Analysis of Steep and Breaking Ocean Surface Waves Using Data from an Airborne Scanning Lidar System
Technical rept. 18 Oct 2001-17 Oct 2002
RHODE ISLAND UNIV NARRAGANSETT GRADUATE SCHOOL OF OCEANOGRAPHY
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It is clear intuitively that at high wind speeds breaking waves become increasingly important to air-sea interaction. Recently, an airborne scanning lidar system was used to obtain 2D spatial topography of ocean surface waves. Such data were used to study the wavenumber spectrum in detail. Here, we applied the wavelet transform to the 1D surface topography in the direction of mean wind. We then estimated the steep wave statistics, LAMBDATAUkappa, and compared the results with other field observations. We have shown that the wavelet analysis methodology is able to track steep wave events and give estimates of the amount of high wave slope events that cover a given area of ocean. Analysis of the results shows that high wave slope crests appear over the entire range of wavenumbers resolved, with a large amount being much shorter in wavelength than the dominant wave. At low wave slope thresholds, the total crest length is approximately independent of wind forcing for all wave fields considered. All wave fields studied have the same amount of wave crests regardless of wind forcing at low slope threshold. If the steep wave statistic is hypothesized to evolve into the breaking wave statistic at a specific wave slope threshold, comparison of LAMBDATAU kappa with previous independent measurements of the breaking wave statistic gives a wave slope threshold of 0.12. In addition, comparison of the steep wave statistic at this extrapolated wave slope threshold with independent breaking wave measurements suggest that other factors besides the wind speed control the level of the steep wave statistic.
- Physical and Dynamic Oceanography