Research On The Diffuse Attenuation Coefficients In The East China Seas

The East China Seas are typical case II waters or turbid waters, the retrieval and validation of the ocean color satellites'data in the China Seas have become one of the most difficult field in the ocean color remote sensing community. The diffuse attenuation coefficients at 490nm are one of the standard products of ocean color remote sensing. Research on the relationship of the diffuse attenuation with inherent optical properties (IOP)/ apparent optical properties (AOP) are carried out based on in situ ocean optics data measured on three independent cruises, which are carried on April and September, 2006 in the Yellow Sea and on February, 2007 in the East China Sea.On the base of in situ IOP data, the diffuse attenuation coefficients K (λ) are calculated form Gordon Model, Kirk Model and Lee model. The retrieved and measured K (λ) are compared and analyzed. The remote-mean-square difference between measured and these three models derived values for log10 scale (RMSlog10) are 0.124,0.076 and 0.092,with the correlation coefficients (R2) of 0.96, 0.98 and 0.98 (N=89), respectively. The results shows that the Kirk model works quit well. The diffuse coefficients are calculated using Kirk model , and then the distribution of K(490) in the East China Seas are obtained .From measured remote sensing reluctance Rrs data, the diffuse attenuation coefficients at 490nm K (490) are derived from Muller algorithm, Morel algorithm and Lee semi-analytical algorithm. Comparison and analysis are carried out with measured K (490) data. The remote-mean-square difference between measured and these three retrieve algorithms derived values for log10 scale (RMSlog10) are 0.275,0.335,0.119 with the correlation coefficients (R2) of 0.73, 0.75 and 0.98(N=74), respectively. The results indicate that Muller and Morel algorithm have lager error if applied in the East China Seas, especially in the turbid waters. The semi-analytical algorithm works well and is suitable for applied in the East China Seas.Based on the analysis of in situ data of three cruises, a new algorithm to derive K (490) is developed. The new algorithm adds red spectral information at 620nm to Muller algorithm to reflect the total suspended material effects on the diffuse attenuation. A data set is simulated according to in situ data and least mean-square error fit is used to derive the parameter of the new algorithm. The algorithm is applied to in situ data of three cruises. The remote-mean-square difference between measured and the new algorithm derived values for log10 scale (RMSlog10) are 0.086 with the correlation coefficients (R2) of 0.98(N=74), which means the new algorithm greatly improve the accuracy of retrieving K (490) in the East China Seas.