Altimeter dual-frequency observations of surface winds, waves, and rain rate in tropical cyclone Isabel - art. no. C01004, Auteur(s) : Quilfen, Yves Tournadre, Jean Chapron, Bertrand Éditeur(s) : American Geophysical Union Résumé : [1] Extreme weather events such as tropical cyclones are difficult to observe with conventional means. Satellite-based observations provide essential measurements of key parameters governing tropical cyclones. They are critical for short-term forecasting. Radiometers onboard the Defense Meteorological Satellite Program satellite series, WindSat and Tropical Rainfall Measuring Mission satellites, scatterometers onboard the ERS, ADEOS, and QuikScat satellites offer unprecedented synoptic observations of surface wind and atmospheric liquid water content, revealing the storm structures with good accuracy. However, satellite estimates do not provide direct measurements of geophysical parameters and can suffer from limitations linked to the sensors characteristics, such as the signal wavelength and polarization or the measurement incidence angle. For example, measurements at Ku band are strongly affected by rain. Still, each observing system can offer specific information that can be combined with the others. In particular, we highlight the capabilities of dual-frequency altimeter to provide very high resolution measurements of rain rate, surface wind speed, and wave characteristics. A method is proposed to obtain continuous along-track 5 km resolution measurements of these parameters in the tropical cyclone Isabel. The results shows that dual-frequency altimeters can provide useful information to complement and validate the operational fields provided by the atmospheric numerical models and by NOAA observing systems. Journal of Geophysical Union - Research C - Oceans (0148-0227) (American Geophysical Union), 2006 , Vol. 111 , N. C1 , P. NIL_38-NIL_50 Droits : 2006 American Geophysical Union http://archimer.ifremer.fr/doc/2006/publication-1033.pdf DOI:10.1029/2005JC003068 http://archimer.ifremer.fr/doc/00000/1033/ | Partager Voir aussi Mesearement limitations Dual frequency altimeter High resolution measurement Tropical cyclone Télécharger |
On the Use of Doppler Shift for Sea Surface Wind Retrieval From SAR Auteur(s) : Mouche, Alexis Collard, Fabrice Chapron, Bertrand Dagestad, Knut-frode Guitton, Gilles Johannessen, Johnny A. Kerbaol, Vincent Hansen, Morten Wergeland Éditeur(s) : Ieee-inst Electrical Electronics Engineers Inc Résumé : The synthetic aperture radar (SAR) Doppler centroid has been used to estimate the scatter line-of-sight radar velocity. In weak to moderate ocean surface current environment, the SAR Doppler centroid is dominated by the directionality and strength of wave-induced ocean surface displacements. In this paper, we show how this sea state signature can be used to improve surface wind retrieval from SAR. Doppler shifts of C-band radar return signals from the ocean are thoroughly investigated by colocating wind measurements from the ASCAT scatterometer with Doppler centroid anomalies retrieved from Envisat ASAR. An empirical geophysical model function (CDOP) is derived, predicting Doppler shifts at both VV and HH polarization as function of wind speed, radar incidence angle, and wind direction with respect to radar look direction. This function is used into a Bayesian inversion scheme in combination with wind from a priori forecast model and the normalized radar cross section (NRCS). The benefit of Doppler for SAR wind retrieval is shown in complex meteorological situations such as atmospheric fronts or low pressure systems. Using in situ information, validation reveals that this method helps to improve the wind direction retrieval. Uncertainty of the calibration of Doppler shift from Envisat ASAR hampers the inversion scheme in cases where NRCS and model wind are accurate and in close agreement. The method is however very promising with respect of future SAR missions, in particular Sentinel-1, where the Doppler centroid anomaly will be more robustly retrieved. Ieee Transactions On Geoscience And Remote Sensing (0196-2892) (Ieee-inst Electrical Electronics Engineers Inc), 2012-07 , Vol. 50 , N. 7 , P. 2901-2909 Droits : 2012 IEEE http://archimer.ifremer.fr/doc/00088/19896/17554.pdf DOI:10.1109/TGRS.2011.2174998 http://archimer.ifremer.fr/doc/00088/19896/ | Partager |
