Bird’s Eye ViewMonitoring Ohio’s Water Quality from the Sky
Growing up 20 miles from Lake Erie, Carolyn Merry remembers learning about its pollution problems during childhood field trips. Now an environmental and civil engineer, she is discovering that the lake is a complicated ecosystem, due to changing nutrient and bacterial levels, toxic substances and contaminated sediments.
Since the mid-1980s, Merry, chair of the Department of Civil and Environmental Engineering and Geodetic Science, has used satellite data to gain a broader understanding of Ohio’s large lake systems. Satellites can detect water quality indicators such as color, toxins, clarity and temperature.
Merry began her research on water quality as a graduate student, when she used a 512-channel airborne spectroradiometer that took reflectance data over Lake Powell in Arizona and Utah. She then compared actual water quality measurements of chlorophyll and suspended sediment concentration to the aircraft data.
Today, she uses much more advanced satellite technology to measure water quality, and she focuses her research on Lake Erie.
Merry first obtained satellite data in 2001 from Landsat, a series of earth-orbiting, remote-sensing satellites that NASA launched in 1972 to get aerial pictures of land and water. However, Landsat does not have the right spectral bands—a finite segment of wavelengths in the electromagnetic spectrum—needed to determine chlorophyll levels.
In her latest work, Merry takes advantage of data from the MODIS Aqua satellite, which uses 36 spectral bands to provide the most sophisticated information yet on the clarity and water color of lakes and rivers. The water color data received via satellite are then compared to water samples collected in Lake Erie to validate water quality algorithms.
In 2005, Merry began incorporating research data from the SeaWifs satellite, a commercial, Earth-orbiting ocean color sensor that uses eight spectral bands to detect subtle changes in ocean color. SeaWifs can detect various types and quantities of marine phytoplankton, microscopic marine plants and algae toxins such as microcystin.
“By digitally mapping Ohio’s water resources, we are able to obtain a big-picture view of changes in water quality over time, which enables us to predict future water changes. We can also verify what the satellites are seeing, which may reduce the need for the number of water samples collected. If a problem or potential problem is detected, we can notify the local or state authorities or the Environmental Protection Agency,”says Merry.
Merry’s research could allow scientists to investigate the dynamics between water quality and land use. By exploring whether land use has affected water quality over time, researchers can determine if the water quality could impact local residents. Her research also could be used to determine if there is a higher prevalence of illness near areas of poorer water quality.
