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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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| 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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| 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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