Massachusetts Institute of Technology researchers are working with the Army to develop a detection system that would involve modifying federal radar stations in nearly three dozen cities.
Congress has so far allocated $15 million to develop the so-called Homeland Defense Chemical Biological Umbrella, with a handful of stations expected to be functional by year's end.
The threat of airborne releases of chemical or biological agents in the skies, once grist for pulp spy novels, took on new urgency after the Sept. 11 attacks. Investigators found evidence that groups of men — which may have included one of the hijackers — made repeated inquiries about crop-duster planes in Florida, possibly to disperse chemical agents like the nerve agent VX, or biological poisons such as anthrax.
Army project leader Arne Johnson said he's confident the system will work. He declined to discuss detailed results of tests, which began last year. "They show the radar does have the capability of this type of event detection," he said.
"We're in midstream here as far as the development cycle, so I honestly don't know what the end system will look like. We're taking the first step here," said team leader Mark E. Weber, who works at Lincoln Laboratory, a high-security MIT campus in Lexington that performs defense research for the Pentagon.
The project will eventually use 45 Federal Aviation Administration radar sites around the country that are located near airports to detect wind shear — the sudden, dangerous air currents that can dash an airplane to the ground as it takes off or lands. The FAA's Terminal Doppler Weather Radar system is separate from the National Weather Service and commercial Doppler radar.
The Army won't discuss how the radar will identify potential attacks, except to say that the computer programs will be able to differentiate between typical air and weather patterns around aircraft, and a chemical or biological event. Once a release is detected, the cloud's movement can be tracked to help local emergency personnel respond and try to protect people in the vicinity.
Some experts have concerns, however, about whether the umbrella makes economic sense — and whether it will be able to accurately warn against deadly agents in the air.
Dr. Tara O'Toole, a physician and bioterrorism expert who heads the Center for Biosecurity at the University of Pittsburgh Medical Center, questioned whether the undertaking was technically possible. Even if it works, she said, it might be hard to distinguish between harmless dust and pollution and something more sinister.
"You get a lot of false positives if you're monitoring the area 24 hours a day, seven days a week," she said. "Each of those false alarms uses up a lot of resources."
Retired Army Lt. Gen. William E. Odom, a National Security Agency director, served on a National Academies committee that released a report last year on tracking hazardous material releases.
He said the radar project may have promise, but it is tackling an "extremely complex" problem.
"Proving that this is technically feasible is the first step. Whether it's financially practical is another question," he said.
The committee's chairman, Robert J. Serafin, a radar specialist and director emeritus of the National Center for Atmospheric Research, said radar could play a role in detecting an airborne biological or chemical terror attack, but he's not convinced it can be relied upon.
"I think it's the kind of work that should be pursued and evaluated, but I don't think that any single observation system like radar in a city will provide the kind of protection that people would want," he said.
The Army has already tested whether Doppler radar — which detects the movement, speed and direction of objects rather than simply pinpointing their location as conventional radar does — could detect substances released into the air.
Last year, a plane sprayed harmless grain alcohol, clay dust and a mix of water and polyethylene glycol — an ingredient in lotions and mascara — over Oklahoma fields. Final tests that would closely mimic an actual release are planned for early May. A demonstration that will be evaluated by observers is tentatively set for late May or June.
Johnson said the Army hopes to have five Doppler locations scanning the skies by year's end, with other places added later. He stressed that the system is just part of a much broader strategy.
"It's one piece of the whole puzzle of protection for the country," he said, "but it's an important piece."
By Theo Emery