Post by BT GeorgePost by Anthony MarshPost by BT GeorgePost by Mark TylerI recently published an animation that recreates the motorcade travelling
https://www.marktyler.org/mc63.html
Hopefully other researchers will find this visual aid useful in their
work.
If anybody spots any errors, or has suggestions for improvements, please
let me know.
You should check your work with Dale Myers. His work to synchronize the
assassination films would allow him to verify your timings as shown on the
Dangerous, Dale Myers was wrong about some of the times.
He faked some of them to try to discredit the acoustical evidence.
I always had long running disagreements with Bob Cutler about the times.
Post by BT Georgehttp://www.jfkfiles.com/jfk/html/acoustics.htm
Rest Tony. Rest. You, Blakey, and GKnoll/Mike Rago are the only people
left on the planet that believe in the Dicatbelt "Evidence". But I am sure
that you 3--and you 3 alone--can save the universe from all the
wrong-headed rest of humanity.
That is simply not true. You don't even know any conspiracy researchers
so you are just making up crap. You don't even know who D.B. Thomas is.
And you intentionally left out W&A and BBN. W&A did further analysis and
found more details, and BBN perfected the science to create technology
that detects the origin of gun shots, used by our military and police.
Maybe you've never been in the real world so you never heard of these
things.
Gunfire locator
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Boomerang, a gunfire locator, being used by British forces in Afghanistan
A gunfire locator or gunshot detection system is a system that detects
and conveys the location of gunfire or other weapon fire using acoustic,
optical, or potentially other types of sensors, as well as a combination
of such sensors. These systems are used by law enforcement, security,
military and businesses 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 displays gunfire alerts
Systems used in urban settings integrate a geographic information system
so the display includes a map and address location of each incident.
Contents
1 History
2 Gunfire characteristics
3 Design
3.1 Sensing method
3.1.1 Acoustic
3.1.2 Optical
3.2 Discriminating gunfire
3.3 Architectures
4 Applications
4.1 Public safety
4.2 Military and defense
4.3 Wildlife poaching
4.4 Open source hardware initiatives
5 See also
6 Notes
7 External links
History
Determination of the origin of gunfire by sound was conceived before
World War I where it was first used operationally (see: Artillery sound
ranging).
In the early 1990s, the areas of East Palo Alto and eastern Menlo Park,
California, were besieged with crime. During 1992 there were 42
homicides in East Palo Alto, which resulted in East Palo Alto becoming
the 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 United
States Geological Survey, approached the Menlo Park police department to
ask if they would be interested in applying seismological techniques to
locate gunshots. 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 time there were no solutions to tracking gunshots, only
a desire to do so. One key attendee was Robert Showen, a Stanford
Research Institute employee and expert in acoustics.[citation needed]
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
one wired and four radio-telemetered microphones was established, with
his home in eastern Menlo Park becoming the command center. 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, Lahr would determine their
location while his wife monitored the police radio for independent
confirmation of their source.
Using this system, 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 tens 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.[citation needed]
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 typical muzzle blast generates an impulse sound wave with a sound
pressure level (SPL) that ranges from 120 dB to 160 dB
A shock wave that occurs as a projectile moves through the air at
supersonic speed. Note, this does not apply to several types of
handguns, whose bullet projectiles do not exceed 1200 feet per second
(i.e. the speed of sound).
Optical flashes can be detected using optical and/or infrared sensing
techniques; however there must be a line of sight from the sensor to the
weapon, otherwise the flash will not be seen. Indirect flashes that
bounce off nearby structures such as walls, trees, and rocks assist in
exposing concealed or limited line-of-sight detections between the
weapon and the sensor. Because only optical flashes are detected, such
systems are typically capable of determining only the bearing of a
discharge relative to sensor unless multiple systems triangulate the
shot range. Multiple gunshots, fired from multiple locations at nearly
the same time, are easily discriminated as separate gunshots because the
sensors generally utilize a focal plane array consisting of many
sensitive pixels. Each pixel in the entire focal plane (e.g. 640×480
pixels) is constantly evaluated.
The projectile generally must travel within 50 to 100 meters of a sensor
in order for the sensor to hear the shockwave. The combination of a
muzzle blast and a shockwave 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's shockwave “snap” can calculate the origin of the
discharge. Multiple gunshots, fired from multiple locations at nearly
the same time, such as those found in an ambush, can provide ambiguous
signals resulting in location ambiguities.
Gunfire acoustics 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 correlates 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, 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
‘spatial filter’ in the first patent issued to ShotSpotter, Inc.[1]
Infrared detection systems have a similar advantage at night because the
sensor does not have to contend with any solar contributions to the
background signal. At night, the signature of the gunshot will not be
partially hidden within the background of solar infrared contributions.
Most flash suppressors are designed to minimize the visible signature of
the gunfire. Flash suppressors break up the expanding gases into focused
cones, thereby minimizing the blossoming effect of the exploding gasses.
These focused cones contain more of the signature in a smaller volume.
The added signal strength helps to increase detection range.
Because both the optical flash and muzzle blast are muffled by flash
suppressors and muzzle blast suppressors (also known as “silencers”),
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 suppressed guns.[citation needed]
Design
Sensing method
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. Both applications can be implemented to detect gunfire
under static and dynamic conditions. Most police related systems can be
permanently mounted, mapped and correlated as the sensors remain in
place for long periods. Military and SWAT actions, on the other hand,
operate in more dynamic environments requiring a fast setup time or a
capability to operate while the sensors are on move.
