WO2014070174A1 - Procédés d'examen acoustique dans des systèmes de localisation d'armes - Google Patents

Procédés d'examen acoustique dans des systèmes de localisation d'armes Download PDF

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Publication number
WO2014070174A1
WO2014070174A1 PCT/US2012/062860 US2012062860W WO2014070174A1 WO 2014070174 A1 WO2014070174 A1 WO 2014070174A1 US 2012062860 W US2012062860 W US 2012062860W WO 2014070174 A1 WO2014070174 A1 WO 2014070174A1
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Prior art keywords
sensors
survey
propagation
location
source
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PCT/US2012/062860
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English (en)
Inventor
Robert Showen
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Shotspotter, Inc.
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Priority to PCT/US2012/062860 priority Critical patent/WO2014070174A1/fr
Publication of WO2014070174A1 publication Critical patent/WO2014070174A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S3/00—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
    • G01S3/80—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using ultrasonic, sonic or infrasonic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
    • G01S5/18—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using ultrasonic, sonic, or infrasonic waves
    • G01S5/22—Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements

Definitions

  • the present innovations relate generally to methods and systems associated with locating events in real time using sensor arrays. More specifically, it relates to techniques for improving the performance of weapon fire location systems using data from an acoustic survey.
  • a useful corollary to the spatial filter is that if a 4th sensor has an impulse at the time expected from the initial triangularization result, the location is robust enough (i.e., unlikely to be from unrelated sounds) so that it can be automatically presented to dispatchers. Multiple gunshots detected at only 3 sensors allow robust detection and hence dispatch from those 3 sensors alone, as they are nearly certainly correlated.
  • the buildings cause refraction, reflection, and blockage of audio waves propagating from gunfire to the various sensors.
  • the errors due to refracting around buildings can be 15 to 30 feet (in a flat area of a mile extent, the error will only be 10 feet).
  • Reflections are usually not important to triangulation if the direct path is also received, as subsequent impulses can be discarded. But in practice, one cannot be certain that the first impulse is a direct path due to the possibility of blockage. Presently the existence of a hole in the coverage area can only be determined if a known shot is not detected. Also, the sensitivity of the array at a given location to a given sized weapon can only be guessed instead of determined by measurement.
  • Systems and methods consistent with the invention are directed to surveying methods in weapons locations systems.
  • a method of determining propagation within a region using a mobile source and a set of sensors comprising surveying detectable propagation paths to the sensors in a coverage area, and recording propagation parameters between each sensor and each source location.
  • propagation parameters including multipath may be processed to enable improved location determination from fewer numbers of sensors.
  • FIG. 1 is a diagram of an exemplary survey route through a coverage area with buildings and sensors, consistent with certain aspects related to the innovations herein.
  • FIG. 2 is an illustration of exemplary complex acoustic waveforms, e.g., the first three sensors from Figure 1 , consistent with certain aspects related to the innovations herein.
  • FIG. 3 is a diagram illustrating the exemplary results of a survey showing at each survey point the number of propagation paths including multipath, consistent with certain aspects related to the innovations herein.
  • FIG. 4 is a block diagram illustrating an exemplary method of augmenting with a survey the present location method, consistent with certain aspects related to the innovations herein.
  • FIG. 5 is a diagram illustrating an exemplary method of creating a spread spectrum signal, consistent with certain aspects related to the innovations herein.
  • a moving acoustic source is provided to produce signals densely inside the region, for example along all roads. If the signal is received at several sensors (say four or more) the propagation is adequate. If there are not enough sensors, the survey results will show where they need to be added. In addition, multipath propagation may produce a channel pattern which will uniquely determine a location even when only one or two sensors detect the signal. In this case, triangulation is replaced or augmented by pattern recognition. Another benefit is that real-time sensitivity for a given strength weapon at each point in the covered area can be determined based on present measured noise levels.
  • the acoustic signal of the survey need not be an impulse such as gunfire, but it could be a coded continuous signal so that the disturbing sounds of gunfire would not disrupt citizens in the area.
  • problems caused by refraction, reflection and blockage can be ameliorated or removed by using data obtained from an acoustic survey of the geographic area covered by the acoustic event locating system, for example, a gunshot location system.
