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The infrasonic sensing array, designed by the U.S. Army Research Laboratory (ARL), was a military device that detected and located explosive events with inaudible frequencies at long ranges, such as artillery, missiles, and helicopters through the use of the array process. [1] It was also used for direction-finding and positioning for navigational purposes and for detecting atmospheric events for battlefield weather prediction. [2]
Infrasound is the area of acoustics that deals with frequencies below the audible region of human hearing. For army infrasound applications, the target frequency range was in the 1–20 Hz band. [3] Infrasound has the ability to reach distances of 100–500 km. There are natural sources of infrasound emissions, such as avalanches, tornados, volcanoes, earthquakes and man-made sources of infrasound, such as aircraft engines, helicopters, artillery, ship engines, bombs, and explosions. [2] Because there were so many different sources of infrasound, methods of detecting were of interest for the military and civilians.
Long distance propagation of infrasound is allowed by ground reflection and molecular attenuation. The ground acts as a reflecting service for incoming energy and molecular attenuation is zero at infrasonic frequencies. [4]
The infrasonic sensing array contained a minimum variance distortion-less response beam former to enhance the detection and estimation performance of the acoustic system by improving the signal to noise ratio. [5] The outputs of a spatially distributed array of sensors were combined by the beam former, where the signals from one direction were added, while the effects of noise and interference from other directions were reduced.
The main obstacle in the detection and analysis of infrasonic signals was the intrinsic pressure fluctuations due to air turbulence/wind noise, which was always present. [6] Wind noise, caused by the passage of air over the microphone, limited the ability to collect infrasonic signature in a covert area. [3] Wind noise levels increased with decreasing frequency and mean noise levels could have been equal or greater than the levels of the signal to be detected. [6] To solve this problem, signal processing, physical wind guards/filters, multiple sensors for spatial averaging, and wind hose/pipe filtering techniques could have been used. [2]
It was shown that wind barriers could be used for wind noise reduction as they break up turbulence and effectively preform spatial average on turbulence scales smaller than the size of the barrier. [3] Microporous hoses stemming from a central microphone were used for applications where the source direction is unknown. These hoses make the filter's instrument response and wind–noise reduction uniform for all signals and wind directions, simplifying the array process. [7]
Infrasonic sensing arrays supported the U.S. Army's 501st Military Intelligence Brigade in South Korea, fielded in 2001. [1] It was also fielded to Iraq and Afghanistan in 2004. Information obtained with the research of infrasonic sensing arrays lead to the development of The Unattended Transient Acoustic MASINT Sensor (UTAMS) computer carried by the Aerostat of Persistent Threat Detection System (PTDS), which was an acoustic sensor used to detect the point of origin and the point of impact of missiles, IEDs, and missiles. [8]
Other applications included use by military or search and rescue teams, by field researchers studying volcanology or seismology, and by other geo-acoustic scientists and engineers. [2] Infrasound sensing systems were used for the global monitoring of international compliance with weapon test ban treaties. Military use also involved long-range detection and direction-finding of air or ground vehicles, and detecting and locating artillery fire.
Radar is a system that uses radio waves to determine the distance (ranging), direction, and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track aircraft, ships, spacecraft, guided missiles, motor vehicles, map weather formations, and terrain.
Sonar is a technique that uses sound propagation to navigate, measure distances (ranging), communicate with or detect objects on or under the surface of the water, such as other vessels.
Infrasound, sometimes referred to as low frequency sound or subsonic, describes sound waves with a frequency below the lower limit of human audibility. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. Although the ear is the primary organ for sensing low sound, at higher intensities it is possible to feel infrasound vibrations in various parts of the body.
Measurement and signature intelligence (MASINT) is a technical branch of intelligence gathering, which serves to detect, track, identify or describe the distinctive characteristics (signatures) of fixed or dynamic target sources. This often includes radar intelligence, acoustic intelligence, nuclear intelligence, and chemical and biological intelligence. MASINT is defined as scientific and technical intelligence derived from the analysis of data obtained from sensing instruments for the purpose of identifying any distinctive features associated with the source, emitter or sender, to facilitate the latter's measurement and identification.
Bioacoustics is a cross-disciplinary science that combines biology and acoustics. Usually it refers to the investigation of sound production, dispersion and reception in animals. This involves neurophysiological and anatomical basis of sound production and detection, and relation of acoustic signals to the medium they disperse through. The findings provide clues about the evolution of acoustic mechanisms, and from that, the evolution of animals that employ them.
An active electronically scanned array (AESA) is a type of phased array antenna, which is a computer-controlled antenna array in which the beam of radio waves can be electronically steered to point in different directions without moving the antenna. In the AESA, each antenna element is connected to a small solid-state transmit/receive module (TRM) under the control of a computer, which performs the functions of a transmitter and/or receiver for the antenna. This contrasts with a passive electronically scanned array (PESA), in which all the antenna elements are connected to a single transmitter and/or receiver through phase shifters under the control of the computer. AESA's main use is in radar, and these are known as active phased array radar (APAR).
A security alarm is a system designed to detect intrusions, such as unauthorized entry, into a building or other areas, such as a home or school. Security alarms protect against burglary (theft) or property damage, as well as against intruders. Examples include personal systems, neighborhood security alerts, car alarms, and prison alarms.
Beamforming or spatial filtering is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in an antenna array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity. The improvement compared with omnidirectional reception/transmission is known as the directivity of the array.
Passive radar is a class of radar systems that detect and track objects by processing reflections from non-cooperative sources of illumination in the environment, such as commercial broadcast and communications signals. It is a specific case of bistatic radar – passive bistatic radar (PBR) – which is a broad type also including the exploitation of cooperative and non-cooperative radar transmitters.
A towed array sonar is a system of hydrophones towed behind a submarine or a surface ship on a cable. Trailing the hydrophones behind the vessel, on a cable that can be kilometers long, keeps the array's sensors away from the ship's own noise sources, greatly improving its signal-to-noise ratio, and hence the effectiveness of detecting and tracking faint contacts, such as quiet, low noise-emitting submarine threats, or seismic signals.
A gunfire locator or gunshot detection system is a system that detects and conveys the location of gunfire or other weapon fire using acoustic, vibration, optical, or potentially other types of sensors, as well as a combination of such sensors. These systems are used by law enforcement, security, military, government offices, schools 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:
A lightning detector is a device that detects lightning produced by thunderstorms. There are three primary types of detectors: ground-based systems using multiple antennas, mobile systems using a direction and a sense antenna in the same location, and space-based systems. The first such device was invented in 1894 by Alexander Stepanovich Popov. It was also the first radio receiver in the world.
Electro-optical MASINT is a subdiscipline of Measurement and Signature Intelligence, (MASINT) and refers to intelligence gathering activities which bring together disparate elements that do not fit within the definitions of Signals Intelligence (SIGINT), Imagery Intelligence (IMINT), or Human Intelligence (HUMINT).
Geophysical MASINT is a branch of Measurement and Signature Intelligence (MASINT) that involves phenomena transmitted through the earth and manmade structures including emitted or reflected sounds, pressure waves, vibrations, and magnetic field or ionosphere disturbances.
In acoustics, microbaroms, also known as the "voice of the sea", are a class of atmospheric infrasonic waves generated in marine storms by a non-linear interaction of ocean surface waves with the atmosphere. They typically have narrow-band, nearly sinusoidal waveforms with amplitudes up to a few microbars, and wave periods near 5 seconds. Due to low atmospheric absorption at these low frequencies, microbaroms can propagate thousands of kilometers in the atmosphere, and can be readily detected by widely separated instruments on the Earth's surface.
Infrasound is sound at frequencies lower than the low frequency end of human hearing threshold at 20 Hz. It is known, however, that humans can perceive sounds below this frequency at very high pressure levels. Infrasound can come from many natural as well as man-made sources, including weather patterns, topographic features, ocean wave activity, thunderstorms, geomagnetic storms, earthquakes, jet streams, mountain ranges, and rocket launchings. Infrasounds are also present in the vocalizations of some animals. Low frequency sounds can travel for long distances with very little attenuation and can be detected hundreds of miles away from their sources.
Counter-IED equipment are created primarily for military and law enforcement. They are used for standoff detection of explosives and explosive precursor components and defeating the Improvised Explosive Devices (IEDs) devices themselves as part of a broader counter-terrorism, counter-insurgency, or law enforcement effort.
Sonar systems are generally used underwater for range finding and detection. Active sonar emits an acoustic signal, or pulse of sound, into the water. The sound bounces off the target object and returns an echo to the sonar transducer. Unlike active sonar, passive sonar does not emit its own signal, which is an advantage for military vessels. But passive sonar cannot measure the range of an object unless it is used in conjunction with other passive listening devices. Multiple passive sonar devices must be used for triangulation of a sound source. No matter whether active sonar or passive sonar, the information included in the reflected signal can not be used without technical signal processing. To extract the useful information from the mixed signal, some steps are taken to transfer the raw acoustic data.
A nuclear detonation detection system (NDDS) is a device or a series of devices that are able to indicate, and pinpoint a nuclear explosion has occurred as well as the direction of the explosion. The main purpose of these devices or systems was to verify compliance of countries that signed nuclear treaties such as the Partial Test Ban treaty of 1963 (PTBT) and the Treaty of Tlatelolco.
Unattended Transient Acoustic MASINT Sensor (UTAMS)Mortar, Rocket, Explosive Locator System is an acoustic localization sensor system developed by the Sensors and Electronic Devices Directorate (SEDD) of the U.S. Army Research Laboratory (ARL) in 2004. This technology is utilized to detect and isolate transient events such as mortar or rocket firings, munition impacts, and other explosive events. It consists of an array of acoustic sensor stations that are linked via radio to a receiving base. Each sensor has the ability to monitor hostile territory, international borders, and/or detect indirect weapon fire covertly with 24-hour surveillance. These small, inexpensive, non-imaging sensors can monitor large areas without a significant need for power sources and manpower.