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12 results on '"lagrangian data"'

1. A Mediterranean drifters dataset: 1998 - 2022.

Author

Ribotti, Alberto, Bussani, Antonio, Menna, Milena, Satta, Andrea, Sorgente, Roberto, Cucco, Andrea, and Gerin, Riccardo

Subjects
*SOLE proprietorship, *ELECTRONIC data processing, *GEOPHYSICS, *OCEANOGRAPHY
Abstract

Over a hundred of experiments were realised between 1998 and 2022 in the Mediterranean Sea using surface Lagrangian drifters, at coastal and offshore level. Raw data were initially unified and pre-processed manually by eliminating spikes and wrong positions or date/time information. The integrity of the received data packages was checked, and incomplete ones were discarded. Deployment information was retrieved from an initial excel database and campaign notes for each drifter and integrated into the PostgreSQL database, realised and maintained by the National Institute of Oceanography and Applied Geophysics (OGS) in Trieste (IT). This database also collects a variety of metadata about the drifter model, project, owner and operator. Subsequently data were processed using standard procedures of editing and quality control developed for the OGS Mediterranean drifter dataset to remove spikes generated by malfunctioning of the sensors and obtain files with common characteristics. Drifter data and plots of each track were also visually checked to remove any point not identified by the automatic procedure and clearly erroneous. Drifters' trajectories were split into two or more segments that have been considered as different deployments, in case of specific drifters' behaviours. Data were interpolated at defined time intervals to temporarily unify tracks. From the original 138 experiments, a dataset of 204 tracks was obtained, available from the public open-access repository in SEANOE (SEA scieNtific Open data Edition) at https://doi.org/10.17882/90537 (Ribotti et al., 2022). [ABSTRACT FROM AUTHOR]

Published
2022
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2. From Large Deviations to Semidistances of Transport and Mixing: Coherence Analysis for Finite Lagrangian Data.

Author

Koltai, Péter and Renger, D. R. Michiel

Subjects
*LAGRANGE equations, *PERTURBATION theory, *LARGE deviations (Mathematics), *DYNAMICAL systems, *ERGODIC theory
Abstract

One way to analyze complicated non-autonomous flows is through trying to understand their transport behavior. In a quantitative, set-oriented approach to transport and mixing, finite time coherent sets play an important role. These are time-parametrized families of sets with unlikely transport to and from their surroundings under small or vanishing random perturbations of the dynamics. Here we propose, as a measure of transport and mixing for purely advective (i.e., deterministic) flows, (semi)distances that arise under vanishing perturbations in the sense of large deviations. Analogously, for given finite Lagrangian trajectory data we derive a discrete-time-and-space semidistance that comes from the “best” approximation of the randomly perturbed process conditioned on this limited information of the deterministic flow. It can be computed as shortest path in a graph with time-dependent weights. Furthermore, we argue that coherent sets are regions of maximal farness in terms of transport and mixing, and hence they occur as extremal regions on a spanning structure of the state space under this semidistance—in fact, under any distance measure arising from the physical notion of transport. Based on this notion, we develop a tool to analyze the state space (or the finite trajectory data at hand) and identify coherent regions. We validate our approach on idealized prototypical examples and well-studied standard cases. [ABSTRACT FROM AUTHOR]

Published
2018
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3. A coherent structure approach for parameter estimation in Lagrangian Data Assimilation.

Author

Maclean, John, Santitissadeekorn, Naratip, and Jones, Christopher K.R.T.

Subjects
*PARAMETER estimation, *PRINCIPAL components analysis, *CHAOS theory, *LAGRANGIAN coherent structures
Abstract

We introduce a data assimilation method to estimate model parameters with observations of passive tracers by directly assimilating Lagrangian Coherent Structures. Our approach differs from the usual Lagrangian Data Assimilation approach, where parameters are estimated based on tracer trajectories. We employ the Approximate Bayesian Computation (ABC) framework to avoid computing the likelihood function of the coherent structure, which is usually unavailable. We solve the ABC by a Sequential Monte Carlo (SMC) method, and use Principal Component Analysis (PCA) to identify the coherent patterns from tracer trajectory data. Our new method shows remarkably improved results compared to the bootstrap particle filter when the physical model exhibits chaotic advection. [ABSTRACT FROM AUTHOR]

Published
2017
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4. Impact of data assimilation on ocean current forecasts in the Angola Basin.

