Can submarine sonar pings kill you

sonar

history

Active sonar

Principle of active sonar: The time from sending the pulse to receiving the reflected signal is proportional to the distance to the object
On-board device of a "fishfinder" sonar

There are low-frequency (50 Hz to 3 kHz), medium-frequency (3 kHz to 15 kHz) and high-frequency active sonars.

Low-frequency sonars are used as long-range sonars with transmission distances of over 20 km or surveillance systems for submarine hunting, i. H. used to locate submarines. This results from the low attenuation of low frequencies. The execution is usually carried out as a towing system. Medium-frequency systems are the traditional underground hunting systems. The torpedo sonar in the head of a torpedo uses 20 kHz to 60 kHz. Mine hunting and mine avoidance sonars use frequencies above 100 kHz because of the high resolution required and the short distance required. Side view sonars are imaging sonar systems that are used in research and mine hunting.

In the civil sector, for example, schools of fish are used with the Fish magnifier located. The demarcation to the echo sounder is fluid there. In addition to locating schools of fish, pelagic trawl fishing uses net probes based on the echo sounder principle, which enable both the depth control of the fishing gear and the monitoring of the distance between the shear boards or the net geometry.[2][3]

The advantage of the active sonar compared to the passive sonar is that it can easily determine not only the direction but also the distance to the target and that it is also suitable for targets that do not emit any noise. Mine hunting and mine avoidance sonars are therefore always active sonars. Their disadvantage is that they reveal the presence of an actively transmitting sonar carrier well beyond the perception range of the system and that they can represent a burden for the environment, especially for marine mammals. Submarines use active sonar extremely sparingly, if at all.

So-called Search light- (“Searchlight” -) Sonars are now out of date and are hardly used any more. With this type of system, the transmitter / receiver is rotated mechanically. This means that you can only detect in one direction at a time. Most of today's anti-submarine sonars (except tow sonars) use a circle or part circle system. There the transmitters / receivers are arranged in a circle and several on top of each other. In this way you can monitor all directions at the same time and still detect them in a targeted manner. You can then electronically control individual groups or all of them and thus send an all-round ping or ping one after the other.

Sonar signals recorded in stereo with two hydrophones? / i

Passive sonar

Passive sonar consists of at least one hydrophone (underwater microphone) and is used to detect underwater noises and other acoustic signals. The passive sonar itself does not emit sound waves and, unlike the active sonar, cannot be located.

Comprehensive hydrophone arrangements are normally used to determine the direction and to separate the sound you are looking for from other sources of noise. This makes it possible to determine the direction of the target, but not its distance. The distance is attempted through complex strategies with algorithms that evaluate one's own movement and the presumed distance of the target with the help of changing the directional bearing (Target Motion Analysis - TMA). Another, more recent approach tries to determine the distance (and depth) of the target from the vertical distribution of the sound field by inverse modeling.

Passive sonar is mainly used by submarines because it does not reveal the location of this submarine through sound emissions. Since around 1975, acoustic tow antennas of up to several kilometers in length have been used to locate submarines from surface ships with the help of the low-frequency radiation, which is difficult to reduce. However, successes in reducing the noise of submarines are now limiting their usability. This is why these towed antennas are supplemented with acoustic transmitters (Active Adjunct), so one goes back to active sonar (when locating by surface ships, not from submarines).

In general, surface ships can be localized primarily by the cavitation noise caused by the collapse of bubbles caused by the “tearing” of the water in the negative pressure area of ​​the propeller. The noises of the drive diesel engine, pump noises, gear noises, all kinds of crackling and rattling noises (transients) and other noises can also be located, which can also enable the type of noise source to be classified.

Bi- and multistatic sonar

In order to find the optimal compromise between the properties of the active and passive sonar, one has recently turned to bi- or multistatic sonar. A bistatic sonar is basically an active sonar, but the transmitter is on a different platform than the receiver. Both can be very far apart. The advantage is that the active signal does not reveal the recipient. As a result, the enemy cannot tactically adjust to the situation so easily with military sonar.

The disadvantage is that the transmitter and receiver have to be coordinated in some way in order to take advantage of the distance determination and thus the fast target positioning. It is also much more difficult to gauge the performance of the system and build a reasonable display.

In the case of multistatic sonar, several receivers (each on a separate platform, e.g. ship or submarine) are used for one transmitter, possibly also several transmitters, all of which have to be coordinated with one another. This ultimately leads to distributed systems.

Individual sonar types

Diving sonar AN / AQS-13 used by an H-3 SeaKing helicopter

In addition to the basic sonar versions mentioned, there are a number of sonars that differ in structure and use:

HMS

HMS stands for Hull Mounted Sonar. The (submarine) sonar is attached directly to the ship, most often in a special bulge on the bow (bow sonar). This bead has a different shape and a different purpose than the bulbous bow that is widespread today to reduce the flow resistance. The more lenticular sonar bulge is at the front and rather lower than the deepest part of the fuselage, in order to achieve a good view to the front and rear.

TAS

TAS (Towed Array Sonar), towed antenna sonar or towed sonar, describes a passive low-frequency sonar for submarine hunting. It is towed behind the ship as a long line antenna, a hose with hydrophones, following a cable. This means that the antenna can be operated at the most favorable depth and is removed from the noise of its own platform.

FAS

FAS (Flankarray Sonar), side antenna sonar, describes a passive sonar on both sides of the hull in submarines.

