A practical new approach to holographic video could also enable 2-D displays with higher resolution and lower power consumption.
Researchers at MIT's Lincoln Laboratory are exploring ways to use the same Doppler radar that provides colorful weather pictures on TV to detect biological and chemical agents used in potential terrorist attacks.
Lincoln Lab helped design the Terminal Doppler Weather Radar that provides automatic alerts of hazardous wind shear near airports.
Doppler radar uses a saucer-shaped dish to sweep through space and send a directed pulse of energy out into the sky. When the energy encounters raindrops, for instance, a small part of the energy is reflected back, picked up and processed by computers. The resulting data map tells the number and size of raindrops and their velocity toward or away from the radar tower. The system is very sensitive and ideal for detecting the structure and movement of storms.
The goal is to use the 45 radar towers scattered at major airports around the country as an early warning system for chemical or biological agents disseminated by airplanes, says group leader Mark E. Weber. The U.S. Army conducted the first of a series of tests to investigate this possibility in April 2002. One year later, Lincoln Lab was enlisted to develop software that would scan the Doppler data for something with a different enough profile from snow, rain, insects and other natural phenomena to warrant a closer look.
"The test will provide the U.S. government with data on the feasibility and current capability of commonly used radars to provide an early warning system for chemical-biological events," reads an Army public affairs document. "If the test effort is successful, this technology may be used to provide a rapid chemical and biological detection umbrella for early warning and national preparedness."
As part of the U.S. Army's Homeland Defense Chemical Biological Umbrella (HDCBU) program, the third in this series of tests was conducted last month at Canadian River, Okla. A Cessna crop duster flown by an Environmental Protection Agency pilot disseminated water mixed with anti-freeze at around 1,200 feet above ground level using specific release rates and aircraft speeds. For another test, a harmless ground-up clay was used to simulate particulate spores like anthrax.
"From a radar detection viewpoint, water or clay are quite similar in appearance" to biological or chemical warfare agents, Weber said. The challenge will be to create software that can point to a plume that looks different enough from natural elements to warrant suspicion.
During a recent talk at the MIT Security Studies Program, United Nations weapons inspector Jack McGeorge said that the public's fear of biological attack from a country such as Iraq may be exaggerated. He said that while it is possible to adapt missiles and other devices to squirt dangerous chemicals, "terrorists have not typically done this. Biological weapons are not simple to use effectively. A biological agent has to have a disseminating device and a suitable delivery means to get it to the target and do its thing."
Without the appropriate means--for instance, some agents need to be inhaled in a fine mist, some may need a dart to penetrate a soldier's protective gear--biological agents will not achieve the enemy's desired effect. "A bottle of green goo is not a weapon," he said.
"The Iraqis made tons of biological agents, but there have been no casualties [from these] because they had awful munitions for biological agents." At any time, there are better agents available than the means to disseminate them, McGeorge said.
A prototype of the detection system will be tested this spring on a non-operational Federal Aviation Administration (FAA) radar in Oklahoma City. If successful, the Army intends to equip a number of additional radars around the country with this capability.
The same Lincoln Lab research group working on the early warning system developed a way to achieve wind-shear alerting capability by adding processing to conventional airport surveillance radars.
The Integrated Terminal Weather System merges data from various national and local weather radars, meteorological sensors, aircraft data and satellite imagery to provide advanced forecasts of weather to air traffic controllers, airlines and airport authorities.
A version of this article appeared in MIT Tech Talk on December 17, 2003.