Erie is the warmest of the Great Lakes, the shallowest and richest in life, and has changed much in recent years. For instance, the lake has experienced a microcystis outbreak every summer since 1995. The warmer the temperature, the bigger the outbreak, Merry said.
Though lakeside towns routinely measure algae levels firsthand, satellite images give scientists a broader view of trends in the lakes.
If we want to really understand whats happening in Lake Erie, we can take these computer models and marry them to other data to get a more complete picture, Merry said.
The models could also apply to other large lakes and seas, such as the Mediterranean.
The key to proving the models valid, she said, is to compare them to actual measurements of algae in the water. Thats what she and Mupparthy did for Lake Erie, by collecting water samples from four sites in October 2000.
They compared the actual algae levels to the levels suggested by 17 different models, each using images of the lake taken by NASAs SeaStar spacecraft.
Model performance varied widely; one demonstrated an error of more than 250 percent, while several were off by less than one percent.
What set the top-performing models apart was how well they enabled the engineers to remove the interference of atmospheric molecules. Over the ocean, carbon dioxide, ozone, and humidity are fairly constant, but amounts of these molecules fluctuate dramatically over lakes depending on the weather and human activity.
The National Oceanic and Atmospheric Administrations Cooperative Institute for Limnology and Ecosystems Research funded this study. Merry and Mupparthy have applied for funding to collect water samples from more sites, with the hope of customizing a model for Lake Erie.