MODIS-derived green Noctiluca blooms in the upper Gulf of Thailand: Algorithm development and seasonal variation mapping

In recent decades, red tides of non-toxic harmful algal blooms have frequently occurred in monsoon-influenced tropical areas, particularly the green form Noctiluca scintillans (hereafter ). However, our understanding mechanism tide formation is hindered by spatial and temporal constraints field data. this study, we used moderate resolution imaging spectroradiometer (MODIS) ocean color data along with a locally developed algal-bloom classification algorithm to investigate seasonal variability dominant across upper Gulf Thailand (uGoT). During July 2018 observation, super bloom extraordinarily high chl-a (>1,469 mg m -3 ) displayed distinct spectral reflectance characteristic among blue-to-green red-to-near infrared wavelengths. According distinctive situ hyperspectral characteristics uGoT blooms, for MODIS normalized at 488, 531, 667 nm, which successfully discriminated three levels namely, (100%), strong (>80%), weak (>40%), from other (i.e., dinoflagellates, diatoms, cyanobacteria, mixed species) as well non-bloom oceanic coastal waters using data, confirmed reports. Monthly MODIS-based discrimination composites 2003 2021 revealed surface distribution frequency according Asian monsoon seasons: southwest (May–September) northeast (October–January following year). Green farther shore estuaries than (dinoflagellates cyanobacteria), were much more frequent between Tha Chin Chao Phraya River mouths during non-monsoon period (February April). The varied season. By comparing MODIS-derived monsoon-induced factors sea winds, precipitation, river discharge), present an unprecedented overview dynamics throughout under conditions. This research contributes impact climate change on phytoplankton dynamics.