This paper presents an experimental study of breaking waves in deep water, as part of the effort to further develop an eddy viscosity model for wave breaking, originally proposed by Tian, Perlin & Choi (2010, J. Fluid Mech. 655, 217–257). In the previous work, the wave breaking time, location, and breaking strength were required a priori for numerical simulations. It is our intention to make further refinement so that the improved eddy viscosity model automatically predicts wave breaking onset, determines local wave parameters at breaking onset, and forecasts post-breaking time and length scales to estimate the magnitude of the eddy viscosity. As the first part of the further development, we conducted wave breaking experiments, in which breaking wave groups are generated using both wave energy focusing and modulational instability. Surface elevations as a function of time are measured and surface profiles as a function of space during active breaking events are captured. Local wave parameters at wave breaking onset (pre-breaking parameters) are defined and determined, as well as the post-breaking time and length scales. Correlations among the parameters at breaking onset and the post-breaking scales are identified. Similarities and differences of the two types of breaking wave groups are provided and discussed.

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