The mix of physical and radio aids to navigation must meet the UK and Ireland’s responsibilities as Contracting Governments to the International Maritime Organisation, SOLAS Convention. In 2011, the GLAs’ published 2025 & Beyond, their marine aids to navigation strategy for the British Isles between 2010 and 2025. With the introduction of eNavigation, the strategy highlights the increased reliance on radio aids in the AtoN mix.
The GLA’s public marine Differential Global Positioning System (DGPS) is part of the mix of visual, audible and electronic aids to navigation. It is an open system – available to all mariners – and is financed from light dues charged on commercial shipping and other income paid into the GLA fund. DGPS can assist the safe passage of all classes of vessels from cargo ships, cruise liners and fishing vessels to small yachts, by:
- monitoring the integrity of the US NAVSTAR Global Positioning System (GPS)
- improving accuracy for safe navigation in waters where the freedom to manoeuvre is restricted.
The DGPS is a network of 14 ground-based reference stations providing transmissions with coverage of at least 50 nautical miles around the coasts of the United Kingdom and the Republic of Ireland. There are four within NLB’s area of Scotland and the Isle of Man.
- Girdle Ness – East Coast
- Sumburgh Head – Orkney & Shetland
- Butt of Lewis – North West
- Stirling – Central Scotland
GPS was developed by the US Department of Defense as a worldwide all weather navigation and positioning and timing resource, mainly for military use. It is based on a constellation of 24 satellites orbiting the earth which act as reference points.
By measuring the travel time of signals transmitted from four satellites, a receiver can measure its distance from each satellite and combine these measurements to calculate its latitude, longitude, altitude, course and speed.
GPS positions are accurate 95% of the time to ± 9 metres and updates can be received every second. A higher accuracy level is required for some specialised navigation and positioning purposes and the integrity of the system needs to be monitored for safety-related applications.
DGPS makes GPS more accurate
DGPS can provide higher accuracies of 5 metres (95%) or better in moving applications and even better in stationary situations, by cancelling out most of the natural and man-made errors arising from normal GPS measurements.
DGPS is no longer simply a navigation technique – it is a means to measure positions and movement of any kind to a high degree of accuracy.
In the marine environment, the output from a suitable DGPS receiver could form the position sensor input to an Integrated Navigation System (INS), an Electronic Chart System (ECS) or an Automatic Identification System (AIS). In these applications the inherent integrity checking, high accuracy and stability of the differential system are particularly important.
In positioning mode, DGPS is used for buoy-laying and hydrographic surveying. DGPS may also be used, often in combination with other systems, for a variety of other marine applications such as dynamic positioning, rig moves, pipe-laying, cable-laying and dredging.
There are marine radiobeacon DGPS services in over 45 countries throughout the world including the majority of North West European States. With advances in technology, the signals from radionavigation systems have progressively transcended national boundaries to provide long-range transmissions from a network of satellite and terrestrial stations.
This has significant benefits for the safety of navigation since it enables a consistent means of navigation throughout all phases of the voyage, during the day or night and in conditions of reduced visibility. Such systems will also help with improved voyage planning to reduce ship operators’ costs. A high level of availability of the right mix of aids to navigation systems also plays some role in determining which ships will visit our ports and in demonstrating that effective measures have been taken to minimise the risk of pollution from ships.
The GLAs DGPS system is provided for maritime use. Implementation was completed in August 1998 and the system achieved Operational Capability on 1 July 2002.
Problems with DGPS receiver equipment should be taken up with the supplier. Users who experience problems with the system are invited to complete and return an Incident Report Form. Please contact us for a form or the appropriate GLA.