Directional and geometric characteristics of breaking-wave whitecaps in a laboratory wave basin

Abstract The directional characteristics of wave breaking are essential for understanding surface wave dynamics. However, the directional representation of breaking in spectral wave models remains poorly constrained by experimental observations. This study analyzes breaking waves using image processing of whitecaps to extract crest-normal directions and geometric properties. The lower boundary of each active whitecap was used as a proxy for the local breaking-wave crest, with the associated direction defined as normal to the estimated crest. Whitecaps were identified and tracked across multiple cases, and the distribution of their crest-normal directions was compared with the directional spectrum of the wave field. The results indicate that narrower spectral distributions are associated with more focused distributions of crest-normal directions, demonstrating a correspondence between wave directional spreading and the directional organization of breaking crests. Geometric analysis further indicates a power-law relationship between whitecap area and crest length, which warrants further investigation across a broader range of conditions. These findings provide insight into the relationship between breaking-crest geometry and the directional properties of the wave spectrum.