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Proceedings Paper

Two-dimensional wave number spectra of short wind waves: results from wind-wave facilities and extrapolation to the ocean
Author(s): Jochen Klinke; Bernd Jaehne
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Paper Abstract

A detailed study of 2-D wave number spectra of short water surface waves is presented. Using a refraction-based optical technique either the along-wind or the cross-wind slope is visualized in image sectors of up to 30 X 40 cm2. The resolution of the images is high enough (down to 1/3 mm) to resolve even the smallest capillary waves. The measurements were performed in the wind/wave facility of the IMST (University of Marseille, France) at 5 through 29 m fetch, the Delft wind wave flume (The Netherlands) from 6 to 100 m fetch, and the 4 m-diameter circular wind/wave facility of the Institute for Environmental Physics at the University of Heidelberg (Germany). A first preliminary analysis of the data is given. The angular dispersion of the waves is most sensitively influenced by the geometry of the facility, especially the width of the water channel. Therefore, it is hardly possible to extrapolate the measured angular dispersion of the waves to the ocean. The unidirectional and along-wind wave number spectra, however, show clear trends which allow for an extrapolation to the ocean. At high fetches and wind speeds, the spectral densities for the wave height are proportional to (kappa) -3.5 well into the capillary wave region until a sharp and almost wind speed independent cutoff occurs at (kappa) approximately equals 1100 m-1 ((lambda) approximately equals 0.6 cm). The increase of the spectral densities with friction velocity depends both on wave number and fetch. While the spectral density for small gravity waves depends only weakly on the friction velocity, it increases strongly at higher wave numbers. Generally, this steepness is smaller at higher fetches.

Paper Details

Date Published: 22 December 1992
PDF: 13 pages
Proc. SPIE 1749, Optics of the Air-Sea Interface: Theory and Measurement, (22 December 1992); doi: 10.1117/12.138853
Show Author Affiliations
Jochen Klinke, Univ. of Heidelberg (Germany)
Bernd Jaehne, Scripps Institution of Oceanography (United States)

Published in SPIE Proceedings Vol. 1749:
Optics of the Air-Sea Interface: Theory and Measurement
Leland Estep, Editor(s)

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