Abstract

The optical intensity signals from surf zone waves in a laboratory flume are analyzed using several different phase-averaging techniques, and a methodology is developed for estimating wave roller lengths and local wave dissipation. The intensity signals (i.e., phase-averaged intensity profiles) of individual breaking waves are compared with the wave profiles measured by in situ wave gauges, and the optical signal of the wave roller is shown to ramp up from the toe of the wave roller on the front face of the wave to a maximum intensity at the wave crest. The remote sensing observations capture the growth, equilibrium, and decay phases of the roller as it propagates over a fixed bed arranged in a bar/trough morphology. Next, for the regular wave conditions considered here, the local maxima of the phase-averaged intensities are shown to better indicate the initial onset of wave breaking and the occurrence of wave breaking in the bar trough, as compared to the more commonly used time-averaged mean intensity. In addition, the phase-averaged profiles are used to measure the size of the roller, and these measurements are compared to previous observations of smaller-scale rollers in equilibrium. The observed roller lengths are shown to agree with predictions from a wave roller model and to provide a new physical link between the remotely sensed signal and roller dissipation. Finally, as an example application of these new data, a simple wave height inversion model is presented that allows an estimation of surf zone wave heights from the remotely sensed roller lengths. Copyright 2009 by the American Geophysical Union.