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Nationwide Differential GPS (NDGPS)
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Maritime Information

Since March 15th, 1999, the U.S. Coast Guard Navigation Center has operated the Nationwide Differential GPS (DGPS) Service, currently consisting of one control center and 83 remote broadcast sites. The DGPS service broadcasts correction signals on marine radiobeacon frequencies to improve the accuracy and integrity to GPS-derived positions.

Users can expect better than 10-meter accuracy throughout all established coverage areas. Typically, the positional error of a DGPS position is 1 to 3 meters. In addition, this maritime service provides 10-meter (2 dRMS) navigation accuracy and integrity alarms for GPS and DGPS out-of-tolerance conditions within ten seconds of detection.

Proposed NDGPS Transition

Over time, a number of factors have contributed to the declining public use of NDGPS, including lack of a carriage requirement, technological advances in GPS, and limited availability of consumer-grade DGPS receivers. Working with the Department of Transportation and U.S. Army Corps of Engineers, which both have responsibility for terrestrial uses of DGPS, the Coast Guard has finalized a Federal Notice that provides the public an opportunity to comment on a proposed plan to continue to provide differential coverage in major ports and waterways. The Federal Register Notice, comments received, and a graphic depicting the proposed changes to the system are accessible via the links below.

Coverage Plots

NDGPS 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. The plots attempt to account for ground conductivity, transmitter output power, and land topography using Millington’s method. To view these coverage areas, simply use the links below.

DGPS Partnerships

The US Coast Guard operates the Nationwide DGPS System for surface users. The primary users of this GPS augmentation system are mariners and surveyors. To provide this free service, the US Coast Guard leverages its partnerships with the US Department of Transportation (DOT) and the US Army Corps of Engineers.