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Nationwide Differential Global Positioning System (NDGPS) Program

PL 105-66, Title III, § 346 (111 Stat. 1449) authorizes the Secretary of Transportation to improve and expand the USCG's Maritime Differential GPS System (MDGPS) into a Nationwide DGPS, or NDGPS, by adding an inland segment. OST-R coordinates this inland program and is acting chair of the NDGPS Policy and Implementation Team. Today, multiple Federal agencies, several states, and scientific organizations are cooperating to provide the combined national DGPS utility, with plans to complete NDGPS system coverage throughout the lower 48 states.

Each NDGPS facility meets all operating parameters established to qualify a MDGPS facility for operational availability, as established by USCG. NDGPS was not designed to meet aviation integrity requirements.

In addition to providing a real-time broadcast of differential corrections, the U.S. DGPS services provide a robust operational backbone to the DOC's CORS application for post-processing survey applications and Web-enabled location solutions, the National Weather Service's Forecast Systems Laboratory for short-term precipitation forecasts, and the University NAVSTAR Consortium (UNAVCO) for plate tectonic monitoring. Where operational considerations allow, additional operational capability may be added, such as the broadcast of navigational or meteorological warnings and marine safety information (i.e., NAVTEX data) to support safe navigation at sea.

The Department of Homeland Security, in coordination with the Department of Transportation, is analyzing the future requirements for the NDGPS to support investment decisions beyond Fiscal Year (FY) 2016. Future investment decisions might include: maintaining NDGPS as currently configured, decommissioning NDGPS as currently configured, or developing alternate uses for the NDGPS infrastructure. Contributing factors to these decisions are: (1) the U.S. Coast Guard change in policy to allow aids to navigation (ATON) to be positioned with a GPS receiver using Receiver Autonomous Integrity Monitoring (RAIM), and to allow USCG navigation in all waters using the WAAS receiver; (2) limited availability of consumer grade NDGPS receivers at retail outlets; (3) no NDGPS carriage requirement on any vessel within U.S. territorial waters; (4) the Presidential Directive turning off GPS SA; (5) continuing GPS modernization and, (6) the Federal Railroad Administration’s determination that neither NDGPS, nor High Accuracy NDGPS, are requirements for the successful implementation of Positive Train Control.

More information on NDGPS is available at

Nationwide Differential Global Positioning System (NDGPS) Program Related Documents