Microwave backscatter from the sea surface: Bragg scattering by short gravity waves

1994 ◽  
Vol 99 (C4) ◽  
pp. 7929 ◽  
Author(s):  
E. M. Poulter ◽  
M. J. Smith ◽  
J. A. McGregor
Keyword(s):  
Gravity Waves ◽  
Sea Surface ◽  
Bragg Scattering ◽  
Microwave Backscatter

An Investigation of Non-Bragg Scattering from the Sea Surface

2001 ◽  
Author(s):  
Ellen E. Lettvin ◽  
William J. Plant
Keyword(s):  
Sea Surface ◽  
Bragg Scattering

Wind-generated gravity-capillary waves: laboratory measurements of temporal growth rates using microwave backscatter

1975 ◽  
Vol 70 (3) ◽  
pp. 417-436 ◽  
Author(s):  
T. R. Larson ◽  
J. W. Wright
Keyword(s):  
Growth Rates ◽  
Water Waves ◽  
Friction Velocity ◽  
Capillary Waves ◽  
Spectral Amplitude ◽  
Bragg Scattering ◽  
Laboratory Measurements ◽  
Wind Speeds ◽  
Tightly Coupled ◽  
Microwave Backscatter

The growth rates of wind-induced water waves at fixed fetch were measured in a laboratory wave tank using microwave backscatter. The technique strongly filters out all wavenumber component pairs except for a narrow window at the resonant Bragg scattering conditions. For these waves the spectral amplitude was measured as a function of the time after a fixed wind was abruptly started. The radars were aligned to respond to waves travelling in the downwind direction at wavelengths of 0·7-7 cm. Wind speeds ranged from 0·5 to 15 m/s. Fetches of 1·0, 3·0 and 8·4 m were used. In every case, the spectral amplitude initially grew at a single exponential rate β over several orders of magnitude, and then abruptly ceased growing. No dependence of the growth rate on fetch was observed. For all wavelengths and wind speeds the data can be fitted by \[ \beta (k,u_{*},{\rm fetch})=f(k)\,u^n_{*}, \] with n = 1·484 ± 0·027. Here u* is the friction velocity obtained from vertical profiles of mean horizontal velocity. For each wind speed, f(k) had a relative maximum near k = kn ≃ 3·6 cm−1. Rough estimates of β/2ω, where ω is the water wave frequency, and of the wind stress supported by short waves indicate that the observed growth rates are qualitatively very large. These waves are tightly coupled to the wind, and play a significant role in the transfer of momentum from wind to water.

The propagation of short surface waves on longer gravity waves

1987 ◽  
Vol 177 ◽  
pp. 293-306 ◽  
Author(s):  
M. S. Longuet-Higgins
Keyword(s):  
Gravity Waves ◽  
Wave Breaking ◽  
Surface Wind ◽  
Short Wave ◽  
Finite Amplitude ◽  
Sea Surface ◽  
Wind Drift ◽  
Method Of Calculation ◽  
Linearized Theory ◽  
The Mean

To understand the imaging of the sea surface by radar, it is useful to know the theoretical variations in the wavelength and steepness of short gravity waves propagated over the surface of a train of longer gravity waves of finite amplitude. Such variations may be calculated once the orbital accelerations and surface velocities in the longer waves have been accurately determined – a non-trivial computational task.The results show that the linearized theory used previously for the longer waves is generally inadequate. The fully nonlinear theory used here indicates that for longer waves having a steepness parameter AK = 0.4, for example, the short-wave steepness can be increased at the crests of the longer waves by a factor of order 8, compared with its value at the mean level. (Linear theory gives a factor less than 2.)The calculations so far reported are for free, irrotational gravity waves travelling in the same or directly opposite sense to the longer waves. However, the method of calculation could be extended without essential difficulty so as to include effects of surface tension, energy dissipation due to short-wave breaking, surface wind-drift currents, and to arbitrary angles of wave propagation.

scholarly journals Bragg scattering of long flexural gravity waves by an array of submerged trenches and the analysis of blocking dynamics

AIP Advances ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 115308
Author(s):  
S. C. Barman ◽  
S. Boral ◽  
T. Sahoo ◽  
Michael H. Meylan
Keyword(s):  
Gravity Waves ◽  
Bragg Scattering ◽  
Flexural Gravity Waves
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