LFAS

LFAS (Low Frequency Active Sonar), low-frequency active sonar, describes active sonars with low frequencies between approx. 100 Hz and 3 kHz, depending on the type.

VDS

VDS (Variable Depth Sonar): Sonar for variable depths, describes a towing sonar that, in contrast to the newer TAS or LFAS, does not use a long line antenna, but a compact device that is towed on a cable behind the ship.

Mine hunting sonar

Mine hunting sonars (e.g. mine hunting sonar DSQS11M) are high-frequency sonars for the detection and classification of sea mines (ground mines | anchor rope mines), which are then identified optically by mine divers or drones.

Mine avoidance sonar

Mine avoidance sonars are high-frequency active sonars for warning of mines.

Diving sonar

A diving sonar is a sonar that is disconnected from the helicopter. In the past, simple hydrophones were also used, therefore similar to a sonar buoy, today active sonars similar to a VDS are preferably used.

Sonoboje (sonar buoy)

Sono buoys (sonar buoys) are dropped from aircraft or helicopters for submarine hunting. They hang a hydrophone at a predetermined depth and send received signals back to the aircraft via UHF radio frequencies. There are also more complicated sonoboys with several hydrophones for direction formation and active sonoboys.

Passive sonoboys can also be used unnoticed to record acoustic "fingerprints" from surface and underwater vehicles. For this they are also released from ships / boats.

Side viewing sonar

The side-scan sonar is an imaging sonar for research and mine hunting.

Harmful effects on marine mammals

As can be seen from autopsies of stranded marine mammals, a number of whale strandings have been linked to military sonar experiments since 1985.

In December 2001, the US Navy admitted complicity in the stranding and death of several marine mammals in March 2000.[4] The interim report co-authored by her[5] concludes that the animals were killed or injured by the active sonar of some Navy ships.

The active low-frequency sonar systems (Low Frequency Active Sonar, LFAS) used in the military sector, with their sound pressure of up to 240 decibels, can frighten and stun marine mammals such as whales and dolphins and, presumably, kill them through the subsequent rapid changes in depth (decompression sickness).[6] Sperm whales can generate similarly high sound pressures. Location signals of up to 180 decibels were measured behind her head, the sound pressure level in front of her head is probably up to 40 decibels higher.[7] More than 180 decibels are given for blue whales.[8]

With this information, it should be noted that a different reference value (1 µPa) is used for the dB unit for pressure with water-borne noise than for air-borne noise (20 µPa). For identical absolute pressures, the specified water-borne sound pressure level is exactly 26 dB higher,[9] a sound pressure level of 26 dB specified for water corresponds to a sound pressure level of 0 dB for air (roughly the human hearing threshold). (The reference values ​​for intensity levels differ even more, the reference value for air is 10−12Watt / m² and for water 6.7 x 10−19 Watt / m², so that with the same absolute value there is a numerical difference of 61.7 dB.)[9]

The animals examined nevertheless show severe physiological damage, including cerebral haemorrhage, vascular injuries, vesicle formation in the blood and cardiovascular collapse. It must also be assumed that there is a high number of unreported cases, as animals that die in the open sea sink to the sea floor and remain undetected.

See also

literature

  • Robert J. Urick: Principles of Underwater Sound. 2nd edition. McGraw-Hill Book Company, New York NY 1975, ISBN 0-07-066086-7.
  • Heinz G. Urban: Manual of water-borne technology. STN Atlas Electronics, Bremen 2000.
  • Gerhard Aretz: Sonar in theory and practice for underwater applications. Monsenstein and Vannerdat, Münster 2006, ISBN 3-86582-393-9.
  • Philippe Blondel, Bramley J. Murton: Handbook of seafloor sonar imagery. Wiley et al., Chichester et al. 1997, ISBN 0-471-96217-1 (Wiley Practice Series in Remote Sensing).
  • Harrison T. Loeser (Ed.): Sonar engineering handbook. Peninsula Publishing, Los Altos CA 1992, ISBN 0-932146-02-3.
  • Are the sonars leaving the ship? In: Hansa - International Maritime Journal. January 2003, pp 38-42.

Web links

Individual evidence

  1. sonar. duden.de; Retrieved August 13, 2011.
  2. Trålsonde. Scanmar, accessed October 5, 2018 (American English).
  3. Network probe systems. Thünen Institute, accessed on October 5, 2018.
  4. Submarine tracking device kills whalesTelepolis, January 14, 2002; Retrieved September 2, 2013.
  5. Joint Interim Report, Bahamas Marine Mammal Stranding, Event of March 15-16, 2000, (Memento from October 4, 2013 in Internet Archive) (PDF; 1.6 MB) bahamaswhales.org, December 2001; Retrieved September 2, 2013.
  6. ↑ Ulf Marquardt: Hell noise in the realm of silence. (PDF) WDR, October 9, 2007, accessed on May 9, 2017.
  7. With the microphone into the deep sea. NZZ.ch, November 20, 2002; Retrieved September 28, 2011.
  8. Our animal friends - real super ears. Planet school; Retrieved September 28, 2011.
  9. abReinhard Lerch, Gerhard Martin Sessler, Dietrich Wolf: Technical acoustics. Basics and Applications. Springer, Berlin / Heidelberg 2009, ISBN 978-3-540-23430-2, page 539 (Chapter 17.1 Sound propagation in water).