Characterizing distribution patterns of small algae patches across the northern and southern sides of the Yellow Sea front using synchronous CZI-MODIS images

The uneven distribution of floating macroalgae often leads to missed detections of small, sparsely aggregated patches in medium-low resolution satellite images. This study evaluates the effectiveness of quasi-synchronous MODIS Terra/Aqua and HY-1 C/D CZI imagery from 2019 to 2022 for green tide detection in the Yellow Sea, revealing previously overlooked regional differences in detection capability between high-resolution and medium-low-resolution sensors. The results indicate significant discrepancies in biomass estimation across different spatial resolutions, with MODIS persistently underestimating algae biomass and failing to detect small algae patches. South of the Yellow Sea turbidity front, MODIS exhibits a higher missed detection rate, but the biomass estimation deviation between CZI and MODIS is smaller due to lower biomass per area (BPA). In contrast, north of the front, undetected small patches exhibit higher BPA, leading to greater biomass estimation deviation. The small algae patches missed by MODIS display distinct spatial distribution patterns, particularly forming narrow, long bands in the radial sand ridge area south of the front, likely influenced by topography, wind, and currents. These findings highlight the importance of high-resolution studies on small algae patches in different regions of the Yellow Sea for early detection and effective green tide management.