Acoustic
Further information: Acoustic source localization and Acoustic location
Acoustic systems "listen" for either 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 a few
seconds slower than optical sensing systems because they rely on the
propagation of sound waves. Therefore, the sound reaching a sensor 1
mile from its origin will take almost 5 seconds. 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.
Because such systems have arrays of highly sensitive microphones that
are continuously active, there have been concerns over privacy with this
broad ability to record conversations without the knowledge of those
being recorded (this is "collateral eavesdropping", because capturing
conversations is only an inadvertent capability of the system's design,
and law enforcement agencies have stated that the recording happens only
after shots have been detected.)[2]
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
a line of sight to the area where the weapon is being fired or the
projectile while it is in motion. Although a general line of sight to
the shot event is required, detections are sometimes available as the
infrared flash event bounces off surrounding structures. Just like
acoustic-based systems, electro-optical systems can generally be
degraded by specialized suppression devices that minimize their sound or
optical signatures.
Optical and electro-optical systems have seen success in military
environments where immediacy of response is critical and because they
generally do not need careful location registration as is generally the
case for more permanently installed "civil" crime fighting systems. Just
as acoustic systems require more than one microphone to locate gunshots,
most electro-optical systems require more than one sensor when covering
360 degrees. Acoustic and optical sensors can be co-located and their
data can be fused thereby 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 systems are (essentially) not limited to the number
of individual shots being fired or the number of different shooters
shooting simultaneously, allowing optical-based sensing to easily
declare and locate shooters conducting ambushes that employ multiple
shooters, shooting from multiple locations during the same time period.
The combination of both approaches (acoustic and infrared) assists in
overcoming each system's own limitations while improving the overall
capability to eliminate false declarations of gunshots and/or ambiguous
declaration locations. Even when these combined systems are employed,
shots fired from far enough away will not be detected because the amount
of gunshot signal (both acoustic and Infrared) eventually fades into the
background signals. For acoustic systems that require the supersonic
shock wave for location determination, the bullet must still be
traveling at supersonic speed when it passes the sensor, and it must
pass the sensor within the lateral span of the shock wave. For infrared
sensing of the flash upon a weapon's discharge, the bullet path is not
determined. Combining these two approaches improves the capability under
various conditions anticipated in a combat scenario.
Both optical and acoustic sensors have been used from vehicles while on
the move in urban and rural environments. These sensors have been tested
on airborne and waterborne platforms as well.
Electro-optical detection systems currently tested (2011) can process
the incoming shot signatures at very fast speeds, providing an excellent
method not only to discriminate between weapon firings and other
non-gunshot events but also to identify categories, characteristics, and
sometimes specific weapon types automatically.
Discriminating gunfire
Many techniques can be used to discriminate gunfire (also referred to as
“classifying gunfire”) from similar noises such as cars backfiring or
fireworks. As discussed previously, the SPL and corresponding acoustic
propagation characteristics of high SPL impulsive sounds gave rise to
the ‘spatial filter’ technique patented and used by ShotSpotter in its
Gunshot Location System. This is 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
network is coded in terms of variation in the sequence of all-or-none
(spike) events, or temporal patterns, transmitted between artificial
"neurons". Identifying the nonlinear input/output properties of neurons
involved in forming memories for new patterns and developing
mathematical models of those nonlinear properties enable the
identification of specific types of sounds. These neural networks 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 or infrared sensing, standard triangulation methods can be used
to locate the source of the gunshot once it has been recognized as a
gunshot.
Optical discriminating had previously consisted of methods, among them
spatial, spectral, and creative temporal filters, to eliminate solar
glint as a false alarm. Earlier sensors could not operate at speeds fast
enough to allow for the incorporation of matched temporal filters that
now eliminate solar glint as a false alarm contributor.
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 (“wide-area acoustic surveillance”). The former are generally
used for immediate detection and alerting to 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 immediately alerting 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 “snap” 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 “snap” sound, even amid heavy background noise and
echoes. Such systems are the accepted norm[citation needed] 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.
Applications
Gunshot location systems are used by public safety agencies as well as
military/defense agencies. They have been used primarily in dispatch
centers for rapid reaction to gunfire incidents. In military/defense,
they are variously known as counter-sniper systems, weapons detection
and location systems, or other similar terms. Uses include alerting
potential human targets to take evasive action, to direct force response
to neutralize threats, including automated weapon cuing.
In addition to using gunshot location systems to convey incident alerts,
they also can relay their alert data to video surveillance systems in
real-time, enabling them to automatically slew cameras to the scene of
an incident. Real-time incident location data makes the video
surveillance smart; once cameras have slewed to the scene, the
information can be viewed to assess the situation and further plan
necessary response; the combined audio and video information can be
tagged and stored for subsequent use as forensic evidence.
Infrared-based detection systems can detect not only ordnance blast
signatures but also large caliber weapons such as mortars, artillery,
Rocket-Propelled munitions, machine guns as well as small arms. These
systems can also detect bomb impact explosions, thereby locating the
impacts of indirect fire weapons like artillery and mortars. The
detector can be used as an automated shot correction sensor for close
arms support.
