS) et sol moisture, using L-band radiometry. To reach a 0.1 -0.2 pss precision on averaged SSS maps (over 10 days and 200 km x 200km), measurements have to be calibrated and validated. Comparisons between in situ salinities, measured at several meters depth, and SMOS salinities, representative of the first centimetre below the oceanic surface will be done. However, this vertical difference can imply high salinity differences in case of precipitations. This work focuses on the vertical salinity differences in the first 10 meters depth and their consequences for the calibration and validation of SMOS data. From in situ salinities, salinity differences are studied in tropical oceanic band (30°N -30°S). A statistical analysis about the influence of rain events on theses vertical differences is realised. Because salinities are rare in the first meter depth, we use theoretical model simulating salinities differences in case or precipitation : NEMO, a coupled ocean-atmosphere model and an unidirectional model PWP ([Price et al., 1986]).L'objectif du satellite européen SMOS (Soil Moisture and Ocean Salinity), lancé le 02 novembre 2009, est de mesurer, par radiométrie en bande L, la salinité de surface des océans (SSS) et l'humidité des sols. Pour atteindre une précision de 0.1 – 0.2 pss sur des cartes de SSS moyennées sur 10 jours et sur 200 km x 200 km, une phase d'étalonnage et de validation des mesures doit être réalisée. Une des techniques retenues est la comparaison entre des salinités in situ, mesurées à plusieurs mètres de profondeur et les salinités SMOS, représentatives du premier centimètre sous la surface océanique. Cette différence verticale peut engendrer des biais de salinité importants, notamment en cas de fortes précipitations. Ce travail, réalisé en collaboration avec le LOCEAN et ACRI-St, se concentre sur la variabilité verticale de la salinité dans les 10 premiers mètres de la couche de surface océanique et sur ses conséquences pour la phase d'étalonnage/ validation de SMOS. Il propose, à partir de mesures in situ, une description des différences verticales de salinité sur l'ensemble des zones océaniques tropicales (30°N – 30°S). Une étude statistique de la relation entre ces différences verticales et un paramètre de pluie, construit à partir des mesures satellitaires de taux de précipitation est également effectuée. Enfin,pour combler le manque de salinités in situ proches de la surface, la possibilité d'utiliser des modèles théoriques pour simuler les différences verticales de salinité en cas de pluie a été étudiée. Les modèles utilisés sont le modèle de circulation océanique NEMO et le modèle unidimensionnel PWP ([Price et al., 1986]) qui calcule la profondeur de la couche de mélange

Vertical variability of Near-Surface Salinity in the Tropics : Consequences for SMOS Calibration and Validation

International audienceThe ESA/SMOS (European Space Agency/Soil Moisture and Ocean Salinity) satellite mission aims to detect Sea Surface Salinity (SSS) using L-band radiometry. At that frequency, the skin depth is 1 centimeter. However, the calibration and validation of SMOS measurements will be done with in situ measurements, mainly taken at 5 m depth. In order to anticipate and understand vertical salinity differences in the first 10 m of the ocean surface layer, in situ vertical profiles are analyzed. Measurements come from autonomous drifter and Tropical Atmosphere Ocean (TAO) moorings for observations on local scale and from thermosalinographs (TSG), floats, eXpendable Conductivity-Temperature-Depth (XCTD) and CTD on the entire tropical band (from 30°S to 30°N). For the first time, vertical salinity differences, classified according to their vertical position, are collocated with precipitation computed by satellite. A rain parameter, 3D max rain rate, is defined to take into account the history of rain events. Vertical salinity differences higher than 0.1 pss-78 are observed in the 3 oceans, mainly between 0° and 15°N, coinciding with the average position of the InterTropical Convergence Zone. The highest differences are mainly located near river mouth. Some differences exceed 0.5 pss-78 locally and persist for more than 10 days, unlike the spatial average of salinity differences between 10 m and 1 m, which stay close to 0. A statistical approach is developed to be used for predicting large vertical salinity differences

Vertical variability of Near-Surface Salinity in the Tropics : Consequences for SMOS Calibration and Validation

International audienceThe ESA/SMOS (European Space Agency/Soil Moisture and Ocean Salinity) satellite mission aims to detect Sea Surface Salinity (SSS) using L-band radiometry. At that frequency, the skin depth is 1 centimeter. However, the calibration and validation of SMOS measurements will be done with in situ measurements, mainly taken at 5 m depth. In order to anticipate and understand vertical salinity differences in the first 10 m of the ocean surface layer, in situ vertical profiles are analyzed. Measurements come from autonomous drifter and Tropical Atmosphere Ocean (TAO) moorings for observations on local scale and from thermosalinographs (TSG), floats, eXpendable Conductivity-Temperature-Depth (XCTD) and CTD on the entire tropical band (from 30°S to 30°N). For the first time, vertical salinity differences, classified according to their vertical position, are collocated with precipitation computed by satellite. A rain parameter, 3D max rain rate, is defined to take into account the history of rain events. Vertical salinity differences higher than 0.1 pss-78 are observed in the 3 oceans, mainly between 0° and 15°N, coinciding with the average position of the InterTropical Convergence Zone. The highest differences are mainly located near river mouth. Some differences exceed 0.5 pss-78 locally and persist for more than 10 days, unlike the spatial average of salinity differences between 10 m and 1 m, which stay close to 0. A statistical approach is developed to be used for predicting large vertical salinity differences

Vertical variability of Near-Surface Salinity in the Tropics : Consequences for SMOS Calibration and Validation

