User Manual for the Type 8300 Compatt 6
(and Variants)
UM-8300-Compatt 6
Issue B3
A.3 Ultra-short Baseline (USBL)
A.3.1 Hardware
The principles of ultra-short baseline (USBL) position measurement are very similar to those of an
SBL system already described. However, instead of the transducers being deployed at widely-spaced
locations on the vessel, they are built into a single transceiver assembly.
Figure A–3 Typical USBL System
A.3.2 Principles
The distance or range measurement principles used in a USBL system are the same as those used for
SBL, but the time differences between signal reception at the difference transducers are significantly
less than for an SBL system.
Systems that use sinusoidal signals measure the time-phase of the signal received by each transducer
element in the transceiver, and compare them with a reference signal generated in the receiver.
These time-phase differences between transducer elements are computed by subtraction, and then
the system is equivalent to an SBL system in the calculation of range and bearing.
Another practical difference is that the transducer elements of a USBL system are in a transceiver
assembly that is installed at some convenient location in the vessel co-ordinate frame.
It is important to recognise that, whereas an SBL system calculates beacon positions in the vessel
frame, a USBL system calculates beacon positions in a frame fixed to the transceiver assembly. To
transform these positions into the vessel’s co-ordinate frame requires the transceiver’s attitude with
respect to the vessel frame to be measured during installation.
Appendix A – Acoustic Positioning Methods
122