Retrieval of Underwater Turbidity in Gyeonggi Bay Using Sentinel-2 Satellite Data

Seawater turbidity is one of oceanic variables that reflects the degree of optical property caused by suspended particles or organisms in the water, and it is one of critical oceanic variables for understanding coastal environments. The western coast of the Korean Peninsula, characterized by shallow depths, tidal currents, and the influence of river-borne sediments, exhibits strong spatio-temporal variability in optical properties of sea water. Therefore, the utilization of satellite data for turbidity estimation holds diverse potential applications from an oceanographic perspective. In this study, Gyeonggi Bay was selected as a research area and a turbidity calculation algorithm was developed. To achieve this, we utilized a combination of in-situ turbidity data from the Korea marine environment management corporation's automated monitoring network as ground truth data and Sentinel-2 satellite data from the Level-2 Multi-Spectral Instrument (MSI) from 2018 to July 2023. A matchup database between satellite data and in-situ measurement data was produced. Various turbidity retrieval methods of previous studies were investigated and their accuracy compared. As a result, a turbidity retrieval formulation based on the green band (560 nm) exhibited a relatively low root mean square error of 0.08 NTU in the Gyeonggi Bay. Turbidity calculated based on satellite optical data is expected to enhance our understanding of seawater's optical characteristics, coastal environmental variability, and provide valuable assistance in various maritime activities.