Sonar – Sound navigation and its use

Sonar offers the possibility to locate and visualize objects under water by sound, this is done according to the echo principle. The term is an acronym in English and means ” sound navigation and ranging”. When using this positioning system , sound waves are emitted and received in space and the evaluation of these echoes enables navigation under water. Obstacles such as mountains or ships can be identified and avoided, and larger objects can also be better avoided. The possibility of locating with water sound was first mentioned as early as the 1500s, but the development of this technology was not attempted until much later.

Function of sound Navigation

Sonar emits sound waves and measures how long it takes for an echo to be received. These sound waves are reflected faster in shallow water than in the deep sea. In deeper water, this sound needs more time to return. With this technology and evaluation of the sound, a distance measurement can be carried out. A basic distinction is made between active and passive sonar systems for distance measurement. The first models were able to locate enemies under water at around 1500 meters, but were not as detailed as necessary.

Active sonic navigation

When using active sonic navigation, particularly high-energy signals are sent, which can also reveal your own position. The signal emitted can also be heard with the naked ear and has an extremely long range.

The echo sounder, a form of active sonar, is not only used on warships, research also uses this technology to analyze the nature and structure of the seabed, and researchers also use side scan sonar, where fan-shaped pulses are transmitted. In addition, the active sonar is used for deep-sea fishing to detect schools of fish; the sonar monitors then show a visualization of the structure of the area, possible disturbance factors or fish.

Passive sonic navigation

Passive sonar is used to detect acoustic signals and sounds underwater , usually using a hydrophone , an underwater microphone. The passive method does not emit its own signals and therefore cannot be located.

Passive sonar is mainly used in submarines in order not to give away one’s own position, navigation is more difficult here than with active sonar. Extensive hydrophone setups are required to determine the direction and separation of the noise from other noise sources; the actual distance must be determined separately. By using algorithms that evaluate the user’s own movement, an approximate distance to the target can be calculated.

Use of sonar on submarines

At the beginning of the 20th century, the echo sounder was developed and patented. This device enabled electro-acoustic measurements to be taken at water depths from inside the submarine and became increasingly important. The fundamental difference between echo sounders and devices with sonar is that echo sounders mainly perform vertical detection and sonar mostly performs horizontal detection .

During the First World War, active sonars were further developed to locate submarines or a nuclear submarine. Due to the complex development, this technology was not used during the war; various versions of passive systems were used.

 

Development of sonar technology after the First World War

During the Second World War, active sonar systems were used in underwater boats, transmitting short pulses in the frequency range between 15 and 40 kHz. The ship’s own noises and exploded depth charges made it difficult to locate the submarine using these active sonar measurement techniques; the actual range of these systems in the submarine is heavily dependent on the water and weather conditions. The use of these systems was made even more difficult by the lack of swivel options. However, enemy submarines were usually only detected when they were surfaced, as they only dived when under attack or in danger. After an attack with depth charges, sonar contact was usually lost immediately afterwards.

An outdated and rarely used technology are so-called Search Light searchlighthere the transmitter/receiver is mechanically rotated and can only transmit in one direction at a time, today’s U-hunting sonar usually use a circular or partial-circuit system; with this technology, the transmitters and receivers are arranged one above the other in a circle, ensuring monitoring in all directions at the same time. With this model, everything can be monitored and yet specifically detected.

Due to the signal propagation time for each angular step, monitoring with active sonar was particularly time-consuming, so a radar was usually used for area monitoring, which works with electromagnetic waves that have a higher propagation speed.

Use of active sonar

Active sonars are primarily used as submarine hunting sonars, which are used to detect and combat enemy submarines. In most cases, a search-light sonar was used. These light searchlight sonars transmit at frequencies between 15 and 40 kHz and send short sound pulses, also known as “pings”. It was important to maintain contact with the target , for example with search beam sonar devices. After the Second World War, panoramic sonar was used, which transmits in sectors and all around.

Different types of sonar

The sonar models mentioned differ in their use and design. The models used are:

HMS, this model is attached directly to the hull of the ships and is designed to provide good forward visibility.

The TAS towing sonar is towed behind the ship on a cable and is used to hunt for submarines, similar to the VDS towing sonar, in which a compact device is towed.

The lateral antenna sonar FAS is mounted on both sides of the fuselage and operates passively.

LFAS models actively transmit at low frequencies, usually between 100 Hz and 3 kHz, in contrast to minehunting sonar, which operates at high frequencies and detects mines and drones.

Some devices are used from airplanes , the sonobuoy is dropped from the plane or helicopter and placed at a predetermined depth, equipped with several hydrophones signals can be received and transmitted to the aircraft in the air.

Damage to marine animals

The military use of these devices at low frequencies can frighten, stun and even kill marine animals with the resulting noise .

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