Muddy Waters: NASA Scientists at Stennis Space Center Study
by Lanee Cooksey of Stennis Space CenterMore articles in People
John C. Stennis Space Center
Stennis Space Center, MS 39529-6000
Nov. 20, 2002
NASA News Chief
HANCOCK COUNTY, Miss. — Dozens of fishing boats creep along a cypress-lined shore, each guided by a seasoned fisherman. One veteran angler senses a clue and glides slowly toward a shallow cove where a trophy-winning fish is certainly lurking — just out of view. There's something there, but it's not a bass.
Buried down in the sand and silt of the lake's bottom lies a rainbow of different noxious chemicals — relics of 100 years of industry in the region. Boat motors stir them up and so do wind- driven waves. The fisherman does not notice what's happening, but a satellite passing 700 km overhead does. It snaps a picture of the lake and beams the data to Earth, where NASA scientists note areas of water that are less reflective than usual — a result of the stirred-up, or re-suspended, sediments.
City officials and environmental regulators can hardly wait to see the data. They hope it will help answer some important questions, such as how much sediment is dumped into the lake by an adjoining river, or whether pollutants buried in a patch of lakebed near an abandoned paper mill pose a threat to swimmers at a beach on the far side of the lake.
NASA scientists at Stennis Space Center hope one day to be able to answer questions like these about re-suspension by using satellites.
Currently, monitoring suspended sediments is done by hand, a challenge for bodies of water that cover hundreds or even thousands of acres. Scant data gathered at a few monitoring stations provide only a glimmer of what's going on.
Around the country, there are dozens of reasons to monitor stirred-up sediments. Shellfish harvests in Northeastern bays, for example, are affected by sediment levels; so is the rich biodiversity of Atlantic, Pacific and Gulf coastal estuaries. Further inland, nutrients released by stirred-up sediments can nourish microscopic phytoplankton in freshwater lakes and trigger algal blooms that choke the lakes' plant and animal life.
This need for wide-area monitoring is what has motivated NASA scientists at Stennis Space Center to explore how satellites might help. And after six months studying Lake Pontchartrain, just north of New Orleans, La., they think they have a system that works.
"We've talked to city planners, [environmental regulators and other] decision makers — and they've said they would welcome NASA's assistance," said NASA's Richard Miller, chief scientist for the Earth Science Applications Directorate at Stennis Space Center and the manager of the project.
Miller's team monitored Lake Pontchartrain using two instruments in space: NASA's SeaWiFS and NOAA's Advanced Very High Resolution Radiometer (AVHRR). Both measure the reflectance of the water — an indicator of turbidity and stirring.
A certain amount of stirring will occur just because of the action of wind-driven waves. This is called "natural re-suspension." To account for it, Miller's group uses a computer model to calculate the expected amount of stirring based on wind speed, wind direction, and the depth and shape of the body of water.
The computer runs its simulation and produces a number the scientists call the index of resuspension intensity. Plotted over the area of the body of water (in the form of false colors or contours) this number maps out the expected resuspension due to wind and waves. "For the environments in Lake Pontchartrain, our index of re-suspension intensity correlates well with our satellite imagery," Miller said.
Sometimes, though, they spot suspended particles in a place not predicted by the computer model. Such irregularities might be evidence of human activity —such as fishing in shallow waters — or perhaps a movement of muddy water from another area, set in motion by a passing storm front. "The results so far are very encouraging," said Miller.
The research team is now starting a new phase of field trials using the Moderate-resolution Imaging Spectro-radiometer (MODIS) sensor, which rides aboard two NASA satellites — Terra and the recently launched Aqua — which together will provide two snapshots per day, one in the morning and one in the afternoon.
Ultimately, the researchers want to construct a system for delivering an executive-summary version of the satellites' observations to the regulators and decision makers who need it. The project's goal, said Miller, is to collaborate with decision-makers in the region to design a system that will suit their needs. He expects that the project could be producing these executive reports in six months' time.
Putting this knowledge into the hands of decision makers will help keep our waterways clean, so that fishers in the future can safely make a meal of the day's catch ... not just a trophy.
News releases provided by NASA's Stennis Space Center are available at www.ssc.nasa.gov/~pao/news/newsreleases/2002.
For more information, call the NASA Public Affairs Office at Stennis at 1-800-237-1821 in Mississippi and Louisiana only, or (228) 688-3341.