(1) Using NDVI index (Rnir-Rred)/(Rnir+Rred) > A1 to identify the possible range of red tide.
(2) Using index (Rgreen-Rred)/(Rgreen+Rred) < A2 to eliminate the mid-low turbid waters .
(3) Using index (Rred-Rblue)/(Rred+Rblue) < A3 to eliminate the high turbid waters .
(4) Using index (Rgreen-Rblue)/(Rgreen+Rblue) > A4 to eliminate the clean seawater