Search

[sərCH]

verb

1. Try to find something by seeking carefully and thoroughly⁴

Difficulties

Submarines are designed to resist detection, meaning that when one goes missing it is extremely difficult to find. There are four main ways to locate a submarine, sound, magnitism, SONAR, and heat signitures. In order to find a sub a combination of these methods, using sensitive hydrophones, magnetic anomaly detectors, SONAR instruments, and infrared cameras.

SOSUS

SOSUS⁵ is a line of highly sensitive hydrophones set up in the GIUK (Greenland, Iceland, and the United Kingdom) gap and various locations in the Pacific and Atlantic Ocean. Part of the Integrated Undersea Surveillance System, SOSUS was created to listen for Soviet submarines leaving northern bases during the Cold War. Hydrophones are essentially just microphones specifically engineered for use underwater. This is necessary as water is a denser material, and thus has different accoustic propetries from air, the most notible being the higher speed of transmission of sound waves. Sound waves are pressure waves, when an object vibrates the molecules around it are temporarily compressed. This compression then propagates outward. Once the sound wave reaches a hydrophone the hydrophone also vibrates slightly. Using piezoelectric transducers, which are simply materials that produce electricity when subjected to a pressure change, an accoustic signiture for individual submarines or classes of submarines can be formed. Hydrophones can also be used to detect underwater explosions and implosions, which produce sound just like their land-based counterparts. Hydrophone networks are responsible for much of the evidence of submarine accidents that we have today.

Magnetic Anomaly Detector

Magnetic anomaly detectors (MAD) are capable of detecting small changes in the Earth's magnetic field. As modern submarines contain large pieces of ferromagnetic material their presents creates a small change in the magnetic field above them. MAD sensors are generally deployed on aircraft and are placed outside of the fuselage on a boom or towed from behind the aircraft to reduce interference from the aircraft itself. MAD sensors are also limited by the strenth of the magnetic field produced by the submarine, which decreases following the inverse cube of distance. This means that the large the submarine the easier it is to detect. Additionally some submarines, have been built using titanium, which provides two benifits. Firstly, titanium is not magnetic and therefor causes the submarine to be more difficult to detect using MAD sensors. Secondly titanium is stronger than steel for the same weight which allows titanium submarines to generally dive deeper.

SONAR

SONAR, or SOund Navigation And Ranging works in a simular way to hydrophones. The difference is that SONAR puts out a 'ping' which is then timed. Based on the time between when the 'ping' is sent out and when it is recieved the distance to various objects can be determined. In order to locate submarines two forms of SONAR can be used, passive and active. Active SONAR activly uses 'pings' to locate objects, and is used by surface ships that do not need to hide. Passive SONAR is typically used only by submarines as it requires more sophisticated equipment. Hydrophones on each side of the sub are used in the same way human ears are to locate sound. Using triangulation and the amount of time in between when the sound hits the first sensor and the second, the distance to sound making objects can be determined.

Infrared Cameras

Submarines are rarely the temperature of the surrounding water. Nuclear submarines are especially prone to temperature differences as nuclear reactions produce large amounts of heat. While some of this heat is used to create steam to drive the turbine that powers the submarine excess heat must be dumped into the surrounding water in order to prevent a melt down. The warmer water emits large amounts of black body radiation. Infrared cameras are then able to detect this black body radiation and report the submarine's location. At least one highly sensitive infrared camera was deployed by NASA to look for the San Juan.