Identification of algae-bloom and aquatic macrophytes in Lake Taihu from in-situ measured spectra data

Identification of algae-bloom and aquatic macrophytes plays a significant role in inland water quality monitoring by remote sensing, which can be used to reflect the water quality status indirectly, and then the result of water can be used to retrieve water quality parameters. However, the mostly used multi-spectral remote sensing data cannot accurately identify algae-bloom and water grass. Only hyperspectral remote sensing data, as the data can be distinguished the subtle differences of the spectral characteristics between algae-bloom and water grass, can be used to identify algae-bloom and water grass with high accuracy. Unfortunately, there have been few of profound researches on the identification of algae-bloom and water from hyperspectral remote sensing data. Lake Taihu is selected to be the study area. Two experiments were carried out in Lake Taihu in July and October of 2006. Reflectance spectra of the floating vegetation, submerged vegetation, algae-bloom, and water were measured. Based on the analysis of the measured spectra, four spectral indexes were defined to build up formulas for identification of the four items. Reflectance spectra measured in October 2006 were used to determine the threshold values in the identification formulas, and reflectance spectra measured in July 2006 were used to validate the identification formulas. The identification results were very good.