Int. J. Environ. Res. Public Health 2010, 7 5. Conclusions 2448 In this study, the potential of hyperspectral data to derive Chl-a concentration in inland waters is discussed. Based on the field measurements in Tangxun Lake, Central China, it is found that three characteristic points of the reflectance spectra exist with reflectance peaks adjacent to 570 nm and 706 nm and an absorption valley ranges from 671 nm to 686 nm. The wavelengths of the characteristic bands are slightly different from those reported in previous studies, which may be attributed to differences in the study area and season. The correlation analysis has indentified the proper wavelengths or band ratios for the extraction of Chl-a concentrations in water. The algorithms of single-band, first-derivative, and reflectance radio were applied and evaluated. Although the single-band algorithm is simple, it is hard to estimate Chl-a concentrations comprehensively. The reflectance radio algorithm for estimating Chl-a concentrations is well-documented because it can highlight the spectral characteristics of absorption and reflection and then reduce the effect of noise. The RNIR/RRED radio was commonly used in previous research, and, for example, Mittenzwey shown a high coefficient of determination (R2) of 0.98 between chlorophyll and the near-infrared (NIR)/red reflectance ratio [35], but in our study it was shown that the results of using RNIR/RRED were poor, with an R2 value of 0.043, which indicated the NIR/RRED is not suitable to estimate Chl-a concentrations in Tangxun Lake. This agrees with the conclusions of Han’s study in Branched Oak Lake [31]. In our case, the reflectance ratio between 861.1 nm and 856.7 nm were correlated significantly with Chl-a concentration (R2 > 0.86). Derivative spectra indicate the rate of change of reflectance with wavelength, so derivative analysis allows one to correlate the shape of the reflectance pattern to Chl-a concentrations. The first-derivative algorithm can reduce pure-water effects on the water effect [36] and is an objective tool for isolating the absorption features of phytoplankton [37]. It had been applied by researchers in estimating Chl-a concentrations in water. The first-derivative at near 690 nm is found to be useful in modeling Chl-a concentration [31]. We found the first-derivative of reflectance at 446.9 nm was most appropriate to estimate Chl-a concentrations in Tangxun Lake. This agrees with Fraser’s finding that the first-derivatives near 440 nm was also correlated significantly with Chl-a [38]. The first-derivative model was the best in estimating Chl-a concentrations in Tangxun Lake with R2 and MRE of 0.863 and 11.2%, respectively. The difference of the most appropriate bands in our study means that it is of primary importance to choose optimal bands for estimating Chl-a concentrations in specific waters. The results suggest that assessment of Chl-a concentration using hyperspectral indices has significant potential. In recent years, more and more hyperspectral sensors data are becoming available. The method presented in this study will help enable departments concerned to continuously monitor water quality with high accuracy in large areas. Acknowledgements This research was supported and funded by Ministry of Science and Technology of China (grant 2008BAC34B06, 2008BAK50B01) and the State Key Laboratory of Resources and Environment Information System. The authors would also like to thank the two anonymous reviewers for their helpful comments and suggestions.