Remote sensing monitoring of Margalefidinium polykrikoides blooms in the South Sea of Korea

Abstract

Harmful Margalefidinium polykrikoides blooms has frequently occurred in the South Sea of Korea (SSK) since 1995. In order to cope with this bloom, it is essential to understand spatio-temporal distribution of M. polykrikoides blooms. Compared to traditional field survey method, remote sensing techniques is efficient in periodic and wide red tide detection, which requires fast and accurate monitoring. Until now, satellite-based red tide detection has been mainly performed, but it is difficult to monitor red tide more precisely because of limitation of spatial-spectral resolution. The objective of this study is to identify accurate distribution and extent of M. polykrikoides blooms using remote sensing data, such as optical image of UAV and hyperspectral data. In situ observations of M. polykrikoides blooms were conducted on August 7 and 8, 2018 in the coastal areas in Yeosu. During the field survey, the spectrum of waters and cell abundance of red tide were measured. At the same time to the field survey, UAV optical images were acquired for obtaining precise information of spatial distribution. It shows distinct spatial distribution of red tide blooms through geometric correction. Also, airborne hyperspectral images were acquired for understanding red tide species and cell abundance. As a result of comparing Rrs calculated by atmospheric correction of hyperspectral image and in situ Rrs, the correlation was good (0.7~0.9). The correlation between hyperspectral band and in situ cell abundance was calculated to obtain band ratio having the highest correlation with cell abundance. Cell abundance map showed the detail distribution of red tide blooms. The two images were combined to calculate red tide distribution and extent. Remote sensing monitoring using high spatial-spectral resolution is expected to be an efficient tool for identifying the distribution and extent of blooms.