ShotSpotter takes hold in D.C. as city moves to thwart rising gun violence

Another bang-up job for Santa Clara-based ShotSpotter. The company has succesfully installed its gunshot detection and location in Washington, D.C. Attached to the city’s forty-eight surveillance cameras, the coffe-can sized devices use acoustic technology to alert the police whenever a shot is fired — the system can filter similar sounds such as car backfire — and direct officers to the scene of the crime. So far, city officials say, the ShotSpotter has guided officers to three murder scenes in the city’s violence-prone Southeast quadrant, and in one case police were fast enough to make an arrest. “We get there sooner, which means we’re more likely to catch the person responsible,” Police Chief Charles H. Ramsey said. “For an injured person, it can be the difference between living and dying.”

D.C. is just the latest city to get on board with the new technology. At least fourteen other municipilaties have contracted with Shotspotter, including Chicago, Los Angeles, and Charleston, South Carolina. D.C., however, has the distinction of receiving federal assistance. The FBI is funding the project with an eye towards provide it to other areas in the future — perhaps to Prince George’s County in Maryland, where gunshots are often picked up by neighboring D.C.’s sensors. Yet planners must be circumspect in moving forward. Gang members shot at technicians installing the system in Oakland and Los Angeles, and the exact location of the sensors must be kept a secret lest would-be murderers destroy them.

This is all pretty impressive stuff, but Gregg Rowland of ShotSpotter told us the company will soon be bringing the technology to Iraq to help counter sniper fire. By attaching sensors to both troops and their vehicles, the system can quickly inform fire control as to the exact location of the threat, thereby permitting a swift response by a Predator drone. The technology is so sophisticated, in fact, that it maintains a record of battle, allowing officers to determine if the rules of engagement are being followed. As for the future, ShotSpotter is currently developing a classification engine that can identify the actual gun being fired. As Rowland explained, there’s a big difference between hearing a .32 caliber pistol on the other side of a hill and hearing a .50 caliber machine gun.

-read more in Allison Klein’s Washington Post report [http://www.washingtonpost.com/wp-dyn/content/article/2006/10/21/AR2006102100826.html]

BLUE BOX

Technology

All the methods used to detect the firing of a weapon relate to the sounds and flash occurring when a gun is fired. To fire a projectile, a gun explodes a propellant, and the explosion which results propels the bullet or projectile through the barrel and toward the target. There is thus, first, a loud explosion (muzzle blast) which radiates out from the weapon in all directions, and the light from the explosion (muzzle flash) which can be seen best in front of the weapon. The projectile may also be audible as it travels, and if it travels faster than the speed of sound, a sonic boom will propagate out behind the projectile. When the projectile reaches the target its impact will have its own noise (impact noise), and the weapon itself may make distinctive noises when ejecting the projectile shell or loading the next round.

One popular location technique is “counter sniper,” in which the system focuses on detecting the sonic boom of a bullet as it passes by. The major disadvantage of such systems is that in order to hear the sonic boom, they must be downrange of the weapon and within a narrow cone swept out by the sound waves. Systems which detect the muzzle flash or the heat from the explosion of the propellant are limited by requiring line of site between the weapon and the detector. Such systems cannot be used to detect gunfire which can be heard but not seen.

ShotSpotter’s gunshot location technology is based on acoustic detection of muzzle blast and, depending on the circumstances, the sound of the projectile while it travels. The advantage here is that acoustic techniques do not require the shooter to be located in the field of view of a sensor, and thus can cover a much larger area than an optical system. Unlike counter sniper systems, however, ShotSpotter systems can detect gunfire which is not fired toward the sensors because they use muzzle blasts which radiate in all directions.

The company says that to allow the system to differentiate between a weapon being fired and events which sound like the muzzle blast of a weapon (car backfires, people hammering nails), the company’s systems use different technologies, including its patented Spatial Filter technology which massively reduces false alarms.