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Due to the influences of the seawater medium, underwater surveying and mapping have not been executed effectively. When the wave propagation is taken into consideration, optical instruments might not be the best tools for investigation through the medium of water. Nevertheless, the innovation and improvement in optical equipment have contributed to reducing the limitations and costs on underwater surveys. Taiwan, as an ocean country, is a major hub for sailing ships and marine facilities. Under the guidance of the offshore wind power strategy in Taiwan, the requirement for underwater photography is increasing for underwater works. The research results can help underwater inspections of constructions, ships and ports as well as reduce the labor and costs associated with underwater works.
In terms of surveying and mapping, underwater photography provides high-resolution and efficient data collection and is used as one of the methods for underwater investigation. By analyzing the working principles of underwater photography and their applications and identifying examples of image recognition, the study provides a useful reference for future researches.
A digital camera with a waterproof shell and photographic lighting was adopted in the research to simulate various speed and distance environments and to illustrate the influences of different parameters, such as the aperture, the shutter and the film speed. The experiment was performed in a swimming pool at night to avoid the interference of light. Specific test objects were designed to evaluate the quality of the images while the image analysis software was used for further comparison.
The study found that digital camera settings have significant influence over the quality of the images. With respect to speed, the faster an object moves, the faster a shutter speed it requires. As for distance, the longer the distance of an object, either the larger the aperture size, or the higher the film speed due to the optical absorption in liquids, which is accompanied by a sharp decrease in luminance.
Although there’s similar principle in terms of adjustment method on land, just like the situation mentioned before, some differences still exist when under the sea. Factors including the decreased brightness caused by long distance, interference in light-filling caused by water impurity, and the uncertain color measurement due to the faded low color temperature light in deep underwater depth must be all considered.
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