Vertical structure observation from spaceborne lidar ICESat-2 in East China Sea.

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Nowadays, spaceborne LiDAR technology, particularly ICESat-2, has become a transformative tool in marine environmental research. Unlike traditional passive optical remote sensing methods, ICESat-2 offers detailed vertical structure mapping of oceanic optical properties. Despite the potential of ICESat-2 for observing the optical vertical structure, its application in the East China Sea with complex hydrological conditions and dynamic ecosystems remains limited. In this study, we introduce an innovative methodology for retrieving the vertical structure of subsurface optical properties in the East China Sea using ICESat-2 spaceborne LiDAR observations. After preprocessing ICESat-2 ATL03 data, we employed a 4 km × 1 m bin with a 0.15 m depth step for sliding accumulation, allowing us to capture LiDAR signals at various water depths. Following deconvolution, we proposed a method to calculate the vertical profiles of the diffuse attenuation coefficient and the particulate backscatter coefficient, thereby obtaining their vertical distributions. Our retrieval results show a high degree of consistency with MODIS products and BGC-Argo data, particularly in clearer open waters. The optical parameters in the East China Sea exhibit a distinct spatial pattern, with elevated values in the western and northern regions and lower values in the eastern and southern regions. This distribution is largely attributed to the proximity of the northern laser track segments to land and the influence of terrestrial runoff from the Yangtze River on the western side of the East China Sea. The influx of suspended particles and nutrients in this region significantly affects the magnitude of optical parameters, resulting in higher root mean square errors (RMSE) compared to the eastern waters. Moreover, our analysis reveals notable differences in the vertical distribution of the diffuse attenuation coefficient and the particulate backscatter coefficient, reflecting varying concentrations of optically active components across different water layers. These findings validate the efficacy of ICESat-2 for retrieving the vertical structure of subsurface ocean optical properties, providing a robust foundation for understanding the dynamic changes within the East China Sea ecosystem.