Issue Date: Wednesday 1 December 1999
Mariners are reminded that the unencrypted public Differential Global Positioning System (DGPS) service provided by the General Lighthouse Authorities of the United Kingdom and the Republic of Ireland (GLAs) continues to operate on a trial basis whilst validation and other checks are undertaken.
The DGPS service is provided primarily for use in monitoring the integrity of GPS and to enable greater accuracy for marine navigation as a secondary feature.
All mariners are advised:
1. DGPS relies inherently on GPS, the operation and characteristics of which are outside the control of the GLAs;
2. All radio navigation systems are susceptible to interference (including jamming) and environmental effects, which can adversely affect their reliability;
3. Various DGPS receiver types are available, some of which may not provide appropriate or timely warnings in respect of the system;
4. To keep the DGPS receiver referenced to WGS 84 datum and to apply the position shift values denoted on the appropriate nautical chart before plotting a position.
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.
Reference should also be made to Volume 8 of the Admiralty List of Radio Signals.