By John McHale
DAYTON, Ohio - Birds colliding with aircraft caused an estimated $357 million in damage between 1985 and 1996, so military and industry scientists want to use an audible radar to warn birds away from approaching aircraft.
Scientists first discovered the audible radar concept during World War II when some people claimed to have heard radar, says Jim Genova, vice president at Raven Inc., in Alexandria, Va. Raven is working under a Small Business Innovative Research program with the Air Force Research Laboratory`s Flight Dynamics Directorate at Wright Patterson Air Force Base in Dayton, Ohio.
"They were thought to be mentally ill," until it was learned that at the right modulation, sharp radar spikes issued microwave pulses that were perceived as sound, explains Malcolm Kelley program manager for bird-strike prevention at the Air Force Research Laboratory in Dayton, Ohio.
"It is much like a microwave oven," Genova explains. "When the microwaves hit the food they change to heat. When the microwave pulses from the radar hit the head, be it a bird or a human, the microwaves changed to heat and interacted with the cochlea of the ear, registering what the subjects perceived as a click."
By using sound created by an audible modulation on a conventional radar to warn the birds of the aircraft`s approach, researchers expect the birds to rely on their own instincts to avoid collision, Kelley says.
Due to limited range - approximately one mile - the modulated radar is ideal for aircraft on their approach to landing and high- altitude flights, while low-flying, high-speed military aircraft would not use the radar, Kelley says.
Between 1985 and 1996 there have been 30,907 total bird strikes in the United States, according to a report from the Bird Aircraft Strike Hazard (BASH) team located at Kirtland Air Force Base in Albuquerque, N.M.
In 1995 the crash of an E-3 Airborne Warning and Control System aircraft at Elmendorf Air Force Base in Anchorage, Alaska, was determined by Air Force officials to have been caused by a collision with a flock of wild geese, says Gene Le Boeuf, bird strike scientist at BASH.
Officials from Israel, which lies in the middle of a major migration zone, claim their air force has lost more lost more planes to birds than enemy fire, Genova says.
The scientists at Raven and the Air Force are concentrating on lower frequencies or infrasound, not only because birds can hear them but also because "low frequencies use up less energy and are therefore less costly," Genova says. "It seems birds associate the infrasound with bad things."
Genova`s team is working with sounds ranging from 1 to 3 kHz, he says, because the infrasound seems to cause a reaction in all species. Other modulations, however, may cause some birds to move away from the aircraft but others may interpret the same sound as friendly greeting and approach the plane, so researchers have more work to do.
"The gold at the end of the rainbow for this project would be to use the right modulation and pulse width to interfere with the bird`s balance, making them dizzy, and forcing them to land," Kelley says.
To research the sounds Kelley`s group is working with researchers at Virginia Commonwealth University in Richmond, Va., to test auditory nerve responses with chickens. Future plans call for a test in the wild.
Once the sounds are determined the next step is modifying the existing radars in aircraft so they can use the microwave technology, Genova explains. "We will probably use a type of modification kit to increase the current system`s power. With the military it will be easier because it may only require a software change."
To handle large flocks of birds such as those in the migration zones of Canada and Israel, Air Force scientists are experimenting with aircraft radar to detect the birds and alert the pilot, Kelley says. He and his team are working with Raytheon Hughes APG-70 radar to detect the migrating birds.
The radar`s range would be about three miles, with probability of detection between 90 and 100 percent depending on the range, he says. This type of approach would benefit the low-flying, high-speed military jets, Genova says. NEXRAD weather radar is also being used to locate the migrating flocks, Kelley says.
For more information on audible radar and Raven, contact Jim Genova by phone at 703-642-3535, by mail at 5500 Cherokee Ave., Suite #310, Alexandria, Va., 22312, by e-mail at email@example.com, or on the World Wide Web at http://www.raven.com.