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Gunshot Location Detection System - China roll form machinery - China metal forming machine by hi joiney
The examples and perspective in this article may not represent a worldwide view of the subject Please improve this article and discuss the issue on the talk page October 2009 A Gunshot Location Detection System is a system that detects and conveys the location of a gunshot or other weapons fire using acoustic optical potentially other types of sensors as well as a combination of such 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 Most systems possess three main components An array of microphones or sensors either co located or geographically dispersed A processing unit A user interface that receives and visualizes gunfire alerts Systems used in urban settings integrate a GIS so the visualization includes a map and address location of each incident Origin In the early 1990s 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 Gunfire Characteristics There are three primary attributes that characterize gunfire and hence enable the detection and location of gunfire and similar weapon discharges An optical flash that occurs when an explosive charge is ignited to propel a projectile from the chamber of the weapon A muzzle blast that occurs when an explosive charge is ignited to propel a projectile from the chamber of the weapon A typical muzzle blast generates an impulse sound wave with a sound pressure level SPL that ranges from 120 dB to 160 dB A nap or rack that occurs as a projectile moves through the air at supersonic speeds Optical flashes can be detected using optical and or infrared sensing techniques note that there must be a line of sight from the sensor to the weapon otherwise the flash will not be seen Because only optical flashes are detected such systems are typically only capable of determining the bearing of a discharge relative to sensor The projectile generally must travel within 50 to 100 meters of a sensor in order for the sensor to hear a supersonic nap The combination of a muzzle blast and a supersonic snap provides additional information that can be used along with the physics of acoustics and sound propagation to determine the range of a discharge to the sensor especially if the round or type of projectile is known Assault rifles are more commonly used in battle scenarios where it is important for potential targets to be immediately alerted to the position of enemy fire A system that can hear minute differences in the arrival time of the muzzle blast and also hear a projectile shockwave nap can calculate the origin of the discharge Gunshots must be distinguished reliably from noises that can sound similar such as firework explosions and cars backfiring Urban areas typically exhibit diurnal noise patterns where background noise is higher during the daytime and lower at night where the noise floor directly correlated to urban activity e g automobile traffic airplane traffic construction and so on During the day when the noise floor is higher a typical handgun muzzle blast may propagate as much as a mile During the night when the noise floor is lower a typical handgun muzzle blast may propagate as much as 2 miles Therefore a co located array of microphones or a distributed array of acoustic sensors that hear a muzzle blast at different times can contribute to calculating the location of the origin of the discharge provided that each microphone sensor can specify to within a millisecond when it detected the impulse Using this information and the knowledge that most urban crimes are committed with handguns citation needed it is possible to discriminate between gunfire and normal community noises by placing acoustic sensors at wide distances so that only extremely loud sounds i e gunfire can reach several sensors this has been termed a patial filter in the first patent issued to ShotSpotter Inc Showen and Dunham 1997 Because both the optical flash and muzzle blast are muffled by flash suppressors and muzzle blast suppressors also known as ilencers the efficacy of gunshot detection systems may be reduced for suppressed weapons The FBI estimates that 1 or fewer of crimes that involve gunfire are committed with silenced gunfire Sensing Methods 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 Systems that use acoustic only techniques are defined as those systems with sensing modalities targeted at acoustic phenomena Such systems 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 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 sensor telemetry data systems deployed for law enforcement public safety and homeland security in the United States have primarily been based on acoustic techniques Acoustic only based systems typically generate their alerts slower than optical sensing systems because they rely on the propagation of sound waves at 1 125 feet second or 768 mile hour in dry air at 68 F Therefore the sound reaching a sensor 1 mile from its origin will take almost 5 seconds Additional delays maybe imposed on the conveyance of alerts for systems that distinguish between single rounds and multiple rounds of gunfire While seconds do matter especially when gunfire is involved a few seconds to accommodate pickup from distant sensors and to discern the number of rounds fired often an indicator of incident severity are both tolerable and a drastic improvement for typical police dispatching scenarios when compared against the several minutes that elapse from when an actual discharge occurs to the cumulative time of several minutes that pass when a person decides to place a 9 1 1 call and that information is captured processed and dispatched to patrol officers Discriminating Gunfire Many techniques can be used to discriminate gunfire also referred to as lassifying gunfire As discussed previously the SPL and corresponding acoustic propagation characteristics of high SPL impulsive sounds gave rise to the patial filter technique patented and used by ShotSpotter in its Gunshot Location System This is but just one of several methods used to distinguish between gunfire and other impulsive sounds Analysis of the spectral content of the sound its envelope and other heuristics are also commonly used methods to distinguish and correctly classify impulsive sounds as gunfire Another method of classifying gunfire uses temporal pattern recognition as referred by its developer that employs artificial neural networks that are 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 Regardless of the methods used to isolate gunfire from other impulsive sounds 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 Acoustic and optical sensors can be co located and their data can be fused enabling the gunshot location processing to have a more exact discharge time that can be used to calculate the distance of the discharge to the sensors with the greatest possible precision Optical flash detectors require a line of sight to the discharge which obviates applicability of their use in urban areas for public safety use where such lines of sight are impossible Architectures Different system architectures have different capabilities and are used for specific applications In general there are 2 architectures stand alone systems with local microphone arrays and distributed sensor arrays ide area acoustic surveillance The former are generally used for immediate detection and alerting of a nearby shooter in the vicinity of the system such uses are typically used to help protect soldiers military vehicles and craft and also to protect small open space areas e g parking lot park The latter are used for protecting large areas such as cities municipalities critical infrastructure transportation hubs and military operating bases Most stand alone systems have been designed for military use where the goal is to immediately alert human targets so they may take evasive and or neutralization action Such systems generally consist of a small array of microphones separated by a precise small distance Each microphone hears the sounds of gunfire at minute differences in time allowing the system to calculate the range and bearing of the origin of the gunfire relative to the system Military systems generally rely on both the muzzle blast and projectile shockwave nap sounds to validate their classification of gunfire and to calculate the range to the origin Distributed sensor arrays have a distinct advantage over stand alone systems in that they can successfully classify gunfire with and without hearing a projectile nap sound even amid heavy background noise and echoes Such systems are the accepted norm for urban public safety as they allow law enforcement agencies to hear gunfire discharges across a broad urban landscape of many square miles In addition to urban cityscapes the distributed array approach is intended for area protection applications such as critical infrastructure transportation hubs and campuses Using common data networking methods alerts of the discharges can be conveyed to dispatch centers commanders and field based personnel allowing them to make an immediate assessment of severity and initiate appropriate and decisive force response Some systems have the capability of capturing and conveying audio clips of the discharges with the alert information that provides additional invaluable information regarding the situation and its severity Similarly for the protection of critical infrastructure where the information is clearly and unambiguously conveyed in real time to regional crisis command and control centers enabling security personnel to cut through often inaccurate and delayed reports so they may react immediately to thwart attacks and minimize subsequent activity 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 and have primarily been used in dispatch centers for rapid reaction to gunfire incid
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