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NDGPS GENERAL INFORMATION

DIFFERENTIAL GPS

 

**NOTICE** The RTCM Special Committee 104 is suggesting retirement of RTCM Message Types 4, 8, 11, 12, and 13. Any users requiring these specific RTCM Message Types, please contact DGPS System Support by 1900Z November 15, 2009.

NAVCEN operates the Coast Guard Maritime Differential GPS (DGPS) Service and the developing Nationwide DGPS Service, consisting of two control centers and over 80 remote broadcast sites. The Service broadcasts correction signals on marine radiobeacon frequencies to improve the accuracy and integrity to GPS-derived positions. The Coast Guard DGPS Service provides 10-meter accuracy in all established coverage areas.

Typically, the positional error of a DGPS position is 1 to 3 meters, greatly enhancing harbor entrance and approach navigation. The System provides service for coastal coverage of the continental U.S., the Great Lakes, Puerto Rico, portions of Alaska, Hawaii, and a greater part of the Mississippi River Basin. Many foreign nations are implementing standard DGPS services modeled after the U.S. Coast Guard’s system to significantly enhance maritime safety in their critical waterways.

 

The Coast Guard's maritime Differential Global Positioning Service achieved Full Operational Capability (FOC) on 15 March 1999 as announced in the DOT press release. The maritime DGPS service provides 10 meter (2 dRMS) navigation accuracy, integrity alarms for GPS and DGPS out-of-tolerance conditions within 10 seconds of detection, availability of 99.7% per month, coastal coverage to the continental United States, the Great Lakes, Puerto Rico/US Virgin Islands, and selected portions of Alaska and Hawaii.

The achievement of FOC culminates a six-year effort to convert existing radiobeacon sites and construct new sites to transmit DGPS corrections. Several equipment upgrades were installed to improve system performance. During the procurement and installation phases of the system upgrades, the maritime DGPS service operated under Initial Operational Capability rules, where the signals provided accurate corrections with integrity to the maximum extent possible.