Development of algorithm for detecting low-salinity plume in the East China Sea during the summer using GOCI

Abstract

The East China Sea (ECS) is a marginal sea that interacts with various surface water systems, including freshwater from the Changjiang River and the Taiwan Warm Current. The Changjiang River Discharge (DRD) disperse over a wide area in theYellow Sea and ECS as a major freshwater source and forms the water type Changjiang Diluted Water (CDW) by mixing with ambient saline water. Particularly, in the summer, CDW extends eastward and disperses from the west of Jeju Island, Korea to the Korea/Tsushima Strait. This is due to the prevailing southerly wind with the increasing CRD. The extension of the CDW during the summer may be associated with increasing sea surface temperature under the formation of strong stratification. To detect and trace offshore surface low-salinity water (LSW) in the ECS, a proxy was developed using surface water beam attenuation coefficient (cp), and salinity matched with synchronous (Geostationary Ocean Color Imager) GOCI satellite data from 17-year summer cruises (1998, 2003-2018) using a two-step empirical approach. The hydrographic data collected from KIOST, NIFS, wave glider observations. For empirical approach, daily GOCI satellite images (~500 m, level 2) covering the ECS were obtained from Korean Ocean Satellite Center (KOSC). For making matching of spectral data in the temporal window, GOCI data were extracted for the location of the ECS sampling points when in situ and GOCI measurements