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Registros recuperados: 15
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A 4D-variational approach applied to an eddy-permitting North Atlantic configuration: Synthetic and real data assimilation of altimeter observations ArchiMer
Ferron, Bruno.
The increasing number of oceanic observations calls for the use of synthetic methods to provide consistent analyses of the oceanic variability that will support a better understanding of the underlying mechanisms. In this study, a 1/3 degrees eddy-permitting model of the North Atlantic (from 20 degrees S to 70 degrees N) is combined with a 4D-variational method to estimate the oceanic state from altimeter observations. This resolution allows a better extraction of the physical content of altimeter data since the model spatial scales are more consistent with the data than coarser assimilation exercises because of a lower error in model representativity. Several strategies for the assimilation window are tested through twin experiments carried out under the...
Tipo: Text Palavras-chave: Ocean modelling; Data assimilation; Variational method; Meso-scale; Sea surface height; Heat transport; Meridional overturning.
Ano: 2011 URL: http://archimer.ifremer.fr/doc/00044/15534/12956.pdf
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A semi-evolutive filter with partially local correction basis for data assimilation in oceanography ArchiMer
Hoteit, I; Pham, Dt; Blum, J.
A new data assimilation scheme derived from the singular evolutive extended Kalman (Seek) filter is introduced. The novel feature of the new filter is its correction basis which is partially local in the sense that it consists of "global" and "local" vectors, the later obtained from a local empirical orthogonal functions (Eof) analysis. Such an analysis was introduced in order to better represent the local variability of the ocean. This not only significantly reduces the implementation cost but may also improve the representativeness of the correction basis of the filter. The performance of this scheme is evaluated through twin experiments conducted in a realistic setting of the OPA model over the tropical Pacific zone. The results are compared against...
Tipo: Text Palavras-chave: Filtre Seek; Analyse Eof; Facteur oublié; Data assimilation; Seek filter; Eof analysis; Forgetting factor.
Ano: 2003 URL: http://archimer.ifremer.fr/doc/00321/43244/42973.pdf
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Analysis of the Holocene climate variability using a data assimilation method in the model LOVECLIM ArchiMer
Mairesse, Aurélien.
The study of past climates and of mechanisms that have influenced their evolution is the key to anticipate the future climate changes. This doctoral thesis focusses on the Holocene climate, the ongoing interglacial, that starts about 11,700 years ago. The current paleoclimate knowledge is based on the one hand, on the climate models results and, on the other hand, on the reconstruction of physical variables derived from climate archives as the ice cores, the marine cores or the pollens for instance. These two types of information are complementary. Here we have combined them to obtain reconstructions of past climates using data assimilation. This technique is standard in many disciplines but not yet in paleoclimatology. The data assimilation method applied...
Tipo: Text Palavras-chave: Climate; Data assimilation; Paleoclimate; Holocene; LOVECLIM model; Proxy record.
Ano: 2014 URL: https://archimer.ifremer.fr/doc/00506/61719/65687.pdf
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Apports des données de la 'couleur de l'eau' à la modélisation couplée physique-biogéochimie en milieu dynamique côtier : Application au Rio de la Plata et au Golfe de Gascogne ArchiMer
Huret, Martin.
Continental margins play a crucial role in biogeochemical fluxes between the continents and the open ocean. They are also highly sensitive to human perturbations. Primary production is highly dependent on the complex dynamics of these coastal zones, and on the river supply in nutrients, as well as in Suspended Particulate Matter (SPM) which limit light availability. The quantification of the production is a prerequisite in many applications, from the understanding of the role of the coastal ocean in climate change, to eutrophication and fisheries resources issues within the frame of the integrated management of the coastal zone. Coupled physical-biogeochemical models are useful in studying and monitoring primary production. Because of the numerous complex...
Tipo: Text Palavras-chave: Parameter estimation; Data assimilation; Suspended Particulate Matter (SPM); Chlorophyll a; Phytoplankton blooms; Physical biogeochemical coupled model; Ocean color; Satellite data; Coastal area; Bay of Biscay; Rio de la Plata; Estimation de paramètres; Assimilation de données; Matières En Suspension (MES); Chlorophylle a; Blooms phytoplanctoniques; Modèle couplé physique biogéochimie; Couleur de l'eau; Donnée satellitale; Milieu côtier; Golfe de Gascogne; Rio de la Plata.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/2005/these-337.pdf
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Assimilation de données par méthode variationnelle utilisant l’adjoint d’un code de circulation côtière tridimensionnel ArchiMer
Devenon, Jean-luc; Dekeyser, I; Leredde, Y; Lellouche, Jm.