  • This acoustic survey may be performed by moving an acoustic source to a very large number of positions within the covered area. Then the sensors of a sensor array associated with the system receive acoustic signals from the source which characterize the propagation between each position on the survey to each sensor. The strength and time delays of every signal path (direct, refracted, or reflected) are stored in a database. While the examples presented here are for an acoustic system, substantially the same method can be used in improving knowledge of radio wave propagation. The method disclosed in this patent can assist in determining the coverage extent or ghosting of cellular, radio, or TV transmissions. Also, the source could be an optical flash with intensity
  • the sensors would need an optical or IR receiver.
  • a surveying source e.g., mounted on a vehicle, potentially a garbage truck or a street-sweeper determines its position (e.g., using GPS) and repetitively sends an acoustic signal in all directions as it "tours" a selected area.
  • the transmission time of each signal is also determined (e.g., using GPS) and stored at the source for later combination with the data from the sensors.
  • the survey may be conducted by transmitting the signals in the opposite direction, i.e., the sensors transmit acoustic signals, which are then received at the surveying site.
  • An additional embodiment is to have a two-way propagation path, where either the moving source or the sensor could transmit, and the other end would have a transponder, which returns a replica of the received signal to the opposite end.
  • an RF signal may be used in place of acoustic signals, provided the RF signal frequencies have similar propagation characteristics as the acoustic signals, by matching their wavelengths. Refraction in an urban setting changes the signal propagation delays.
  • the straight line assumption made in location determination by triangulation (also sometimes called trilateralization) is not as valid as desired.
  • triangulation also sometimes called trilateralization
  • the absolute error in location caused by refraction of acoustic waves are typically 15 to 30 feet when using widely-spaced sensors.
  • Use of the recorded survey results can allow a correction to the standard triangularization method, giving superior location accuracy.
  • Reflections are often not confusing, as when the direct path is observable and the echoes arriving later can be identified and discarded.
  • the first arriving impulse is the direct path signal or is a reflected signal.
  • path blockage occurs (e.g., due to obstruction of the direct path by a building)
  • the first arriving echo or multipath may be misconstrued as being the direct path, leading to a false location.
  • This situation accounts for occasional errors in location of up to hundreds of feet, depending on the echo path.
  • sensor redundancy i.e., having many sensors detect a typical event
  • a superior, more economical approach is to use the survey data to help provide a correct location.
  • TOA time of arrival
  • the stored data for the survey point closest to this trial location is then retrieved and inspected. If the trial location was reasonably accurate (say, within 200 ft.), then the stored survey result arrival times will match fairly well to those times for the unknown event. Then nearby survey points can be interpolated to improve the location. For example, the relative arrival times from the 2 nd and 3 rd sensors with respect to the initial reporting sensor can be compared to the database.
  • the survey positions will be at discrete locations, like 100 feet apart along a street, and up to a few hundred feet between streets.
  • the relative arrival times will be smoothly varying when interpolating between the survey points.
  • interpolation between the discrete data base points in North-South and East-West directions can be made to minimize the error of the unknown event's measured relative arrival times.
  • the "best fit" location is determined. The magnitude of the error can be reported to give the user an estimate of the goodness of fit. This procedure will potentially correct for refraction errors. If, however, the unknown event gives a poor location— or no location at all because there were not enough responding sensors to triangulate— a search of the survey route still can be made. The search can start at route locations near the sensor that detected the earliest impulse.
  • the search above can be constrained if exactly two sensors respond by searching along the hyperbola which is defined by the single relative time available.
  • Azimuthal data should be included if available.
  • the azimuthal directions can guard against using echoes and hence not using an incorrect hyperbola in that circumstance.
  • Azimuthal data will in some cases improve the results by lifting ambiguities, such as when an oblique triad is used with two valid mathematical solutions.
  • An important benefit of the invention is the ability to determine if a given strength weapon is detectable at a particular location against the noise level at the event time. Also, if a weapon is located, its strength can also be known, which may assist in classification. And if the system sensitivity were low as a result of high local noise or out-of-service sensors, then the expected imperfect coverage could be known and allowed for.
  • Diagram 100 of FIG. 1 illustrates exemplary sensor positions, survey routes, buildings, and events.
