Int. J. Environ. Res. Public Health 2010, 7 2440 living requirements and it is thus necessary to develop methods for monitoring the Chl-a concentration both temporally and spatially. 2.2. In-situ Measurements Two datasets of hyperspectral reflectance data and Chl-a concentration data were used in this study. The field work was carried out between 10:00 and 12:00 h local time on April 16, 2009. The two types of data were collected simultaneously. The location of Tangxun Lake and that of the ten sampling sites are shown in Figure 1. Figure 1. Study area and sampling locations. Hyperspectral reflectance was measured with a SVC HR-1024 spectroradiometer with a spectral resolution of less than 3.5 nm in the spectral range from 350 to 1,000 nm. The spectral resolution was resampled by the equipment’s software. In the measurement, the instrument was held manually over the deck of an anchored ship approximately one meter above the water surface. At each sampling