High Resolution Sentinel-2 and Sentinel-3 Satellite Imagery in Monitoring Green Noctiluca scintillans Blooms in Complex Coastal Waters: A Case Study in Gulf of Mannar

The Gulf of Mannar (GoM) includes the GoM Marine National Park and Biosphere Reserve and is globally recognised as a unique marine system with diverse habitat and rich biodiversity. The present study investigated a massive dinoflagellate bloom caused by the green Noctiluca scintillans during September–October 2022 in GoM. Multi-temporal remote sensing satellite imagery and the Normalized Difference Chlorophyll Index (NDCI) were assessed utilizing data from Sentinel-2 and Sentinel-3 satellites. These satellites offer high spatial and spectral resolutions, complemented by effective atmospheric and sunglint correction achieved through the Sen2Cor and C2RCC processors. This Remote Sensing approach presents a straightforward and practical method for the accurate and timely identification and mapping of green N. scintillans. The total coverage of bloom was calculated to be 1825 and 5433 km² during the bloom period of 22nd and 27th September 2022, respectively. The highest NDCI value of 0.8 was observed on 27th September 2022 at 42 km away from the shoreline of Ervadi, Puthumadam and Vembar coastal belt. This study highlights the advance monitoring methods of N. scintillans blooms and their spatio-temporal variability, also advantages of Sentinel-3 and Sentinel-2 satellites in algal bloom monitoring in complex coastal waters.