  • a region of interest is presented with sensor positions, the survey route (or tour), and an event.
  • the survey route 120 with beginning and end is shown using the streets in the region.
  • buildings 150 including tall buildings 152 and low buildings 154 over or across which signals may travel in refracted paths.
  • a survey impulse event 130 (real or simulated gunshot) is fired. Note the event produces waves heading to the sensors, sometimes interfered with by buildings. Of the six sensors illustrated, four (1 10A, 1 1 OB, 1 10C, & 1 10F) receive impulses (one sensor is too far, another is blocked).
  • Sensor 1 10A receives two impulses, a direct impulse 140 and an echo/multipath 144
  • sensor 1 10B receives one direct impulse 140
  • sensor 1 10C receives one refracted impulse 142
  • sensor 1 1 OF receives one echo/multipath impulse 144.
  • a path 146 to sensor 1 10E is blocked and not received. The survey data at the closest point to the event would indicate four sensors responding, with one having multipath.
  • the standard triangulation method uses relative arrival times; if it selected the sensor triad ABF, there would have been a considerable error in calculated location. If the triad selected was ABC, then the error would have been quite small due to the slightly refracted path. But the near collinear geometry of that triad would lead to dilution of accuracy and possibly to an ambiguous result where the hyperbolae from each pair might intersect at two locations.
  • Figure 2 illustrates a plot 200 of acoustic signatures for sensors 1 10A, 1 10B, and 1 10C from figure 1 .
  • An illustration of the postulated acoustic times series for the first three sensors 1 10A, 1 10B, and 1 10C of Figure 1 is presented here.
  • sensor A 1 10A both the direct and the echo (multipath) signal is seen, while for sensors 1 10B and 1 10C, only one strong path is present.
  • sensor 1 10C the position of the actual onset is delayed and the impulse has a lower strength due to refraction around a building. Note also that higher noise levels reduce the amount of multipath and also make weaker sensors harder to detect.
  • the survey is preferably conducted densely, for example along every street and accessible alleyway.
  • the separation between database points along the survey route should also be small, nominally about 100 feet. This will provide a dense dataset which can provide accurate corrections using interpolation.
  • the number of survey points would be of order 1 ,000 per square mile if the assumption is made that streets in an area having 10 x 10 blocks are surveyed.
  • a limited survey may be performed whose purpose is to characterize a mini hole such as in an alleyway.
  • the expectation is that while only one or two sensors might hear the mini-survey signals, the echo environment will be so rich that the mutipaths will permit location at the various points inside the alleyway.
  • a loud and impulsive acoustic signal (e.g., such as from weapons fire) is generated at regular spacing down the length of the alleyway, and the multipath arrivals at the sensors are recorded.
  • the acoustic signals used by the survey could in principle be loud impulsive sounds or could be continuous or partially continuous sounds.
  • the simplest method is to fire off a rifle or a surrogate (gas explosions, M80s) along the survey route.
  • An automated locator such as a GPS receiver co-located with the survey vehicle would assist in survey documentation. Knowledge of the exact time of a signal is preferred, as then propagation times to sensors are absolute and not relative. This could assist in directly showing any error in assumed sensor locations or in directly determining refraction effects along a single sensor path.
  • a less intrusive signaling method would be to use a coded acoustic signal to spread out the energy from a rifle sound (nominally 2 ms) to perhaps 2 second or longer, so the sound would be noise-like and hence far less obvious.
  • Figure 3 is a diagram 300 showing exemplary sensors, survey route, buildings, and propagation results. This illustrates the survey source movement, and shows where along the route there was propagation to 1 , 2, 3, 4 or more sensors, as well as indicates where there was multipath. The number of cross-hatches gives the number of multipaths present at that point in the survey.
  • An analysis of the survey (tour) data can provide knowledge of where there are holes in the coverage (i.e., not enough sensors) and where there is unnecessary redundancy (i.e., an excess number of sensors). Note that between sensors F and E none of the sensors are reached, due to blockage from the buildings. Hence to provide coverage in this region at least one additional sensor is required. After this new sensor is installed this region needs to be surveyed again. If that sensor has enough multipath to use for determining locations near it, then only one new sensor would be required. The survey should be redone whenever the sensor set is changed or buildings are significantly altered.
  • the survey should include areas well outside of the array limits, out to distances where just one sensor has measurable multipath.
  • the survey location method can assist the most, by using multipath in addition to the scarce direct paths.
  • the survey is preferably performed on both calm and windy days in order to characterize the propagation under both conditions. Since the wind velocity increases with height, a source near the ground will have rays emitted
  • the effect on the coverage area with respect to a fixed array is that coverage may be slightly skewed towards the upwind side of the array, and that it will be eroded on the downwind side.
  • the survey should be performed once for each cardinal wind direction commonly occurring at that city.
  • the strength of the signals used in the survey should be strong enough to be equivalent to, if possible, typical loud gunfire.
  • the absolute survey signal strength should be known. Since the background noise is lower at night, the most sensitivity will come when the survey is performed at night.
  • the array noise and the signal strength should be measured at each sensor during the survey to determine the signal to noise ratio (SNR) for each recorded path. For the conditions of the survey, a map can be generated showing where 4 or more paths are received, and hence gunfire could be detected and confirmed.
  • the survey will allow prediction in real-time of the system sensitivity to a specific strength of weapons or events, given the current noise level.
  • a real-time, dynamic coverage map of the area can be constructed. The prediction is easily made by scaling the given weapon strength compared to the survey strength, and the survey noise to the current noise. If the resulting predicted SNR is above unity a given path can be detected and so detectability of each survey path is determined for the currently-measured noise. If there are 4 or more paths at a given point detectable, the point can be included in the present coverage map. The boundaries of that map will shrink as noise increases, and any included holes should expand in size.
  • Another, similar procedure can be made, once a new unknown event is located, to determine its absolute strength using the acoustic survey results. Take the set of measured propagation strengths, and compare each of them with the survey strengths by taking their ratio. If the ratios are roughly similar, then the average of the ratios gives the unknown strength with respect to the known survey strength.
  • wind is a consideration for propagation. For the precise accuracy demanded on the timings, the average wind velocity should be measured during the survey and the survey timings compensated. Likewise, the current wind direction and speed are to be measured, and the survey with the wind closest to the present direction should be used. Interpolation to better match the wind direction can also be done.
  • Figure 4 is a diagram incorporating exemplary survey results 400, which illustrates a system diagram of how the survey data together with pattern recognition improves present system results.
  • Improvement above the standard location method relies on having an adequate survey database with arrival times and amplitudes for all propagation paths (direct, refracted, and echo) between each point on the survey and every sensor that detects a signal from that point.
  • the impulses are detected at various sensors 420; in the case illustrated the first pulse arrival is at sensor "j.” All the received impulses are sent to the straight-line location routine 432 and to the survey database 444.
  • the database is organized to accept inputs either from an "arrival time port” 442 or from a "trial location port” 446.
  • the pattern recognition can begin with inputting and sorting the arrival times before the triangulation routine finishes and provides a trial location.
  • the database is entered where j arrivals are the earliest. Then the time to the 2nd-arriving sensor is compared with corresponding database times, finding the best matches in relative arrival times for the initial impulses in each subsequent reporting sensor. A 'match' occurs when that survey point is found where the survey and current relative arrival times have minimum differences, or more properly, the minimum squared error (MSE) between relative onset times is found. A 'better match' is found by interpolation between adjacent survey points to obtain a more exact source location. Then multipath times (if existing) are compared with the database multipath to obtain the 'best match' location. Meanwhile the straight-line location routine processes a location from the input times.
  • MSE minimum squared error
  • FIG. 4 Aspects and advantages of the FIG. 4 should also be noted with regard to processing without survey information 430 as well as processing augmented with survey information 440. For example, representative systems involving
  • processing without survey information are typically characterized by: requiring 3 sensors to locate a weapon fire incident as well as a fourth sensor to confirm the location; refraction errors, as the necessary data and data processing are absent; occasional large errors stemming from echos; and possible ambiguous location information when, e.g., a set of 3 sensors does not receive adequate signal information (though this latter problem may be correctable with azimuthal sensors).
  • processing is typically characterized by: a requirement of only 3 or 4 total paths (i.e., 1 to 4 sensors) to locate and confirm weapon fire incidents; capability of correcting for refraction errors; the ability to resolve echoes and 3-sensor ambiguities via pattern matching; and knowledge of absolute source strength and present system sensitivity.
