Gunfire locator

A Gunshot Location Detection System is a system which identifies the location of a gunshot or other weapons-fire using acoustic, optical or potentially other types of sensors. These systems are used by law enforcement, homeland security, military and commercial customers to identify the source and, in some cases, the direction of gunfire and/or the type of weapon fired. The efficacy of these systems is generally reduced by flash suppressors and silencers, and most of them do not detect weapons fired indoors or under ground.

Origin

In the early 1990 the areas of East Palo Alto and eastern Menlo Park, California, were besieged with crime related to drug traffic. During 1992 there were 42 homicides in East Palo Alto, making it the per capita murder capital of the United States. The Menlo Park police department was often called upon to investigate when residents reported gunshots; however there was no way to determine their source from scattered 911 calls. In late 1992 John C. Lahr, a PhD seismologist at the nearby U.S. Geological Survey, approached the Menlo Park police department to ask if they would be interested in applying seismological techniques to locate gun shots. Others had also approached the Menlo Park police department suggesting ways to help the police by means of gunshot location systems. The police chief arranged a meeting with local inventors and entrepreneurs who had expressed an interest in the problem. At that point there were no solutions to tracking gunshots, only a desire to do so. One key attendee was Dr. Robert Showen, an SRI employee and expert in acoustics.

Dr. John Lahr decided to go ahead with his plans to demonstrate the feasibility of locating the gunshots, relying on his background in the earthquake location techniques and monitoring in Alaska. A network consisting of 1 wired and 4 radio-telemetered microphones was established, with his home in eastern Menlo Park becoming the command center. Dr. Lahr modified the software typically used for locating earthquakes and recorded the data at a higher sample rate than is used for regional seismology. After gunshots were heard Dr. Lahr would determine their location while his wife monitored the police radio for independent confirmation of their source. Using this system, Dr. Lahr was able to demonstrate to the police and others that this technique was highly effective, as the system was able to locate gunshots occurring within the array to within a few 10's of meters. Although additional techniques from the seismic world were known that could better automate the system and increase its reliability, those improvements were outside the scope of this feasibility study.

Types of Gunshot Location Detection Systems

Gunshot location systems generally require one or more sensing modalities to detect either the fact that a weapon has been fired or to detect the projectile fired by the weapon. To date, only sound and visual or infrared light have successfully been used as sensing technologies.

Acoustic

Acoustic systems are defined as those systems with sensing modalities targeted at acoustic phenomena. Such system "listen" either for the bullet bow shockwave (the sound either of the projectile or bullet as it passes through the air), the sound of the muzzle blast of the weapon when it fires the projectile, or a combination of both. Because sound waves can bend (refract) as they travel through the air, and because sound can travel as far as a mile or more away from its origin, it is possible for acoustic gunshot location systems to detect gunfire events at long ranges, and such systems generally do not require that they be within line of sight of the weapon being fired. Acoustic systems can generally be defeated by suppressors.

Due to their ability to sense at great distances, to sense in a non line-of-sight manner, and the relatively low bandwidth required for transmitting their data, systems deployed for law enforcement, public safety and homeland security use in the United States have primarily been acoustic. Such systems tend to be slower than optical systems (due in large measure to the vast difference in the speed at which sound travels versus that at which light travels).

Temporal Pattern

One class of acoustic gunshot location systems, called "temporal pattern recognition systems" by its developer, employ artificial neural networks to be trained and then listen for a sound signature in acoustic events. Like other acoustic sensing systems they are fundamentally based on the physics of acoustics, but they analyze the physical acoustic data using a neural network. Information in the brain is coded in terms of variation in the sequence of all-or-none (spike) events, or temporal patterns, transmitted between nerve cells. Identifying the nonlinear input/output properties of neurons involved in forming memories for new patterns, and developing mathematical models of those nonlinear properties, provide a revolutionary pathway to neural-based classifications of sounds, which can then be trained as "recognizers" of a target sound, like a gunshot, even in the presence of high noise. Standard triangulation methods can then be used to locate the source of the gunshot once it has been recognized as a gunshot.

Optical

Optical or electro-optical systems detect either the physical phenomenon of the muzzle flash of a bullet being fired or the heat caused by the friction of the bullet as it moves through the air. Such systems require that they have a clear line of sight to the weapon being fired or the projectile while it is in motion. Such systems can generally be defeated by specialized flash suppressors.

Optical and electro-optical systems have seen success in military environments where immediacy of response is critical. To date, no such system has delivered 360-degree sensing capability, and therefore multiple optical sensors with relatively narrow fields of view must be used.

Uses

Gunshot location systems are used by public safety agencies as well as military/defense agencies. In public safety, they are usually referred to as "gunshot location systems," but in military/defense, they are variously known as counter-sniper systems, weapons detection and location systems, or other similar terms.

Public safety

In public safety and law enforcement, gunshot location systems are often used in high crime areas to speed police response to gunfire, thus increasing arrests rates and improving officer safety, as well as in the long run to deter gun crimes, shootings and especially "celebratory gunfire" (the practice of shooting weapons in the air for fun). Systems have also been used in domestic terrorism cases, most notably during the 2003-2004 Ohio highway sniper attacks, when a system was deployed by FBI and the Franklin County Sheriff. Cities using gunshot location systems include Washington, D.C.; Oakland, CA; Minneapolis, MN; Rochester, NY; Charleston, SC; Glendale, AZ; Redwood City, CA; Gary, IN; Chicago, IL; Boston, MA; Baton Rouge, LA; East Palo Alto, CA; and Bellwood, IL.

Military and defense

Weapons detection and location systems and counter-sniper systems have been deployed by the US Department of Defense as well as by the militaries of other countries.

External links