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| Registros recuperados: 15 | |
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| Tran, Ngan; Chapron, Bertrand; Vandemark, D. |
| This letter uses a large ocean satellite data set to document relationships between Ku-band radar backscatter (sigma-0) of the sea surface, near-surface wind speed (U), and ocean wave height (SWH). The observations come from satellite crossovers of the Tropical Rainfall Mapping Mission (TRMM) Precipitation Radar (PR) and two satellite altimeters, namely: 1) Jason-1 and 2) ENVISAT. At these nodes, we obtain TRMM clear-air normalized radar cross-section data along with coincident altimeter-derived significant wave height. Wind speed estimates come from the European Centre for Medium-Range Weather Forecast. TRMM PR is the first satellite to measure low incidence Ku-band ocean backscatter at a continuum of incidence angles from 0 degrees to 18 degrees. This... |
| Tipo: Text |
Palavras-chave: Space borne radar; Scattering; Radar cross section; Altimetry. |
| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/publication-3299.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... |
| Tipo: Text |
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| Ano: 2002 |
URL: https://archimer.ifremer.fr/doc/00000/10225/9578.pdf |
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| Elfouhaily, Tanos; Chapron, Bertrand; Katsaros, Kristina; Vandemark, D. |
| Review of several recent ocean surface wave models finds that while comprehensive in many regards, these spectral models do not satisfy certain additional, but fundamental, criteria. We propose that these criteria include the ability to properly describe diverse fetch conditions and to provide agreement with in situ observations of Cox and Munk [1954] and Jahne and Riemer [1990] and Hara et al. [1994] data in the high-wavenumber regime. Moreover, we find numerous analytically undesirable aspects such as discontinuities across wavenumber limits, nonphysical tuning or adjustment parameters, and noncentrosymmetric directional spreading functions. This paper describes a two-dimensional wavenumber spectrum valid over all wavenumbers and analytically amenable to... |
| Tipo: Text |
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| Ano: 1997 |
URL: http://archimer.ifremer.fr/doc/00091/20226/17877.pdf |
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| Tournadre, Jean; Chapron, Bertrand; Reul, Nicolas; Vandemark, D. |
| [1] About 5% of Ku-band altimeter ocean data are degraded by the occurrence of high radar return cross sections (sigma(0)), usually called sigma(0) blooms. During blooms, which occur during no or low wind conditions, the mean altimeter waveform can significantly depart from the expected shape. In about 60% of the cases the waveforms are distorted to such an extent that either the range tracker loses lock or the off-nadir angle estimate becomes unrealistic. The analysis of high data rate altimeter waveforms during bloom events reveals the presence of V-shaped patterns similar to the ones observed during rain events. These patterns trace small-scale (i.e., smaller than the altimeter footprint) changes in surface backscatter. Such variations of surface... |
| Tipo: Text |
Palavras-chave: Slick; Sigma blooms; Altimeter waveforms. |
| Ano: 2006 |
URL: http://archimer.ifremer.fr/doc/2006/publication-1353.pdf |
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| Vandemark, D; Chapron, Bertrand; Elfouhaily, T; Campbell, J. |
| [1] New aircraft observations are presented on the range determination error in satellite altimetry associated with ocean waves. Laser-based measurements of the cross correlation between the gravity wave slope and elevation are reported for the first time. These observations provide direct access to a long, O(10 m), gravity wave statistic central to nonlinear wave theory prediction of the altimeter sea state bias. Coincident Ka-band radar scattering data are used to estimate an electromagnetic ( EM) range bias analogous to that in satellite altimetry. These data, along with ancillary wind and wave slope variance estimates, are used alongside existing theory to evaluate the extent of long-versus short-wave, O( cm), control of the bias. The longer wave bias... |
| Tipo: Text |
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| Ano: 2005 |
URL: http://archimer.ifremer.fr/doc/2005/publication-4549.pdf |
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| Vandemark, D; Mourad, Pd; Bailey, Sa; Crawford, Tl; Vogel, Camille; Sun, J; Chapron, Bertrand. |
| A research aircraft was recently flown over the Mid-Atlantic Eight during a mild cold air outbreak to sample the planetary boundary layer at low levels of 15-20 m above the sea surface. Aircraft sensors measured near-surface atmospheric turbulence and, at the same time, variations in sea surface roughness using laser and radar. The aircraft turbulence observations indicate a coherent secondary flow consistent with boundary layer roll vortices of crosswind scale 1.5-2.0 km. Modulation in measured laser and radar-inferred sea surface slope variance occurs at similar scales. Remarkable correlation is found between the radar backscatter and near-surface wind speed data, showing that the short wave slope variance is responsive to these large eddies. Associated... |
| Tipo: Text |
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| Ano: 2001 |
URL: http://archimer.ifremer.fr/doc/00000/10364/9498.pdf |
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| Elfouhaily, T; Thompson, Dr; Chapron, Bertrand; Vandemark, D. |
| In this paper we describe modifications to a previous theory for the altimeter electromagnetic bias (EM bias) of Srokosz [1986]. A major correction introduces a scaling of Srokosz's model by nonnegligible dimensionless ratios that depend on the slope variance of both long and short waves. With these modifications the EM bias is no longer simply a function of the cross skewness between surface elevation and slope but now depends on the variance ratios that represent the modulation between short and long waves, Inclusion of these ratios can reduce previous EM bias estimates by as much as 50%. Different directions for the longwave and shortwave field are also accounted for in the two-dimensional development of our approach. A radar frequency dependence... |
