| Summary: | 碩士 === 國立成功大學 === 海洋科技與事務研究所 === 105 === The main purpose of this study is to estimate offshore floating oyster raft numbers by analyzing the sea surface images that are acquired with nautical X-band radar. The softwares provided by ArcGIS were applied to identifying radar echoes of oyster rafts with an image classification tool, and then to estimating amount of oyster rafts with a spatical analysis tool. Finally, statistics were compared against and used for error analysis for the information derived from the aerial photographs, which were obtained by an unmanned aerial vehicle.
The strength of the radar echo that bounces back from oyster rafts fluctuated when the distance between the oyster rafts and the radar station changed. The shorter the distance, the stronger the echo and the better recognizability became; the further the distance, the weaker the echo and the worse recognizability became. In order to reduce the effect of distance on image clustering analysis, we divided the total area into five independent identification zones based on the distances between the oyster rafts and the radar station. The images of the oyster rafts closest to the radar station were recognized more efficiently, and the estimated number and distribution of these oyster rafts then became closer to how they were shown on the aerial photograph. The estimated number of oyster rafts located in the nearest area (within 225 meters), was 94 percent matched with the number shown in the aerial photograph. The estimated number of 1000-meter-away oyster rafts only reached more than 60 percent of the number shown on the aerial photograph because the radar echoes became too weak from there.
The advantage of using X-band radars for the quantitative monitoring of oyster rafts located in the shallow sea area is that real-time and uninterrupted monitoring can be conducted despite bad weather.Therefore, the placement of oyster rafts can be automatically monitered in a long-term and continuous manner in order to efficiently manage offshore oyster farming. This study has potential expected results on providing more precise estimation of oyster yield, assessment of economic loss after disasters, and evaluation of the impact of the oyster farming on the marintime environment, as well as serving as a basis for the aid payments issued after natural disasters.
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