  An experimental study of the dynamics and droplet production in three
mechanically generated plunging breaking waves is presented in this two-part
paper. In the present paper (Part 1), the dynamics of the three breakers are
studied through measurements of the evolution of their free surface profiles
during 10 repeated breaking events for each wave. The waves are created from
dispersively focused wave packets which are generated by a highly accurate
programmable wave maker. The wave maker motions that create the three breakers
differ primarily only by small changes in their overall amplitude. Breaker
profiles are measured with a cinematic laser induced fluorescence technique
covering a streamwise region of approximately one breaker wavelength and over a
time of 2.6 breaker periods. The 10 repeated sets of breaker profiles are
spatially and temporally aligned to the location and time of jet impact. The
aligned profile data is used to create spatio-temporal maps of the ensemble
average surface height and the standard deviation of both the local normal
distance and the local arc length relative to the instantaneous mean profile.
It is found that the mean and standard deviation maps contain strongly
correlated localized features and indicate that the transition from laminar to
turbulent flow is a highly repeatable process. Regions of high standard
deviation include the splash created by the plunging jet impact and subsequent
splash impacts at the front of the breaking region as well as the site where
the air pocket entrained under the plunging jet at the moment of jet tip impact
comes to the surface and pops on the back face of the wave. In Part 2, these
features are used to interpret various features of the distributions of droplet
number, diameter and velocity.