Author

Phillipson, Luke and Toumi, Ralf

Subjects
*OCEAN currents, *SALINITY, *OCEAN temperature, *ALTIMETRY
Abstract

The ocean current predictability in the data limited Angola Basin was investigated using the Regional Ocean Modelling System (ROMS) with four-dimensional variational data assimilation. Six experiments were undertaken comprising a baseline case of the assimilation of salinity/temperature profiles and satellite sea surface temperature, with the subsequent addition of altimetry, OSCAR (satellite-derived sea surface currents), drifters, altimetry and drifters combined, and OSCAR and drifters combined. The addition of drifters significantly improves Lagrangian predictability in comparison to the baseline case as well as the addition of either altimetry or OSCAR. OSCAR assimilation only improves Lagrangian predictability as much as altimetry assimilation. On average the assimilation of either altimetry or OSCAR with drifter velocities does not significantly improve Lagrangian predictability compared to the drifter assimilation alone, even degrading predictability in some cases. When the forecast current speed is large, it is more likely that the combination improves trajectory forecasts. Conversely, when the currents are weaker, it is more likely that the combination degrades the trajectory forecast. [ABSTRACT FROM AUTHOR]

Published
2017
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5. Modelling surface currents in the Eastern Levantine Mediterranean using surface drifters and satellite altimetry.

Author

Issa, Leila, Brajard, Julien, Fakhri, Milad, Hayes, Daniel, Mortier, Laurent, and Poulain, Pierre-Marie

Subjects
*MATHEMATICAL models of oceanography, *ALTIMETRY, *NATURAL satellites, *ADVECTION
Abstract

We present a new and fast method that blends altimetric and drifter positions data in order to predict the surface velocity in the Eastern Levantine Mediterranean. The method relies on a variational assimilation approach where a velocity correction is continuously obtained by matching observed drifter positions with those predicted by a simple advection model. The background velocity used in the advection of the drifters is the aggregate of a geostrophic and a wind-driven component and the velocity correction is constrained to be divergence free. The algorithm employs a sliding time window that assimilates at once and inside each frame, an entire trajectory of drifters. We show that with few drifters, our method improves the estimation of velocity in two typical situations: an eddy between the Lebanese coast and Cyprus, and velocities along the Lebanese coast. [ABSTRACT FROM AUTHOR]

Published
2016
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6. Blending drifters and altimetric data to estimate surface currents: Application in the Levantine Mediterranean and objective validation with different data types

Author

Georges Baaklini, Milena Menna, Julien Brajard, Leila Issa, Gina Fifani, Laurent Mortier, Milad Fakhri, Isabelle Taupier-Letage, Anthony Bosse, Variabilité de l'Océan et de la Glace de mer (VOG), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Department of Computer Science and Mathematics [Lebanese American University] (CSM/SAS/LAU), Lebanese American University (LAU), National Center for Marine Sciences [Lebanon], National Council for Scientific Research = Conseil national de la recherche scientifique du Liban [Lebanon] (CNRS-L), Processus et interactions de fine échelle océanique (PROTEO), National Institute of Oceanography and Experimental Geophysics (OGS), Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)

Subjects
Drifters, Atmospheric Science, 010504 meteorology & atmospheric sciences, Meteorology, Lagrangian data, Oceanography, 01 natural sciences, Mediterranean sea, Data assimilation, Computer Science (miscellaneous), 14. Life underwater, Altimeter, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography, 0105 earth and related environmental sciences, 010505 oceanography, Ocean current, Levantine Mediterranean, Geotechnical Engineering and Engineering Geology, Surface velocity field, Drifter, Eddy, 13. Climate action, Ocean color, Altimetry, Geostrophic wind, Geology
Abstract

International audience; An improved estimation of the surface currents in the Levantine Basin of the Mediterranean sea is crucial for a wide range of applications, including pollutants transport and nutrients distribution. This estimation remains challenging due to the scarcity or shortcomings of various data types used for this purpose. In this paper, we present an objective validation of a variational assimilation algorithm that blends geostrophic velocities derived from altimetry, wind-induced velocities, and drifter positions, to continuously obtain velocity corrections. The assessment of the validation impact was based on available independent in-situ data (current meters, gliders, and independent drifters) and satellite ocean color images. In all cases, the improvement was shown either qualitatively (position of the eddies) or quantitatively.

