MONITORING OF MACROALGAL BLOOMS BY SAR AND OPTICAL REMOTE SENSING IN THE YELLOW SEA

Abstract

The world's largest macroalgal bloom (MAB) occurred in the Yellow Sea in 2008, and since then it is occurring there every year. Numerous studies have already been accomplished using optical satellite data in this region; however, there are limitations because the optical data is influenced by several atmospheric factors viz. clouds, rain, fog, solar angle, etc. Synthetic Aperture Radar (SAR) data can be used to mitigate these effects. Thus, this study aims to study MAB in the Yellow Sea during April 2021 by using combinations of both optical and SAR satellite data. Therefore, in this study macroalgae were mapped by detections from Landsat-8 and Sentinel-1 data. Landsat-8 data were first preprocessed, and then the MAB areas were detected by applying the floating algae index (FAI). For Sentinel 1, data were first preprocessed using the Sentinel Application Platform (SNAP) software which mainly includes thermal noise removal, radiometric calibration, speckle filtering followed by MAB area masking, and finally detection of MAB by applying threshold. From Landsat-8 and Sentinel-1 around 594.566 km2 and 16.125 km2areas were detected as MAB respectively for the date(s) of 2021/04/06 and 2021/04/07. Combining both sensor based results are in progress. Furthermore, finding out the smaller patches with MAB to find out their early growth stage as well as differentiation between green and brown algae are also in progress.