Characterization Of Diffuse Attenuation Coef-ficinet And Evaluation Of Light Ecological En-viroment In Taihu Lake

The in-situ measured data (i.e. the apparent optical properties (AOPs), the inherent optical properties (IOPs) and the information of water concentration) were obtained in spring, summer and autumn from 2006 to 2010. Based on these data, the seasonal differ-ences of the diffuse attenuation coefficients were analyzed. Meanwhile, the absorption co-efficient and back-scattering coefficient of different water components were considered as attenuation factors to figure out the trend of the contribution. And then the necessity re-search of diffuse attenuation coefficient was interpreted. And the quantitative estimation models including empirical model and semi-analysis model were constructed to calculate the diffuse attenuation coefficient by remote sensing reflectance. Based on these researches, the spatial distribution of underwater light field structure, the euphotic depth and primary productivity were analyzed to assess the light ecological environment in Taihu Lake. The research issues and main conclusions are as follows:(1) The spectral characteristics of diffuse attenuation coefficient and the contribution of attenuation factor in different seasons in Taihu LakeIn spring, the spectral characteristics were similar with that in autumn. But the spec-tral curve was complex in summer without rules. At the same time, the contribution of each factor showed strong seasonal differences in 440nm,532nm,676nm and 735nm. In addi-tion, the contribution of each factor did not have the same spectral curve in the different seasons.(2)The quantitative estimation model of diffuse attenuation coefficient in different seasonsOn the basis of the analysis about sensonal difference of diffuse attenuation coeffi-cient in spring, summer and autumn in Taihu Lake, the value of coefficient could be calcu-lated by empirical model by remote sensing. The analysis indicated that:the estimation model from single band had higher precision than that from band ratio model. Moreover, empirical model randomly underestimated the actual value. Based on analysis of the inter-nal impact mechanism of the diffuse attenuation coefficient, the quantifying models which could obtain the absorption and back-scattering coefficient from remote sensing were built. Based on these models, the estimation model of diffuse attenuation coefficient from semi-analysis method was put forward to obtain the value. To some extent, these semi-analysis models which overcome the problem of universal would be appropriate for the different range of diffuse attenuation coefficient. (3) The spatial distribution of light ecological environment in different seasons in Taihu LakeThe PAR intensity, the normalized PAR intensity and the percentage of the normalized PAR intensity to the surface in different depth decayed with the depth in different seasons in Taihu Lake. However, the euphotic depth almost had no differences in different seasons, and the regression equations of quadratic function and power function could ideally fit the relationship between the normalized PAR intensity and the euphotic depth. On the whole, primary productivity in summer was higher than that of spring and autumn. Furthermore, Level 1 [0～500mg/(m2·d)] and Level 2 [500～1000mg/(m2·d)] occupied 90% of Taihu Lake in spring, the lake was covered by Level 2 [500～1000mg/(m2·d)] and Level 3 [1000～2000mg/(m2·d)] in summer and autumn.