[Inversion Model and Daily Variation of Total Phosphorus Concentrations in Taihu Lake Based on GOCI Data].

The TP concentration is an important index of water quality and an important influencing factor of eutrophication and algae blooms. Remote sensing technology has advantages of wide scope and high time limited efficacy. Monitoring the concentration of TP by satellite remote sensing is important for the study of water quality and eutrophication. In situ datasets collected during the three times of experiments in Taihu Lake between 2013 and 2014 were used to develop the TP inversion model based on GOCI data. The GOCI data in spring, summer, autumn and winter in 2014 were selected to analyze the time and space changes of TP concentration in Taihu Lake. The results showed that the TP algorithm was built up based on the variables, which was to use the eight band combination of GOCI data as variable, and build model using Multi factor linear regression method. The algorithm achieved more accurate TP estimation with R² = 0.898, MAPE = 14.296%, RMSE = 0.026 mg · L⁻¹. Meantime, a analysis on the precision of the model by using the measured sample points and the synchronous satellite images with MAPE = 33.642%, 22.551%, RMSE = 0.076 mg · L⁻¹, 0.028 mg · L⁻¹ on August 5, 2014 and October 24, 2014. Through the analysis of the 30 images on the four days of the four seasons, it showed that the absolute concentration of total phosphorus was different in different seasons. But temporal and spatial distribution of total phosphorus concentration was similar in the morning and afternoon. In spatial distribution, the TP concentration in Meiliang Bay, Zhushan Bay, Gonghu Bay, Xiaomei Port and Changdou Port in the southwest coast was at a continuously high position. The TP concentration change in different regions was influenced by wind direction, wind speed and other factors. The TP concentration highest in the morning, and then gradually decreased, this phenomenon reflected that the TP concentration was affected by temperature and light.

[Preliminary exploring of hyperspectral remote sensing experiment for nitrogen and phosphorus in water].

The content of nitrogen and phosphorus in the waters is an important index to measure water quality, and the technique of remote sensing plays a large role in monitoring the change in environment. The reflectance spectra of nitrogen and phosphorus with different concentrations were measured to discover their special features under pure water condition in the laboratory by hyperspectral remote sensing technique. The result shows that nitrogen has reflectance peaks at 404 and 477 nm, and phosphorus at 350 nm, and these reflectance peaks have a good correlation with their concentrations, then a quantitative retrieval model was deduced for nitrogen and phosphorus based on that. These results will lay an important basis for further monitoring nitrogen and phosphorus by remote sensing technique in the big inland lakes, reservoirs and rivers.

[Evaluating eutrophic state of Taihu Lake by in situ hyperspectra].

In situ experiments including water quality analyzing and spectra measuring were conducted on Jun., 2004 and Aug., 2004 in Taihu Lake for 21 samples. Then eutrophic state of Taihu Lake was evaluated by measured hyperspectra data, and the evaluating index was eutrophic state index (TSI). Firstly, the simulation model of water reflectance was built by analytic model using inherent optical properties (IOPs). Then Chlorophyll a content (Chl-a) was inversed by optimizing method by Matlab software; Secondly, TSI was calculated by inversed Chl-a, and the eutrophic state of Taihu Lake was evaluated by using ArcView' s interpolation function. The evaluation figures show that: there are notable differences between Jun., 2004 and Aug., 2004. The proportion of mesotropher state is as high as 61% in June, while the proportion of light eutrophic is as high as 52% in August. In totally, the most serious eutrophic state occurs in north of Taihu Lake. Eutrophlic state wears off from north to south. The lowest eutrophic region is in the east of Taihu Lake.