南海珊瑚礁光学浅水海域多光谱遥感水深反演

海洋水深信息对研究珊瑚礁海域资源与环境具有重要作用。南海珊瑚礁海域测深数据受多种条件限制施测困难，在时间与空间方面数量非常有限。文章针对南海岛礁海域以I类水体为主导的海水光学特性，以南沙群岛库归沙洲海域为例，使用Sentinel-2多光谱卫星遥感影像和同期过境的MODIS卫星数据，构建底质光谱，采用半分析半经验模型计算海水表面遥感反射率与海水叶绿素浓度，通过对数比值模型进行该地区光学浅水海域遥感水深反演分析，并进一步通过多时相反演水深融合提升精度。经与多波束实测水深数据验证，研究区域反演水深总体均方根误差和平均相对误差分别为2.68 m 和9.99%。该方法通过叶绿素浓度推演部分海水光学特性，可以从多光谱卫星影像中快速获取南海岛礁光学浅水海域初步水深信息，供相关海洋领域分析与应用。

Water Depth Inversion from Multispectral Imagery over OpticallyShallow Waters of Coral Reefs in South China Sea

The bathymetry information is fundamental to characterizing the coral reef environment and natural resources of the South China Sea. However, the data on bathymetry is incomplete and spatially limited due to the difficulty of obtaining accurate and well-distributed soundings in remote oceans. In light of the inherent optical properties (IOP) of the coral reefs dominated by case I water, we used Sentinel-2 images and MODIS data acquired on the same date to derive bathymetry, taking Kugui Reef as a case study. First, we constructed reflectance spectra for different benthic substrates in optical shallow waters, and the remote sensing reflectance and chlorophyll (Chl-a) concentrations were estimated by a semi-analytical model. Then we adopted the ratio algorithm model to carry out the water inversion. Finally, the water depths derived from multitemporal images were averaged to reduce noise signals and to improve the result accuracy. The overall root-mean-square error and mean relative error of retrieved water depths were 2.68 m and 9.99%, respectively, by validating with soundings. This approach used Chl-a concentration as a proxy to deduce IOP parameters and rapidly obtained the preliminary water depths in optically shallow waters of coral reefs from multispectral satellite images in the South China Sea. The depth estimation method can be applied to similar marine environments for related studies.