Ultra Short Baseline

Ultra Short Baseline ( USBL ) is an underwater navigation system based on maturities of underwater sound between the object and the plurality of reference points. USBL systems can be used to determine the position of objects or devices under water.

Are usually on board a ship which is equipped with an USBL system, installed for receiving a plurality of hydrophones. Also the object under water, whose position is to be determined, has a hydrophone. So that an acoustic signal is sent, which is received on board the vessel from the receiving hydrophones.

The distance to the object is obtained by knowing the speed of sound from absolute maturities for which the moment of emission must be known. It used accurate clocks or Sendehydrophon the command transmitted to send, also by sound or electrically via a cable (eg for applications with an ROV ).

The time difference with which the signal reaches the individual hydrophones, allow the determination of the incidence direction of sound waves with respect to the ship. Changes in this direction are not only based on the actual movements of the object, but especially on pitch and roll of the ship, which therefore has inertial sensors.

The relative position with respect to the ship can be converted into an absolute position ( relative to the base ) when the location and orientation of the ship is known, for example by satellite navigation.

By thermohaline stratification and corresponding variation of the sound speed, the direction of incidence of the wave fronts of the direction deviates from the object, during the passage of internal waves and swaying. Another reason the stationary hydrophone improves the accuracy of the method significantly. In a large, precisely measured array of hydro- phonon at the bottom is called a Long Baseline System ( LBL).

Swell

• Http://www.ise.bc.ca/WADEnavandpos.html (English)
• Http://www.hydro-international.com/issues/articles/id872-LBL_Underwater_Positioning.html (English)

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