User Manual for the Type 8300 Compatt 6
(and Variants)
UM-8300-Compatt 6
Issue B3
Appendix A – Acoustic Positioning Methods
A.1 Long Baseline (LBL)
A.1.1 Hardware
A long baseline system has two parts or segments:
The first segment comprises of a number of acoustic transponder beacons in an array moored in fixed
positions on the seabed. The positions of the beacons are described in a co-ordinate frame fixed to the
seabed. The straight-line distances between them form the ‘baselines’ used by the system.
Figure A–1 Typical LBL System
The second segment comprises an underwater acoustic transducer on a transceiver. The transceiver
is usually installed on the vessel either in an over-the-side arrangement as shown in
, or in
a fixed through-the-hull arrangement. It can also be installed on a towfish, if necessary.
A.1.2 Principles
The distance from the transducer to a transponder beacon can be measured by causing the
transducer to transmit a short acoustic signal to which the transponder beacon responds.
The transceiver makes an accurate measurement of the interval between the instant when it transmits
and the instant when it receives the transponder’s response. Because the sound velocity in water is
known at the location, it is possible to develop a good estimate of the range between the transceiver
and the transponder beacon.
This measurement process is repeated for all the beacons in the array, and the position of the
transceiver is then calculated or estimated relative to the array.
Appendix A – Acoustic Positioning Methods
119