Distinguishing between chlorophyll-a and suspended solids in lake water using hyperspectral data

摘要

Classifying surface water bodies according to trophic status by remote sensing techniques has had limited success in lakes with relatively high nonalgal turbidity levels. Since the trophic status of a lake is typically defined based on its chlorophyll-a concentration, and since relatively high suspended solids concentrations masks chlorophyll absorption and reflectance peaks, determining trophic status remotely is typically only partially successful. Here, we were interested in exploring hyperspectral data analysis for estimating trophic status. Hyperspectral data (10 nm resolution between 262 and 850nm) of light attenuation were measured in Lake Texoma (USA) at the surface, 0.1, 0.5, 1.0 and 1.5 meters in depth, while simultaneously analyzing thewater column for chlorophyll-a and suspended solids concentration. Data were collected at five sampling stations, each representative of a major zone in the 36,000 hectare lake, approximately monthly, during 1996/97 hydrologic year. Downwelling and upwelling vertical attenuation coefficients were calculated using Bouger-Lambert's law. First and second order derivatives, as well as higher order derivatives were applied to the spectral data. The results showed a clear correlation between first order derivatives and turbidity, while the second order derivatives were correlated to chlorophyll-a concentrations.