Submarine Detection

Like any object, the boat affects the environment with its presence. In other words, the boat has its own physical fields . The more famous physical fields of the submarine include hydroacoustic, magnetic, hydrodynamic, electrical, low-frequency electromagnetic, as well as thermal, optical. The selection of the boat’s physical fields against the background of the fields of the ocean (sea) underlies the main detection methods.

Detection methods by type of physical fields:

1. Acoustic
2. Magnetometric
3. Radar
4. Gas
5. Thermal
6. Electrolytic
7. Optical (visual)

In addition, there are indirect detection methods:

• Radio intelligence and surveillance
• Narrowness observation
• Correlation analysis

No single method guarantees detection, and does not even guarantee a stable level of operation. Therefore, all methods are used together. They are constantly being researched and developed, and new ones are being searched.

The acoustic mode is the first in importance. Sound propagates in water much faster than in air (about 1,500 m / s) and at distances much greater than any other disturbances. On average, the acoustic detection range is two orders of magnitude superior to the magnetometric method following it. Acoustics allows you to detect submarines at all depths, does not depend on the time of day and does not depend much on weather conditions and the season. However, the distance, accuracy and reliability of the detection itself vary greatly (by tens of times) depending on the hydrological conditions of the sea. For example, the presence of an underwater sound channel (in the diagram) can dramatically increase the detection range. On the contrary, the jump layer serves as a barrier and can make the boat acoustically “invisible”.

Passive

The passive method is the detection of noise and sonar signals (the latter is uncharacteristic) issued by the submarine itself. Depending on the particular device used, it is also called noise detection, noise location, sonar observation, or wake detection.

The advantages of the passive method are its secrecy - the target does not know about the fact of detection, a relatively large range - in some cases, very noisy objects are detected at distances of 100 ÷ 150 miles - and the ability to classify targets according to the nature of the noise.

For the purpose of classification, the so-called acoustic signature of the target is compiled. It may include: mechanical noise, noise of equipment, flow noise, blade sound, sound at a speed of rotation, cavitation noise, noise of protruding parts. For submarines, the most noisy object is the propellers. The second most noticeable (typical for atomic submarines) is the circulation pump (CN) of the primary reactor loop. ^[1] Acoustic signatures allow Captor mine torpedoes to selectively hit only submarines. ^[2]

The disadvantage of the passive method is the inability to directly determine the distance to the target: it gives only direction - bearing to the target. Indirect methods have to be used to determine distances in the passive mode.

The passive method is the main one used by submarines and stationary surveillance systems. He is the only one in the standby channel of acoustic guidance systems for naval weapons - mines and torpedoes .

Active

With the active method, the sonar receiver detects sound reflected from the target ( echo ) emitted by the synchronized transmitter. Accordingly, the method is also called echo direction finding or echo location . Sonar (GAS) or sonar buoys ( RSAG ) operate on this principle.

The advantage of the active method is the ability to directly determine not only the bearing, but also the distance to the target.

The disadvantages are the detection range is shorter than the passive method - the reflected signal attenuates with a distance below the useful level, and attempts to increase the range lead to an exponential increase in signal intensity , which is technically limited; lack of detection stealth - the submarine hears the emitted signal at a distance of about twice as much as the search GAS hears an echo; the impossibility of classifying targets is the only thing that can be reliably determined is the coordinates of the target.

For these reasons, the active method is characteristic of: surface ships, since the conditions for passive detection for them are limited by their own noise; for sonar buoys and omitted GAS; for submarines, specifying the elements of the movement of the target immediately before the attack; and in the combat channel of naval weapon guidance systems.

The magnetometric method is based on the search for distortions in the Earth's magnetic field - magnetic anomalies . The presence of large masses of ferromagnets , such as the submarine case, creates anomalies large enough to be detected by a magnetometer .

The anti-submarine indicator loop was an underwater cable lying on the seabed and used to detect the passage of enemy submarines. Its first practical application was in the Firth of Fort in August 1915 by the Scottish physicist Alexander Crichton Mitchell with the help of the Royal Navy research institution in HMS Tarlair (Aberdour). Unfortunately, his report to the Investigation and Research Council (SRiI) was misinterpreted, and his findings were rejected as irrelevant. Scientist William Bragg from the SRiI conducted relevant studies in the SRiR, but since the SRiI was not dependent on the control of the Royal Navy, who was outraged by the fleet, he faced serious obstacles even when he transferred to HMS Tarlair. Bragg moved to the BIR experimental station in Harwich, Essex, England. At the suggestion of Bragg, Mitchell’s work was revised, interest in the Mitchell loop again increased in 1917, which led to its successful development in mid-1918. Loops were widely used by the Allies during World War II to protect ports from underwater attack. ^[3]

In the Chicago Museum of Science and Technology , in the "submarines" section, there is an exposition where the visitor can perform a simple experiment. Nothing on the plywood tablet except the grid. There are several iron objects under the tablet. Their number and places are not known in advance. By moving the magnet evenly on the tablet, you can determine the coordinates in which the movement meets resistance - the coordinates of the anomalies.

Among anti-submarine forces, the only carrier of aeromagnetometers, or magnetic anomaly sensors ( English Magnetic Anomaly Detector, MAD ), is aviation. It is planes and helicopters capable of exploring large areas in a short time, and their own magnetic fields are small. But even so, you have to take the magnetometer away from the case. Therefore, the anti-submarine aircraft is recognizable by a rigid tail rod, and the helicopter by the stabilizer cone of the cable produced.

