Coral reef geomorphology of the Spratly Islands: A simple method based on time-series of Landsat-8 multi-band inundation maps

• Published in: ISPRS journal of photogrammetry and remote sensing 2019-11, Vol.157, p.137-154
• Main Authors: Dong, Yanzhu, Liu, Yongxue, Hu, Chuanmin, Xu, Bihua
• Format: Article
• Language: English
• Subjects: Coral reef geomorphology; Inundation map; Landsat-8 OLI; Time series analysis
• ISSN: 0924-2716; 1872-8235
• DOI: 10.1016/j.isprsjprs.2019.09.011

•A method is proposed for mapping coral reef inundation from time-series OLI images.•The reef-water reflectance contrast varying with bands and water level was adopted.•An inventory of 137 coral reefs in the Spratly Islands is established.•The extent, inundation frequency, and geomorphic zones of coral reefs are derived. Coral reefs are crucial for the maintenance of the marine ecological environment and for the sustainability of local societies and economies. The use of remote sensing methods with the support of field data has been proposed for mapping coral reef habitats and bathymetry. However, the geomorphology of coral reefs over substantial areas is poorly documented, because of the absence of field data, especially in disputed areas where in situ investigation is difficult. In this study, we developed a simple method for mapping the inundation frequency (within the penetration range of optical remote sensing) of coral reefs using time-series Landsat-8 OLI images. The method uses the reef-water reflectance contrast (which varies with bathymetry, bands, and water level) in time-series optical multi-band images in order to derive the inundation frequency and geomorphic zonation of coral reefs. The method was applied to the Spratly Islands—the largest coral reef system in the South China Sea (SCS) using more than 1,100 Landsat-8 OLI images. We established an inventory which comprises 137 reefs/sandbanks/islands, including their spatial extent, inundation frequency, and geomorphic zonation. We also interestingly found that the inundation frequency of reef flats around reclaimed areas has decreased since island construction, which probably reflects the influence of anthropogenic activity on the coral reef ecosystem. Our approach was validated by a study of the Great Barrier Reef in Australia, which demonstrated that the inundation frequency of coral reefs can serve as an indirect representation of their bathymetry.