Abstract: Red tide is one of the most serious marine hazards. It not only destroys marine fishery production, deteriorates the marine environment, affects coastal tourist industry, but also causes human health problems. The East China Sea is the region of the “high incidence” of the red tide disaster in China: both in the frequency and the area are significantly higher than others. Remote sensing technology has been proved to be one of the most effective means of red tide monitoring. From the spectral curves, we can see that the spectral of the red tide water and non-red tide water has significant difference: there are two peaks and two valleys in red tide water, while there are no these two peaks and two valleys in non-red tide water. Based on the spectral differences, a new algorithm was developed with conditions of R_rs 555/ R_rs 488> 1.5, and R_rs 678- R_rs 667 > 0 to extract the red tide information. The algorithm can determine effectively the locations from satellite data of red tide, and it is good corresponding to the results in the official bulletin. Therefore, this algorithm is suitable to monitor the red tide from satellite data in the East China Sea.

Key words: spectrum, red tide, MODIS, the East China Sea