Reversing Time to Catch Snipers

At last week's 75th anniversary meeting of the Acoustical Society of America in New York City, researchers presented a system that uses "time-reversed" acoustics to pinpoint the exact locations of gunfire and explosions in an urban environment.

Coming from the U.S. Army's Cold Regions Research and Engineering Laboratory and the University of Connecticut, the researchers (Donald.G.Albert@erdc.usace.army.mil and Lanbo.Liu@erdc.usace.army.mil) tested the system in a small "training" village consisting mainly of two-story concrete-block buildings.

In their tests, they fired a gun at an arbitrary location within the village. The gunshot echoed from building walls and other surfaces. A network of simple audio sensors recorded the reverberations at unique vantage points.

The researchers then turned to a computer, which contained a 2-D computer model of the village. Inside this "virtual village," the computer generated a backwards version of each recorded sound wave. Displaying a map of the village, the computer broadcasted the time-reversed waves from the locations corresponding to the sensors that recorded the original waves. In the computer map of the village, the time-reversed waves eventually returned and converged at the spot corresponding to the source of the gunshot.

The researchers are hoping to develop the system for real-world use, for example by reducing the amount of computer processing time associated with the procedure so that it can potentially pinpoint snipers and explosions in real-time. (Paper 5aPAb5 at meeting; additional text, movies and pictures in lay-language paper.)