Int. J. Environ. Res. Public Health 2010, 7 3. Analysis 3.1. Reflectance Spectra Analysis 2442 We selected the spectroradiometer data with wavelengths between 380 and 900 nm for analysis according to previous research. The spectral reflectance curves of the samples are shown in Figure 3. Figure 3. Reflectance spectra at 10 sampling sites in Tangxun Lake. The reflectance spectra show a clear reflectance peak around 570 nm, which then decreases gradually. Another peak appears around 706 nm. The curves show less diversity when the wavelength is larger than 730 nm. According to previous studies, the reflectance peak near 570 nm may be caused by low absorption of algal pigments or the scattering of inorganic suspended materials and phytoplankton cells. The absorption valley from 670 nm to 686 nm may be caused by the maximum absorption of chlorophyll-a in the red-band. The other reflectance peak near 706 nm may be due to fluorescence of Chl-a [20,27-29]. The magnitude and shape of the reflectance curves (Figure 3) are all similar to that of typical turbid water. 3.2. Correlation Analysis Three types of hyperspectral indices, including single-band reflectance, first derivative of reflectance and reflectance ratio, were extracted from spectral profiles involving all bands of hyperspectral sensor. Correlation analysis was conducted to identify the most appropriate bands for those algorithms. 3.2.1. Single band reflectance VS Chl-a concentration The correlation analysis was conducted between Chl-a concentration and reflectance of all 384