The optimal control technique using an adjoint method is applied to fit the parameters of a 3-D primitive equation coastal model due to a data assimilation procedure. Two of the main unknowns of coastal modelling operations - open boundary conditions and turbulent mixing processes in stratified conditions - are successively considered. The aim of the boundary control procedure is to identify boundary forcing to ensure the best fit between data and model results by minimising a function that measures model and data discrepancies. A methodology for proceeding from the continuous to the discrete formulation of a control problem is given. The robustness of the method is tested for the typical barotropic case of a semi-enclosed basin Kelvin wave. The data...
Tipo: Text Palavras-chave: Data assimilation; 3-D coastal circulation; Boundary conditions fitting; Adjoint method; Turbulence; Data assimilation; 3-D coastal circulation; Boundary conditions fitting; Adjoint method; Turbulence.
Ano: 2001 URL: http://archimer.ifremer.fr/doc/00322/43337/42890.pdf
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Assimilation of SMOS L-band Wind Speeds: Impact on Met Office Global NWP and Tropical Cyclone Predictions ArchiMer
Cotton, J.; Francis, P.; Heming, J.; Forsythe, M.; Reul, Nicolas; Donlon, C..
A new generation of L-band sensors, such as ESA's Soil Moisture Ocean Salinity (SMOS) mission, have the capability to provide information on the ocean-surface wind speed under high wind and rain conditions. In this study we evaluate the use of SMOS wind speeds within Met Office numerical weather prediction (NWP). Observation minus model background (O-B) departure statistics are used to investigate SMOS error characteristics, quality flags, and develop a quality control method. Observation errors and spatial correlation distances are estimated using a statistical method. Observing system experiments are performed to diagnose the impact of SMOS on NWP forecasts and analyses, including tropical cyclone (TC) predictions. The quality of SMOS retrievals appears...
Tipo: Text Palavras-chave: SMOS; L-band wind speed; Data assimilation; Tropical cyclones; NWP.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00417/52868/53782.pdf
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Combining Argo profiles with a general circulation model in the North Atlantic. Part 1: Estimation of hydrographic and circulation anomalies from synthetic profiles, over a year ArchiMer
Forget, Gael; Ferron, Bruno; Mercier, Herle.
Argo is a global array of profiling floats that provides temperature (T) and salinity (S) profiles from 2000 m to the surface every ten days with a nominal spatial resolution of 3 degrees. Here we present idealized experiments where the adjoint method is used to synthesize simulated sets of Argo profiles with a general circulation model, over a one-year period, in the North Atlantic. Using a number of drifting profilers consistent with Argo deployment objectives, the simulated array permits one to identify large-scale anomalies in the hydrography and circulation, despite the presence of a simulated eddy noise of large amplitude. Model dynamics provide an objective means to distinguish eddy noise from large-scale oceanic variability, and to infer the...
Tipo: Text Palavras-chave: General circulation model; Argo; Twin experiment; 4DVAR; Data assimilation.
Ano: 2008 URL: http://archimer.ifremer.fr/doc/2008/publication-3721.pdf
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Combining Argo profiles with a general circulation model in the North Atlantic. Part 2: Realistic transports and improved hydrography, between spring 2002 and spring 2003 ArchiMer
Forget, Gael; Mercier, Herle; Ferron, Bruno.
A set of Argo profiles collected in the North Atlantic between May 2002 and April 2003 is combined with a low-resolution general circulation model (GCM) using the adjoint method. Fitting the real hydrographic observations leads to vast improvements in the model circulation., including the sea surface height and the meridional heat transport. We find striking differences in basin-scale transports compared with previous assimilation experiments that use the same GCM and a similar spatial resolution. Based on forward modeling studies, it is argued that these differences are due to different assimilation experiment durations. Over 1 year, the hydrography interpolated with the GCM from Argo profiles better represents the contemporary structures than does a...
Tipo: Text Palavras-chave: General circulation model; Argo; In situ observations; 4DVAR; Data assimilation.
Ano: 2008 URL: http://archimer.ifremer.fr/doc/2008/publication-3920.pdf
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Data assimilation in a marine ecosystem model of the Ligurian Sea. ArchiMer
Magri Hoeltzener, Stephanie; Brasseur, Pierre; Lacroix, Geneviève.
The objective is to explore the potentialities of sequential statistical estimation methods to assimilate observations in a primary production biological model coupled to a vertical 1D hydrodynamical model characterised by a k-l turbulent closure. The assimilation method is derived from the SEEK filter (Singular Evolutive Extended Kalman filter), which uses an error subspace represented by multivariate empirical orthogonal functions (EOFs). Real data assimilation experiments collected at sea have been realised to reconstruct the variability of the Ligurian Sea ecosystem during the FRONTAL field experiment.
