The reflecting peak in green is caused by the strong
reflection of phytoplankton, the higher the concentration is, the bigger the reflecting peak is. The reflecting peak in red is majorly caused by red tide biology, and is the character of the red tide[2,3]. But normally it is
not covered by HJ-CCD、MODIS. Both HJ-CCD and MODIS have three bands which are covered by red tide’s blue,
green, and red bands. Single spectral index can’t extract red tide information correctly because of the interference of the
suspended and yellow material. In order to monitor red tide of Case 2 waters in coast zone, this paper uses multi-spectral
remote sensing data, proposes a normalized difference indices combination method to extract red tide information. The
method as follows: