ADG Degaussing Vessels
Carl Friedrich Gauss (1777-1855) is considered to be the greatest German mathematician of the nineteenth century. His discoveries and writings influenced and left a lasting mark in the areas of number theory, astronomy, geodesy, and physics, particularly the study of electromagnetism. Gauss's law for the electric field describes the static electric field generated by a distribution of electric charges. Gauss also developed a consistent system of magnetic units. The potency of a magnetic field is measured in terms of Gauss. And therefore, by definition, degausse means to reduce/eliminate the strength of the magnetic field.
The degaussing is achieved by use of direct current coils (degaussing coils) that produce a magnetic field which is directed in the opposite direction of the original magnetic field of the ship. Magnetic signature techniques are employed in asset location and triggering systems. Thus, the control of magnetic fields is an important consideration in detection avoidance. For example, it is known to use magnetic triggering in naval mines. Magnetic mines are deployed in roads and other likely transit points and adapted to detonate based on a detected magnetic signature of a vessel within the effective range of the explosive device. Magnetic naval mines are deployed in harbors and shipping lanes. The mines are equipped with magnetic sensing devices to trigger detonation in proximity to passing naval vessels.
It is important for military vessels on voyage to have the ability to go undetected by surveillance methods which utilise the change in magnetic and electric fields produced by the presence of a vessel. The present invention relates to methods of, and apparatus for, assessing the magnetic signature of a vessel. Once such a signature has been assessed, it is then possible to control or modify the signature in a desired manner.
Vessels which are constructed of ferromagnetic material have a magnetic field which is combination of two magnetic artefacts: the induced field and the permanent field. The induced field is proportional to the instantaneous incident field (i.e. the Earth's field). The permanent field changes in complex ways related to the magnetic history of the vessel and is dependent on the stress on the hull.
The general concept of degaussing is to reduce the magnetic signature of a vessel by installing a number of direct current carrying coils on board the vessel. In principle, by applying suitable currents to these coils, a magnetic field can be generated which matches the ferromagnetic field associated with the vessel, but with opposite sign, thus reducing the signature to zero. In practice of course, this ideal zero field is not actually achievable and the degaussing problem becomes one of optimising/minimising the field with respect to some appropriate measure. Methods have been developed over the years to accomplish this and are generally very successful at reducing the field to the required levels for a limited period of time.
Degaussing can be carried out by several methods. And all of this is done to protect the ship from exploding on mines which have proximity magnetic or magnetic induction fuses, and from torpedoes. An electrical field is a kind of catalytic agent, which hastens corrosion of the hull. A magnetic field effects the operation of magnetic compasses. The ship stops deviation only after appropriate processing.
The performance of a degaussing technique is typically assessed using a degaussing range, which typically consists of an array of magnetometers which measure the magnetic signature of a vessel as it traverses the range. The data collected from a degaussing range is also used to calculate the optimum currents for the degaussing coils. These current settings are then kept for the duration of the voyage until the vessel's next visit to a degaussing range. This is known as open loop degaussing (OLDG). It is known that, whilst at sea, and particularly in the case of submersibles whilst diving, the permanent magnetic field of the vessel can change significantly enough so that the signature is no longer within acceptable levels. An OLDG system cannot respond to this, and so the currents will be kept the same until the vessel is ranged again, which in itself is a costly and time consuming process.
A measuring team begins the work of degaussing; it determines all the necessary parameters using a special apparatus. From these data a picture of the fields is complied and the type and amount of processing are determined. A cable is wound around the ship in all directions. An electrical current is fed through it. In It turns out that the vessel has been along side the short, the wedge is driven out by a wedge.
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