Lake water quality monitoring using hyperspectral airborne data—a semiempirical multisensor and multitemporal approach for the Mecklenburg Lake District, Germany

This study presents an approach for the determination of the trophic parameters Secchi disk transparency and chlorophyll-a from hyperspectral airborne casi and HyMap data with multitemporal validity. Based on in situ water sampling and reflectance measurements, algorithms have been developed. For Secchi disk transparency, the area between a base line and the spectrum from 400 to 750 nm was calculated and correlated to the Secchi disk transparency measured in situ; chlorophyll-a concentration was quantified using the existing reflectance ratio at 705 and 678 nm, which showed a linear relationship to chlorophyll-a concentration from laboratory spectrophotometric measurements. The algorithms have been adapted to the spectral characteristics of the airborne sensors and applied to these data recorded in September 1997 and 1998 and May and June 1999. The validation using independent in situ reference data showed mean standard errors of 1.2–1.3 m for Secchi disk transparency and of 10.2–10.9 μg/l chlorophyll-a.