EVALUATION OF THE EFFECTIVENESS OF CORAL REEFS MAPPING IN KERAMA ISLANDS BY SATELLITE-BASED CLASSIFICATION

摘要

Coral reefs are referred to as "tropical rainforests of the sea" to provide for richness of biological diversity. However, coral reefs are seriously degrading for global warming effects. In Japan, Kerama Islands are 20 to 40 km west of the main Okinawa prefecture and known for abundant coral reefs in the world. Coral reefs mapping is important to spatially interpret the current habitats. Until now, coral reefs mapping is performed by visual interpretation. The purpose of study is to understand availability if satellite-based remote sensing technique is substituted in the near future. The study introduces how to map coral reefs distribution by satellite image processing and evaluate the map with the ground truth data and the visible interpretation method. In the error matrix utilizing all 93 ground survey points, the overall accuracy was achieved 78%, which indicated similar trend with the ground truth. In error matrix with rasterized visible interpretation map, the overall accuracy was 55%. The reason is why "less than 5% Coral cover on Sand and Rock bottom" and "5-50% Coral cover" were caused misclassification in the offshore. However, the inshore area in the classification result is able to show coral structure in more details, and the image was able to see the deeper depth by the water column correction. Therefore, satellite-based remote sensing is appreciable to use the coral reefs mapping. In the future, we need to consider the classification class types and pro-processing to achieve high accuracy.