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| Royer, Francois; Fromentin, Jean-marc; Gaspar, P. |
| Archival tagging provides a unique way to study the spatial dynamics and habitat of pelagic fish. This technique generates lagrangian data of a particular type in marine ecology: although highly informative about processes at different scales (e.g. horizontal movements versus diving behaviour), such data are impaired by location errors and the lack of combination with actual environmental variability. The present paper introduces a framework for modelling bluefin tuna movement in relation to its habitat, using records of light, depth and temperature from archival tags. Based on data assimilation concepts and methods, we show how an explicit formulation of the observation process and the statistics of external variables (e.g. ambient temperature) can... |
| Tipo: Text |
Palavras-chave: Tag; Archival; Habitat; Movement; Bluefin tuna. |
| Ano: 2005 |
URL: http://archimer.ifremer.fr/doc/2005/publication-671.pdf |
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| Vandemark, D; Tran, N; Beckley, Bd; Chapron, Bertrand; Gaspar, P. |
| A new sea state bias modeling approach is presented that makes use of altimeter-derived marine geoid estimates. This method contrasts with previous models that require differencing between repeat altimeter passes for SSB isolation, along with complex bivariate inversion, to derive a relation between wind speed, wave height and SSB. Here one directly bin-averages sea height residuals over the wind and wave correlatives. Comparison with the most current nonparametric repeat-pass model shows close agreement and provides a first validation of this simpler and more direct technique. Success is attributed mainly to extensive space and time averaging. Ease in implementation and benefits in working with absolute levels provide much appeal. Further advantages and... |
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| Ano: 2002 |
URL: https://archimer.ifremer.fr/doc/00000/10225/9578.pdf |
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| Le Traon, Pierre-yves; Stum, J; Dorandeu, J; Gaspar, P; Vincent, P. |
| A global statistical analysis of the first 10 months of TOPEX/POSEIDON merged geophysical data records is presented. The global crossover analysis using the Cartwright and Ray (1990) (CR) tide model and Gaspar et al. (this issue) electromagnetic bias parameterization yields a sea level RMS crossover difference of 10.05 cm, 10.15 cm, and 10.15 cm for TOPEX-TOPEX, POSEIDON-POSEIDON, and TOPEX-POSEIDON crossovers, respectively, All geophysical corrections give reductions in the crossover differences, the most significant being with respect to ocean tides, solid earth tide, and inverse barometer effect. Based on TOPEX-POSEIDON crossovers and repeat-track differences, we estimate the relative bias between TOPEX and POSEIDON at about -15.5 +/- 1 cm. This value... |
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| Ano: 1994 |
URL: http://archimer.ifremer.fr/doc/00079/18983/16627.pdf |
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| Chapron, Bertrand; Vandemark, D; Elfouhaily, T; Thompson, Dr; Gaspar, P; Labroue, S. |
| A nonparametric SSB model, derived using the TOPEX altimeter, is analyzed to show a new decomposition of the form SSB = bH(s) + f(sigma (o)), where b is 0.03 and the function of radar cross section (sigma (o)) is an absolute second-order range correction residing outside the conventional nondimensional SSB model. Expected variability in the dominant bH(s) term and its ties to the long wave orbital velocity and shorter-scale slope variances are discussed using a physic ally-motivated restatement of recent EM bias theory. The geometry of steep near-breaking waves, neglected within current theory, is invoked as one plausible explanation for the observed H-s-independent SSB component. |
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| Ano: 2001 |
URL: https://archimer.ifremer.fr/doc/00000/10275/10691.pdf |
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| Gaspar, P; Ogor, Florian; Le Traon, Pierre-yves; Zanife, Oz. |
| TOPEX (Ku band) and POSEIDON altimeter measurements at crossover points are used to estimate the sea state bias (SSB) of these two instruments. Different SSB models are tested, ranging from a constant fraction of the significant wave height (SWH) to more elaborate models involving up to four adjustable parameters. For TOPEX, the data show a decrease in the magnitude of the relative bias (SSB/SWH) with SWH. This behavior is well reproduced using a simple empirical model with two adjustable parameters. The three-parameter SSB model used in the NASA geophysical data records does well in explaining the wind-induced variations of the bias. A model including four adjustable parameters is needed to account for both the wind- and SWH-related variability of the... |
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| Ano: 1994 |
URL: http://archimer.ifremer.fr/doc/00079/18984/16628.pdf |
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