Public safety
In public safety and law enforcement, gunshot location systems are often
used in high-crime areas for rapid alerts and awareness into the
communications and dispatch center where the alerts are used to direct
first responders to the scene of the gunfire, thus increasing arrest
rates, improving officer safety, securing witnesses and evidence, and
enhancing investigations, as well as in the long run deterring gun
crimes, shootings and especially "celebratory gunfire" (the practice of
shooting weapons in the air for fun). Gunshot location systems based
upon wide-area acoustic surveillance coupled with persistent incident
data storage transcends dispatch-only uses because reporting of urban
gunfire (via calls to 9-1-1) can be as low as 25%,[3] which means that
law enforcement agencies and their crime analysts have incomplete data
regarding true activity levels and patterns. With a wide-area
acoustic-surveillance-based approach combined with a persistent
repository of gunfire activity (i.e., a database), agencies have closer
to 100% activity data that can be analyzed for patterns and trends to
drive directed patrols and intelligence-led policing.[citation needed]
Additional benefits include aiding investigators to find more forensic
evidence to solve crimes and provide to prosecutors to strengthen court
cases resulting in a higher conviction rate. With the accuracy of a
gunshot location system and the ability to geo-reference to a specific
street address, versus a dearth of information that typically is the
case when citizens report gunfire incidents to 9-1-1, agencies can also
infer shooters by comparing with known criminal locations, including
those on parole and probation; investigators can also at times infer
intended victims and hence predict and prevent reprisals.
Gunshot location systems have been used domestically in urban areas
since the mid-1990s by a growing list of cities and municipalities that
are embracing gunshot location systems as a mission-essential tool in
their arsenal for fighting violent crime. Federal and homeland security
agencies too have embraced gunshot location systems and their benefits;
notably the FBI successfully used a ShotSpotter gunshot location system
during the 2003–2004 Ohio highway sniper attacks, in conjunction with
the Franklin County Sheriff.
The technology was tested in Redwood Village, a neighborhood of Redwood
City, CA, in April 1996. Through 2007, the manufacturer touted the
device as having benefits, but local officials were split as to its
effectiveness. It is effective in reducing random gunfire. Surveys
conducted for the DOJ showed it was most effective as a "perception" of
action.
A ShotSpotter system installed in Washington, DC, has been successfully
relied upon to locate gunfire in the area of coverage. The Washington,
DC Police Department reported in 2008 that it had helped locate 62
victims of violent crime and aided in 9 arrests. In addition to
assaults, the system detected a large amount of "random" gunfire, all
totaling 50 gunshots a week in 2007. Based on the system's success, the
police department decided to expand the program to cover nearly a
quarter of the city.[4]
As of 2016, detection systems were deployed to a number of cities,
including Bellwood, Illinois; Birmingham, Alabama; Boston; Cambridge,
Massachusetts; Chicago; Hartford[5]; Kansas City; Los Angeles;
Milwaukee; Minneapolis; New Bedford, Massachusetts; Oakland; Omaha,
Nebraska; San Francisco; Springfield, Massachusetts;[6] Washington,
D.C.; Wilmington, North Carolina;[7] New York City;[8] and some in the
United Kingdom and Brazil.[citation needed] Integration with cameras
that point in the direction of gunfire when detected is also
implemented.[6] Utility sites in USA use 110 systems in 2014.[9] San
Antonio, Texas discontinued its $500,000 ShotSpotter service, after
finding it had only resulted in four arrests.[10][11]
In August 2017, the United States Secret Service began testing the use
of ShotSpotter technology to protect the White House and the United
States Naval Observatory.[10][12]
Military and defense
See also: Artillery sound ranging
Determination of the origin of gunfire by sound was conceived before
World War I where it was first used operationally. Early sound-based
systems were used primarily for large weapons. 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.[13]
Acoustic threat-detection systems include the Unattended Transient
Acoustic MASINT Sensor (UTAMS), Serenity Payload and FireFly, which were
developed by the Army Research Laboratory.[14]
Wildlife poaching
In South Africa's Kruger National Park, gunfire locators are being used
to prevent rhino poaching.[15][16]
Open source hardware initiatives
In the United States, gunfire locator projects have been developed using
cost effective open source hardware. The Soter (SO+ER) project[17] was
created for research partners, advocacy, crime watch, and civil liberty
groups to explore the positive impact of responsible use open source,
internet of things (IoT), and cloud technology can have in creating
safer spaces. The project's vision is to empower schools, communities,
hospitals, and other public places to build and manage their own
decentralized gunfire detection and rapid response networks available to
first responders. The current hardware and software is available online.
See also
Boomerang (countermeasure) – gunfire locator by BBN and DARPA
Counter-sniper tactics
Counter-insurgency
Notes
US application/patent 8134889, Showen, Robert L. (Los Altos, CA, US)
Calhoun, Robert B. (Oberlin, OH, US) Dunham, Jason W. (San Francisco,
CA, US), "Systems and methods for augmenting gunshot location using echo
processing features", published 2012-03-13, issued 2012-03-13
ShotSpotter used to record conversations (KBCW CW San Francisco news
report, posted to YouTube on May 23, 2014)
Schlossberg, Tatiana. "New York Police Begin Using ShotSpotter System to
Detect Gunshots". New York Times. Retrieved 22 May 2017.
Klein, Allison (2008-07-05). "District Adding Gunfire Sensors". The
Washington Post. Washington Post. Retrieved 2010-02-10.
"Gunshot Detection System Will Soon Cover All Of Hartford", Hartford
Courant, March 28, 2016
Handy, Delores, "Surveillance Technology Helps Boston Police Find
Location Of Gunfire", WBUR-FM, December 23, 2011.
Freskos, Brian, "Police chief details gunfire location system",
starnewsonline..com, February 21, 2012.
Schlossberg, Tatiana, "New York Police Begin Using ShotSpotter System to
Detect Gunshots", New York Times, March 16, 2015.
Tomkins, Richard. "Raytheon's gunshot detection system being deployed by
utility companies" United Press International, 17 June 2014. Accessed:
19 June 2014. Archived on 17 June 2014.
Farivar, Cyrus (August 26, 2017). "Secret Service conducts live test of
ShotSpotter system at White House". Ars Technica.
Davila, Vianna (August 17, 2017) [August 16, 2017]. "San Antonio police
cut pricey gunshot detection system". San Antonio Express-News. "In the
15 months it’s been in operation, officers have made only four arrests
and confiscated seven weapons that can be attributed to ShotSpotter
technology, Police Chief William McManus said."
United States Secret Service (August 25, 2017). "GPA 30 17 Gunshot
Detection System" (PDF). DocumentCloud. Retrieved August 26, 2017.
"Anti-Sniper/Sniper Detection/Gunfire Detection Systems at a Glance".
DefenseReview.com (DR): An online tactical technology and military
defense technology magazine with particular focus on the latest and
greatest tactical firearms news (tactical gun news), tactical gear news
and tactical shooting news. Retrieved 2018-05-31.
History of the U.S. Army Research Laboratory. Government Printing
Office. p. 73. ISBN 978-0-16-094231-0.
"High-Tech Gunfire Locator May Nab Rhino Poachers in South Africa".
Scientific American. Retrieved 2018-05-31.
South Africa tries gunfire location system to catch rhino poachers
Soter (SO+ER) Project - Free, Open Source Hardware, Real Time
Implementation of a Gunshot Detection System on GitHub
External links
Microflown AVISA
Safety Dynamics, Inc.
ShotSpotter, Inc. also known as SST, Inc. per Christopher Mims,
"Creating a ‘Fire Alarm’ for Terror Attacks", Wall Street Journal,
November 23, 2015.
Location of Acoustic Sources Using Seismological Techniques and
Software, USGS Open-File Report 93-221
Earthquake Technology Fights Crime, USGS Fact Sheet-096-96
Peleng360
Raytheon BBN Technologies
Barrie, Allison (2 March 2017). "Incredible tech detects gunfire
across America". Fox News.
Categories:
Weapon operationWeapons countermeasuresSensorsCounter-sniper
tacticsSecurity technology
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Learn Why 100+ Cities Trust ShotSpotter
Eddie Johnson
Since the city first adopted the ShotSpotter program in 2014, the
homicide rate has plummeted by 35%. Gunshot incidents as an activity has
been reduced by about 50% in the same period of time. MAYOR FRANCIS
SUAREZMiami FL | Customer since 2014
Eddie Johnson
The one technology that has made the most difference in Chicago’s
reduction in gun violence in the last 12 months has been ShotSpotter –
it’s a game changer. POLICE SUPERINTENDENT EDDIE JOHNSONChicago PD |
Customer since 2012
John Cranley
We’re seeing a 40% reduction in gun violence in areas we’re using
ShotSpotter. We’re proud to be a ShotSpotter city. MAYOR JOHN
CRANLEYCINCINNATI, OH | Customer since 2017
ShotSpotter helps solve crimes –
and it can help save lives, too. MAYOR TONI HARPNew Haven, CT | Customer
since 2011
Scott Ruszkowski
After almost 30 years in law enforcement, I’ve yet to find a more
profound and proven way to increase community/police relations than
ShotSpotter. CHIEF SCOTT RUSZKOWSKISouth Bend, IN | Customer since 2014
Jerry Dyer
With ShotSpotter’s immediacy and accuracy, response time to gunshots is
cut in half. It is the easiest, most accurate technology I’ve been
associated with. CHIEF OF POLICE JERRY DYERFresno PD | Customer since 2015
Allwyn Brown
Our cops rely on ShotSpotter
to do their jobs better. CHIEF OF POLICE ALLWYN BROWNRichmond PD |
Customer since 2012
Hillar Moore
ShotSpotter is an important forensic tool that is more reliable than
witnesses. My office relies on it to provide hard evidence on which gun
fired first and from what precise location to help prosecute criminals.
DISTRICT ATTORNEY HILLAR MOOREEAST BATON ROUGE, LA | Customer since 2007
Eddie Johnson
Miami, FL
Eddie Johnson
Chicago, Illinois
John Cranley
Cincinnati, Ohio
New Haven, Connecticut
Scott Ruszowski
South Bend, Indiana
Jerry Dyer
Fresno, California
Allwyn Brown
Richmond, California
Hillar Moore
Baton Rouge, Lousianna
How ShotSpotter Works
SENSORS AND SOFTWARE
Acoustic sensors are strategically placed in a coverage area. When a gun
is fired, the sensors detect shots fired. Audio triangulation pinpoints
gunfire location and machine-learning algorithms analyze the sound.