International audienceThe ESA/SMOS (European Space Agency/Soil Moisture and Ocean Salinity) satellite mission aims to detect Sea Surface Salinity (SSS) using L-band radiometry. At that frequency, the skin depth is 1 centimeter. However, the calibration and validation of SMOS measurements will be done with in situ measurements, mainly taken at 5 m depth. In order to anticipate and understand vertical salinity differences in the first 10 m of the ocean surface layer, in situ vertical profiles are analyzed. Measurements come from autonomous drifter and Tropical Atmosphere Ocean (TAO) moorings for observations on local scale and from thermosalinographs (TSG), floats, eXpendable Conductivity-Temperature-Depth (XCTD) and CTD on the entire tropical band (from 30°S to 30°N). For the first time, vertical salinity differences, classified according to their vertical position, are collocated with precipitation computed by satellite. A rain parameter, 3D max rain rate, is defined to take into account the history of rain events. Vertical salinity differences higher than 0.1 pss-78 are observed in the 3 oceans, mainly between 0° and 15°N, coinciding with the average position of the InterTropical Convergence Zone. The highest differences are mainly located near river mouth. Some differences exceed 0.5 pss-78 locally and persist for more than 10 days, unlike the spatial average of salinity differences between 10 m and 1 m, which stay close to 0. A statistical approach is developed to be used for predicting large vertical salinity differences

Air-sea CO₂ flux variability in frontal regions of the Southern Ocean from CARbon Interface OCean Atmosphere drifters

International audienceNine CARbon Interface OCean Atmosphere (CARIOCA) drifters were deployed in the Southern Ocean (south of the subtropical front, STF) between 2001 and 2006. They recorded 65 months of measurements in all seasons between 57°S and 40°S. Hydrological fronts detected by altimetry indicate that one buoy explored the polar zone (PZ) of the Atlantic Ocean and the western Indian Ocean; the remaining buoys explored the northern andsouthern parts of the subantarctic zone (SAZ) from the mid–Indian Ocean (73°E) to the eastern Pacific Ocean (112°W). The air–sea CO$_2$ fluxes along the buoy trajectories are primarily driven by the spatial variability of the fugacity of CO$_2$ in seawater, fCO$_2$: in the SAZ, they vary between $-$1.1 and $-$4.2 mol$^{-2}$yr$^{-1}$, and the largest sinks occur close to the STF; in the PZ they vary between $-$1.6 and 0.6 mol m$^{-2}$ yr$^{-1}$. When spatially extrapolated over each region, the yearly fluxes amount to $-$0.8 Pg C yr$^{-1}$ in the SAZ and to $-$0.1 Pg C yr$^{-1}$ in the PZ, with very small seasonal variation. In winter–spring, the sea-surface salinity and sea-surface temperature indicate mixing with deep water close to the subantarctic front and an episodic signature of north Atlantic deep water close to the polar front (PF). These events are associated with fCO$_2$ close to equilibrium. On a small scale (of a few km), close to the STF, fCO$_2$ variations of 1–2 Pa (10–20 $\mu$atm) are associated with the presence of compensated mixed layers

Vertical variability of near-surface salinity in the tropics: Consequences for L-band radiometer calibration and validation

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Overview of SMOS Level 2 Ocean Salinity processing and first results

International audienceSMOS (Soil Moisture and Ocean Salinity), launched in November 2, 2009 is the first satellite mission addressing the salinity measurement from space through the use of MIRAS (Microwave Imaging Radiometer with Aperture Synthesis), a new two-dimensional interferometer designed by the European Space Agency (ESA) and operating at L-band. This paper presents a summary of the sea surface salinity retrieval approach implemented in SMOS, as well as first results obtained after completing the mission commissioning phase in May 2010. A large number of papers have been published about salinity remote sensing and its implementation in the SMOS mission. An extensive list of references is provided here, many authored by the SMOS ocean salinity team, with emphasis on the different physical processes that have been considered in the SMOS salinity retrieval algorithm

SMOS: Objectives and Approach for Ocean Salinity Observations

International audienceSMOS (Soil Moisture and Ocean Salinity), launched in November 2, 2009 is the first satellite mission addressing the salinity measurement from space through the use of MIRAS (Microwave Imaging Radiometer with Aperture Synthesis), a new two-dimensional interferometer designed by the European Space Agency (ESA) and operating at L-band. This paper presents a summary of the sea surface salinity retrieval approach implemented in SMOS, as well as first results obtained after completing the mission commissioning phase in May 2010. A large number of papers have been published about salinity remote sensing and its implementation in the SMOS mission. An extensive list of references is provided here, many authored by the SMOS ocean salinity team, with emphasis on the different physical processes that have been considered in the SMOS salinity retrieval algorithm

SMOS: Objectives and Approach for Ocean Salinity Observations

International audienceSMOS (Soil Moisture and Ocean Salinity), launched in November 2, 2009 is the first satellite mission addressing the salinity measurement from space through the use of MIRAS (Microwave Imaging Radiometer with Aperture Synthesis), a new two-dimensional interferometer designed by the European Space Agency (ESA) and operating at L-band. This paper presents a summary of the sea surface salinity retrieval approach implemented in SMOS, as well as first results obtained after completing the mission commissioning phase in May 2010. A large number of papers have been published about salinity remote sensing and its implementation in the SMOS mission. An extensive list of references is provided here, many authored by the SMOS ocean salinity team, with emphasis on the different physical processes that have been considered in the SMOS salinity retrieval algorithm