The distinction of green and golden tides using reflectivity characteristics

Abstract

The occurrence of macroalgae blooms (MABs) has been reported since the early 20th century (Cotton, 1910). Since the 1970s, MABs have expanded due to coastal eutrophication as the world has become more industrialized (Smetacek and Zingone, 2013). The main genera responsible for MABs are Ulva and Sargassum, which are named ‘green tide’ and ‘golden tide’, respectively. The Yellow Sea (YS) and East China Sea (ECS) have the world’s largest supply of floating algae. The greenand 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 green and golden tides appearing in the YS and ECS were investigated, based on which a classification method was proposed and applied to multi-satellite sensors. First, we measured the reflectance of Ulva prolifera and Sargassum horneri using TriOS-RAMSES (TriOS), which are the major causative species of green and golden tides in the YS and ECS, respectively. To investigate the reflectivity of U. prolifera and S. horneri, algae samples were collected from Muan and Shinan, Jellanam-do Korea, respectively. Under visible light, the reflectance of U. prolifera increas