This briefing document was commissioned by IMCA to promote a greater awareness of the capabilities of hydroacoustic positioning systems and the factors involved in optimisng their performance during installation and use.

Aimed primarily at DP operators and designers, the study aims to increase knowledge at a fairly basic level of:

1. The different hydroacoustic positioning system principles commercially available for:
   - DP positioning
   - Survey
   - Deepwater drilling
   - Deepwater construction operations
2. Other technical system solutions potentially available but not currently commercially available for such applications
3. The capabilities and limitations of each operational type of system (SBL, SSBL, USBL, LBL), with respct to:
   - Accuracy
   - Causes of interference
   - Means of calibration
   - Redundancy and how to achieve it

The report does not attempt to conclude which systems are best. It is simply intended to provide information to enable a better understanding of hydroacoustic position reference systems. In this way, the decision- making process to determine the optimum type of system for a particular application can be made easier.