28.4 Acoustic Positioning

The speed of sound in water is about 1500 m/s. Acoustic positioning systems measure the time taken for an acoustic pulse to travel from an emitter to a receiver and convert it to distance. A so called long baseline

acoustic array is a set of acoustic transponders (AT) dropped to the seabed that can measure distances between themselves or distances from any mobile transponder such as on a Remote Operated Vehicle (ROV)

to navigate relative to the array. Ultra Short Baseline Acoustics use multiple (at least three) high accuracy receivers to measure, not just the distance, but can also use the phase difference of the incoming signals to determine the horizontal and vertical angle to the source.

In order to establish the position of any permanent acoustic transponders on the seabed, two techniques are commonly used. These are ‘Boxing In’ and USBL.