Canadian Coast Guard
www.ccg-gcc.gc.ca
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Differential Global Positioning System (DGPS)
GPS / DGPS Made Easy
What is DGPS?
Differential GPS is a method of increasing the accuracy of positions derived from GPS receivers. With DGPS receivers, position accuracy is improved, going from 30 metres to better than 10 metres.
Canadian Coast Guard (CCG) reference stations correct most of the errors in the GPS signal and transmit these corrections to anyone within the CCG or USCG coverage area who is equipped with a DGPS receiver.
DGPS Coverage in Canada
If your receiver is designed and equipped for differential corrections, then it will apply the Coast Guard corrections to your position - making your position much more accurate.
A GPS receiver can be upgraded to receive DGPS signals only if it has been designed as "DGPS ready." This is a useful option for those who do not need the more accurate technology immediately, but think they will in the near future. If you require 10 metre accuracy right now, you can also purchase a DGPS receiver initially.
CAUTION: While many GPS receivers are advertised as differential "ready", please note that this does NOT mean that the differential receiver is already built into the unit. The unit requires an additional receiver module along with a low-frequency antenna.
Here's how GPS/DGPS fits into the navigation picture.
Things just get better and better!
DGPS also provides integrity monitoring. Whenever the accuracy provided by the reference station falls below established limits, a warning signal is automatically transmitted to advise the mariner that the service is unreliable.
Should the differential signal be lost altogether, a DGPS receiver can continue to operate in the GPS mode.
* Consult your operator&'s manual to verify your receiver&#&39;s ability to process and display the integrity monitoring signal.
Levels of Service Standards for the Coast Guard DGPS service:
- Accuracy to 10 metres 95% of the time
- Signal availability 99.0% of the time
- Broadcast reliability 99.8% of the time
- Integrity monitoring warning within 10 seconds
- Double or enhanced coverage in all Vessel Traffic Services (VTS) zones
The GPS/DGPS signal could be reflected from the surfaces of nearby obstructions. It that happens, the signal may reach the receiver antenna indirectly and positional accuracy may be degraded.
Obstructions can include other vessels, mountains, trees and even parts of your own vessel. Indeed, if you stand too close to the antenna, you could become the obstruction.
Remember, for GPS/DGPS to work you must have clear visibility of the full sky (meaning, line of sight?).
Installation and Maintenance
To take full advantage of this service, users should ensure that they have high quality GPS / DGPS receiver equipment which is properly installed in accordance with the manufacturers' instructions.
Remember...
** Read your manual carefully for installation instructions. **
