Issue Date: 01 July 2002
Mariners will be aware that the unencrypted public Differential Global Positioning System (DGPS), provided by the General Lighthouse Authorities of the United Kingdom and the Republic of Ireland (GLAs) has operated on a trial basis during validation of the system. Validation has now been successfully completed and Operational Capability achieved.
DGPS is provided as a marine aid to navigation, giving 24 hour-a-day, all-year-round service with overlapping signal coverage up to 50 nautical miles around the coasts of the United Kingdom and the Republic of Ireland. The signal provides mariners equipped with a suitable receiver with both real time integrity monitoring of GPS derived positions and the capability of fixing their positions to better than 5 metres (95% probability) in moving applications. Greater accuracy can be achieved in stationary applications.
All mariners are advised:
1. DGPS relies inherently on GPS, the operation and characteristics of which are outside the control of the GLAs.
2. The DGPS service is provided primarily for use in monitoring the integrity of GPS to enhance the safety of marine navigation. The provision of greater accuracy for marine navigation is a secondary feature.
3. Signal reception may become unreliable, under certain extreme environmental conditions, towards the limits of the geographical coverage.
4. All radio navigation systems are susceptible to interference (including jamming) and environmental effects, which can adversely affect their availability. The GLAs strongly advise that no single aid to navigation system should be used in isolation and that DGPS users should use all alternative means available to cross check the information received. Users should also ensure that they have a receiver which gives sufficient warning of the complete loss of the DGPS signal and reversion to GPS.
5. Various DGPS receiver types are available, some of which may not provide appropriate or timely warnings in respect of the system.
6. To keep the DGPS receiver referenced to WGS84 Datum. If the appropriate nautical chart is not referenced to WGS84 Datum, then the position shift values denoted on this chart should be applied.
7. To contact the suppliers of their receivers for guidance on system installation, as incorrect siting and installation of aerials can cause interference thus leading to a degradation of the coverage, accuracy, and availability of the service received by the user.
By Order, T. M. Boyd, Chief Executive.
8. To also refer to Volume 8 of the Admiralty List of Radio Signals.