A novel method for discriminating Prorocentrum donghaiense from diatom blooms in the East China Sea using MODIS measurements

Abstract

The dinoflagellate Prorocentrum donghaiense (P. donghaiense) is one of the most common species making up harmful algal blooms in the Yangtze River Estuary and the adjacent area of the East China Sea. Based on the differences between the absorption characteristics of P. donghaiense and diatoms from the East China Sea and an extensive in-situ remote sensing reflectance (Rrs) dataset, a multispectral approach for discriminating P. donghaiense blooms from other water types was developed based on MODIS Rrs spectral shape discrimination. The procedure is separated into two steps. First, the bloom waters are identified by the low Rrs(555) and high RAB owing to their relatively low reflectance and high spectral slope in the green bands. Second, two new indices of P. donghaiense index (PDI) and diatom index (DI) are developed for discriminating P. donghaiense from diatom blooms, based on the distinct spectral differences found in the green and red spectral ranges of phytoplankton absorption between the two algal groups. The validation using observations collected during near-con-current field surveys showed that the application of our practical method to MODIS imagery can provide reliable information on the inferred pattern and spatial distribution of the algal bloom, and that the classification technique for P. donghaiense bloom is considered successful, which may allow coastal mangers to better mitigate the harmful effects of P. donghaiense blooms in the East China Sea.