Abstract
Over the past decade, the use of imaging devices to perform quantitative measurements has seen wide-scale adoption and has become integral to the emerging fields of research, such as computer vision and artificial intelligence. Recent studies, published across a wide variety of fields, have demonstrated a vast number of ways through which image-based measurement systems can be used in their respective fields. A growing number of studies have demonstrated applications in coastal and ocean research. Edge detection methods have been used to measure water surface and bedform elevation from recorded video taken during wave flume experiments. The turbulent mixing of air and water, induced by the breaking waves and the runup processes, poses a particular problem for the edge-detection methods, since they rely on a sharp contrast between air and water. In this paper, an alternative method for tracking water surface, based on color segmentation, is presented. A set of experiments were conducted whereby the proposed method was used to detect water surface profiles for various types of breaking waves interacting with a rubble mound breakwater. The results were further processed to compute the surface velocity during runup. The time-history of surface velocity is shown to closely parallel the point measurements taken nearby the instrumented armor unit. These velocities can potentially serve as boundary conditions for determining the dynamic loads exerted on the armour units. Further, the image processing results are used to remove the time-varying buoyant force from the measured force acting on an individual armour unit, providing additional insight into how the forces develop over time.
Highlights
Measurements of temporal and spatial variation in water surface elevation are fundamental for understanding most ocean and coastal processes
Since the buoyancy-corrected force signal oscillated around FP = 0 N at the time when the minimum measured force was observed, it could be inferred that the measured slope-parallel force at this time was largely caused by the increase in the apparent weight of the armor unit
In this study, the authors present a detailed description of an innovative image-processing method developed to track water surface elevation under a wide range of wave conditions
Summary
Measurements of temporal and spatial variation in water surface elevation are fundamental for understanding most ocean and coastal processes. In the field of full-scale measurement of ocean waves, recent improvements to stereo image processing algorithms has enabled relatively quick and accurate ocean surface reconstruction (Bergamasco et al [1]). Observed distortions are used to determine the surface topology by calculating the displacement field with respect to the reference image, as it appears in calm water conditions This technique relies on a transparent water column with no discontinuities in order to maintain a clear line of sight to the projected image. The method presented entails a relatively simple setup procedure and offers an inexpensive means of performing detailed spatial measurements of water surface profiles in wave flume tests
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