Coastal bathymetry analysis of Saleh Bay Indonesia, using the band ratio method on Sentinel-2 Imagery to support coral reef conservation

Abstract Accurate information on shallow water bathymetry and coral reef distribution is essential for coastal management in tropical marine environments. This study evaluates Sentinel-2 imagery for mapping bathymetry and coral reef features in Saleh Bay, Indonesia, using the Stumpf band ratio algorithm, the Lyzenga method, and datasets from the Allen Coral Atlas. Bathymetric estimates derived from Sentinel-2 imagery using the Stumpf algorithm were validated against reference depth data from the Indonesian National Bathymetry dataset (BATNAS), while reef related classes were compared with coral reef extent and geomorphic maps from the Allen Coral Atlas. The Stumpf based model showed strong agreement with BATNAS reference depth data, achieving an R² of 0.79 and an RMSE of 1.73 m. Depth estimates were obtained to approximately 27 m under the prevailing optical water conditions of the study area. The comparison of reef datasets reveals complementary spatial patterns. The Allen Coral Atlas delineates narrow reef zones along coastlines and island margins, whereas the Lyzenga based classification identifies broader shallow water areas and is more sensitive to local variations in benthic substrates. Results indicate that coral reef distribution in Saleh Bay is closely associated with shallow coastal environments, particularly at depths shallower than 10 m, including reef flats, island platforms, and upper reef slope zones. Integrating satellite derived bathymetry, geomorphic reef data, and benthic classification improves the interpretation of coral reef spatial patterns in tropical coastal waters. This approach supports marine spatial planning, habitat monitoring, and coral reef conservation in data limited regions.