Haline hurricane wake in the Amazon/Orinoco plume: AQUARIUS/SACD and SMOS observations Auteur(s) : Grodsky, Semyon A. Reul, Nicolas Lagerloef, Gary Reverdin, Gilles Carton, James A. Chapron, Bertrand Quilfen, Yves Kudryavtsev, Vladimir N. Éditeur(s) : Amer Geophysical Union Résumé : At its seasonal peak the Amazon/Orinoco plume covers a region of 10^6 km2 in the western tropical Atlantic with more than 1m of extra freshwater, creating a near-surface barrier layer (BL) that inhibits mixing and warms the sea surface temperature (SST) to >29oC. Here new sea surface salinity (SSS) observations from the Aquarius/SACD and SMOS satellites help elucidate the ocean response to hurricane Katia, which crossed the plume in early fall, 2011. Its passage left a 1.5psu high haline wake covering >10^5 km2 (in its impact on density, the equivalent of a 3.5oC cooling) due to mixing of the shallow BL. Destruction of this BL apparently decreased SST cooling in the plume, and thus preserved higher SST and evaporation than outside. Combined with SST, the new satellite SSS data provide a new and better tool to monitor the plume extent and quantify tropical cyclone upper ocean responses with important implications for forecasting. Geophysical Research Letters (0094-8276) (Amer Geophysical Union), 2012-10 , Vol. 39 , N. L20603 , P. 1-8 Droits : 2012. American Geophysical Union. All Rights Reserved. http://archimer.ifremer.fr/doc/00094/20540/18943.pdf DOI:10.1029/2012GL053335 http://archimer.ifremer.fr/doc/00094/20540/ | Partager |
Comparison of spaceborne measurements of sea surface salinity and colored detrital matter in the Amazon plume Auteur(s) : Fournier, Severine Chapron, Bertrand Salisbury, J. Vandemark, Douglas Reul, Nicolas Éditeur(s) : Amer Geophysical Union Résumé : Large rivers are key hydrologic components in oceanography, particularly regarding air-sea and land-sea exchanges and biogeochemistry. We enter now in a new era of Sea Surface Salinity (SSS) observing system from Space with the recent launches of the ESA Soil Moisture and Ocean Salinity (SMOS) and the NASA Aquarius/Sac-D missions. With these new sensors, we are now in an excellent position to revisit SSS and ocean color investigations in the tropical northwest Atlantic using multi-year remote sensing time series and concurrent in situ observations. The Amazon is the world's largest river in terms of discharge. In its plume, SSS and upper water column optical properties such as the absorption coefficient of colored detrital matter (acdm) are strongly negatively correlated (<-0.7). Local quasi-linear relationships between SSS and acdm are derived for these plume waters over the period of 2010-2013 using new spaceborne SSS and ocean color measurements. Results allow unprecedented spatial and temporal resolution of this coupling. These relationships are then used to estimate SSS in the Amazon plume based on ocean color satellite data. This new product is validated against SMOS and in situ data and compared with previously developed SSS retrieval models. We demonstrate the potential to estimate tropical Atlantic SSS for the extended period from 1998 to 2010, prior to spaceborne SSS data collection. Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2015-05 , Vol. 120 , N. 5 , P. 3177-3192 Droits : 2015. American Geophysical Union. All Rights Reserved. http://archimer.ifremer.fr/doc/00255/36610/35742.pdf DOI:10.1002/2014JC010109 http://archimer.ifremer.fr/doc/00255/36610/ | Partager Voir aussi Amazon-Orinoco river plume SMOS SSS conservative mixing ocean color salinity satellite oceanography Télécharger |
Demonstration of ocean surface salinity microwave measurements from space using AMSR-E data over the Amazon plume Auteur(s) : Reul, Nicolas Saux Picart, Stephane Chapron, Bertrand Vandemark, D. Tournadre, Jean Salisbury, J. Éditeur(s) : American Geophysical Union Résumé : Microwave Sea Surface Salinity (SSS) measurements can be performed by isolating the emissivity response to salinity changes from numerous geophysical effects, including surface temperature and wind waves. At L-band frequencies (1 to 2 GHz), the sensitivity to SSS is sufficient but it falls off quickly as frequency is increased. Nevertheless, methods using higher microwave frequencies with much lower SSS sensitivity than at L band, can already be tested. In particular, combining 6 and 10 GHz data in vertical polarization efficiently minimizes sea surface roughness and thermal impacts. Using AMSR-E data, the retrieved bi-monthly maps of SSS at 0.5 degrees resolution over the region of the Amazon plume show relative accuracy in-line with the future L-band dedicated mission objectives. Citation: Reul, N., S. Saux-Picart, B. Chapron, D. Vandemark, J. Tournadre, and J. Salisbury (2009), Demonstration of ocean surface salinity microwave measurements from space using AMSR-E data over the Amazon plume, Geophys. Res. Lett., 36, L13607, doi:10.1029/2009GL038860. Geophysical Research Letters ( GRL ) (0094-8276) (American Geophysical Union), 2009-07 , Vol. 36 , P. 1-5 Droits : 2009. American Geophysical Union. All Rights Reserved http://archimer.ifremer.fr/doc/2009/publication-6620.pdf DOI:10.1029/2009GL038860 http://archimer.ifremer.fr/doc/00000/6620/ | Partager |
