Research on mapping trophic state of water bodies based on Landsat TM images in Taihu Lake

Abstract

Methods and techniques for mapping the trophic state of water bodies in Taihu Lake based on synchronous Landsat TM images were studied. The rapid deterioration of water quality of Taihu Lake in recent years demanded effective monitoring methods. The remote sensing technology had provided effective and low-cost means of monitoring synoptic water quality over inland waters. The Landsat TM images acquired on July 13th, 2002, together with in situ measurements of chl-a, were used to retrieve chl-a concentration in Taihu Lake. The visible bands of TM images were carefully corrected for atmospheric effects using clear-water approach, and the remotely sensed reflectance of water at these bands were estimated. Then, chl-a concentration in Taihu Lake was estimated by the statistical relationship between the atmospherically corrected water reflectance at these bands and in situ measurements. In accordance with the definition of Carlson's trophic state and his formula from his previous studies, TSI (chl) was expressed as TSI(chl) = 9.81* ln(chl-a) + 30.6. The Taihu Lake map of trophic state was generated. The spatial distribution of trophic state in Taihu Lake was analyzed, as well as the errors in estimation of chl-a content and trophic state of Taihu Lake from remotely sensed data.