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International Symposium on Imaging in Transport Processes.
May, 25-29, 1992, Athens, Greece

DOI: 10.1615/ICHMT.1992.IntSympImgTranspProc


ISBN Print: 978-1-56700-012-2

IMAGE SEQUENCE ANALYSIS OF OCEAN WIND WAVES

pages 257-268
DOI: 10.1615/ICHMT.1992.IntSympImgTranspProc.250
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RESUMO

Almost no measurements of the small-scale spatial structure of the ocean surface are presently available. New optical techniques, which take image sequences of the slope of the short wind-waves, have been used recently in wind-wave facilities and will soon be available for oceanic field measurements. Here, we discuss various image processing techniques for wave slope image sequences which allow for a deeper insight into the kinematics and dynamics of the wind-driven ocean surface, specifically, energy input by wind, non-linear wave-wave interaction, phase speed, interaction with the turbulent shear flow, and wave dissipation. These techniques are demonstrated using images recently taken in the large wind-wave facility of Delft Hydraulics, the Netherlands.
Short ocean wind waves play a major role in small-scale air-sea interaction processes. The energy put by the turbulent wind field into wind waves is another channel, besides direct shear stress, by which mechanical energy is transferred from the atmosphere into the ocean. Generally speaking, the shape of the ocean surface mirrors in one way or the other the small-scale exchange processes at the water surface. In contrast to a rigid surface, a free water surface has an additional degree of freedom. It reacts to the stress and pressure fluctuations applied to it not only by the formation of a turbulent boundary layer but also by the generation of waves. This is the reason for the complexity of small-scale air-sea exchange processes. Waves of different scales interact with each other and the turbulent shear layer. The change in the shape of the water surface provides a feedback mechanism which alters boundary layer profiles in the air and water phases and, in turn, influences the exchange processes significantly.

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