Reflectivity Characteristics of the Green and Golden Tides from the Yellow Sea and East China Sea

The Yellow Sea (YS) and East China Sea (ECS) have the world's largest supply of floating algae. The green and golden tides appear mainly in the YS and ECS, respectively, but become entangled as they drift. The floating algae obstructs navigation and is a huge socioeconomic problem in the vicinity of coastal areas. To manage these floating algae more systematically, a method of distinguishing between the green and golden tides is required. In this study, the reflectivity characteristics of the green and golden tides appearing in the YS and ECS were investigated based on which a classification method was proposed and applied to satellite sensors. First, the reflectance of Ulva prolifera and Sargassum horneri was measured, which are the major causative species of the green and golden tides in the YS and ECS, respectively. Under visible light, the reflectance of U. prolifera increased at 555 nm, and that of S. horneri increased at 602 and 646 nm and decreased at 632 nm. To distinguish the two algae, slope of red-green (SRG) method was applied with the red and green reflectance slope. U. prolifera exhibited SRG that was always negative, whereas that of S. horneri was always positive. When SRG was applied to the difference in reflectance values between floating algae and nearby water detected in satellite imagery, the green tide was always negative, and the golden tide was always positive. Classification and detection of floating algae using multi-satellite sensors and SRG system can reduce the associated management cost and time.