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3rd ERS SYMPOSIUM Florence 97 - Abstracts and Papers
Scattering by the ocean surface under non-fully developed state : two scale model validation.
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Scattering by the Ocean Surface under Non-Fully Developed State : Two Scale Model Validation and Inversion of Radar Measurements.

David Lemaire, Piotr Sobieski and Albert Guissard Université Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium. Tel :+32 10 478 082 - Fax : +32 10 472 089

E-mail : dlemaire@tele.ucl.ac.be

URL : http://www.tele.ucl.ac.be

Abstract and Conclusion

A new full-range amplitude spectrum is derived for sea surface waves. Its high frequency part is considered directly related to the wind friction velocity and is updated using very recent wavenumber spectra measurements. Its gravity part represents waves independently of their origin. An expression of the spectral exponent is derived for the gravity range, depending on the fetch and the significant slope. For ocean-like values of those parameters, this exponent converges to commonly observed ones. Finally, the amplitude factor of the gravity spectrum is constrained to keep consistency with the surface significant slope.

The spectrum is validated through C and Ku bands backscattering coefficient simulations for large ranges of wind speeds and incidence angles, using a two-scale model and open ocean values for the fetch and the significant slope. The wind speed has been related to the wind friction velocity assuming neutral conditions. This validation procedure yields results consistent with assimilated ground-truth data and empirical models, in both altimeter and scatterometer configurations.

Finally, from the developed models, an inversion algorithm is implemented. Collocated TOPEX altimeter and ERS1 scatterometer data are then inverted and the results compared with corresponding ECMWF wind fields. The use of TOPEX measurements seems not to allow the retrieval of the wind together with the significant slope. For the other cases, the results obtained are of a good quality. The combination altimeter-scatterometer is mainly useful for the retrieval of the significant slope, since for wind retrieval only, the results obtained are roughly identical to those obtained with the scatterometer alone. Assuming that ECMWF fields are correct, the inversion of ERS1 scatterometer data yields particularly good results. The slope of linear regressions is improved compared to standard products provided by CMOD-IFR2 algorithm. Futhermore, it is also important to mention that the coherence between the retrieved and ECMWF winds is maintained for very strong winds (up to 25m/s).

References

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[3] R.E. Glazman, M.A. Srokosz, 1992, Equilibrium wave spectrum and sea state bias in satellite altimetry, Journal of Physical Oceanography, Vol 21, Nr 11, pp 1609-1621.

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[6] T. Hara, E.J. Bock, D. Lyzenga, 1994, In situ measurements of capillary-gravity wave spectra using a scanner slope gauge and microwave radars, J. Geoph. Res., Vol 99, Nr C6, pp 12,593-12,602.

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[9] P.A. Hwang, S. Atakturk, M.A. Sletten, D.B. Trizna, 1996, A study of the wavenumber spectra of short water waves in the ocean, Journal of Physical Oceanography, Vol 26, pp 1266-1285.

[10] B. Jähne, K.S. Riemer, 1990, Two-dimensional wavenumber spectra of small-scale water surface waves, J. Geoph. Res., Vol 95, Nr C7, pp 11,531-11,546.

[11] J. Klinke, B. Jähne, 1992, 2D wavenumber spectra of short wind waves - results from wind wave facilities and extrapolation to the ocean, Optics of the Air-Sea Interface, Vol 1749, pp 245-257.

[12] H. Liu, J. Lin, 1982, On the spectra of high-frequency wind waves, J. Fluid Mech., Vol 123, pp 165-185.

[13] P.C. Liu, 1988, What is the slope of equilibrium range in the frequency spectrum of wind waves, 21th Coastal Engineering Conf., Vol 2, pp 1045-1057.

[14] H. Mitsuyasu, 1977, Measurement of the high-frequency spectrum of ocean surface waves,Journal of Physical Oceanography, Vol 7, pp 882-891.

[15] Y. Toba, 1973, Local balance in the air-sea boundary processes. Part III : On the spectrum of wind waves, Journal of the Oceanographical Society of Japan, Vol 29, pp 209-220.


David Lemaire Mon Mar 24 17:01:48 MET 1997

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry