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.
Sound Surveillance System (SOSUS) was the original name for a submarine detection system based on passive sonar developed by the United States Navy to track Soviet submarines. The system's true nature was classified with the name and acronym SOSUS classified as well. The unclassified name Project Caesar was used to cover the installation of the system and a cover story developed regarding the shore stations, identified only as a Naval Facility (NAVFAC), being for oceanographic research. The name changed to Integrated Undersea Surveillance System (IUSS) in 1985, as the fixed bottom arrays were supplemented by the mobile Surveillance Towed Array Sensor System (SURTASS) and other new systems. The commands and personnel were covered by the "oceanographic" term until 1991 when the mission was declassified. As a result, the commands, Oceanographic System Atlantic and Oceanographic System Pacific became Undersea Surveillance Atlantic and Undersea Surveillance Pacific, and personnel were able to wear insignia reflecting the mission.
Acoustic homing is the process in which a system uses the sound or acoustic signals of a target or destination to guide a moving object. There are two types of acoustic homing: passive acoustic homing and active acoustic homing. Objects using passive acoustic homing rely on detecting acoustic emissions produced by the target. Conversely, objects using active acoustic homing make use of sonar to emit a signal and detect its reflection off the target. The signal detected is then processed by the system to determine the proper response for the object. Acoustic homing is useful for applications where other forms of navigation and tracking can be ineffective. It is commonly used in environments where radio or GPS signals can not be detected, such as underwater.
A sonobuoy is a small expendable sonar buoy dropped from aircraft or ships for anti-submarine warfare or underwater acoustic research. Sonobuoys are typically around 13 cm (5 in) in diameter and 91 cm (3 ft) long. When floating on the water, sonobuoys have both a radio transmitter above the surface and hydrophone sensors underwater.
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.
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 multibeam echosounder (MBES) is a type of sonar that is used to map the seabed. It emits acoustic waves in a fan shape beneath its transceiver. The time it takes for the sound waves to reflect off the seabed and return to the receiver is used to calculate the water depth. Unlike other sonars and echo sounders, MBES uses beamforming to extract directional information from the returning soundwaves, producing a swathe of depth soundings from a single ping.
Stalwart-class auxiliary general ocean surveillance ships (T-AGOS) are a class of United States Naval Ship (USNS) auxiliary support Ocean Surveillance Ships commissioned between April 1984 and October 2000. Their original purpose was to collect underwater acoustical information using the Surveillance Towed Array Sensor System (SURTASS), a towed array passive sonar.
Project Artemis was a United States Navy acoustics research and development experiment from the late 1950s into the mid 1960s to test a potential low-frequency active sonar system for ocean surveillance. The at sea testing began in 1960 after research and development in the late 1950s. The project's test requirement was to prove detection of a submerged submarine at 500 nmi. The experiment, covering a number of years, involved a large active element and a massive receiver array.
Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water, its contents and its boundaries. The water may be in the ocean, a lake, a river or a tank. Typical frequencies associated with underwater acoustics are between 10 Hz and 1 MHz. The propagation of sound in the ocean at frequencies lower than 10 Hz is usually not possible without penetrating deep into the seabed, whereas frequencies above 1 MHz are rarely used because they are absorbed very quickly.
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.
USNS Victorious (T-AGOS-19) is a Victorious-class ocean surveillance ship which was acquired by the U.S. Navy in 1991 and assigned to the Military Sealift Command (MSC) Special Missions Program.
USNS Impeccable (T-AGOS-23) is an Impeccable-class ocean surveillance ship acquired by the U.S. Navy in 2001 and assigned to Military Sealift Command's Special Missions Program.
MV Cory Chouest is an ocean surveillance ship leased by the U.S. Navy in 1989 and assigned to the Navy’s Special Missions Program. Cory Chouest had all SURTASS equipment removed and was returned to her original owners in 2008 completing nearly 20 years of service.
The interactions between marine mammals and sonar have been a subject of debate since the invention of the technology.
The Impeccable-class ocean surveillance ship is a single-ship class of United States Navy special mission-support ship. The original intention was to build six undersea ocean-surveillance ships carrying a SURTASS passive towed array and a Low Frequency Active transducer array. Only the lead ship, USNS Impeccable (T-AGOS-23), was built.
Bistatic sonar is a sonar configuration in which transmitter and receiver are separated by a distance large enough to be comparable to the distance to the target. Most sonar systems are monostatic, in that the transmitter and receiver are located in the same place. A configuration with multiple receivers is called multistatic.
The SACLANT ASW Research Centre was the predecessor to the NATO Undersea Research Centre. It was known as The SACLANT ASW Research Centre from 1959 through 1986, and the SACLANT Undersea Research Centre from 1987 through 2003. The centre was commonly referred to as SACLANTCEN.
A towed pinger locator is a water-borne device used to locate the sonar "ping" from the underwater locator beacon which is fitted to the Cockpit Voice Recorders and Flight Data Recorders installed in commercial airliners. They can locate pingers at depths of up to 20,000 feet (6,100 m) underwater.
Low Frequency Analyzer and Recorder and Low Frequency Analysis and Recording (LOFAR) are the equipment and process respectively for presenting a visual spectrum representation of low frequency sounds in a time–frequency analysis. The process was originally applied to fixed surveillance passive antisubmarine sonar systems and later to sonobuoy and other systems. Originally the analysis was electromechanical and the display was produced on electrostatic recording paper, a Lofargram, with stronger frequencies presented as lines against background noise. The analysis migrated to digital and both analysis and display were digital after a major system consolidation into centralized processing centers during the 1990s.