Published
2021
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7. Advances in hydrodynamic modelling of flow in rivers and estuaries using Lagrangian drifter data

Author

Mardani, Neda

Subjects
Fluid dynamics, Eulerian instruments, Observation locations, Model calibration, Estuary, Twin experiment, Rating curve, OSSE, Hydrodynamic modelling, Lagrangian data, data assimilation, Open-source tool
Abstract

The major environmental challenges to society, for example, climate change, environmental degradation and the extreme weather effects, require comprehensive information for a resourceful response, including informed decision making related to future actions. Estuaries are especially exposed to the footprints of climate change because alterations in climatic variables that impact freshwater and marine systems will also influence estuaries. While this knowledge is useful, scientists currently lack detailed information on the impact of global change in a diverse range of morphological estuary types across continental and global regions (Scanes et al., 2020). By identifying the processes and attributes responsible for estuary change, the dynamics of estuaries is more accurately predictable around the globe. However, to achieve this goal, two remaining components are needed: (1) a tool for collecting information; and (2) a robust method to elaborate this information. In other words, observations (measurements) support the first component, and the latter component is provided by models. The mechanisms to secure these two avenues of investigation are distinct: observations are directly connected with the system under investigation through measurement devices, while models have an indirect connection with the system, being an expression of measurements and represent an abstraction of reality. To make use of the information incorporated in observations and models, it is essential to understand the characteristics of this information. In particular, the errors and limitations associated with both observations and models. Errors in models are generated through incomplete implementation of the model as well as their imperfect simulation of real world processes. Another basic attribute of observations is that they are spatially and temporally discrete, which results in gaps in the information provided by them. To fill these gaps, it is important to first make observations more complete, with better spatial coverage, and hence more useful; secondly, use observation on the behaviour of the system to extend the observations for the purpose of reflecting the reality (e.g., using a model) (W. Lahoz et al., 2010). The model can then propagate the information from observations and better represent the real state of the system under investigation. The idea behind choosing a model for a particular environment is that the model provides a set of consistent principles which when registered, makes the most efficient use of observations.

Published
2021
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8. From Large Deviations to Semidistances of Transport and Mixing: Coherence Analysis for Finite Lagrangian Data

Author

Péter Koltai and D. R. Michiel Renger

Subjects
37N10, 60F10 (primary), 60J22, 76F25, 37M10, 05C12 (secondary), 500 Naturwissenschaften und Mathematik::510 Mathematik::510 Mathematik, 37M10, Primary 37N10, Lagrangian data, Space (mathematics), 01 natural sciences, Measure (mathematics), Article, 010305 fluids & plasmas, Large deviation, Transport distance, Mixing, 0103 physical sciences, State space, Statistical physics, Mathematics - Dynamical Systems, 010306 general physics, Coherent sets, Mixing (physics), Mathematics, Applied Mathematics, General Engineering, 76F25, Flow (mathematics), Modeling and Simulation, Trajectory, Secondary 60J22, Graph (abstract data type), Large deviations theory, Mixing distance, 05C12, 60F10
Abstract

One way to analyze complicated non-autonomous flows is through trying to understand their transport behavior. In a quantitative, set-oriented approach to transport and mixing, finite time coherent sets play an important role. These are time-parametrized families of sets with unlikely transport to and from their surroundings under small or vanishing random perturbations of the dynamics. Here we propose, as a measure of transport and mixing for purely advective (i.e., deterministic) flows, (semi)distances that arise under vanishing perturbations in the sense of large deviations. Analogously, for given finite Lagrangian trajectory data we derive a discrete-time and space semidistance that comes from the "best" approximation of the randomly perturbed process conditioned on this limited information of the deterministic flow. It can be computed as shortest path in a graph with time-dependent weights. Furthermore, we argue that coherent sets are regions of maximal farness in terms of transport and mixing, hence they occur as extremal regions on a spanning structure of the state space under this semidistance---in fact, under any distance measure arising from the physical notion of transport. Based on this notion we develop a tool to analyze the state space (or the finite trajectory data at hand) and identify coherent regions. We validate our approach on idealized prototypical examples and well-studied standard cases., Comment: J Nonlinear Sci, 2018

Published
2018

9. Observation of the dynamics and horizontal dispersion in a shallow intermittently closed and open lake and lagoon (ICOLL)

Author

Suara, Kabir Adewale, Mardani, Neda, Fairweather, Heather, McCallum, Adrian, Allan, Christopher, Sidle, Roy, Brown, Richard, Suara, Kabir Adewale, Mardani, Neda, Fairweather, Heather, McCallum, Adrian, Allan, Christopher, Sidle, Roy, and Brown, Richard

Abstract

Among the 135 or more estuaries on the southeast Australian coastline, 45% are intermittently open. A number of others, which would normally have an intermittently open entrance, are kept permanently open to improve the flushing and water quality that are functions of the horizontal dispersion of the estuarine system. Field studies that investigate the dynamics and horizontal dispersion processes of open and closed states of Intermittenly Closed and Open Lakes and Lagoons (ICOLL) are conducted. Clusters of Lagrangian drifters were used to characterise the surface flow. Horizontal dispersion coefficients (K) under study varied significantly for different tidal phases; the mean ebb tide K (~4.7±3.8 m2 s-1) is an order of magnitude higher than that of the flood tide. During the closed state, K values were up to two orders of magnitude lower than those observed in the open state. These results highlight the contribution of tidal dispersion to transport and mixing processes within an ICOLL. The results showed that tidal pumping effects and tidal-induced horizontal velocity gradients are responsible for the horizontal surface transport and dispersion occurring during the open inlet state. The horizontal surface dispersion processes identified at different inlets and environmental conditions within this site are valuable for managing transport of particles, freshwater mixing, larvae transport, waste, and pest control.

Published
2018

10. Improvement of hydrodynamic models of shallow water bodies using combined Eulerian and Lagrangian observations

Author

Mardani, Neda, Fairweather, Helen, Sidle, Roy, Brown, Richard J., Suara, Kabir, Mardani, Neda, Fairweather, Helen, Sidle, Roy, Brown, Richard J., and Suara, Kabir

Abstract

Intermittently Closed and Open Lakes or Lagoons (ICOLLs) are a subcategory of estuaries that exhibit limited exchange with the ocean and river flows. [1] This study focuses on improving hydrodynamic modelling in shallow water estuaries using GPS tracked Lagrangian drifter data. The inclusion of drifter data will improve hydrodynamic models, which are commonly used to assess and manage risks of flooding, sediment transport, and pollutants. Traditionally, Eulerian hydrodynamic models used in shallow water systems are calibrated using observations from fixed instruments. With the recent availability of inexpensive GPS tracked drifters that can be deployed in shallow estuaries [2], a higher density of data can be collected to improve the confidence in the hydrodynamic model outputs. The numerical model [3] is set up for an ICOLL in South East Queensland (Currimundi Lake).This model will be calibrated and validated using both Lagrangian and Eulerian data. The effectiveness of assimilated Lagrangian drifter data on improving the prediction of velocity and water heights in the ICOLL is investigated. The calibrated numerical model will further be used for modelling advection-dispersion of potential contamination, sediment transport, and flood modelling within the ICOLL.

