[Hyperspectral remote sensing of total suspended matter concentrations in Lake Taihu based on water optical classification].

Four field investigations were carried out in the Taihu Lake for collecting in situ observation data in Nov. 2008, Apr. 2009, May and Aug. 2010. On the basis of water optical classification, different retrieval algorithms were developed, specific for different types of waters. Based on the preformance of each model comparion in each type of waters, the optimal models obtained were (1) the band ratio model for Type 1 water; (2) the semi-analysis algorithm model 2 for Type 2 water; (3) the first-order differential model for Type 3 water. Meanwhile, an optimal retrieval model was also established using the same collection of calibration data. Some comparisons were done between the developed models for the classified and non-classified waters. The comparison results showed that the models for the classified waters had better performances than that for the non-classified water, in both the retrieval accuracy and the model stability. Then, analyses of the optical classification leading to the accuracy decrease of the semi-analysis algorithm model were processed. Finally, the results of this study in hyperspectral remote sensing date showed a great application potential by analysis. The findings of this study are significant for promoting the development of water color remote sensing for optically complex turbid inland waters.

[Hyperspectral remote sensing of chlorophyll a concentrations in the Lake Taihu, based on water optical classification].

Four field investigations into the Lake Taihu were carried out for collecting in situ observed data in Nov., 2006, Nov., 2008, May and Aug. , 2010. On the basis of water optical classification, different retrieval algorithms were developed, specifically for different types of waters. The obtained optimal models were (1) the four-band model for Type 1 water; (2) the first-order differential model for Type 2 and Type 3 waters. Meanwhile, an optimal retrieval model was also established using the same aggregated calibration data. Some comparisons were done between the developed models for the classified and non-classified waters. The compared results showed that models for the classified waters had better performances than that for the non-classified water, in both retrieval accuracy and model stability. The findings of this study are significant for promoting the development of water color remote sensing for optically complex turbid inland waters.

[Scattering and backscattering characteristics of Lake Chaohu].

Lake scattering characteristics are of great significance for remotely-sensed retrieval model development. In this study, scattering and backscattering coefficients of Lake Chaohu were observed through AC-S and ECO-BB9 meters, and their spectral properties were correspondingly analyzed. Then Power function is utilized to model particulate scattering and backscattering spectra, and spectral slope parameters obtained by simulation are 0.86 and 3.24, separately. The proposed scattering and backscattering models present relatively low predicative errors. Particulate scattering coefficients are closely related to TSM and ISM, with corresponding correlative coefficients of 0.91 and 0.94. Their relationships can be simulated well through linear function, and further specific scattering coefficients of TSM and ISM were proposed to be 0.636 4 (10(-3) m2 x mg(-1)) and 0.910 8 (10(-3) m2 x mg(-1)). In addition, particulate backscattering ratio in Lake Chaohu has a variation range of 0.003-0.026, and refractive index varies from 1.02 to 1.06, which displays no large variation spans when compared with that in previous studies.

[Depth profile of suspended particle scattering coefficient and its impact factors in Taihu Lake].

To acquire the depth profile of suspended particle scattering coefficient and the mechanism of surface reflection, three different depths of Taihu Lake scattering coefficient and backscattering coefficient are obtained in Nov. 2008, respectively. And their characteristic variation with depth is studied. Profiling distribution of the slope of particulate size distribution (PSD) is computed by the attenuation coefficient. Profiling distribution of the concentration and composition of suspended particle is computed according the relationship between the scattering coefficient and the suspended particle concentration. Impact dominant factors on scattering coefficient of the depth of water are divided according to the range of refractive index. At the three depths (0, 50, 100 cm), the particle scattering, with the percentage 14%, 17%, 12% of the samples are dominated by algae, respectively. 35%, 30%, 34% of the samples are dominated by inorganic particulate matter and Non-algal organic particulate matter,and 51%, 53%, 51% of the samples are dominated by the above all. The results can be concluded as: scattering and backscattering coefficient of Taihu Lake water body changes with depth slightly. The concentration of total suspended particles is of more diversity in different lake area, but there is less difference at different depths except those samples near the inflow rivers. The main factors of scattering coefficient of most aquatic scattering in Taihu Lake had little difference at different depths, except several samples beside the inflow rivers.

