U.S. soldiers in Iraq face a bewildering array of threats. Since American and British troops occupied the country last spring, Iraqi insurgents have downed helicopters with heat-seeking missiles, detonated roadside bombs along the routes of army convoys and launched mortar rounds at U.S. bases. One of the biggest frustrations is the elusiveness of the enemy: the insurgents typically slip away before American forces can respond to an attack.
Now the Pentagon's R&D arm, the Defense Advanced Research Projects Agency (DARPA), is trying to provide some high-tech assistance. The agency is pushing to deploy experimental systems that could quickly locate the positions of enemy snipers and mortar crews. One of the most startling examples is a ground-based carbon dioxide laser designed to pinpoint a sniper by measuring the movements of dust particles in the air caused by the shock wave of a speeding bullet. DARPA director Anthony J. Tether announced last fall that the anti-sniper laser, which would reportedly have a range in the tens of kilometers, would be sent to Iraq early this year.
Developed by Mission Research Corporation, a defense contractor based in Santa Barbara, Calif., the system relies on a Doppler lidar, a laser radar that can measure the velocity of moving objects in much the same way that a radar gun gauges the speed of cars on the highway. Because the wavelength of the laser light is roughly comparable to the diameter of a dust particle--about one to 10 microns--some of the light will scatter when it encounters airborne dust. The frequency of the scattered light will be higher if the dust particles are moving toward the laser and lower if the particles are moving away. By analyzing the returning signals, the Doppler lidar can determine wind velocities; in fact, these systems already find use in studies of the atmosphere and at airports to detect wind shear and other turbulence.
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Some defense analysts, however, are skeptical that such a device could track a bullet. Because the shock wave would be so localized and short-lived, the system would need to crisscross the sky with laser beams to pick up signs of the atmospheric disturbance and determine the bullet's trajectory. Another challenge would be distinguishing between a sniper's gunshot and bullets fired by friendly forces or by civilians shooting into the air in celebration (a fairly common occurrence in Baghdad and other Iraqi cities). Says Philip E. Coyle, who was the Pentagon's director of testing and evaluation during the Clinton administration: "Before you can let the troops shoot back, you need a high-confidence system producing accurate results."
Although it is unusual for the military to field experimental prototypes in war zones, DARPA spokesperson Jan Walker notes that it is not unprecedented. For example, the airborne surveillance system known as JSTARS was deployed in Bosnia in 1996, and the unmanned Global Hawk reconnaissance aircraft was rushed into battle in Afghanistan in 2001. But the success rate for new military technologies is not inspiring: during the 1990s, the great majority of army systems that went into operational testing achieved less than half their required reliability, and most air force tests had to be halted because the systems were simply not ready.
Walker says the Pentagon is confident that the anti-sniper laser will prove useful to the soldiers in Iraq. But Coyle, who is now a senior adviser at the Center for Defense Information, a Washington, D.C., think tank, is less optimistic. "There's nothing wrong with trying it to see if it works," he says. "But often these things don't pan out."
