22 December 1992 Critical theoretical review of optical techniques for short-ocean-wave measurements
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Optical techniques to measure the small-scale shape, i.e., the short wind waves of the ocean surface are theoretically reviewed. The well-known `shape from shading' and `shape from stereo' paradigms from computer vision are applied to a specular reflecting surface such as the ocean surface and used to study a variety of techniques with a common and elegant concept. The analysis shows that all techniques which have been used so far to take images of short wind waves such as Stilwell photography and various stereo techniques have significant deficiencies. Techniques based on light reflection (`shape from reflection') are basically only useful to derive wave slope statistics. A technique has been developed -- using an artificial light source to measure the 2-D probability density function of wave slope -- which is an extension of the successful sun glitter technique of Cox and Munk. Stereophotography is plagued by insufficient height resolution for small waves and, even more troublesome, by the problem that features seen in one of the images are not necessarily found in the other (correspondence problem) due to the specular nature of reflection at the water surface. Techniques based on light refraction (`shape from refraction') turn out to be most suitable to take wave slope images. They have been successfully used in the laboratory, but will be applied to the ocean in the near future.
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Bernd Jaehne, Stefan Waas, Jochen Klinke, "Critical theoretical review of optical techniques for short-ocean-wave measurements", Proc. SPIE 1749, Optics of the Air-Sea Interface: Theory and Measurement, (22 December 1992); doi: 10.1117/12.138849; https://doi.org/10.1117/12.138849


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