This study aims to develop an image-based monitoring system for observations of surf zone hydrodynamics especially focusing on evolution and propagations of long wave components. Laboratory experiment was first performed to link between measured surface water fluctuations inside the surf zone and shoreline changes captured by images. Long wave components extracted from observed shoreline changes agree well with those based on measured surface water fluctuations in terms of their alongshore distributions of phases and amplitudes. The same image-based technique was applied to the field, the Seisho coast when the typhoon 1112 approached the site. It was found through the analysis that extracted longwave components were consistent with offshore wave data and showed characteristics of edge waves.