Tipo: Text Palavras-chave: Ligurian Sea; Kalman filter; Data assimilation; Numeric modelling; Physical/biogeochemical model; Mer Ligure; Filtre de Kalman; Assimilation de données; Modélisation numérique; Océanographie physique/biogéochimique.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/2005/publication-687.pdf
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Data-driven assimilation of irregularly-sampled image time series ArchiMer
Fablet, Ronan; Viet, P.; Lguensat, R.; Chapron, Bertrand.
We address in this paper the reconstruction of irregurlarlysampled image time series with an emphasis on geophysical remote sensing data. We develop a data-driven approach, referred to as an analog assimilation and stated as an ensemble Kalman method. Contrary to model-driven assimilation models, we do not exploit a physically-derived dynamic prior but we build a data-driven dynamic prior from a representative dataset of the considered image dynamics. Our contribution is here to extend analog assimilation to images, which involve high-dimensional state space.We combine patch-based representations to a multiscale PCA-constrained decomposition. Numerical experiments for the interpolation of missing data in satellite-derived ocean remote sensing images...
Tipo: Text Palavras-chave: Data assimilation; Irregular sampling; Image time series; Data-driven methods; Kalman methods.
Ano: 2017 URL: https://archimer.ifremer.fr/doc/00403/51440/52009.pdf
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From Observation to Information and Users: The Copernicus Marine Service Perspective ArchiMer
Le Traon, Pierre-yves; Reppucci, Antonio; Alvarez Fanjul, Enrique; Aouf, Lotfi; Behrens, Arno; Belmonte, Maria; Bentamy, Abderrahim; Bertino, Laurent; Brando, Vittorio Ernesto; Kreiner, Matilde Brandt; Benkiran, Mounir; Carval, Thierry; Ciliberti, Stefania A.; Claustre, Hervé; Clementi, Emanuela; Coppini, Giovanni; Cossarini, Gianpiero; De Alfonso Alonso-muñoyerro, Marta; Delamarche, Anne; Dibarboure, Gerald; Dinessen, Frode; Drevillon, Marie; Drillet, Yann; Faugere, Yannice; Fernández, Vicente; Fleming, Andrew; Garcia-hermosa, M. Isabel; Sotillo, Marcos García; Garric, Gilles; Gasparin, Florent; Giordan, Cedric; Gehlen, Marion; Gregoire, Marilaure L.; Guinehut, Stephanie; Hamon, Michel; Harris, Chris; Hernandez, Fabrice; Hinkler, Jørgen B.; Hoyer, Jacob; Karvonen, Juha; Kay, Susan; King, Robert; Lavergne, Thomas; Lemieux-dudon, Benedicte; Lima, Leonardo; Mao, Chongyuan; Martin, Matthew J; Masina, Simona; Melet, Angelique; Buongiorno Nardelli, Bruno; Nolan, Glenn; Pascual, Ananda; Pistoia, Jenny; Palazov, Atanas; Piolle, Jean-francois; Pujol, Marie Isabelle; Pequignet, Anne Christine; Peneva, Elisaveta; Pérez Gómez, Begoña; Petit De La Villeon, Loic; Pinardi, Nadia; Pisano, Andrea; Pouliquen, Sylvie; Reid, Rebecca; Remy, Elisabeth; Santoleri, Rosalia; Siddorn, John; She, Jun; Staneva, Joanna; Stoffelen, Ad; Tonani, Marina; Vandenbulcke, Luc; Von Schuckmann, Karina; Volpe, Gianluca; Wettre, Cecilie; Zacharioudaki, Anna.
The Copernicus Marine Environment Monitoring Service (CMEMS) provides regular and systematic reference information on the physical and biogeochemical ocean and sea-ice state for the global ocean and the European regional seas. CMEMS serves a wide range of users (more than 15,000 users are now registered to the service) and applications. Observations are a fundamental pillar of the CMEMS value-added chain that goes from observation to information and users. Observations are used by CMEMS Thematic Assembly Centres (TACs) to derive high-level data products and by CMEMS Monitoring and Forecasting Centres (MFCs) to validate and constrain their global and regional ocean analysis and forecasting systems. This paper presents an overview of CMEMS, its evolution,...
