Merchant ships use sonar
The sinking of the Titanic after the collision with an iceberg showed how necessary it is to be able to locate underwater. The result was the echo sounder and sonar, which were invented after the First World War. They use sound waves to measure the water depth or to identify underwater obstacles.
Radio waves always travel at the same speed, the speed of light. The speed of sound waves, on the other hand, varies depending on the medium in which they travel. They spread much faster in water than in air. The speed depends on the water depth, temperature and salinity. In order to be able to determine the depth with the echo sounder, for example, you not only have to know what time has passed between the transmission of the signal and the reception of the reflection. One must also take into account the other characteristics of the water in order to arrive at an exact measurement.
The navy is particularly interested in sound waves in the sea and their technical possibilities and limits. That is why the Defense Technology Service for Ships and Naval Weapons, Maritime Technology and Research - WTD71 for short - conducts fundamental research in the field of sound waves and especially in the development of location and communication devices.
Camouflage is particularly important with submarines. The so-called acoustic signature, i.e. the typical noise made by a ship's engines, must be as low as possible. The submarine can also target positions where ground structures make it difficult to locate. WTD 71 is working out details for its use as part of its research program.
Numerous facilities are available for this purpose. Among other things, several modern test ships, including the research ship "Planet". The double-hull ship with floating bodies below the surface of the water is particularly suitable for studies in rough seas.
Shipbuilding and weapons technology
In addition to questions of hydroacoustics - i.e. sound under water - the WTD 71 deals with issues of shipbuilding and weapons technology. "In principle, research is only carried out where there are no institutions outside of the Bundeswehr that can do this, so the WTD 71 has a unique selling point," says Dr. Uwe Kretschmer, Head of Maritime Research at WTD 71.
Passively locating sound is one research topic, another is active search with sound, the search for submarines or mines. Both marine use cases work differently. High-frequency sound is used to search for mines. This has a significantly shorter range, but it allows a detailed detection of found objects. It can also be used to identify very small structures and then analyze whether it could be a sea mine.
With submarines, on the other hand, it is more about being able to locate them from a greater distance. It is known that whales can communicate acoustically over thousands of kilometers. They do this with low frequency sound waves. Therefore, the navy also works with low-frequency waves in order to use their greater range. However, in order to be able to precisely determine the position of a submarine, it is not sufficient to emit sound waves and intercept the reflected waves in the same place.
The WTD 71 is therefore developing and testing a system in which at least two warships are involved, a bistatic system. A ship sends out the waves. "The light switches on," explains Kretschmer. It and other ships, which are in turn linked by satellite, register the waves. The submarine can then be located very precisely from the travel time of the sound waves, their direction and the positions of the transmitter and receiver. The WTD 71 is developing an overall system for "submarine hunting in a network" including a submerged and thus covertly operating submarine.
More and more noise
The work of WTD 71 is also important for the civil use of the seas. Even if the oceans are huge, humans intervene more and more by extracting more and more natural resources or simply operating more and more and larger trading ships. He's making more and more noise.
Environmentalists are concerned that this noise could be harmful to wildlife. This is currently particularly the case for the construction of offshore wind farms. The WTD 71 therefore advises the licensing authorities and tries to prevent negative effects on the marine environment - the overarching research area of the WTD 71.
The Defense Technology Service for Ships and Naval Weapons, Maritime Technology and Research (WTD 71) belongs to the business area of the Federal Office for Equipment, Information Technology and Use of the Bundeswehr. It is located in Eckernförde (Schleswig-Holstein) and was founded in 1957. It covers the entire range of maritime defense technology in all phases of the development of defense material. The activities are primarily geared towards the overall ship system and the interaction of different components on and with this system in the maritime environment. The main topics are water-borne noise and geophysics.
In addition, the WTD71 has systems for the magnetic measurement and treatment of ships and components, acoustic measuring points for ships in deep and shallow water, underwater and surface measuring systems, underwater test systems, torpedo shooting range and lane. WTD 71 currently employs around 600 people.
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