  • an RF signal or an acoustic signal may be used in lieu of the other, with the expectation that the RF or acoustic signals would have similar propagation characteristics as the other, if their wavelengths were roughly matched.
  • Reasons to use one as a surrogate for the other include that a particular transducer is more realizable, that the desired bandwidth was more easily achieved, that the nuisance of using one was reduced more by one than by the other.
  • RF is meant here to include all electromagnetic frequencies; likewise, acoustic is to include all frequencies and propagation in fluids or solids. The combination of RF and acoustic propagation in a magnetic field as Alfven waves is also included.
  • Such exemplary surveying implementations may also be employed using a scale model of the complex area to be investigated.
  • the model may be used instead of the actual city.
  • Sensor positions are more readily adjusted in a scale model than in an actual city, the sources can be sent anywhere, and no citizens would be disturbed.
  • the wavelengths of the sources are adjusted by the scale factor.
  • Such scale model implementations may also be employed when the model is larger than the actual area under investigation. An example of this is if a circuit chip with quasi-planar features required a characterization
  • Figure 5 illustrates plot 500 showing a coded continuous signal, and includes illustration of a portion of a discrete code produced at the survey source, and the compressed response after decoding.
  • Waveforms commonly used in radar or communications system may be adapted to provide the desired properties.
  • Many coding schemes are available to choose from, including linear chirps (which might sound obnoxious) to pseudo noise codes which would sound like colored white noise or hiss.
  • One reference is Spread spectrum Communications Handbook, McGraw-Hill, electronics edition, 2002 (Originally 1985).
  • Figure 5 illustrates a pseudo code 510 on the left showing reversals of the code phase at multiples of the baud (chip) rate.
  • a low frequency sinusoid would be transmitted, with phase reversals occurring where the code changes sign. This spreads the original tone into a waveform which will be perceived by humans as hiss.
  • this code When decoded (or compressed), this code has the form of the impulse shown on the right with only small sidelobes 520. The width of that lobe is approximately a chip length. The peak amplitude is equal to the code length (total number of bauds or chips).
  • These codes have lengths given by 2 -1 , where practical integers N might be from 6 to 13, giving code lengths of 63 to 8191 .
  • a code length of 1023 would hence give a compression ratio of about 30 dB, meaning that the continuous sound of the code can be 30 dB below the strength of gunfire.
  • the tone frequency will be chosen to give desired propagation distance in the atmosphere up to 2 miles; likely values are between 300 and 2000 Hz.
  • the baud or chip length (duration) would be chosen to give the required spatial resolution and to be a small multiple of the tone period. Values from 1 to 5 ms give modulation sidebands of 1 kHz down to 200 Hz, and spatial resolution of about 1 to 5 feet. Another constraint exists: the coherence of the propagation over the length of the code for the distances and refractions encountered.
  • the code parameters can be selected to give the desired lower and upper frequency span of the transmission. Different parameters can then be used to interrogate the propagation channel at different frequencies, which could determine the frequency capacity of the channel. Because
  • a practical way to conduct the survey might be to mount an omni-speaker on a garbage truck or a street sweeper. At a velocity of 5 mph (7 fps), a street sweeper it would have over 12 seconds between survey points if the point separation were 100 ft. This will be adequate time to transmit a coded
  • the decoding needs to be adjusted to take into account the known uniform phase changes over the duration of the code, as is a common practice in coherent radars imaging a moving target.
  • the strength of the signal required would ideally be equivalent to that of a loud rifle, or 160 dB SPL re 1 m.
  • the compression is 36 dB, so the equivalent continuous wave power would be (160 - 36) or 124 dB. This is probably too loud to be acceptable, as a street sweeper has an intrinsic noise of 95 dB SPL.
  • gunfire from the community may provide a distributed set of sources. These source event positions would usually not be known except by location calculations from the gunshot location system itself (unless confirming evidence from witnesses or shell casings were available).
  • this "community survey” may not be accurate enough to correct for refraction, but it could provide patterns of reverberation or multipath during good acoustic conditions which could provide a "community database.” Then, if a new shot came in under less than ideal acoustic conditions (large noises, winds) but the sensors still received some associated multipath information, then the community database could be interrogated to provide a match and give a reasonable solution which would otherwise not be possible.
