In-situ data from cruises in the Pearl River estuary and adjacent marine areas were collected during March to May 2001. The absorption coefficients of the water color components were studied in detail containing total suspended matter （TSM）, chlorophyll-a （chl-a）, colored dissolved organic matter （CDOM）, and de-pigment particles. For absorption coefficient of TSM, ap, and that of de-pigment particles, ad, correlations of ap（440）-TSM, ad（440）-TSM, ap（440）-chl-a and ad-chl-a were done （the italicized term means the concentration）. There was a good correlation between ap（440） and chl-a concentration. An empirical relationship model between aph（675） and chl-a was developed showing a strong correlation of 0.93. Based on the two models the chl-a and aph（2） were correlated. The values of calculated empirical spectral slope for CDOM absorption coefficients and that of de-pigment particles, 0.017 0 and 0.011 6 respectively, both are within a relative standard error of 10.0%.
The spectral characteristics of the coastal waters in East China Sea was studied using in situ measurements,and the multiband algorithms of remote sensing for bloom waters was discussed and developed. Examples of red tide detection using the algorithms in the East China Sea were presented. The results showed that the algorithms could provide information about the location and the area coverage of the red tide events.
Red tides are abnormal ecological phenomena, which bring lots of damage in China every year. Research on detecting red tides is necessary. Water color will change abnormally while red tides bloom out, i.e. the absorption and scattering characteristics of waters will appear different. With these varieties, algorithms can be developed to retrieve water constituents from spectral reflectance. Furthermore, red tides detection methods can be applied with retrieval chlorophyll concentrations. Though absorption characteristics of waters play important parts in bio-optical algorithms development of ocean color remote sensing, no stable useful absorption coefficients of waters can be used in the high frequency red tides areas of the East China Sea.During 2002～2005 we have performed 11 cruises and done a lot of measurements in the research areas. After analyzing multi-years in-situ data, we have drawn the absorption relations of waters as follows:Good correlations have been contained when analyzing the relationships among different absorption bands of phytoplankton pigments. Taking both 440 nm and 675 nm as reference bands together, the simulation results attained much closest to in-situ measurements. The relationships between absorption coefficients and concentrations of chlorophyll-a have also been indicated. With 440nm or 675 nm as the reference bands, good results have shown with correlations 0.915 and 0.938 respectively.After 400 nm is taken as the reference band, mean spectral slope has been specified as 0.0102 nm-1 with regard to suspended sediment absorption and 0.0173 nm-1 about CDOM absorption.
