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| Registros recuperados: 10 | |
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| Wright, Corwin J.; Scott, Robert; Ailliot, Pierre; Furnival, Darran. |
| Using the world's largest data set of in situ ocean current measurements, combined with a high-resolution topography roughness data set, we use a model-assisted hierarchical clustering methodology to estimate the global lee wave generation rate at the ocean floor. Our analysis suggests that internal wave generation contributes 0.750.19 TW (2 standard deviation) to the oceanic energy budget but with a strong dependence on the Brunt-Vaisala (buoyancy) frequency climatology used. This estimate is higher than previous calculations and suggests that internal wave generation may be a much more significant contributor to the global oceanic mechanical energy budget than had previously been assumed. Our results imply that lee wave generation and propagation may be... |
| Tipo: Text |
Palavras-chave: Lee waves; Deep ocean; Current meters. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00192/30306/28798.pdf |
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| Ailliot, Pierre; Baxevani, Anastassia; Cuzol, Anne; Monbet, Valerie; Raillard, Nicolas. |
| The surface of the ocean, and so such quantities as the significant wave height, equation image, can be thought of as a random surface that develops over time. In this paper, we explore certain types of random fields in space and time, with and without dynamics that may or may not be driven by a physical law, as models for the significant wave height. Reanalysis data is used to estimate the sea-state motion which is modeled as a hidden Markov chain in a state space framework by means of an AR(1) process or in the presence of the dispersion relation. Parametric covariance models with and without dynamics are fitted to reanalysis and satellite data and compared to the empirical covariance functions. The derived models have been validated against satellite... |
| Tipo: Text |
Palavras-chave: Space-time model; Significant wave height; State-space models. |
| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00363/47443/47472.pdf |
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| Tandeo, Pierre; Ailliot, Pierre; Autret, Emmanuelle. |
| Satellites provide important information on many meteorological and oceanographic variables. State-space models are commonly used to analyse such data sets with measurement errors. In this work, we propose to extend the usual linear and Gaussian state-space to analyse time series with irregular time sampling, such as the one obtained when keeping all the satellite observations available at some specific location. We discuss the parameter estimation using a method of moment and the method of maximum likelihood. Simulation results indicate that the method of moment leads to a computationally efficient and numerically robust estimation procedure suitable for initializing the Expectation-Maximisation algorithm, which is combined with a standard numerical... |
| Tipo: Text |
Palavras-chave: State-space model; Irregular sampling; Ornstein-Uhlenbeck process; EM algorithm; Sea surface temperature. |
| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00039/15047/12441.pdf |
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| Tandeo, Pierre; Autret, Emmanuelle; Piolle, Jean-francois; Tournadre, Jean; Ailliot, Pierre. |
| The Advanced Along-Track Scanning Radiometer (AATSR) onboard Envisat is designed to provide very accurate measurements of sea surface temperature (SST). Using colocated in situ drifting buoys, a dynamical matchup database (MDB) is used to assess the AATSR-derived SST products more precisely. SST biases are then computed. Currently, Medspiration AATSR SST biases are discrete values and can introduce artificial discontinuities in AATSR level-2 SST fields. The new AATSR SST biases presented in this letter are continuous. They are computed, for nighttime and best proximity confidence data, by linear regression with different MDB covariables (wind speed, latitude, aerosol optical depth, etc.). As found, the difference between dual-view and nadir-only SST... |
| Tipo: Text |
Palavras-chave: Validation; Sea surface temperature (SST); Remote sensing; Advanced Along Track Scanning Radiometer (AATSR). |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/publication-6135.pdf |
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| Raillard, Nicolas; Prevosto, Marc; Ailliot, Pierre. |
| Many records in environmental science exhibit asymmetries: for example in shallow water and with variable bathymetry, the sea wave time series shows front–back asymmetries and different shapes for crests and troughs. In such situation, numerical models are available but their computational cost and complexity are high. A stochastic process aimed at modeling such asymmetries has recently been proposed, the Laplace moving average process, which consists in applying a linear filter on a non-Gaussian noise built using the generalized Laplace distribution. The objective is to propose a new non-parametric estimator for the kernel involved in the definition of this process. Results based on a comprehensive numerical study will be shown in order to evaluate the... |
| Tipo: Text |
Palavras-chave: Laplace moving average; Non-linear time series; FIR estimation; Splines; High-order spectrum; Asymmetries. |
| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00201/31189/29588.pdf |
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| Registros recuperados: 10 | |
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