Spatial and temporal coherence between Amazon River discharge, salinity, and light absorption by colored organic carbon in western tropical Atlantic surface waters Auteur(s) : Salisbury, J. Vandemark, D. Campbell, J. Hunt, C. Wisser, D. Reul, Nicolas Chapron, Bertrand Éditeur(s) : Amer Geophysical Union Résumé : The temporal evolution and spatial distribution of surface salinity and colored detrital matter (cdm) were evaluated within and adjacent to the Amazon River Plume. Study objectives were as follows: first, to document the spatial coherence between Amazon discharge, salinity, cdm, and the nature of the salinity-cdm relationship; second, to document the temporal and spatial variability of cdm along the trajectory of the low-salinity Amazon Plume, and third, to explore the departure of cdm from conservative mixing behavior along the plume trajectory into the open ocean. Time series (2003-2007) of surface salinity estimated using the Advanced Microwave Scanning Radiometer-Earth Observing System and corresponding satellite cdm absorption (acdm) data documented a plume of freshened, colored water emanating from the Amazon. Salinity and acdm were generally coherent, but there were regions in which spatial patterns of salinity and acdm did not coincide. Salinity was oppositely phased with discharge, whereas acdm was in phase but lagged discharge and typically remained high after maximum discharge. Along the river plume trajectory, acdm was inversely correlated with salinity, yet there was considerable deviation from conservative mixing behavior during all seasons. Positive anomalies in a linear relationship between salinity and acdm corresponded to areas of enhanced satellite-retrieved net primary productivity, suggesting the importance of phytoplankton biomass or its subsequent remineralization as a source of cdm. Negative anomalies tended to predominate at the distal sections of the plume trajectories, an observation consistent with the process of photo-oxidation of cdm over observed time scales of days to weeks. Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2011-07 , Vol. 116 , N. C00H02 , P. 14 p. Droits : 2011 American Geophysical Union. All Rights Reserved. http://archimer.ifremer.fr/doc/00041/15218/12593.pdf DOI:10.1029/2011JC006989 http://archimer.ifremer.fr/doc/00041/15218/ | Partager |
Ocean remote sensing data integration - examples and outlook Auteur(s) : Chapron, Bertrand Bingham, A Collard, Fabrice Donlon, Craig Johannessen, Johnny A. Piolle, Jean-francois Reul, Nicolas Éditeur(s) : ESA Publication Résumé : Satellite remote sensing has emerged as an essential and necessary observing system to acquire global information about the state of the ocean. Complemented with in situ observing networks, the ultimate goals are to be able to make accurate estimates of selected key sets of geophysical variables, with the intention of either making operational predictions across time and spatial boundaries, or advancing fundamental knowledge through development of empirical relationships and theoretical models. For satellite oceanography, improvements are then constantly being sought in our understandings of the geophysical processes, the sensor physics, the electromagnetic and microwave properties and interactions at the complex air-sea interface. Challenges appear as unlimited as the variety of sea surface dynamics and boundary layer meteorological conditions with their broad range of spatial and temporal scales across the globe. To face these challenges, numerous efforts took places over the passed decade to build an ever-increasing quality, quantity, duration and integration of ocean observations. In parallel, simulation capabilities largely improved. All these efforts are then all critically calling for improved methodologies to better structure the wealth of information that is made readily accessible. This latter aspect is a very demanding new component for future multidisciplinary scientific research. Major innovations to consolidate sensor data repositories, to automate tailored queries, to extract, reveal and quantify relationships will then closely associate computer science developments and applied statistics with comprehensive theoretical and experimental thematic studies. Proceedings of OceanObs'09: Sustained Ocean Observations and Information for Society (ESA Publication), 2010 Droits : info:eu-repo/semantics/openAccess http://archimer.ifremer.fr/doc/00029/14046/11241.pdf DOI:10.5270/OceanObs09.pp.12 http://archimer.ifremer.fr/doc/00029/14046/ | Partager |
