Features

Monitoring Coastal Waters from Outer Space

Back in the Dark Ages of the mid-1980s, Frank Muller-Karger was a doctoral student in search of a better way to monitor coastal water quality. Unlike most marine scientists at the time, he chose to look up.
 
“NASA [National Aeronautics and Space Administration] had launched satellites that were taking pictures from space,” Muller-Karger said. “I wanted to see if we could accurately measure the color of the ocean with those images, and from that, map changes in water quality over time.” 

The problem was the 1970s-era satellite imaging technology produced extremely low resolution images — 1 pixel equaled about 1 km² — making color detection difficult. “The technology wasn’t there yet,” he said.

But Muller-Karger saw the possibilities.

Fast-forward 20 years. Now dean of the School of Marine Science and Technology at the University of Massachusetts, Dartmouth, Muller-Karger also leads a research group at the University of South Florida (Tampa) that has continued to study remote sensing. Thanks to dramatic advances in satellite imaging, one of his doctoral students has made great strides in finishing the work he started.

That researcher —  Zhiqiang Chen  —  and his colleagues studied 8 years of imagery and data from instruments aboard two current NASA satellites, finding ways to make it usable for mapping coastal water quality. Their findings, Muller-Karger said, have direct applications for resource managers who are developing restoration plans for coastal water ecosystems, as well as federal and state regulators charged with defining water quality standards.

Coastal Challenges
Prior to Chen’s research, satellite images already had been used to observe changes in water turbidity  in the open ocean, where the water is generally clear and atmospheric conditions make it relatively easy for satellite color sensors to measure the light reflected and absorbed by the water.  

But coastal water is more optically complex than that in the open ocean, according to Chen. 

“River plumes, sediment, dissolved materials, coral reefs, algae, and shallow bottoms can all affect the water color seen from space,” he explained.

One of his team’s major challenges, therefore, was determining which colors in a satellite image were related to pollution or some other man-made factor, and which were related to a shallow bottom or the atmosphere.

In their research, Chen’s team focused on Tampa Bay, Fla., where sediments had for many years entered rivers that emptied into Tampa Bay. As a result, phytoplankton had grown in the water column, shading the ocean’s bottom and limiting sea grass growth, according to Muller-Karger, a co-author of the study.

“Ultimately, we want to be able to use satellite imagery to track the source of those sediments and see if they were a natural phenomenon, the result of coastal development, or something else” said Muller-Karger. “Then, if the source is human-related, we can try to manage that human activity.”

For this particular research, however, the researchers concentrated on ways to accurately measure two key indicators of water quality — turbidity and water clarity. To determine water clarity, they relied on satellite data that measured the amount of light reflected by the water, putting it through a two-step calculation to arrive at a measure of water clarity. To assess turbidity, they compared data from another satellite instrument to ground measurements of turbidity, mapping the results.

The bottom line: When compared to independent field measurements, the researchers found that the satellites had accurately measured Tampa Bay’s water quality. What’s more, the satellites were already collecting the same basic data for coastal waters worldwide.

This finding, they believe, is a quantum leap forward, compared to today’s ground-based methods of monitoring coastal waters.

“Today, scientists are still taking monthly boating excursions to set spots along the coasts, and taking water samples to measure things like turbidity and phytoplankton,” said Chen. 

The data that results from these tests is limited. “While they used to represent a large area, the test results really are only a measure of the water quality at the precise testing site,” said Chen.

Because tests are taken only monthly, they also don’t capture how rapid changes in winds, tides, pollution, and runoff can affect coastal areas.

By using satellite imagery, however, researchers can dramatically increase both the frequency and the size of the sampling. “The satellite enables us to cover an entire estuary in less than a minute,” said Chen. “And it passes over that estuary several times a week. The result is a series of complete snapshots that we can use for comparison over time.” 

The frequent measurements, the researchers said, could help resolve questions about the causes of water quality changes with the seasons and through the years.

What’s Ahead?
Before satellite data can have widespread application, according to Chen, more work must be done to turn satellite’s raw data into a more usable form.

“We’re in the push now,” he said. “It’s time to migrate from the research to the operational phase,” said Chen. That, of course, will require investment.

One problem, said Muller-Karger, is that the satellites from which the research team drew data are both prototypes. The one equipped to collect ocean color data has been operating since 1997. The other, which collects measurements from the entire Earth’s surface every day or two, was launched in 2002.

“NASA only launches research satellites like these once,” explained Muller-Karger. “When they break, there are no plans to launch another one as a replacement — even if they’re providing a valuable service.”

Before that happens, Muller-Karger and Chen both hope other agencies will step in to transfer the technology.

“Two decades ago, only the military and NASA had the powerful computers and networks to use the data from these satellites,” said Muller-Karger. “Now that this data is accessible to virtually anyone, it’s time it was changed into a form that we can also use to make decisions from.”

— Mary Bufe, WEF Highlights

Monitoring the Potomac
“World Water Monitoring Day is one of the stars of our public education program,” said 2006–2007 WEF President Mohammed Dahab.

Although the program is targeted toward young students, WWMD welcomes the participation of people of all ages, according to Dahab, who called it “a community environmental education program.”

Students from Kimball Elementary School (Washington, D.C.), Melvin J. Berman Hebrew Academy (Rockville, Md.), and Beth Tfiloh Dahan Community Day School (Reisterstown, Md.) participated at the Alexandria event, rotating through more than 10 stations that highlighted various aspects of water quality.

At the three monitoring stations, students tested the water samples from the Potomac River for temperature, turbidity, dissolved oxygen, and pH levels. Other stations were hosted by EPA, USGS, the Washington, D.C. Water and Sewer Authority, the Smithsonian Environmental Research Center (Edgewater, Md.) — which displayed blue crabs — and CH2M Hill (Englewood, Colo.).

Mary Corton, who teaches science to prekindergarten students at Beth Tfiloh Dahan Community Day School, said the students loved the opportunity to attend WWMD. She said her students were very excited to attend this year’s event and said that WWMD was great hands-on learning.

Corton and her students participated in the 2006 event, monitoring a pond on school grounds. Three students trekked to the pond every day to take measurements.

“The pond is really, really clean,” she said regarding the students’ findings.

Stewards for Water
WWMD’s main objective, creating stewards for water, was highlighted throughout the day. Moran called the work done by WWMD very important because it builds stewards for water resources, saying “each citizen will be a little more knowledgeable about their own watershed and empowered to protect them.”

Ben Grumbles, EPA assistant administrator for Water, agreed. 
 
“EPA is proud to be a partner in the growing global movement to connect citizens with their watersheds,” he said.

Hirsch cited the more than 1400 federal, state, local, and citizen groups USGS works with on maintaining and improving water quality. He also discussed the importance of scientists and citizens working together to monitor water sources.

“Progress depends on partnerships,” Hirsch said.

Hirsch went on to emphasize the significance of measuring water sources in order to manage them, noting the importance of point source control, non-point source control, and monitoring water sources.

“You can’t manage what you don’t measure,” he said.

Grumbles also said he hoped that WWMD could help encourage the public and citizens to engage in water quality monitoring in a similar way that the “Reading is Fundamental” program has promoted literacy.

“Monitoring is fundamental,” he said. “An ounce of education is worth a pound of regulation or litigation.”

For more information on World Water Monitoring Day, visit www.wwmd.org.

— Michael Bonsiewich, WEF Highlights