Abstract
A simple video-based system has been developed for depth estimation based on wave propagation characteristics. A numerical simulation of a long-crested monochromatic wave propagating over a beach with straight and parallel contours is used for testing the depth inversion system. An oblique video, simulating field conditions, is recorded, digitized and rectified for its further analysis. Pixel intensity time series from a virtual array in the rectified images are analyzed using the depth estimation technique developed by Stockdon and Holman. The linear dispersion equation is applied for depth estimation at every cross-shore position and the resulting values are compared with the depth values used to feed the numerical model. Error analysis confirms good performance for depth estimation using this video-system for completely controlled conditions in small-scale experiments. The relative depth estimation error for this idealized case is 2.3%. This accuracy is explained by the use of a linear model for the wave propagation simulation. The methodology proposed here allows the testing of a new video-system and separation of errors resulting from the depth inversion algorithm from those inherent to photogrammetry techniques in small areas. The use of this system could easily be extended for physical models and field studies.
Highlights
Knowledge of sea bottom topography is of great importance in coastal engineering[1]
The purpose of this study is to develop and validate a simple video-based system for depth estimation in an idealized planar beach
The errors on the video-based water depth estimation for the wave propagation simulation are associated with the image rectification process and with the use of only the first mode of the Complex Principal Component Analysis (CPCA) for wave number estimation
Summary
Knowledge of sea bottom topography is of great importance in coastal engineering[1]. Often studies which have great environmental impact require data of the spatial and temporal evolution of the sea bottom in order to quantify the proportion and direction of sediment transport. The use of a planar projective transformation method for image rectification presented some advantages over other methods, in that it does not require any information about the intrinsic and extrinsic parameters of the camera, since they are implicit in the solution of the system of (2) For this reason the method was deemed suitable for small-scale experiments due to the simplicity of surveying a large number of Ground Control Points (GCPs). Knowing the wave number components and the wave frequency, the water depth h(x,y), can be estimated as: Case 2: Large scale test: Image rectification from a multiple-camera system at El Puntal Spit (Santander, Spain) was used to test the rectification algorithm performance under field conditions. Holland et al.[4] presented a method that requires two GCPs, or even one GCP, given the intrinsic parameters of the camera
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