Automated Detection of Breaking Wave Height Using an Optical Technique

Abstract

I www.JCRonline.org SHAND, T.D.; BAILEY, D.G., and SHAND, R.D., 2012. Automated detection of breaking wave height using an optical technique. Journal of Coastal Research, 28(3), 671-682. West Palm Beach (Florida), ISSN 0749-0208.Obtaining accurate information of nearshore wave characteristics including the position and height of individual breaking waves is essential to understanding the drivers of coastal processes, for engineering design and hazard prediction. Demand for such information in real time for recreational planning and hazard assessment is also high. Remote optical techniques would offer considerahle economic and spatial coverage advantages over conventional in situ instrumentation. However, optical methods for obtaining wave height information have been slow to develop and those available remain computationally expensive and require "favourable" environmental conditions. This paper presents a relatively simple yet robust approach to detecting and quantifying breaking wave position and height across a wide surf zone using a twin video camera configuration coupled with an image time-stack analysis approach. A numerical algorithm, HbSTACK, is developed and successfully tested under the environmental conditions experienced during field trials. Errors and uncertainties may arise in both the photogrammetric transformation from pixels to real-world coordinates and in the detection of wave crest and trough positions. These errors have been assessed using both field verification of the transformation model and manually detected crest and trough locations by experienced practitioners. Errors in output wave heights were thus estimated to be less than 1%.ADDITIONAL INDEX WORDS: Wave height. Wave breaking. Surf zone. Optical detection.

Remote Measurement and Prediction of Breaking Wave Parameters

“…(2) to account for this effect. The effect of wave set down has previously been assumed negligible in published studies (Shand et al, 2012). However given that the mean wave induced set down was calculated to be 0.120 m, 0.15m and 0.09m at the Hook, Sewers Peak and Tropicana Beach respectively, they were deemed significant enough to warrant further analysis.…”

“…Automatic extraction of breaking wave heights from video data is currently ongoing (de Vries et al, 2010;Shand et al, 2012), yet all published methods identify significant numbers of false positive wave height readings in the automatic algorithms. As a result, manual methods were employed in this study to identify wave crest and trough locations.…”

“…2. Corrected water depth at trough(h c ): In order to account for the fact that wave troughs are generally located below the SWL (Flick et al, 1981;Le Mehaute, 1976), Shand et al (2012) suggests using h c = h t + 1/3*H b for water depth measurements. 3.…”

“…Breaking wave studies are generally completed using laboratory flumes, large scale field research programs or in numerical environments (Goda, 2010;Rosati et al, 1990;Shand et al, 2012;Smith and Kraus, 1991). Unfortunately, laboratory investigations of breaking waves are often based on regular or monochromatic waves, rather than more realistic irregular wave systems (See Table 2) and are inherently limited by tank dimensions (Robertson et al, 2013a).…”

“…Positively, recent advances in video remote sensing have allowed for excellent spatial resolution of individual breaking position, wave height and period (de Vries et al, 2010;Gal et al, 2011;Shand et al, 2012). Through the integration of remotely sensed wave heights and positions, with site specific seafloor bathymetric surfaces and directly measured shallow water incoming wave conditions, this novel study presents a novel, low cost, robust, and repeatable method to directly measure all the necessary parameters, which affect breaking wave characteristics, from the surf zone.…”