Optical instruments for measuring surface-wave characteristics provide abetter spatial and temporal resolution than other methods, but they facedifficulties while converting the results of indirect measurements intoabsolute levels of the waves. We have solved this problem to some extent. Inthis paper, we propose an optical method for measuring the 3D power spectraldensity of the surface waves and spatio-temporal samples of the wave profiles.The method involves, first, synchronous recording of the brightness field overa patch of a rough surface and measurement of surface oscillations at one ormore points and, second, filtering of the spatial image spectrum. Filterparameters are chosen to maximize the correlation of the surface oscillationsrecovered and measured at one or two points. In addition to the measurementprocedure, the paper provides experimental results of measuringmultidimensional spectra of roughness, which generally agree with theoreticalexpectations and the results of other authors.
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