| Tipo: Text |
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| Ano: 2000 |
URL: http://archimer.ifremer.fr/doc/00000/10585/9395.pdf |
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| Chapron, Bertrand; Kerbaol, V; Vandemark, D; Elfouhaily, T. |
| We recall the simple statistical concept that non-Gaussian distribution peakedness results from the compounding of random processes. This idea is applied to observations and analysis of sea surface slopes as inferred using optical and microwave-scattering measurements. Our study emphasizes the importance of identifying and quantifying the distribution variance and kurtosis from observations. Data are shown to indicate consistently non-Gaussian peakedness, to indicate the need to report at least two parameters in an even order analysis, and to indicate near equivalence between radar and optical data. Physical interpretation for observed infrequent steep slopes is given via compounding statistical processes where normally distributed short-scale waves are... |
| Tipo: Text |
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| Ano: 2000 |
URL: http://archimer.ifremer.fr/doc/00000/10503/9399.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. |
| Tipo: Text |
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| Ano: 2001 |
URL: https://archimer.ifremer.fr/doc/00000/10275/10691.pdf |
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| Tran, N; Vandemark, D; Chapron, Bertrand; Labroue, S; Feng, H; Beckley, B; Vincent, Patrick. |
| Sea level determination via satellite altimetry is subject to numerous error sources. One of these is the sea state bias where changing surface wave conditions alter an altimeter's estimate of mean sea level. Recent work suggests that present day methods for correcting this bias, based solely on wave and wind information from the altimeter, may be improved if additional surface gravity wave field measurements become available. This paper tests this hypothesis by developing several new sea state bias correction models using a year long combination of Jason-1 data with wave field statistics generated from an hindcast of the WaveWatch3 ocean wave model. Each candidate model is produced in the same manner; through a nonparametric mapping between Jason-1 sea... |
| Tipo: Text |
Palavras-chave: Ocean wave model; Altimetry; Sea state bias. |
| Ano: 2006 |
URL: http://archimer.ifremer.fr/doc/2006/publication-1824.pdf |
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| Elfouhaily, T; Thompson, Dr; Chapron, Bertrand; Vandemark, D. |
| The modulation of short ocean waves by longer ones is a likely contributor to the radar altimeter's electromagnetic ranging bias (EM bias). An analytic model to account for this component of the EM bias is developed here under a two-scale two-dimensional hydrodynamic assumption. Following the principle of wave action balance, a standard hydrodynamic modulation transfer function is used to establish that the longer modulating waves enter the EM bias formulation not only through their elevation and slope variables but also through their quadratures. These latter contributions help to explain the role of long-wave slope and orbital velocity fields within the EM bias problem. Simplified analytical expressions are derived using linear Gaussian statistics for... |
| Tipo: Text |
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| Ano: 2001 |
URL: https://archimer.ifremer.fr/doc/00000/10365/9499.pdf |
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| Chen, G; Chapron, Bertrand; Ezraty, Robert; Vandemark, D. |
| More than a dozen of wind speed (U) algorithms have been proposed during the past 2 decades, as a result of a continuing effort to improve altimeter wind measurement. The progress in terms of accuracy, however, is seen to be rather slow. The reported root mean square (RMS) error of prevailing algorithms varies mostly between 1.6 and 2.0 m/s for the dominant wind regime. As far as the TOPEX altimeter is concerned, three measured quantities, namely, the radar cross sections from Ku and C band (sigma(Ku) and sigma(C)), as well as the significant wave height (H-s), have been used in previous algorithm developments, resulting in a variety of single-, dual-, and three-parameter model functions. On the basis of the finding of a banded dependency of the... |
| Tipo: Text |
Palavras-chave: Sea surface wind speed; Retrieval; TOPEX; Altimeter; Dual frequency. |
| Ano: 2002 |
URL: https://archimer.ifremer.fr/doc/00000/10224/9579.pdf |
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| Feng, H; Vandemark, D; Quilfen, Yves; Chapron, Bertrand; Beckley, B. |
| The study presents assessment of an operational wave model (Wavewatch III), focusing upon the model sensitivity to wind-forcing products. Four wind fields are used to drive the model, including the NCEP/NCAR reanalysis and three other products that assimilate various satellite wind measurements having high spatial resolution, including the QuikSCAT scatterometer. Three wave field statistics: significant wave height, mean zero-crossing wave period, and mean square slope are compared with collocated TOPEX altimeter derivatives to gauge the relative skill of differing wind-forced model runs, as well as to demonstrate an extended use of the altimeter beyond simply supplying wave height for wave model validation and assimilation. Results suggest that model... |
| Tipo: Text |
Palavras-chave: Sea state bias; Wind forcing; Scatterometer; Altimeter; Wave modeling. |
| Ano: 2006 |
URL: http://archimer.ifremer.fr/doc/2006/publication-1861.pdf |
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| Registros recuperados: 15 | |
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