Likely gunshots are transmitted to the Incident Review Center.
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RTN arrow up 198.87 (+0.26)
Overview and History of the Acoustical Evidence in the Kennedy
Assassination Case
by D.B. Thomas
Part 1 Part 2 Part 3
INTRODUCTION
In 1979 the House Select Committee on Assassinations (HSCA) reported
that President Kennedy’s death was probably the result of a conspiracy.
The primary basis for that conclusion was acoustical evidence of a
gunshot from the Grassy Knoll. Not only has this evidence withstood
serious challenge, it has now been amply corroborated. Nonetheless, it
is evident from commentary on the web, television, and even in
scientific journals, that the acoustics and its corroborative evidence
are widely misunderstood. This essay attempts to explain the technical
and non-technical aspects of the evidence and in that light to discuss
the issues and controversies that have arisen since the original HSCA
study. Most importantly, coupling the audio evidence with the video
evidence provides us with a coherent reconstruction of the murder.
THE PHYSICAL EVIDENCE
Gray Audograph Disc Recorder like the one used by DPD to record channel
two radio traffic
Gray Audograph Disc Recorder like the one used by DPD to record channel
two radio traffic.
On the day that President Kennedy was assassinated, the Dallas Police
Department (DPD) was communicating over two radio frequencies, both of
which were recorded. The primary channel, designated by them as channel
one (Ch-1), was used for routine transmissions and was recorded by a
Dictaphone belt recorder. An auxiliary channel, designated by them as
channel two (Ch-2), was used for special events, in this case, for the
police escort of the President’s motorcade. This channel was connected
to a Gray Audograph disc recorder. Both machines were needle-in-groove
type recorders in that each used a sharp stylus which cut an acoustical
groove into a soft vinyl surface to make the recordings. The respective
machines could then be switched to play back mode using the same stylus.
During the Warren Commission era, the recordings were subjected to
multiple playbacks for the making of transcripts and copies. Because
they were not designed for multiple playbacks, the recordings suffered
significant attrition at that time. Although both recordings still exist
in the possession of our National Archives, neither can be safely played
back today. However, in 1963, the officer in charge of the DPD
communications department, James C. Bowles, made high quality
electromagnetic tape copies of both recordings. Because of the poor
condition of the originals, the Bowles tapes are considered to be the
“best” record of the evidence on the recordings. During the subsequent
HSCA investigation, new playback copies were made by the acoustical
experts who analyzed the recordings, and in 1982, the FBI also made
playback copies of the original disc and dictabelt. But because the disc
and dictabelt were already aged and use-worn by that time, these copies
contain artifacts and do not have the fidelity of the Bowles tapes.
Model AT2C Dictaphone Belt Recorder like the one used by DPD to record
channel one radio traffic
Model AT2C Dictaphone Belt Recorder like the one used by DPD to record
channel one radio traffic.
The Dictaphone machine used by the Dallas Police was a piggyback unit.
When one belt became full, the machine would automatically begin to
record on the second unit. Because a belt can only contain about 15 min
of continuous recording a technician was constantly on hand to replace
belts as they became full. To extend the time between belt changes, the
machine was outfitted with a sound actuation switch which would stop the
recorder during dead air (after about 4 sec), and automatically resume
recording when a transmission was received. The Audograph disc resembled
a more traditional phonograph record, except that this recording machine
had a stylus on a fixed arm. The turntable is mounted on an axis which
rides in a slot such that the axis is driven perpendicular to the stylus
arm by a worm screw as the turntable rotates. Hence, unlike a
traditional phonograph record, the Audograph disc is recorded (and
played back) from the inside out, and playback is at linear track speed
(inches per minute) instead of revolutions per minute. This arrangement
prevents the problem common to floating stylus arms wherein the needle
can be “stuck” in one groove until corrected manually. Also, it
maximizes recorded message density in terms of signal per inch of
acoustical groove, compared to the less efficient phonograph. Audograph
Discs came in two sizes, 9 min and 30 min capacity. This machine was
also outfitted with a sound actuation switch.
AUTHENTICITY OF THE RECORDINGS
Photo of the actual dictabelt
Photo of the actual dictabelt - note the grease pen labeling.
Essentially all of the physical evidence in the Kennedy assassination
has been compromised, and this includes the DPD recordings. The DPD in
1963 was particularly negligent in its duty to mark evidence or maintain
proper chains of possession. Following the murder of the only suspect in
the case, while in the custody of the DPD, police officers purloined
most of the physical evidence for souvenirs. Much but not all of the
evidence was retrieved by the FBI for the Warren Commission’s
investigation. The recordings now in evidence were recovered from the
private home of a police officer by the HSCA in 1978. The Dictabelt held
by the National Archives has writing on its surface made with a white
grease pen indicating that it is belt No. 10 from the date of 22
November 63. The DPD technician with the responsibility for operating
the recorders in 1963 was able to identify the writing as hers. The
problem is that in the transcripts made by the FBI during the Warren
Commission era, the corresponding belt is identified as belt No. 5. The
FBI may have used its own numbering system in making the transcripts and
ignored the labels on the recordings. But typically the FBI evidence
numbers begin with a letter Q. The two different numbers suggests, but
does not prove, that there were at one time, two different belts, of
which one would have to be a copy.
