Detection of Early Occurrences of Green Tide in the Western Coastal Regions of the Korean Peninsula

Abstract

In our previous study some green tide (GT) patches were detected in various places of the western parts of the Korean Peninsula during July and August of 2015 and 2016 from Geostationary Ocean Colour Imager (GOCI). Those patches were small compared to those in the Yellow Sea, and found to be dissipated very soon. Though high temporal resolution of GOCI facilitated continual monitoring over a large area, very small patches could not be detected by 500 m spatial resolution GOCI data. Therefore, in order to precisely monitor the GT including detection of small patches during their generation period high resolution (30 m) Landsat 8 data from 2015 to 2016 is used in this study. The Floating Algae Index (FAI) and commonly used Normalized Difference Vegetation Index (NDVI) were separately used to detect the GT pixels. The results show that using the commonly used threshold value of 0, FAI could more precisely detect most of the GT patches than NDVI. Moreover, many small patches were detected close to the Gyeonggi Bay and other parts of the western coastal regions of the Korean Peninsula during May 2015 and 2016, which indicates that they have generated two months earlier than the GOCI NDVI-based first GT detection in the same area. Thus, along with GOCI-observations Landsat-8 FAI-based detection could be suitable for precise monitoring of GT.compared to those in the Yellow Sea, and found to be dissipated very soon. Though high temporal resolution of GOCI facilitated continual monitoring over a large area, very small patches could not be detected by 500 m spatial resolution GOCI data. Therefore, in order to precisely monitor the GT including detection of small patches during their generation period high resolution (30 m) Landsat 8 data from 2015 to 2016 is used in this study. The Floating Algae Index (FAI) and commonly used Normalized Difference Vegetation Index (NDVI) were separately used to detect the GT pixels. The results show that using the commonly used threshold value of 0, FAI could more precisely detect most of the GT patches than NDVI. Moreover, many small patches were detected close to the Gyeonggi Bay and other parts of the western coastal regions of the Korean Peninsula during May 2015 and 2016, which indicates that they have generated two months earlier than the GOCI NDVI-based first GT detection in the same area. Thus, along with GOCI-observations Landsat-8 FAI-based detection could be suitable for precise monitoring of GT.