Sea Surface Salinity Observations from Space with the SMOS Satellite: A New Means to Monitor the Marine Branch of the Water Cycle Auteur(s) : Reul, Nicolas Fournier, Severine Boutin, Jacqueline Hernandez, Olga Maes, Christophe Chapron, Bertrand Alory, Gael Quilfen, Yves Éditeur(s) : Springer Résumé : While it is well known that the ocean is one of the most important component of the climate system, with a heat capacity 1,100 times greater than the atmosphere, the ocean is also the primary reservoir for freshwater transport to the atmosphere and largest component of the global water cycle. Two new satellite sensors, the ESA Soil Moisture and Ocean Salinity (SMOS) and the NASA Aquarius SAC-D missions, are now providing the first space-borne measurements of the sea surface salinity (SSS). In this paper, we present examples demonstrating how SMOS-derived SSS data are being used to better characterize key land–ocean and atmosphere–ocean interaction processes that occur within the marine hydrological cycle. In particular, SMOS with its ocean mapping capability provides observations across the world’s largest tropical ocean fresh pool regions, and we discuss from intraseasonal to interannual precipitation impacts as well as large-scale river runoff from the Amazon–Orinoco and Congo rivers and its offshore advection. Synergistic multi-satellite analyses of these new surface salinity data sets combined with sea surface temperature, dynamical height and currents from altimetry, surface wind, ocean color, rainfall estimates, and in situ observations are shown to yield new freshwater budget insight. Finally, SSS observations from the SMOS and Aquarius/SAC-D sensors are combined to examine the response of the upper ocean to tropical cyclone passage including the potential role that a freshwater-induced upper ocean barrier layer may play in modulating surface cooling and enthalpy flux in tropical cyclone track regions. Surveys In Geophysics (0169-3298) (Springer), 2014-05 , Vol. 35 , N. 3 , P. 681-722 Droits : Springer Science+Business Media Dordrecht 2013 http://archimer.ifremer.fr/doc/00152/26334/24430.pdf DOI:10.1007/s10712-013-9244-0 http://archimer.ifremer.fr/doc/00152/26334/ | Partager Voir aussi Sea surface salinity SMOS satellite Passive microwave remote sensing Oceanic freshwater cycle Télécharger |
Multisensor observations of the Amazon-Orinoco river plume interactions with hurricanes Auteur(s) : Reul, Nicolas Quilfen, Yves Chapron, Bertrand Fournier, Severine Kudryavtsev, Vladimir Sabia, Roberto Éditeur(s) : Amer Geophysical Union Résumé : An analysis is presented for the spatial and intensity distributions of North Atlantic extreme atmospheric events crossing the buoyant Amazon-Orinoco freshwater plume. The sea surface cooling amplitude in the wake of an ensemble of storm tracks traveling in that region is estimated from satellite products for the period 1998-2012. For the most intense storms, cooling is systematically reduced by approximate to 50% over the plume area compared to surroundings open-ocean waters. Historical salinity and temperature observations from in situ profiles indicate that salt-driven vertical stratification, enhanced oceanic heat content, and barrier-layer presence within the plume waters are likely key oceanic factors to explain these results. Satellite SMOS surface salinity data combined with in situ observations are further used to detail the oceanic response to category 4 hurricane Igor in 2010. Argo and satellite measurements confirm the haline stratification impact on the cooling inhibition as the hurricane crossed the river plume. Over this region, the SSS mapping capability is further tested and demonstrated to monitor the horizontal distribution of the vertical stratification parameter. SMOS SSS data can thus be used to consistently anticipate the cooling inhibition in the wake of TCs traveling over the Amazon-Orinoco plume region. Journal Of Geophysical Research-oceans (0148-0027) (Amer Geophysical Union), 2014-12 , Vol. 119 , N. 12 , P. 8271-8295 Droits : 2014. American Geophysical Union. All Rights Reserved. http://archimer.ifremer.fr/doc/00252/36326/34855.pdf http://archimer.ifremer.fr/doc/00252/36326/34856.pdf DOI:10.1002/2014JC010107 http://archimer.ifremer.fr/doc/00252/36326/ | Partager Voir aussi hurricanes Amazon-Orinocco river plume SMOS SSS cooling inhibition barrier-layer haline stratification Télécharger |