Phase Speed and Angle of Breaking Waves Measured with Video Techniquesby T. C. Lippmann, Oregon State Univ, Corvallis, United States,
R. A. Holman, Oregon State Univ, Corvallis, United States,
Abstract: The phase speed and incident angle of breaking surface gravity waves in the surf zone are measured using video processing techniques. The analysis of video data follows two lines. The first focuses on the time series of image intensity at points corresponding to known surf zone locations, and comparisons with in situ pressure gages. Celerity spectra of video and pressure data from a single location show similar results. Wavenumber spectra at the peak frequency from two longshore arrays of intensity time series compares favorably with similarly spaced current meter data. The second part of the analysis focuses on individual waves. A method for identifying breaking waves with video is presented. Analysis of travel-time of individual breakers estimated from 2 pairs of spatially separated sensors in an orthogonal array is done in both the time domain, using the cross-covariance function, and the frequency domain, via the phase spectrum. Phase speeds and wave angles of individual waves are then computed using the time lag and sensor separation. Results are similar for each method. Mean values of phase speeds and wave angles are consistent with first order shoaling theory.
Subject Headings: Breaking waves | Imaging techniques | Gravity waves | Wave shoaling | Surface waves | Surf zones | Wave measurement
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