User Manual for the Type 8300 Compatt 6
(and Variants)
UM-8300-Compatt 6
Issue B3
A.4 Long / Ultra-short Baseline (L/USBL)
A.4.1 Hardware
The long / ultra-short baseline (L/USBL) system is a special case of the USBL system. It uses USBL
hardware in a configuration similar to the one described for the LBL system.
Figure A–4 Typical L/USBL system
A.4.2 Principles
An L/USBL system follows the same methods for calculating range and bearing measurements as the
basic USBL system. However, because there are more beacons deployed on the seabed, a
considerable improvement in accuracy can be achieved by the L/USBL system.
A.4.3 Non-Critical Operations
If a basic L/USBL system is not to be used for highly accurate survey work, a system such as the one
shown in
will perform a top-down calibration automatically as soon as it is placed in
Navigation mode with the beacons declared as References.
This calibration technique relies on multiple range and time-phase difference measurements between
the USBL transducer and each transponder on the seabed in turn. Provided an accurate
measurement of sound velocity is used, over a period of time the system calculates repeatable
positions for the seabed array relative to the USBL transducer.
A.4.4 Critical Operations
If the L/USBL system is to be used for survey work where accuracy is critical, the seabed array must
be calibrated separately or by using baseline measurements. If a DGPS input is available to the
L/USBL system it is feasible to locate each beacon on the seabed directly in a geographical frame of
reference to an accuracy determined by that of the DGPS measurements.
Appendix A – Acoustic Positioning Methods
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