The advantages of the magnetometric method are its simplicity and independence from the measurement medium - the Earth's magnetic field in water behaves almost the same as in air. In addition, the method is passive, that is, the target does not know about the detection.

The main disadvantage is the short detection range. Magnetic anomalies quickly smooth out with distance. To determine the presence of an anomaly, it is required to pass from it no further than 1 ÷ 3 miles. At modern aviation speeds, this means almost directly above the boat. Moreover, the lower the flight, the easier it is to notice the anomaly. Accordingly, the boat, to reduce the likelihood of detection, can go to a depth.

Water is impervious to wavelengths used in radar . Therefore, radar detection of submarines is possible only when any part of them is above the water.

That is, detection is mainly limited to diesel submarines in the periscope position. Nuclear boats may not float under the periscope long enough to avoid detection. This is the main disadvantage of this method.

On the other hand, its advantage is high precision. Modern radars are capable of detecting retractable submarine devices even against the background of interference from waves 2–3 points. Thus, radar detector heads are detected by radar at distances of 12–15 miles, periscopes at distances of 4–5 miles, and radio direction finders and radio intelligence antennas are at 1–2 miles. ^[four]

Thus, radar plays an auxiliary role and is used for additional reconnaissance of submarines previously discovered by other methods. Despite this, the radar is a mandatory part of anti-submarine forces equipment.

Gas analyzers detect the presence of hydrocarbons in the air, which are characteristic of combustion products. In other words, the presence of diesel exhaust from submarines. The equipment, literally, imitates the capabilities of the human nose. In English, it is directly called English. sniffer - a snuffer .

The method was invented by the Allies and was widely used during the Second World War . With the development of atomic submarines, its value decreased. However, it did not go out of use because even under the RPD the boats produce enough exhaust to detect. The main carrier of gas analyzers is aviation.

Obviously, this method is only suitable against submarines using diesel. This is its main drawback . In addition, its reliability is highly dependent on weather conditions - wind strength, humidity and temperature.

The advantage of the method is its passive nature.

Thermal detection is a type of infrared method aimed at detecting atomic submarines.

Outboard water is used as a cooler of the external circuit of the nuclear submarine reactor . After dumping back overboard, the water is warmer than the surrounding.

The method gained distribution because the thermal footprint left by the boat is much larger in size than the boat itself, and therefore it is more easily detected. In addition, the track has the ability to rise to the surface over time (at the same time eroding and cooling down). The trail that has come to the surface is detected even from space. But his durability is low: less than half an hour.

The temperature difference is usually not enough to detect a boat with a single measurement. Comparison and comparison of many measurements is required. Therefore, the application is limited to networks of specialized RSLBs, space reconnaissance and, less commonly, stationary monitoring systems.

The advantages of this method are its long range and its passive nature.

The disadvantages are the lack of reliability of a single measurement, instability to interference and as a result a limited range of applications - only against nuclear submarines.

An express method for detecting nuclear submarines following traces of cesium radionuclides in sea water was developed in the 1980s. ^[5] In the second half of the 80s, the technique was used experimentally in the USSR Navy. The author stated the introduction. ^[five]

With an increase in the secrecy of atomic submarines, the difference, for example, between the temperatures of the cooler and the water outside, decreased so much that it became poorly distinguishable from existing interference with existing sensors. The same can be said about the magnetic anomaly of a submarine with a titanium case.

Since a noticeable increase in the sensitivity of the sensors is not expected, the emphasis is shifted to the integrated processing of data from several detection methods. So, the temperature difference from the cooler is supplemented by the difference from stirring the water with a screw , the acoustic signature of the wake trace , the electric potential between the upper and lower surfaces of the boat hull, and others. The power of the signal processor and the accumulation of observation data come to the fore to highlight the target against the natural background of the sea. Thus, the use of an extended towed antenna (PBA) of the SURTASS system , which consists of many hydrophones, has qualitatively increased the acoustic contrast of targets.

Practice shows that complex methods can not only detect modern atomic submarines, but also maintain contact. ^[6]

Indirect detection methods have played and play a large role. A boat cannot constantly maintain the highest level of stealth, just as it cannot be under water forever. Sooner or later, she is forced to reveal herself. All indirect methods are based on attempts to predict the place and time when the boat will lower stealth, and use this.

The main forces for detecting and destroying submarines are anti-submarine aircraft and ships , torpedo and multipurpose submarines, anti-submarine helicopters , and their means are sensors based on the above methods, and specialized information processing processors.

Also, for defense purposes, anti-submarine weapons are installed on other types of warships and on strategic submarines.

In 2010, the US Department of Defense Advanced Defense Engineering Agency ( DARPA ) in the United States began developing a project for autonomous anti-submarine ships with fully automatic control - ACTUV . ^[7] It is planned to use active echolocation as the main means of detection. ^[7]

Detection of submarines does not guarantee defeat. In order for the anti-submarine forces to come closer and successfully attack, the established contact must be maintained until their approach. Due to the low reliability of all methods, maintaining contact results in a separate task, called tracking submarines .

• Anti-submarine defense

• http://nvo.ng.ru/armament/2007-01-12/6_ushi.html
• https://web.archive.org/web/20071013135653/http://war-nk.narod.ru/stats/kubot.htm
• IL-38 - about the thorny path of creating an anti-submarine aircraft