RETRIEVING OF DISSOLVED ORGANIC CARBON BASED ON IRRADIANCE REFLECTANCE IN TYPICAI LAKE ZONES OF LAKE TAIHU

Underwater irradiance and irradiance reflectance in typical lake zones of Lake Taihu were measured using a Macam SR9910 scanning spectroradiometer in April 2004. Extensive water quality parameters such as Total Suspended Solids (TSS), Dissolved Organic Carbon (DOC) and chlorophyll a (Chl-a) were measured simultaneously with the spectral data. The features of the spectral irradiance reflectance of the lake waters are discussed. An optimum band combination is found and a local algorithm model for DOC concentration estimation is developed. The results show that DOC concentration ranges from 6.60 to 17.17 mg/L with an average of 9.99 mg/L. Most peaks of subsurface irradiance reflectance are recorded between 560 and 590 nm. The ratio of irradiance reflectance of red waveband to green waveband can be used to estimate DOC concentration satisfactorily. Determination coefficients between lg(R670/R530) and lg(DOC) is 0.82. The retrieving model of DOC concentration is: lg(DOC)=0.654( 0.012)lg\R(670)/R(530)\]+1.007( 0.086). The maximal, minimal and average relative errors of model are 20.3%, 6.7% and 12.3%, respectively. This paper has demonstrated the potential of the method for deriving CDOM and DOC from measurements of irradiance reflectance in lake Taihu. The accuracy of the method needs to be improved if it is to be of practical use, and this will involve more and careful measurements.