Measuring Breaking Waves Heights Using Video

Abstract

The dominant process for the transfer of mass and energy into the surf zone is wave breaking. Typhoons and heavy storms create extreme conditions wherein storm surge, coastal setup, and large swell combine to cause flooding and direct damage to coastal infrastructure via wave energy. The majority of research in the nearshore has been conducted under moderate conditions, presumably due to the logistical difficulties of maintaining instrumentation under storm conditions, as well as the infrequency of such events. This paper describes in detail a method for remotely measuring breaking wave heights over a range of environmental conditions using video, and its on-going application in a high-energy nearshore environment. A 640x480 pixel analog surveillance camera, with a view of approximately 0.04 km2 and a mean horizontal resolution of 0.5 m, was affixed to a rigid structure overlooking a uniform shallow reef near Ipan, Guam. Image data were collected at 2 Hz along a shore-normal transect continuously for three months. Broken wave heights, offshore and secondary swell wavelengths and velocities, and wave refractions are successfully resolved using this technique. A novel feature-detection algorithm was developed for accurately and autonomously generating a time series of broken wave heights. Initial comparisons between video measurements of breaking wave height show a strong correspondence with in-situ pressure sensor data.