USBL (ultra-short baseline, also known as SSBL for super short base line) is a method of underwater acoustic positioning. A USBL system consists of a

transceiver In radio communication, a transceiver is an electronic device which is a combination of a radio ''trans''mitter and a re''ceiver'', hence the name. It can both transmit and receive radio waves using an antenna, for communication purposes. The ...

, which is mounted on a pole under a ship, and a transponder or responder on the seafloor, on a towfish, or on an ROV. A computer, or "topside unit", is used to calculate a position from the ranges and bearings measured by the transceiver.

Mechanism

An acoustic pulse is transmitted by the transceiver and detected by the subsea transponder, which replies with its own acoustic pulse. This return pulse is detected by the shipboard transceiver. The time from the transmission of the initial acoustic pulse until the reply is detected is measured by the USBL system and is converted into a range. To calculate a subsea position, the USBL calculates both a range and an angle from the transceiver to the

subsea Subsea technology involves fully submerged ocean equipment, operations, or applications, especially when some distance offshore, in deep ocean waters, or on the seabed. The term ''subsea'' is frequently used in connection with oceanography, marin ...

beacon. Angles are measured by the transceiver, which contains an array of

transducers A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and contro ...

. The transceiver head normally contains three or more transducers separated by a baseline of 10 cm or less, hence the "short baseline" name. A method called “ phase-differencing” within this transducer array is used to calculate the direction to the subsea transponder. The presence of environmental noise reduces USBL positioning accuracy. Combining

Kalman filter In statistics and control theory, Kalman filtering (also known as linear quadratic estimation) is an algorithm that uses a series of measurements observed over time, including statistical noise and other inaccuracies, to produce estimates of unk ...

ing with an element array has been used to filter the signals and improve accuracy, using the minimum mean-square error rule.

Applications

USBLs are used in "inverted" (iUSBL) configurations, with the transceiver mounted on an

autonomous underwater vehicle An autonomous underwater vehicle (AUV) is a robot that travels underwater without requiring continuous input from an operator. AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification tha ...

, and the transponder on the ship/shore that launches it. In this case, the "topside" processing happens inside the vehicle to allow it to locate the transponder for applications such as automatic docking,

target tracking Target may refer to: Warfare and shooting * Shooting target, used in marksmanship training and various shooting sports ** Bullseye (target), the goal one for which one aims in many of these sports ** Aiming point, in field artiller ...

, and the exchange of text messages.

References

External links

* * * {{hydroacoustics Navigation Surveying