| Summary: | 碩士 === 國立臺灣海洋大學 === 河海工程學系 === 93 === Wave heights are usually measured using various types of wave gauges with rather accurate results. On the other hand, there are also some (rather severe) limitations associated with measurements with wave gauges. Due to their surface contacting nature, errors may also occur as there are possible interactions between the waves, wave gauges and the props. This is especially true in laboratory, where all the experiments are to be carried out in reduced scales. When the spatial distribution of wave heights is to be studied, either a large quantity of wave gauges has to be deployed and measurements carried out simultaneously; or the wave gauges arrays have to be relocated with the same experiments repeated. Furthermore, wave gauges, together with their supports, may also obstruct activities such as navigation and fishing, and, as a result, there are no less reports of measuring instruments torn down by angry fishers. It should also be mentioned the deployment of surface contacting measuring devices may also be a problem. This is especially true for severe weather conditions, such as when there is surge, rainstorm, hurricane or typhoon. In passing, it should also be pointed out that the results of these instruments are only point measurements, which is insufficient for the description of the whole wave field.
Measurements of wave heights using image sequences from a CCD camera were carried out in this study. Sinusoidal, as well as uni- and directional, waves were used for the experiments. A transfer function was obtained by calibrating the magnitudes of the gray values of the images with the results of wave gauges measurements for the case of directional waves. Using this transfer function, wave heights for the case of regular waves were deducted. It is shown that the average relative errors were less than 16% for both uni- and directional waves.
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