  • embodiments and features of the invention may be implemented through computer-hardware, software and/or firmware.
  • the systems and methods disclosed herein may be embodied in various forms including, for example, a data processor, such as a computer that also includes a database, digital electronic circuitry, firmware, software, or in combinations of them.
  • signal processing components such as software, systems and methods consistent with the present invention may be implemented with any combination of hardware, software and/or firmware.
  • the above-noted features and other aspects and principles of the present invention may be implemented in various environments.
  • Such environments and related applications may be specially constructed for performing the various processes and operations according to the invention or they may include a general-purpose computer or computing platform selectively activated or reconfigured by code to provide the necessary functionality.
  • the processes disclosed herein are not inherently related to any particular computer, network, architecture, environment, or other apparatus, and may be implemented by a suitable combination of hardware, software, and/or firmware.
  • various general-purpose machines may be used with programs written in accordance with teachings of the invention, or it may be more convenient to construct a specialized apparatus or system to perform the required methods and techniques.
  • the systems and methods disclosed herein may be implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., in a machine readable storage medium or element, for execution by, or to control the operation of, data processing apparatus, e.g., a programmable processor, a computer, or multiple computers.
  • a computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.
  • a computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

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  • Engineering & Computer Science (AREA)
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Abstract

La présente invention concerne un procédé d'examen apportant des améliorations dans des systèmes de localisation de coups de feu. Dans un système urbain avec un réseau distribué au milieu de nombreux bâtiments qui bloquent les chemins de signal ou créent des échos, des procédés sont prévus pour mesurer la propagation de signal. Un examen ou un parcours de la région couverte utilise une source de signal mobile pour sonder la propagation à l'intérieur de la région. Les résultats d'examen peuvent indiquer où des capteurs plus ou moins nombreux sont nécessaires. Les résultats d'examen ainsi que le bruit mesuré actuel donnent une prédiction de la sensibilité instantanée du système. De plus, la propagation par trajets multiples peut être utilisée pour déterminer un emplacement, même si seulement un ou deux capteurs détectent le signal. Dans de tels cas exemplaires, la triangulation peut être remplacée ou complétée par une reconnaissance de formes. De plus, les signaux de l'examen ne sont pas nécessairement des impulsions acoustiques tels que des coups de feu, mais peuvent être des signaux RF, ou des signaux continus codés de sorte que les sons de type coups de feu ne gênent pas les citoyens dans la zone.
PCT/US2012/062860 2012-10-31 2012-10-31 Procédés d'examen acoustique dans des systèmes de localisation d'armes WO2014070174A1 (fr)

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US10586109B1 (en) 2016-04-26 2020-03-10 Shooter Detection Systems, LLC Indoor gunshot detection with video analytics
US10627292B1 (en) 2016-04-26 2020-04-21 Shooter Detection Systems, LLC Indoor gunshot detection analysis during ongoing fire alarm
US10657800B1 (en) 2016-04-26 2020-05-19 Shooter Detection Systems, LLC Gunshot detection within an indoor environment
US10830866B1 (en) 2016-04-26 2020-11-10 Shooter Detection Systems, LLC Testing of gunshot sensors
US11282358B1 (en) 2016-04-26 2022-03-22 Shooter Detection Systems, LLC Gunshot detection in an indoor environment
US11282353B1 (en) 2016-04-26 2022-03-22 Shooter Detection Systems, LLC Gunshot detection within an indoor environment with video analytics
US11604248B1 (en) 2016-04-26 2023-03-14 Shooter Detection Systems, LLC Low power gunshot sensor testing
US11688414B1 (en) 2016-04-26 2023-06-27 Shooter Detection Systems, LLC Low power gunshot detection
US12094485B1 (en) 2016-04-26 2024-09-17 Shooter Detection Systems, LLC Low power gunshot detection implementation
US11417183B1 (en) 2016-08-24 2022-08-16 Shooter Detection Systems, LLC Cable-free gunshot detection
WO2019098956A3 (fr) * 2017-08-08 2019-09-19 Kandil Yusuf Écran acoustique formé par ondes acoustiques ultrasonores

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