Mary Ferrell
Mary Ferrell, who along with Gary Mack brought the DPD recordings to the
HSCA's attention.
It is known that multiple legitimate and illicit copies of the
recordings were made by the DPD, many for the souvenir hunters in the
department. It is also known that possession of the recordings shifted
between the DPD and the FBI without proper paperwork. It is thought that
all or most of these taped copies originate with the first Bowles tape
copy. The tape copy first provided to the HSCA by Mary Ferrell was
determined to be a multiple generation copy. It is also known that
Bowles rented a Dictaphone machine to playback the Dictabelt for the
taped copy of the Ch-1 transmissions, as well as for the preparation of
transcripts. Copies are often detectable because the recording process
introduces a hum from the recording machine’s motor. Indeed, overlapping
hums are evident on Dictabelt No. 10 (a background hum of 120 Hz
resulting from two 60 Hz hums out of phase). James Barger, the lead
scientist with the HSCA study has suggested that this secondary hum may
indicate that it is a copy, rather than the original. Obviously, to make
a copy of the belt one would require two instruments, one to playback
the original belt and one to create the copy. Alternatively, Linsker et
al. (2006) point out that the second hum only proves that there were two
instruments on line when the recording was made and it isn’t known for
certain what the second instrument was. Hence, the second hum does not
prove that the belt in the archives is a copy, although it is consistent
with that suspicion.
In 2004 it was reported that the National Archives had arranged with
Lawrence Livermore Laboratory to make a virtual playback copy of the DPD
Dictabelt using Laser technology. This technology has been successfully
applied to produce playbacks of the acoustical grooves in the old Edison
cylinder recordings which were in use before the invention of the
phonograph machine. This was necessary because the original belt has
become shrunken and brittle with cracks in the margins. Of course a true
copy will also include any artifacts inflicted on the belt over the
years, hence, for historical as well as acoustical studies, the best
recording will remain the Bowles tapes which were made with high
fidelity equipment when the belt was still in relatively new condition.
The advantage of the Laser copy is that it will be an authentic copy of
the evidence recording in the sense that it will be an untampered copy,
which is not necessarily the case with the recordings available on
E-Bay. However, as of this writing, the dictabelt is still in the
archives and any plans for a laser copy are on indefinite hold.
CIRCUMSTANCES SURROUNDING THE RECORDING
The broadcast transmissions from the Presidential motorcade are recorded
on the Audograph disc of Ch-2. Prior to the assassination most of the
broadcasts originated from the Chief of Police Jesse Curry who was in
the lead car of the motorcade. Curry would state the location of the
motorcade as it wound through the streets of downtown Dallas. The first
broadcast indicating that the shooting had happened was a shouted order
by Curry telling the escort to proceed directly to Parkland Hospital. A
transcript of these broadcasts over Ch-2 during the relevant time
interval is provided here.
Table 1.- Transcript of DPD Ch-2 at approximately 12:30 p.m. 22 Nov. 1963
_______________________________________________________________________
Caller & Call Number Broadcast
_______________________________________________________________________
Lawrence [125] I'm at the Trade Mart now. I'll head back out that way.
Fisher [4]: Naw, that's all right, I'll check it.
Lawrence [125]: 10-4.
Curry [1]: [garbled] the Triple Underpass.*
Dispatcher: 10-4, 1 - 15 Car 2.
Dispatcher: 12:30 - KKB364.
Lawrence [125]: 125 to 250.
Dispatcher: 15 Car 2.
Curry [1]: . . . to the hospital! We're going to the hospital officers!
Go to the hospital! We're on our way to Parkland Hospital! Have them
stand by!
*The first word in this transmission is not clear. An early transcript
made by the DPD interprets the first word as "approaching." Listen
to Audio Recording
Photograph of clock showing 12:30, the time of the gunfire in Dealey Plaza
Photograph of clock showing 12:30, the time of the gunfire in Dealey Plaza.
A significant aspect of these recordings is that as a part of radio
protocol the radio dispatcher would append a time notation to his
broadcasts. This was especially significant because recorded time is not
actual time because of the sound actuation feature. It was also a part
of radio protocol that the dispatcher was responsible for broadcasting
the station’s call numbers at regular intervals. Because of adherence to
the protocol we know that the assassination occurred very close to 12:30
local time, because the dispatcher made his 12:30 station identification
just moments before Curry made his broadcast ordering the escort to go
to Parkland Hospital.
Over on Ch-1, the primary police channel, a most unusual but fortuitous
event occurred. For approximately 5-1/2 minutes the frequency is
dominated by the sound of a motorcycle motor. Somewhere in Dallas the
microphone on a patrolman’s radio had become stuck in the on position.
Because the dispatchers on this channel (there were two) were also
making time notations, we know that this motorcycle segment begins at
approximately 12:28 and runs until approximately 12:34 local time. It
thus overlaps the time of the assassination. The Ch-1 dispatchers were
on opposite sides of a large radio console which provided them with the
means of maintaining radio contact with the hundreds of patrol units
simultaneously. Each dispatcher had his own digital clock for the
purpose of making the time notations. The Ch-2 dispatcher had a separate
console and his own clock. According to JC Bowles, who provides a
detailed account of the communications department operation, these
clocks were regularly synchronized with one another and with a master
analog wall clock. The wall clock was synchronized to official time once
a month. All of these clocks should have been within one minute of one
another, but may have been as much as two minutes apart.
