The retrieval algorithms of diffuse attenuation and transparency for the Case-Ⅱ waters of the Huanghai Sea and the East China Sea

The Huanghai Sea and the East China Sea are typical coastal Case-Ⅱ water with high sediment load and complicated optical properties.On the basis of the data of 2003 joint ocean color cruises,the statistic algorithms to retrieve 490 nm band diffuse attenuation coefficient(K_d490) and Secchi depth transparency are established.The remote sensing reflectance at bands of 490,555 and 670 nm is used in the algorithms.The correlation coefficients(R²) of retrieved and in situ values are 0.96 with a averaged relative error of 17.2% for the K_d490,and 0.95 with 16.8% for transparency respectively.The input error sensitivity analysis shows that the introducing ±5% remote sensing reflectance error results in 27.3% and 22.7% error increase in the retrieval results.The algorithms are established based on one cruise and validated with data from the other cruise,it is shown that the average relative errors are 25.0% and 16.5% for K_d490 and transparency respectively.The relations of K_d490 to other ocean color wavelengths are also given in linear equations,and all the correlation coef ficients are above 0.98.From this result,the diffuse at tenuation coefficient at anyother bands can be derived by a known diffuse attenuation coefficient,so that the unknowns in ocean color models and applications are reduced.