Accurate measurement of six Degree Of Freedom small-scale ship motion through analysis of one camera images     

A. Benetazzo 《Ocean Engineering》2011,38(16):1755-1762

A new six Degree Of Freedom (6DOF) motion measurement technique for small-scale physical models of floating bodies is presented, based on analysis of image sequence from one camera. The proposed system consists of one camera and one target: the method estimates the 3-D rigid motion following the time evolution of the target of known pattern fixed to the moving body and framed by the camera. In particular, the rotation matrix and the translation vector of the 3-D rigid motion between initial still position and a generic moved position are calculated by assuming the existence of a planar homography between the camera CCD plane and the plane passing through the flat target surface. Geometrical relationship allows one the calculation of wanted 6DOFs for every point of the modeled body. In the paper, the method is mathematically presented in terms of equations of rigid motion with its associate accuracies. The image-based technique is illustrated on some tests carried out in an experimental multipurpose wave basin.  相似文献   

Numerical modeling of space-time wave extremes using WAVEWATCH III     

Francesco Barbariol  Jose-Henrique G. M. Alves  Alvise Benetazzo  Filippo Bergamasco  Luciana Bertotti  Sandro Carniel  Luigi Cavaleri  Yung Y. Chao  Arun Chawla  Antonio Ricchi  Mauro Sclavo  Hendrik Tolman 《Ocean Dynamics》2017,67(3-4):535-549

A novel implementation of parameters estimating the space-time wave extremes within the spectral wave model WAVEWATCH III (WW3) is presented. The new output parameters, available in WW3 version 5.16, rely on the theoretical model of Fedele (J Phys Oceanogr 42(9):1601-1615, 2012) extended by Benetazzo et al. (J Phys Oceanogr 45(9):2261–2275, 2015) to estimate the maximum second-order nonlinear crest height over a given space-time region. In order to assess the wave height associated to the maximum crest height and the maximum wave height (generally different in a broad-band stormy sea state), the linear quasi-determinism theory of Boccotti (2000) is considered. The new WW3 implementation is tested by simulating sea states and space-time extremes over the Mediterranean Sea (forced by the wind fields produced by the COSMO-ME atmospheric model). Model simulations are compared to space-time wave maxima observed on March 10th, 2014, in the northern Adriatic Sea (Italy), by a stereo camera system installed on-board the “Acqua Alta” oceanographic tower. Results show that modeled space-time extremes are in general agreement with observations. Differences are mostly ascribed to the accuracy of the wind forcing and, to a lesser extent, to the approximations introduced in the space-time extremes parameterizations. Model estimates are expected to be even more accurate over areas larger than the mean wavelength (for instance, the model grid size).  相似文献   

Relative current effect on short wave growth     

Guimarães  Pedro Veras  Ardhuin  Fabrice  Perignon  Yves  Benetazzo  Alvise  Bouin  Marie-Noëlle  Garnier  Valerie  Redelsperger  Jean-Luc  Accensi  Mickael  Thomson  Jim 《Ocean Dynamics》2022,72(8):621-639

Ocean Dynamics - Short waves growth is characterized by nonlinear and dynamic processes that couple ocean and atmosphere. Ocean surface currents can have a strong impact on short wave steepness and...  相似文献   

Measurements of short water waves using stereo matched image sequences     

Alvise Benetazzo   《Coastal Engineering》2006,53(12):1013-1032

Image analysis techniques are used for retrieving water surface elevation fields spatially and temporally from CCD-images and CCD-image-sequences. The technique proposed herein utilizes binocular stereogrammetry to recover topographic information from a sequence of synchronous, overlapping video images. The method used differs from the traditional stereo-photogrammetric analysis of a single stereo-pair because the use of video allows for a continuous sequence of stereo-images to be digitally sampled and analyzed. For data acquisition two synchronized progressive-scan cameras were used.A partially supervised 3-D stereo system (called WASS, Wave Acquisition Stereo System) is shown here. It is used to reconstruct the 3-D shape of water surface waves, acquired at frame rate, with small computational time needed. The stereo method is presented, including the derivation of a relationship relating the geometry of the stereo rig and the expected errors. Finally, the 3-D calculated scattered points give the complete spatio-temporal distribution of the water surface elevations. The measurable length-scales depend on the pixel resolution, the triangulation accuracy, and the acquisition frame rate. Limitations in the stereo measurements are also discussed.Two experiments to test and to demonstrate the system took place: one on the Venice lagoon, north of the city of Venice in September 2004 and the second on the coast of California at San Diego in December 2005. For the second experiment, qualitative and quantitative intercomparisons of the stereo-matching and in-situ sensor measurements are presented. All the measurements of water surface waves indicate that the proposed approach is both accurate and applicable for measuring water surface waves. Moreover, shape estimates are accurately and extremely dense both in space and time, and the remote location of the instruments alleviates some difficulties associated with in situ instrumentation.  相似文献