Because it happened during the assassination, at one time it was
suspected that one of the motorcycle police officers might have
deliberately held his microphone open in order to jam police
communications. Ostensibly this would have facilitated the escape of the
perpetrators by interfering with a coordinated police response mediated
by radio communication. It is now accepted that the motorcycle segment
was accidental. Firstly, the open motorcycle segment is only one of
several that day, and not just at the time of the shooting. The
microphone relay button worked by making a contact which when depressed
closed the circuit so that the radio is in transmit mode. The switch had
a spring which held it in the off position when not depressed. If the
spring broke or came loose, the relay became free to slide between the
contact and non-contact position. Hence, when the motorcycle was in
motion the relay would slide making intermittent contact. The motorcycle
broadcasts happened at least four times in the hour leading up to and
following the assassination. Secondly, because the motorcycle segment
ended only three minutes after the shooting there was little
interference with any response the police might have made because in the
immediate aftermath there was mostly confusion anyway. Thirdly, anyone
wanting to jam communications to interfere with police action in
response to the assassination would have jammed Ch-2, the motorcade
channel, not Ch-1.
Based on the Ch-2 dispatcher’s time notation, the assassination occurred
at approx. 12:30. At 12:33 in response to the motorcycle noise on Ch-1,
the Ch-2 dispatcher made a crucial broadcast saying,
"There’s a motorcycle officer up on Stemmons with his mike stuck open on
channel one. Could you find someone to tell him to shut it off!"
Listen to Audio Recording
This raised the crucial question, what made the dispatcher so certain
that the motorcycle was on the Stemmons freeway? The most likely clue
was the fact that at 12:32 one can hear sirens in the background over
the motorcycle motor. Because the one emergency at the time was the
assassination, and because the motorcade was at that moment on the way
to Parkland hospital, and because the fastest road from Dealey Plaza,
the scene of the shooting and Parkland hospital was the Stemmons
freeway, the dispatcher had made the inference that the open microphone
must be on Stemmons. If this inference is correct, given that there were
18 motorcycles assigned to escort the President’s motorcade, then there
was a possibility, if not likelihood, that the unit with the open
microphone might have been one assigned to the motorcade. That being the
case then there was also the possibility that the open microphone could
have been in Dealey Plaza with the motorcade when the shooting occurred.
And that being so, then the gunshots could have been captured over the
open microphone and might be detectable on the Ch-1 recording, somewhere
in the background of the motorcycle noise.
ACOUSTICAL ANALYSIS OF THE DPD RECORDING
National Guardsmen and student protesters at Kent State in 1970
National Guardsmen and student protesters at Kent State in 1970.
Acoustic analysis proved that three Guardsmen fired the first shots, and
identified them by location.
Mary Ferrell and Gary Mack were among the first to realize the
significance of the motorcycle sequence and brought this to the
attention of the HSCA. Investigators for the HSCA recovered dictabelt
No. 10 and contacted the Acoustical Society of America for advice on an
analysis of the recording. The ASA provided a short list of three
laboratories with the required expertise, at the top of which was the
Cambridge MA firm of Bolt, Baranek & Newman (now BBN Technologies). This
was the laboratory which had analyzed the Watergate tapes. More
importantly, this was the lab which had analyzed the Kent State shooting
tapes, the first forensic application of acoustics in a criminal case.
The acoustical experts at BBN were able to show that not only had the
National Guard soldiers fired on the students, contrary to their
subsequent claims that they had only returned fire, but were able to
pinpoint the three individual soldiers who had fired the first shots.
All three, identified in photographs by the FBI, admitted in
interrogation that they had discharged their weapons.
Vehicles equipped with Boomerang anti-sniper echo location system
Vehicles equipped with Boomerang anti-sniper echo location system.
These same scientists were now asked to bring the same technology to
bear on the DPD dictabelt recording. The principle involved is echo
location; the same method by which a submarine is able to navigate
without windows, and bats are able fly in caves. In fact the same
principles were used by the same BBN scientists to develop the Boomerang
technology now deployed by our soldiers in Iraq to instantly locate
sniper positions.
The first step in the analysis was to determine if the gunshots are even
on the dictabelt. This was not as simple as it sounds (no pun intended).
A gunshot makes a sound classified as a white noise, which is to say
that it does not have a characteristic frequency as do most of the
ambient sounds in our environment. Sound is a disturbance in the air.
The gun disturbs the air because the bullet in passing from the chamber
to the muzzle causes the column of air in the barrel to collide
violently with the air in front of the muzzle. Hence it is called a
muzzle blast. Among the characteristics of a muzzle blast are that it is
very loud and very brief. Only noises like rock concerts and jet engines
are as loud, but those noises are not brief in duration. The problem is
that loudness is a function of both the energy that goes into disturbing
the air, its intrinsic loudness, but also the distance between the
source and the listener. If one is a mile away from the gun, then the
muzzle blast will not be very loud. Conversely, a clap of the hands next
to the ear will seem very loud to the listener. The problem then is, if
one finds a loud, brief noise on a recording, how does one know that the
sound is a gunshot as opposed to some other sudden impulsive white noise
with a source close to the microphone. The answer lies in the fact that
an intrinsically loud noise made in an urban environment, such as
downtown Dallas, will reverberate off of the buildings. Such echoes will
be audible at considerable distances. By processing the motorcycle
segment through an oscillograph, an instrument which produces a visible
representation of the sound waves, the acoustical experts searched for
high amplitude sound impulses that were in clusters that would represent
the muzzle blast and its succeeding echoes.