[Optical properties and remote sensing retrieval model of diffuse attenuation coefficient of Taihu Lake water body].

The spectral and chemical analytical data of Taihu Lake water quality in Nov. 8-22, 2007 were used to analyze the spectral characteristics of diffuse attenuation coefficient (Kd) of the water body in autumn and related affecting factors. On the basis of this analysis, the Kd at band 490 nm, Kd (490), was used as a variable to build the relationship between Kd and remote sensing reflectance. The results indicated that within the scope of visible band, the Kd of the water body at most locations of Taihu Lake presented an exponent decreasing trend with the increase of wave length. Due to the higher concentration of phytoplankton in some locations, a peak value of Kd was presented at band 675 nm. Non-organic suspended particles, because of their higher content in suspended sediment, had larger effects on Kd than organic suspended ones. There was a good correlation between Kd and remote sensing reflectance. Taking Rrs (550), Rrs (675) and Rrs (731) as independent variables and doing regression analysis with Kd (490), a good linear relationship was found between Kd (490) and Rrs (731), and multi-variate linear regression analysis using variables Rrs (550), Rrs (675) and Rrs (731) could get better effect (R2 > 0.96) than the regression analysis using variable Rrs (731).

[Characteristics of the diffuse attenuation coefficient and its impact on aquatic ecology environment].

According to the optical property data measured in Taihu Lake at October and November 2006, the characteristics of the diffuse attenuation coeffcient (Kd), the contribution of each factor effecting on Kd and the effect of Kd on the aquatic ecology environment were analyzed. The results indicate that, the diffuse attenuation coefficient Kd of Taihu Lake has two main trends in the whole visible wavelength range (400-700 nm). The first type is that, Kd decreases with the wavelengths by exponential style in the range of less than 571 nm wavelengths, and the second type is that, Kd is in the form of fluctuations in the range of larger than 571 nm wavelengths. In the range of 400-700 nm wavelength, the absorption coefficient of pigment particles is the first contributors of diffuse attenuation coefficient. Non-pigment particles absorption and scattering coefficients is the second contributor, and the rate of contribution of yellow substance is the smallest. The Kd of Taihu Lake determines the light factor of the Taihu water ecosystem. The "water window" shaped by the Kd provides the light base for different kinds of ecosystem and the appearance of Microcystic aentginosa which is the preponderant algae in the "algal blooms" phenomenon.

[Seasonal variation of in water constituents' absorption properties in Meiliang Bay of Taihu Lake].

Seasonal variance in absorption properties of water constituents was analyzed and predominant factor of spectrum absorption in different seasons was discussed using the data sets collected in August and November 2006 and March 2007 from Meiliang Bay in Taihu Lake. The results indicate that, the absorption of water constitutions has seasonal variation characteristic. Total suspended sediment has the greatest absorption coefficient in summer, the average absorption at band 440 nm is (7.49 +/- 3.0) m(-1), while the least absorption presents in spring, with average absorption value of (2.86 +/- 0.73) m(-1) at band 440 nm. The total absorption type varies with seasons. Non-algal particle absorption has less seasonal variation than total absorption. The difference of non-algal particle absorption coefficient and slope S were caused by different concentration and composition of non-algal particles. Because of high chlorophyll a concentration, phytoplankton absorption coefficient was great in summer, with average absorption value of (5.49 +/- 3.5) m(-1) at band 675 nm. The average of phytoplankton absorption at band 675 nm in autumn is (2.03 +/- 1.14) m(-1), less than that in summer. The least absorption presents in spring, with average absorption value of (0.62 +/- 0.25) m(-1) at band 675 nm. Difference of chromophoric dissolved organic matter (CDOM) concentration and constitution, mainly resulted by different source of CDOM, causes the seasonal variation of its absorption coefficient and slope S value. The predominant absorption factor varies with seasons. In spring and autumn, non-algal particles were the predominant spectrum absorption factor in water, because the concentration of inorganic matter is higher than organic matters in the two seasons. While in summer, phytoplankton becomes the main effect factor of spectrum absorption in water.

[Differences of inherent optical properties of inland lake water body in typical seasons].

