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Doppler measurements of the effects of gravity waves on wind-generated ripples

Published online by Cambridge University Press:  12 April 2006

Peter H. Y. Lee
Peter H. Y. Lee
Affiliation:
Engineering Sciences Laboratory, TRW/DSSG, One Space Park, Redondo Beach, California 90278 Present address: University of California, Lawrence Livermore Laboratory, P.O. Box 808, Mail Station L-549, Livermore, California 94550.
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Abstract

The effects of gravity waves on wind-generated ripples are studied experimentally by means of Doppler spectra obtained through microwave Bragg backscattering. The measurements were made at 9·23 GHz with incidence angles of between 45° and 55°. It is found from the Doppler frequency shift that an increase in the speed of Bragg waves (ripples) of wavelength approximately 2 cm can be detected when a gravity wave is propagated into a pre-existing wind-wave field. The Doppler frequency shift corresponds, to first order, to the orbital speed of the gravity wave. Further studies, using a conditional sampling technique, reveal that the Bragg scatterers are localized on the gravity wave's crest. The mechanism leading to the ‘localization’ is as yet unidentified. Ratios of gravity wavelength to Bragg (ripple) wavelength ranging from 13 to 35 have been studied.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 81 , Issue 2 , 24 June 1977 , pp. 225 - 240
Copyright
© 1977 Cambridge University Press

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