Advances in system design and sensor performance, together with high accuracy GNSS surface positioning, have led to a significant increase in the capability, performance and accuracy of modern ultra-short baseline (USBL) acoustic positioning solutions. This has made it possible for such solutions to be used where previously more time-consuming and expensive solutions would have been employed, thus enabling marine contractors to bring additional value to their clients.
At the same time, client expectations and technical specifications have moved forward together with technology and industry experience. This progress has led the International Marine Contractors Association (IMCA) to publish Guidance on Vessel USBL Systems for Use in Offshore Survey and Positioning Operations (IMCA S 017). This new publication is intended for use by offshore construction, survey and inspection companies when chartering third-party vessels with USBL system(s) already installed, when commissioning new USBL installations on new-build or existing vessels, or when maintaining existing systems.
The two main applications of a USBL position system are in dynamic positioning (DP) of a vessel relative to an acoustic transponder/beacon installed at a fixed location on the seabed; and navigating an ROV, tow-fish, plough, or other subsea object, using a mobile acoustic transponder/beacon or responder.
"High performance vessel USBL systems, operating to a high specification, have become a critical part in meeting the very demanding technical and contractual requirements in modern offshore operations," explains Hugh Williams, Chief Executive of IMCA. "It is possible for a properly installed USBL system to achieve positioning accuracy of a few metres at the seabed in water depths of 1,000m. In parallel with the development of long range high accuracy USBL systems, similar advances have been made with more portable USBL systems providing reliable tracking in shallow water when working from less sophisticated vessels such as cable lay barges or from small survey vessels. Although the accuracy achieved with portable systems is not as refined, the principles and guidance in our new document can be applied equally well to portable systems."
Guidance on Vessel USBL Systems for Use in Offshore Survey and Positioning Operations discusses the issues affecting USBL system performance and describes topics associated with the installation, configuration and documentation of the systems on offshore vessels involved in subsea positioning. Illustrations aid understanding of the capability and features of these systems. Members can download the new publication from the members-only section of the website or order printed copies at £15.00. Printed copies for non-members are available at £30.00 (plus 20% for delivery outside Europe) from www.imca-int.com/publications and publications[at]imca-int[dot]com.