Inherent optical property is one of the important properties of water body, which lays the foundation for the establishment of water color analytical models. By using quantity filter technology (QFT) and BB9 backscattering meter, the absorption coefficients of chromophoric dissolved organic matter (CDOM) and total suspended matters (TSM) and the backscattering coefficient of TSM in the water body at Meiliang Bay of Taihu Lake were measured in summer and winter. Based on the spectral comparison of the absorption and backscattering coefficients, their differences between the two seasons were demonstrated, and the reasons that caused these differences were also explored in the context of their relations to the changes in water quality. Consequently, water environment condition could be revealed by using the inherent optical property. The relationship between the backscattering coefficient and the TSM concentration was established, which could provide supporting coefficients to the analytical models to be developed.

[Spatio-temporal distribution of chlorophyll a concentration and its estimation in Taihu Lake].

The temporal and spatial distribution of chlorophyll a concentration in Taihu Lake was analyzed using the data measured from January to October in 2005. Otherwise, chlorophyll a retrieval model was built using the synchronous spectrum data obtained in different season to evaluate the effect of chlorophyll a concentration temporal and spatial variation on the retrieval model. Firstly, temporal distribution of chlorophyll a concentration was analyzed. Then, chlorophyll a concentration was induced by Inverse Distance Weight method. Lastly, the chlorophyll a concentration estimation models based on spring, summer, autumn and different trophic states were built. An obvious spatial-temporal distribution was found for chlorophyll a concentration in Taihu. Chlorophyll a concentration had the maximal value in summer and the minimal value in winter,and the average chlorophyll a concentration was 56.29 microg/L, 13.61 microg/L respectively. Due to the effect of autumn, the average chlorophyll a concentration in autumn was higher than that in spring, and the average chlorophyll a concentration was 26.43 microg/L, 34.78 microg/L respectively. Marked spatial difference for chlorophyll a concentration was found in summer,while in winterthe spatial variation was ambiguous. The spatial variation in autumn was greater than that in spring as influenced by summer. Spatially, the variation in north area was greater than those in the other areas and the south area had less variation during the year. Because of the different chlorophyll a concentration, different season had different retrieval model. Band-ratio had better retrieval result in spring and autumn as there were lower concentration and less variation correspondingly. While in summer, because of the high chlorophyll a concentration and great spatial variation, among the arithmetic built in summer, the differential arithmetic was the optimal model, and the difference of Chl-a concentration retrieval model of different trophic state was minor.

[Water color parameter spatial distribution character and influence on hygrophyte photosynthesis in Taihu Lake].

Using 64 stations water quality data collected in Taihu Lake, the spatial distribution of water color parameters and euphotic depth was analyzed, and the potential effect on hygrophyte photosynthesis was discussed. The result showed that the most variation was found for Chl a concentration, the value varies from 1.67 microg x L(-1) to 159.94 microg x L(-1), with the standard deviation of 41.03 mg x L(-1). The high Chl a concentration was recorded in Meiliang Bay, Zhushan Lake, Jiapu port and Xiaomei port with obviously spatial variation and compressive isoclines. The spatial variation of total suspended matter (TSM) concentration was lower than that of Chl a with a standard deviation of 31.63 mg x L(-1), and the concentration varies from 6.47 mg x L(-1) to 143.47 mg x L(-1). The high value was found in the area near Dapu port and Xiaomei port, with obviously spatial variation and compressive isoclines. No markedly spatial variation was found for colored dissolved organic matter (CDOM) in the whole lake. Euphotic depth was influenced by TSM and Chl a concentrations, while the influence by TSM was greater than that by Chl a. Therefore, the characteristics of spatial distribution for euphotic depth are reverse with TSM.

[Scattering characteristics of Taihu Lake and its relationship models with suspended particle concentration].

Water scattering characteristics are closely related to water quality parameters, such as suspended particles and their concentrations. Through the observing system of water inherent optical properties, which were developed by WETlabs Inc, the backscattering and scattering coefficients of Lake Taihu had been obtained in Oct. 2006 and Nov. 2006. Based on analysis of data, the backscattering coefficient spectra model had been established. In addition, the water refraction indexes were computed by backscattering ratio. According to the change scopes of refraction index, the dominant factors of in-water particles were divided into three categories: (1) phytoplankton; (2) inorganic particles; (3) both of the above. By analyzing the correlations between scattering coefficients with inorganic particle, organic particle and total particle concentration, the relationship between scattering coefficient and inorganic particle concentration was simulated well by power function for three different categories respectively.