A portion of the oscillograph showing one of the impulse patterns
A portion of the oscillograph showing one of the impulse patterns, in
this case the one identified as the grassy knoll shot. The horizontal
dotted lines show the cut-off level, which spikes must exceed in order
to be counted as part of an impulse sequence.
There are many other technical details that the acoustical experts
applied in this search, which can be found in their report to the HSCA.
Most of these are not at issue so there is no need to repeat them here.
Suffice it to say that in their oscilloscope screening of the 5-1/2
minutes of motorcycle recording, they located a sequence of sounds which
on acoustical criteria could be the assassination gunfire. The sequence
was ten seconds long, occurred almost exactly two minutes into the
motorcycle segment (and thus almost exactly at 12:30) and contained five
candidate impulse patterns. There is some confusion on this point
because a sixth pattern was also suspicious. It was an attenuated
pattern which was considered only because it was in close proximity to
the others, a sort of guilt by association. It was assumed that the
assassination gunfire were shots from a rifle. The presence of the
attenuated pattern might indicate a pistol shot.
Because white noises are commonplace in radio transmissions, there are
many potential explanations for the sound patterns on the dictabelt.
They might have been nothing more than bursts of static from overhead
wires, or shorts in the motorcycle’s electrical system. There might have
been a lightning storm in the distance; it did rain in Dallas that
morning. Anything that would produce brief impulsive noises in a cluster
on a radio broadcast might look the same as a gunshot echo pattern. The
laboratory study was a preliminary screen meant to determine whether or
not such suspect sounds were even present on the recording. What was
significant about the suspect sound patterns, was that they were grouped
into a sequence as expected from the circumstances of the shooting and
that they were deposited on the recording at or very near to the time of
the shooting. Nonetheless, the definitive test would be to compare these
suspect sounds with recordings of real rifle shots in Dealey Plaza. The
suspect patterns on the DPD tape had the acoustical characteristics of
gunshots in the generic sense. Test shots would show exactly what an
echo pattern from Dealey Plaza would look like.
FIELD TESTS IN DEALEY PLAZA
Photo taken of microphones on Elm Street in Dealey Plaza during the
HSCA's acoustical testing
Photo taken of microphones on Elm Street in Dealey Plaza during the
HSCA's acoustical testing.
(view larger version)
In August 1978, with the help of the DPD, gunshots were fired and
recorded on microphones placed along the President’s motorcade route
through Dealey Plaza. When these test patterns were then compared to the
suspect sound patterns on the dictabelt, they were found to match. That
is, all five of the suspect sound patterns identified on acoustical
criteria in the laboratory analysis were found to match to the echo
patterns of test shots fired in Dealey Plaza. The odds of this happening
if the sounds were not the assassination gunfire were remote. It would
certainly be possible for a stray noise pattern to match closely to one
of the sounds on the recording, especially if it were from a white noise
source that tended to occur in clusters; but for all five to match was
very unlikely (the suspicious attenuated sound that preceded the others
failed to match to any of the test shots, even though the test shooting
included firing a pistol on the grassy knoll and firing of a rifle with
its muzzle withdrawn inside the book depository building).
Some details are provided here. Comparisons were based on echo delay
time. Echo delay time is the time in milliseconds (thousandths of a
second) between the arrival of the muzzle blast at the microphone and
the succeeding echoes. Because there are five large buildings facing the
motorcade route in Dealey Plaza, it is expected that a gunshot sound
would reflect off the face of each building, but there would also be a
refractive echo from the corner of each building. Hence, around ten
large echoes would be expected, with the actual number depending on the
actual position of the microphone relative to the buildings. Because of
the dimensions of the plaza (about 500 ft across), and the speed of
sound (about 1100 ft/sec), all of the echoes should arrive within a
quarter to a half second (500 msec) following the muzzle blast. A match
was scored if an impulse in the suspect pattern was at or close to the
same echo delay time as an impulse in a test pattern. By close it is
meant that they were within 6 msec of one another. The slack was due to
the fact that the microphones were arrayed at 18 ft spacings. The degree
of match was determined by calculation of a coefficient using a simple
formula.
C = M² / N n
Where, N is the number of large impulses on the test pattern
n is the number of large impulses on the suspect pattern
and, M is the number that matched among them.
For example, if there were ten impulses in each pattern and nine of them
matched, the value of the coefficient would be 0.8, or if 8 impulses
matched then the value would be 0.6. Only comparisons which gave a score
of at least 0.5 would be statistically significant (no more than a 5%
likelihood to occur by chance), and this value served as the “detection
threshhold.” Four of the five suspect patterns matched to a test pattern
with a correlation coefficient of 0.8; one suspect pattern (the third)
matched to a test pattern with a score of 0.6.
But there was an even more convincing aspect to the results beyond the
matching of the sound patterns. It was the order in the matches.
Continue on to Part 2
© Mary Ferrell Foundation. All Rights Reserved
