Breaking wave measurement using Terrestrial LIDAR: validation with field experiment on the Mallipo Beach

Beach erosion and bedform change in the nearshore can be most commonly attributed to energetic breaking of waves in the surf zone among other physical facings such as winds, tides, river runoff, currents, etc. Typically, beach profile shapes develop in response to incident breaking waves. The in-situ sensors are limited in covering the entire measurement of the spatial wave transformation. In recent years, development of field survey techniques using laser has provoked various applications of 3-D laser scanners (LIDAR) to beach monitoring. Since bubbles and foam induced by wave breaking cause laser beams to be back-scattered, the Terrestrial LIDAR can also detect the beam signals reflected by breaking and broken waves in the nearshore. In this study, the Terrestrial LIDAR was used to survey height of breaking waves across the surf zone on the Mallipo Beach, in the west coast of Korea. In addition, the measurements by the Terrestrial LIDAR were compared with optical records of sea surface oscillations along a vertical staff. The spatial resolution was set to approximately 2 cm at a distance of 100 m from the LIDAR location installed foreshore. The sampling time interval was 0.33 s. As a result, crest elevations of 26 waves incoming in the surf zone were indentified by the Terrestrial LIDAR. Meanwhile, the concurrently recorded optical data showed that only 24 breaking waves passed by the staff. The difference is explained that two of the LIDAR-detected wave crests didn’t break but propagated under foam produced by the precedent breaking wave. The variation of the elevation of the breaking wave crests across the surf zone detected by the Terrestrial LIDAR can be further used to investigate the characteristics of coastal processes.