Characterizing the spectral reflectance of algae in lake waters with high suspended sediment concentrations

Remote sensing has the potential to provide truly synoptic views of water quality, the assessment of which is known to be affected by suspended sediment, phytoplankton biomass (chlorophyll alpha (Chl alpha) concentration) and dissolved organic carbon. These three components also control the spectral reflectance characteristics of waterbodies. This Letter uses in situ reflectance measurements of water in Lake Balaton on three different occasions, supplemented by controlled tank experiments, to characterize the influences of suspended sediment concentrations (SSC) and Chl alpha on spectral reflectance and simulated Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) response. The results confirm that Chl alpha cannot be estimated directly from Landsat reflectance data in waters characterized by heterogeneous SSC. However, principal component analysis (PCA) demonstrated that spectrally unique end-members can be identified, indicating that a spectral linear mixture modelling approach combined with a multivariate regression analysis may be used to provide estimates of Chl alpha concentrations, which would be independent of SSC