Coastal development activities – such as land reclamation for harbours and dredging for navigation channels – in coral reef regions of the world can have a negative impact on the habitats of diverse marine organisms and on tourism resources. Thus, for coastal development it is extremely important to evaluate its impacts, mitigate or avoid adverse effects, and consider alternative measures.
Here, we would like to introduce an accurate method to grasp coral distribution in coral reef regions using remote sensing. Using this method, the area – of up to several tens of square kilometers – of distribution and coverage of coral reefs can be accurately grasped and analyzed.
As an example, we will report the results of our work using remote sensing technology in Okinotori Island, Japan. Okinotori Island is an atoll – a ring-shaped reef and chain of rocks made of coral – that is roughly 4.5 km from east to west and 1.7 km from north to south and has a depth shallower than 10 m. As a result of obtaining satellite images of the entire island, and of assigning the teacher data(training data) of the coral reef coverage based on image clustering and on-site survey, it was possible to analyze the coral reef distribution and coverage with 80% accuracy. Moreover, we also obtained the satellite images from over several years, and using the same analysis method as above, we were able to grasp the secular changes in coral reef coverage. This technology is an effective tool to determine quantitatively the impacts of coastal development, such as dredging for navigation channels.