U.S. Water News Online
MINNEAPOLIS -- Scientists are finding that being high in the air in Minnesota is a good way to measure the water running on the ground.
Researchers from the University of Minnesota and elsewhere have been flying a specially equipped airplane along the Mississippi River and other waterways in Minnesota for two years, measuring water quality with a camera-like sensor.
The data is used to produce brilliantly colored maps that tell the complex story of the Mississippi River in the Twin Cities.
So far, officials are not solving pollution problems with the digital maps, but that could soon change. "The science and the technology of it work," said lead researcher Marvin Bauer, a professor of remote sensing in the university's College of Natural Resources in St. Paul.
The science of monitoring inland waterways from the sky is taking off, and much of the research has been launched in the Midwest.
Three years ago, Bauer's team used Landsat satellite images to determine the clarity of 10,500 Minnesota lakes. At the time, researchers also wanted to measure river water quality from the sky, but they faced problems -- satellite images were unsuitable or too expensive.
So Bauer and another university scientist, Leif Olmanson, asked for help from University of Nebraska researchers who were testing an airplane equipped with a device called a hyperspectral sensor. It's based on the same scientific principle as satellite sensing -- algae and suspended particles in water absorb or reflect sunlight in distinct ways that allow water properties to be mapped from high-altitude measurements.
Minnesota researchers didn't have enough money to buy an airplane or the $275,000 sensor from a company in Finland.
Instead, they contracted for Nebraska's sensor-equipped Piper Saratoga to fly along five metro-area rivers on several clear summer days in 2004 and 2005. University of Nebraska geoscientist Rick Perk operated the onboard sensors and computer.
To verify the airplane-based monitoring, scientists arranged for crews in boats to take dozens of water samples at various river locations around the time the plane flew over.
Bauer and Olmanson say the airplane data closely tracked the traditional test results.
Remote sensors don't diagnose every pollution problem in a river.
They measure whether the water is clear or has a lot of suspended sediment or loads of algae. They can also discern some types of algae. High levels of sediment or algae often can be signs of trouble -- indicating excessive nutrients, erosion or other environmental problems.
Scientist Bruce Wilson of the Minnesota Pollution Control Agency said the high-altitude monitoring can help regulators pinpoint places that need expanded ground-based testing.
"It's like taking someone's blood pressure," Wilson said. "It's not a diagnostic tool. It isn't a CAT scan." Traditional sampling for such things as mercury or harmful bacteria still will be needed, he added.
The sensor-derived river maps will give regulators -- and the public -- the big picture of pollution.
"We can look at the water clarity on a long length of stream and identify impacts you may not have seen," said Steve Kloiber, an environmental analyst at the Metropolitan Council, which has supported the research and monitors rivers and streams in the Twin Cities.
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