Laboratory study of the fine structure of short surface waves due to breaking: Two‐directional wave propagation

Rozenberg, A. D.; Ritter, M.

doi:10.1029/2004jc002396

Cited by 9 publications

(4 citation statements)

References 30 publications

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“…The crests of longer breaking waves with wave number k < k b disrupt and produce mechanical perturbations of the sea surface. These mechanical perturbations generate ''freely'' propagating surface waves in all directions as reported by Rozenberg and Ritter [2005]. The rate of their generation is defined by…”

Section: Appendix a : The Main Relations Of Semiempirical Spectrum Modelmentioning

confidence: 96%

“…Anticipating that energy of waves traveling against the wind is comparably small (i.e.,

B_{u p} ≪ B_{d}

), Δ is strongly dependent on spectral level in cross‐wind directions. In these directions, the spectral level is assumed to be dominated by energy pumping from surface disturbances caused by breaking crests (see equation ), as also suggested by Rozenberg and Ritter [] from laboratory experiments. Our experimental data (Figure ) are used to infer the constant c b in the energy source

Q_{b}^{w}

defined by .…”

Section: Revised Semiempirical Spectral Modelmentioning

confidence: 99%

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Directional short wind wave spectra derived from the sea surface photography

et al. 2013

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[1] New field measurements of 2-D wave number short wind wave spectra in the wavelength range from few millimeters to few decimeters are reported and discussed. The measurement method is based on stereophotography and image brightness contrast processing. As found, the spectra of decimeter waves are almost isotropic and weakly dependent on the wind speed. Both directional anisotropy and wind sensitivity rapidly increase at wave numbers larger than 100 rad/m. These aspects are consistent with other previously reported optical and radar data. Following these new in situ measurements, a revision of a semiempirical model of short wind wave spectrum is suggested. This revised model can readily be implemented in other studies (radar scattering, air-sea interaction issues) where detailed knowledge of short wind wave spectra is crucial.Citation: Yurovskaya, M. V., V. A. Dulov, B. Chapron, and V. N. Kudryavtsev (2013), Directional short wind wave spectra derived from the sea surface photography,

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Section: Appendix a : The Main Relations Of Semiempirical Spectrum Modelmentioning

confidence: 96%

“…Anticipating that energy of waves traveling against the wind is comparably small (i.e.,

B_{u p} ≪ B_{d}

Q_{b}^{w}

defined by .…”

Section: Revised Semiempirical Spectral Modelmentioning

confidence: 99%

Directional short wind wave spectra derived from the sea surface photography

et al. 2013

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“…The role of small-scale nonlinear structures on the profile of short Gravity-Capillary Waves (GCW), often characterized as bound waves, in microwave scattering has been extensively studied in a number of wave tank experiments (see, e.g., [14][15][16][17][18][19]). It was obtained when analyzing radar Doppler spectra that the velocities of microwave scatterers can differ from the intrinsic velocities of linear free GCW with Bragg wavelengths and the scatterers can be associated with the nonlinear structures moving with the phase velocities of carrying cm-dm-scale waves [15,18,20]. Correspondingly, radar Doppler spectra can be bimodal [17,18,21] thus indicating two types of microwave scatterers-free Bragg waves and bound waves.…”

Section: Introductionmentioning

confidence: 99%

Suppression of Wind Ripples and Microwave Backscattering Due to Turbulence Generated by Breaking Surface Waves

et al. 2020

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The role of wave breaking in microwave backscattering from the sea surface is a problem of great importance for the development of theories and methods on ocean remote sensing, in particular for oil spill remote sensing. Recently it has been shown that microwave radar return is determined by both Bragg and non-Bragg (non-polarized) scattering mechanisms and some evidence has been given that the latter is associated with wave breaking, in particular, with strong breaking such as spilling or plunging. However, our understanding of mechanisms of the action of strong wave breaking on small-scale wind waves (ripples) and thus on the radar return is still insufficient. In this paper an effect of suppression of radar backscattering after strong wave breaking has been revealed experimentally and has been attributed to the wind ripple suppression due to turbulence generated by strong wave breaking. The experiments were carried out in a wind wave tank where a frequency modulated wave train of intense meter-decimeter-scale surface waves was generated by a mechanical wave maker. The wave train was compressed according to the gravity wave dispersion relation (“dispersive focusing”) into a short-wave packet at a given distance from the wave maker. Strong wave breaking with wave crest overturning (spilling) occurred for one or two highest waves in the packet. Short decimeter-centimeter-scale wind waves were generated at gentle winds, simultaneously with the long breaking waves. A Ka-band scatterometer was used to study microwave backscattering from the surface waves in the tank. The scatterometer looking at the area of wave breaking was mounted over the tank at a height of about 1 m above the mean water level, the incidence angle of the microwave radiation was about 50 degrees. It has been obtained that the radar return in the presence of short wind waves is characterized by the radar Doppler spectrum with a peak roughly centered in the vicinity of Bragg wave frequencies. The radar return was strongly enhanced in a wide frequency range of the radar Doppler spectrum when a packet of long breaking waves arrived at the area irradiated by the radar. After the passage of breaking waves, the radar return strongly dropped and then slowly recovered to the initial level. Measurements of velocities in the upper water layer have confirmed that the attenuation of radar backscattering after wave breaking is due to suppression of short wind waves by turbulence generated in the breaking zone. A physical analysis of the effect has been presented.

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“…For very small incidence angles, the rough breaking patches are expected to have a lower NRCS than the smooth regular surface (so-called contrast inversion that is not yet detected experimentally). Numerous laboratory experiments have been done to investigate wave breaking radar signatures [31][32][33][34][35][36][37][38][39][40][41], but their results are not easily applicable to the real sea surface due to the scaling of wind and wave fields in a tank.…”

Section: Introductionmentioning

confidence: 99%

Ka-Band Radar Cross-Section of Breaking Wind Waves

et al. 2021

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The effective normalized radar cross section (NRCS) of breaking waves, σwb, is empirically derived based on joint synchronized Ka-band radar and video records of the sea surface from a research tower. The σwb is a key parameter that, along with the breaker footprint fraction, Q, defines the contribution of non-polarized backscattering, NP =σwbQ, to the total sea surface NRCS. Combined with the right representation of the regular Bragg and specular backscattering components, the NP component is fundamental to model and interpret sea surface radar measurements. As the first step, the difference between NRCS values for breaking and non-breaking conditions is scaled with the optically-observed Q and compared with the geometric optics model of breaker backscattering. Optically-derived Q might not be optimal to represent the effect of breaking waves on the radar measurements. Alternatively, we rely on the breaking crest length that is firmly detected by the video technique and the empirically estimated breaker decay (inverse wavelength) scale in the direction of breaking wave propagation. A simplified model of breaker NRCS is then proposed using the geometric optics approach. This semi-analytical model parameterizes the along-wave breaker decay from reported breaker roughness spectra, obtained in laboratory experiments with mechanically-generated breakers. These proposed empirical breaker NRCS estimates agree satisfactorily with observations.

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Laboratory study of the fine structure of short surface waves due to breaking: Two‐directional wave propagation

Cited by 9 publications

References 30 publications

Directional short wind wave spectra derived from the sea surface photography

Directional short wind wave spectra derived from the sea surface photography

Suppression of Wind Ripples and Microwave Backscattering Due to Turbulence Generated by Breaking Surface Waves

Ka-Band Radar Cross-Section of Breaking Wind Waves

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