Lake Erie is part of the Great Lakes systems in North America, which represent the largest continental lake systems in the world. Anthropogenic eutrophication in the Western Basin of Lake Erie, a Case II environment, has an adverse impact on the surrounding ecosystems and the regional economy. The optical complexity found in Lake Erie is a feature of many aquatic environments making it a challenging setting for remote-sensing applications. To assess the controls on these optical properties, we sampled 20 locations, encompassing a variety of optical environments in the Western Basin and Sandusky Bay during four research cruises. Strong correlations between light extinction and phycocyanin (correlation coefficient, r≥0.95), suspended sedi-ment (r= 0.90), and chlorophyll-a(r≥0.86) indicate that surface conditions are representative down to at least the first optical depth. Application of varimax-rotated principal component analysis to lab-based, hyperspectral reflectance data identified three components related to a diatom/green algae community, and two blue-green algae communities, one of which was associated with suspended sediment. Phycocyanin and chlorophyll-a content inferred using a semi-analytic red/near-infrared algorithm correlated well with concentrations measured in situ using a multiparameter sonde. Chlorophyll-a retrievals from a regional, blue : green algorithm developed for the Western Basin of Lake Erie compared well with retrievals from the semi-analytic algorithm for all samples from the Western Basin and 25% of samples from Sandusky Bay. Chlorophyll-a retrieval errors using the blue : green algorithm occurred when high ratios of suspended sediment to phycocyanin biased samples from the extremely turbid waters of Sandusky Bay. The bias likely resulted when suspended sediment altered the blue : green ratio or when phycocyanin interfered with the chlorophyll-a absorption peaks. This approach can be applied to other Case II environments to provide insights during the design of experimental field studies and for spectral band selection with the next generation of visible near-infrared remote-sensing instruments.
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