Published
2018

11. Impact of data assimilation on ocean current forecasts in the Angola Basin

Author

Ralf Toumi and Luke Phillipson

Subjects
Atmospheric Science, 010504 meteorology & atmospheric sciences, Meteorology, GULF-OF-MEXICO, OSCAR, Lagrangian data, Oceanography, 01 natural sciences, Data assimilation, Computer Science (miscellaneous), Meteorology & Atmospheric Sciences, Altimeter, 0405 Oceanography, Predictability, SURFACE VELOCITY, 0105 earth and related environmental sciences, Science & Technology, VARIATIONAL ASSIMILATION, 010505 oceanography, Ocean current, NUMERICAL WEATHER-PREDICTION, Geotechnical Engineering and Engineering Geology, Numerical weather prediction, Drifter, Sea surface temperature, DRIFTER DATA, Angola Basin, 4D-Var, MODELING SYSTEM ROMS, Climatology, Physical Sciences, Environmental science, CONGO RIVER, VELOCITY OBSERVATIONS, Altimetry, CIRCULATION MODEL
Abstract

The ocean current predictability in the data limited Angola Basin was investigated using the Regional Ocean Modelling System (ROMS) with four-dimensional variational data assimilation. Six experiments were undertaken comprising a baseline case of the assimilation of salinity/temperature profiles and satellite sea surface temperature, with the subsequent addition of altimetry, OSCAR (satellite-derived sea surface currents), drifters, altimetry and drifters combined, and OSCAR and drifters combined. The addition of drifters significantly improves Lagrangian predictability in comparison to the baseline case as well as the addition of either altimetry or OSCAR. OSCAR assimilation only improves Lagrangian predictability as much as altimetry assimilation. On average the assimilation of either altimetry or OSCAR with drifter velocities does not significantly improve Lagrangian predictability compared to the drifter assimilation alone, even degrading predictability in some cases. When the forecast current speed is large, it is more likely that the combination improves trajectory forecasts. Conversely, when the currents are weaker, it is more likely that the combination degrades the trajectory forecast.

Published
2017

12. Modelling surface currents in the Eastern Levantine Mediterranean using surface drifters and satellite altimetry

Author

Pierre-Marie Poulain, Laurent Mortier, Daniel Hayes, Milad Fakhri, Leila Issa, Julien Brajard, Department of Computer Science and Mathematics [Lebanese American University] (CSM/SAS/LAU), Lebanese American University (LAU), Processus de la variabilité climatique tropicale et impacts (PARVATI), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Coupling environmental data and simulation models for software integration (CLIME), Inria de Paris, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria), National Center for Marine Sciences [Lebanon], National Council for Scientific Research = Conseil national de la recherche scientifique du Liban [Lebanon] (CNRS-L), Cyprus Oceanography Center, University of Cyprus (UCY), Variabilité de l'Océan et de la Glace de mer (VOG), Istituto Nazionale di Geofisica e di Oceanografia Sperimentale (OGS), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), and University of Cyprus [Nicosia] (UCY)

Subjects
Atmospheric Science, Drifters, 010504 meteorology & atmospheric sciences, Meteorology, Lagrangian data, Oceanography, 01 natural sciences, Physics::Geophysics, Divergence, Data assimilation, Computer Science (miscellaneous), Altimeter, Trajectory (fluid mechanics), Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences, 010505 oceanography, Advection, Ocean current, Geotechnical Engineering and Engineering Geology, Geodesy, [INFO.INFO-MO]Computer Science [cs]/Modeling and Simulation, Surface velocity field, Drifter, Altimetry, Geostrophic wind, Geology, Eastern Levantine Mediterranean
Abstract

We present a new and fast method that blends altimetric and drifter positions data in order to predict the surface velocity in the Eastern Levantine Mediterranean. The method relies on a variational assimilation approach where a velocity correction is continuously obtained by matching observed drifter positions with those predicted by a simple advection model. The background velocity used in the advection of the drifters is the aggregate of a geostrophic and a wind-driven component and the velocity correction is constrained to be divergence free. The algorithm employs a sliding time window that assimilates at once and inside each frame, an entire trajectory of drifters. We show that with few drifters, our method improves the estimation of velocity in two typical situations: an eddy between the Lebanese coast and Cyprus, and velocities along the Lebanese coast.

Published
2016
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