Vision for waves

For almost a century, researchers have tried to use imaging techniques for spatial measurement of short wind waves. A comparative survey of these techniques is given. The early techniques were all based on stereo imaging, while more recently shape from reflection (Stilwell photography) and shape from refraction techniques such as laser scanning slope gauges and imaging surface gradient methods have been used by a number of researchers. Theoretical analysis and experimental evidence clearly show that the shape from refraction techniques are the most suitable method for spatial measurements of short gravity and capillary waves. Although these techniques give an unprecedented insight into the dynamics of short wind waves, only digital image processing techniques open the way for a quantitative analysis. A number of techniques beyond Fourier analysis including scale-space analysis, Hilbert transformation, and various advanced filter techniques are envisioned to have a major impact in the near future.