Sentinel-2 satellite image application for establishing a coral reef distribution map in Bai Tu Long National Park, Quang Ninh Province, Vietnam

Coral reef ecosystems are crucial in coastal areas, providing valuable ecosystem services to humans. They are highly biodiverse and act as significant carbon sinks. Coral reef ecosystem conservation is a pressing issue for the world's most vulnerable ecosystems. Mapping coral reef ecosystems using satellite imagery enables informed decision-making for their restoration and protection, facilitating effective management strategies. With the help of machine-learning models and object-based image analysis (OBIA), this study constructed a map showing where coral reef ecosystems are found in Bai Tu Long National Park, Vietnam. The map was created using Sentinel-2 satellite images. The classification results revealed an overall accuracy (OA) of 91.70%, corresponding to a kappa coefficient of 0.89. The highest spectral reflection characteristic for coral reef ecosystems is in the blue spectral band and the lowest is in the SWIR2 spectral band. To understand the composition of these reefs, field surveys were conducted. The results of field surveys revealed that the coral reef ecosystem in Bai Tu Long National Park included nine families, 20 varieties and 32 species. Finally, this study has shown that a map of the distribution of coral reef ecosystems via satellite images and an object-based image analysis method combined with a machine-learning model is a valuable tool for the management and conservation of coral reef ecosystems. The findings of this study play an important role in providing data for the restoration and conservation of coral reef ecosystems in coastal areas.