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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.  Each NDGPS facility meets all operating parameters established to qualify an MDGPS facility for operational availability, as established by U.S. Coast Guard (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.

The Department of Homeland Security (US Coast Guard), in coordination with the Department of Transportation and the US Army Corps of Engineers (USACE), analyzed the future requirements for the NDGPS to support investment decisions beyond Fiscal Year (FY) 2016. Future investment decisions included: 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.

Based on this review and comments received in response to the August 18, 2015, Federal register notice, the decision was made to shut down and decommission 37 NDGPS sites on August 4, 2016.  Of these, 9 are operated by the USCG and 28 are inland DOT sites.

In March 2018, the USCG announced the discontinuance of its remaining 38 maritime DGPS sites. The USCG will implement the closures through a phased reduction in service, which will commence in September of 2018, and conclude by September of 2020.

For more information, visit the NDGPS website

Nationwide Differential Global Positioning System (NDGPS) Program Related Documents