Water Quality and Trophic State Analysis Based on Hyperspectral Remote Sensing Data in the Mecklenburg Lake District

Kurzfassung

Secchi disc depth and chlorophyll-a content are widely used indicators for the trophic state of lakes. Secchi disc depth and chlorophyll-a are calculated from hyperspectral remote sensing data to estimate the trophic state of 25 lakes. A remote sensing database was established for the Mecklenburg Lake District in 1997 comprising field reflectance and analytical reference data on several distinct dates and airborne hyperspectral data recorded by the Compact Airborne Hyperspectral Imager (casi). The in situ reflectance spectra were analysed to develop and test a model for hyperspectral determination of the phytopigments chlorophyll-a, phycocyanin, and carotenoids, and Secchi disc depth. For Secchi disc depth the area between a base line and the spectrum from 400 nm to 750 nm was calculated and correlated to the Secchi disc depth measured in situ. Chlorophyll-a concentration was quantified using the reflectance ratio at 705 nm and 678 nm and showed a linear relationship to chlorophyll-a content from laboratory spectro-photometric measurements. The accessory phytopigments carotenoids and phycocyanin were determined from the spectral data using their absorption depths at 485 nm and 624 nm, respectively. The algorithms have then been transferred to the hyperspectral airborne data. This study presents an application of hyperspectral remote sensing data in the quantitative analysis of several water constituents. From Secchi disc depth and chlorophyll-a concentration trophic state has been analysed for the first time for all lakes in this district.