Tipo: Text Palavras-chave: Ocean; Observing systems; Satellite; In situ; Data assimilation; Services.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00498/60983/64389.pdf
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HF Radar Activity in European Coastal Seas: Next Steps toward a Pan-European HF Radar Network ArchiMer
Rubio, Anna; Mader, Julien; Corgnati, Lorenzo; Mantovani, Carlo; Griffa, Annalisa; Novellino, Antonio; Quentin, Céline; Wyatt, Lucy; Schulz-stellenfleth, Johannes; Horstmann, Jochen; Lorente, Pablo; Zambianchi, Enrico; Hartnett, Michael; Fernandes, Carlos; Zervakis, Vassilis; Gorringe, Patrick; Melet, Angélique; Puillat, Ingrid.
High Frequency Radar (HFR) is a land-based remote sensing instrument offering a unique insight to coastal ocean variability, by providing synoptic, high frequency and high resolution data at the ocean atmosphere interface. HFRs have become invaluable tools in the field of operational oceanography for measuring surface currents, waves and winds, with direct applications in different sectors and an unprecedented potential for the integrated management of the coastal zone. In Europe, the number of HFR networks has been showing a significant growth over the past 10 years, with over 50 HFRs currently deployed and a number in the planning stage. There is also a growing literature concerning the use of this technology in research and operational oceanography. A...
Tipo: Text Palavras-chave: High frequency radar; Operational oceanography; Coastal observing systems; Radar remote sensing; Surface currents; Surface waves; Model assessment; Data assimilation.
Ano: 2017 URL: https://archimer.ifremer.fr/doc/00368/47879/47895.pdf
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Interpolation par assimilation variationnelle de séquences multimodales d’images satellitaires de l’océan ArchiMer
Ba, Sileye O.; Corpetti, Thomas; Chapron, Bertrand; Fablet, Ronan.
In this paper we address the problem of missing data interpolation in multi-modal geophysical satellite observation sequences. Main issues relate to the large percentage of missing data, from 20 % to 90 % for daily high-resolution observations; and the requirement for reconstructing fine-scale structures in accordance with the underlying turbulent dynamics. To solve the missing data interpolation problem, a variational data assimilation model is developped. Using synthetic and real ocean surface observations, numerical and qualitative evaluations demonstrate the relevance of two key components of the proposed model: the fusion of multi-modal observations through a geometric front-driven constraint and the proposed variational assimilation setting using an...
Tipo: Text Palavras-chave: Assimilation variationnelle de données; Interpolation de données manquantes; Inpainting.; Data assimilation; Variational method; Missing data interpolation; Geophysical tracers dynamics; Multimodal interpolation.
Ano: 2012 URL: http://archimer.ifremer.fr/doc/00139/24980/23061.pdf
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Neural Network Based Kalman Filters for the Spatio-Temporal Interpolation of Satellite-Derived Sea Surface Temperature ArchiMer
Ouala, Said; Fablet, Ronan; Herzet, Cedric; Chapron, Bertrand; Pascual, Ananda; Collard, Fabrice; Gaultier, Lucile.
The forecasting and reconstruction of oceanic dynamics is a crucial challenge. While model driven strategies are still the state-of-the-art approaches in the reconstruction of spatio-temporal dynamics. The ever increasing availability of data collections in oceanography raised the relevance of data-driven approaches as computationally efficient representations of spatio-temporal fields reconstruction. This tools proved to outperform classical state-of-the-art interpolation techniques such as optimal interpolation and DINEOF in the retrievement of fine scale structures while still been computationally efficient comparing to model based data assimilation schemes. However, coupling this data-driven priors to classical filtering schemes limits their potential...
Tipo: Text Palavras-chave: Data assimilation; Dynamical model; Kalman filter; Neural networks; Data-driven models; Interpolation.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00481/59286/61979.pdf
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Spatio-Temporal Interpolation of Cloudy SST Fields Using Conditional Analog Data Assimilation ArchiMer
Fablet, Ronan; Huynh Viet, Phi; Lguensat, Redouane; Horrein, Pierre-henri; Chapron, Bertrand.
The ever increasing geophysical data streams pouring from earth observation satellite missions and numerical simulations along with the development of dedicated big data infrastructure advocate for truly exploiting the potential of these datasets, through novel data-driven strategies, to deliver enhanced satellite-derived gapfilled geophysical products from partial satellite observations. We here demonstrate the relevance of the analog data assimilation (AnDA) for an application to the reconstruction of cloud-free level-4 gridded Sea Surface Temperature (SST). We propose novel AnDA models which exploit auxiliary variables such as sea surface currents and significantly reduce the computational complexity of AnDA. Numerical experiments benchmark the proposed...
Tipo: Text Palavras-chave: Ocean remote sensing data; Data assimilation; Optimal interpolation; Analog models; Multi-scale decomposition; Patch-based representation.
Ano: 2018 URL: http://archimer.ifremer.fr/doc/00426/53806/54741.pdf
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