Diffuse Attenuation Coefficient Inversion for the Yangtze Estuary and Its Adjacent Sea Areas on the GOCI Images and Application in the Preevaluation of Airborne Laser Bathymetry

Abstract

Due to high turbidity, high primary productivity, complex hydrodynamic conditions, and tidal effects, monitoring the dynamic changes of diffuse attenuation coefficient is of great significance for underwater light detection and laser observation of underwater topography and landforms in the Yangtze Estuary and adjacent waters. In this study, the $K_{d} (490)$ inversion in the Yangtze Estuary and its adjacent sea areas is carried out based on GOCI data. The research focused on the various characteristics and influencing factors of $K_{d} (490)$ in the Yangtze Estuary and its adjacent sea areas during half tidal period. The feasibility of laser sounding in the sea areas is evaluated according to the variation characteristics of $K_{d} (490)$. The result indicates that:1) The Yangtze Estuary and its adjacent waters are typical type II water. The maximum suspended sediment content can be rapidly reduced from 1000 mg/L in Hangzhou Bay to below 10 mg/L. Therefore, the piecewise diffuse attenuation coefficient inversion algorithm is suitable for the study area;2) The inversion results suggest that the $K_{d} (490)$ of the Yangtze Estuary and its adjacent sea areas vary in the range of $0.10 \pm 0.02 {\mathrm {m}}^{-1}-2.8 \pm 0.2 {\mathrm {m}}^{-1}$, and increases in the inner estuary and then decreases with the decrease of offshore distance. The $K_{d} (490)$ values of the Yangtze Estuary and its adjacent sea areas are generally lower in low tide period than in high tide period. The suspended sediment concentration and the tidal level are important factors affecting $K_{d} (490)$ values in the low tide period; 3) During the low tide period, the detectable laser depth in the Yangtze Estuary and Hangzhou Bay is from less than 5 m to 30 m, which is more suitable for LiDAR observation at the lowest tide level. It can be seen that GOCI’s daily resolution of 8 scenes per hour can realize the dynamic change monitoring of $K_{d} (490)$. The research provides technical support for the further development of airborne LiDAR detection.