Analysis and Interpretation of Frequency–Wavenumber Spectra of Young Wind Waves

Type Article
Date 2015-10
Language English
Author(s) Leckler Fabien1, Ardhuin FabriceORCID2, 3, Peureux Charles2, 3, Benetazzo Alvise4, Bergamasco Filippo5, Dulov Vladimir6
Affiliation(s) 1 : Serv Hydrog & Oceanog Marine, Brest, France.
2 : IFREMER, Ctr Brest, Lab Oceanog Spatiale, Plouzane, France.
3 : UMR 6523 CNRS IFREMER IRD UBO, Lab Phys Oceans, Plouzane, France.
4 : Natl Res Council CNR ISMAR, Inst Marine Sci, Venice, Italy.
5 : Univ Ca Foscari Venezia, Venice, Italy.
6 : Inst Marine Hydrophys, Sebastopol, Russia.
Source Journal Of Physical Oceanography (0022-3670) (Amer Meteorological Soc), 2015-10 , Vol. 45 , N. 10 , P. 2484-2496
DOI 10.1175/JPO-D-14-0237.1
WOS© Times Cited 55
Keyword(s) Circulation, Dynamics, Waves, oceanic, Observational techniques and algorithms, Remote sensing
Abstract The energy level and its directional distribution are key observations for understanding the energy balance in the wind-wave spectrum between wind-wave generation, nonlinear interactions, and dissipation. Here, properties of gravity waves are investigated from a fixed platform in the Black Sea, equipped with a stereo video system that resolves waves with frequency f up to 1.4 Hz and wavelengths from 0.6 to 11 m. One representative record is analyzed, corresponding to young wind waves with a peak frequency fp = 0.33 Hz and a wind speed of 13 m s−1. These measurements allow for a separation of the linear waves from the bound second-order harmonics. These harmonics are negligible for frequencies f up to 3 times fp but account for most of the energy at higher frequencies. The full spectrum is well described by a combination of linear components and the second-order spectrum. In the range 2fp to 4fp, the full frequency spectrum decays like f−5, which means a steeper decay of the linear spectrum. The directional spectrum exhibits a very pronounced bimodal distribution, with two peaks on either side of the wind direction, separated by 150° at 4fp. This large separation is associated with a significant amount of energy traveling in opposite directions and thus sources of underwater acoustic and seismic noise. The magnitude of these sources can be quantified by the overlap integral I(f), which is found to increase sharply from less than 0.01 at f = 2fp to 0.11 at f = 4fp and possibly up to 0.2 at f = 5fp, close to the 0.5π value proposed in previous studies.
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