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Program Insider: Small-Arms Fire Detector

By Staff Writer | February 1, 2008

The Defense Advanced Research Projects Agency (Darpa) is tapping an advanced-technologies firm to adapt its ground-sniper detection system to warn helicopter crews of the source of small-arms fire.

The agency on Dec, 18, 2007 awarded BBN Technologies a $3.6 million contract to modify its Boomerang system for use on helicopters. Headquartered in Cambridge, Mass., BBN developed the Boomerang system, which is widely used by U.S. forces in Iraq and Afghanistan to alert them to shots and identify where the shooter most likely is. The system (elements of which are shown right) measures sound from the shock wave of the shooter’s bullet and the muzzle blast of his gun to calculate his azimuth, elevation, and range with a high degree of confidence.

The shock wave in particular is unique, said Dave Schmitt, BBN’s director of programs. "It isn’t replicated in nature. That gives you a high level of confidence that yes, indeed, it is a gunshot."

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Helicopters present distinct advantages and disadvantages in adapting such a system. The ground system clusters numerous microphones in a mace-like set-up on a mast that can be placed atop a vehicle; the varied positions help nail down the directions from which the sound came. The mace wouldn’t work on an airframe, for aerodynamic reasons, but it doesn’t have to; mikes can be placed further apart on the airframe, making it easier to isolate the direction of the sound.

However, a helicopter is a very noisy environment, and not just because of the beating and wash of the rotors. BBN engineers already know they won’t be able to detect a muzzle blast amid all that noise. But the shock wave alone can be used to figure the shooter’s azimuth.

The BBN team conducted its first flight test in November, flying a miked-up Black Hawk at Fort Rucker, Ala. through a variety of banks and turns at high and low speeds to characterize the noise environment around the UH-60. Now they are working on optimizing the number and type of microphones.

The next flight test is set for May, with another slated for July, after which Darpa officials will decide whether they want to proceed with the development, and if so how.

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