Detecting the Phaeocystis globosa bloom and characterizing its bloom condition in the northern Beibu Gulf using MODIS measurements

Phaeocystis globosa is the most common species making up harmful algal blooms. For better detect P. globosa bloom, a multispectral approach was developed based on extensive in-situ investigation and MODIS remote sensing reflectance (R_rs) dataset. A novel proxy R_PG was created based on the feature of R_rs spectral shape and P. globosa bloom was identified when R_PG was >1.6. Normalized Fluorescence Line Height (nFLH) was applied to discriminate the bloom events and nFLH of bloom waters was almost higher than 0.095 Wm⁻²μm⁻¹sr⁻¹. The R_PG associated with nFLH exhibited the P. globosa bloom areas comparable to that in field investigation, which indicated this practical method was successful on the spatial and temporal distribution of P. globosa blooms. Several environmental factors derived from MODIS products and field survey were analyzed to characterize the bloom conditions. Redundancy analysis suggested that nutrients and temperature are vital for triggering P. globosa bloom.