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Nationwide Differential GPS (NDGPS)
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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 38 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.

Discontinuance of the USCG DGPS Service

The U.S. Coast Guard (USCG) will discontinue service from its remaining 38 Differential Global Positioning System (DGPS) over the next three years.   This staged reduction of the remaining DGPS broadcast service sites will begin in 2018 and end with the curtailment of the Coast Guard broadcast of GPS corrections over medium frequency (MF) in 2020.
Due to the increasing accuracy and integrity of the Global Positioning System (GPS), the Coast Guard no longer has a mission requirement for DGPS.  Specifically, GPS provides sufficient positional accuracy to meet international navigation requirements for harbor approaches and to position Federal Aids to Navigation (ATON).  Additionally, other commercial and government GPS augmentation systems are available for GPS users.  The accuracy of un-augmented GPS increasingly exceeds the 10-meter accuracy requirements for harbor navigation and harbor approaches.  
The National Differential GPS (NDGPS) system was significantly reduced in 2016 with the discontinuance of: all 28 of the Department of Transportation inland broadcast sites, all 7 U.S. Army Corps of Engineers (USACE) broadcast sites, and 10 U.S. Coast Guard maritime broadcast sites
Since 2016, the Coast Guard has continued assessments and outreach affirming that the positional accuracy provided by un-augmented GPS and GPS augmented by the U.S. Wide Area Augmentation System (WAAS) is sufficient to meet Coast Guard mission requirements and navigational safety requirements for harbor approach.
The DGPS service will be discontinued in a phased manner over the next three years.  The Coast Guard will release the actual broadcast termination dates via local notices to mariners.
In Fiscal Year 2018, the Coast Guard is planning to terminate the DGPS broadcast at the following sites: Annapolis, Maryland; New Bern, North Carolina; Robinson Point, Washington; Pigeon Point, California; and Bobo, Mississippi.
In Fiscal Year 2019, the Coast Guard is planning to terminate the DGPS broadcast at the following sites: Whidbey Island, Washington; Appleton, Washington; Fort Stevens, Oregon; Cape Mendocino, California; Lincoln, California; Point Loma, California; Kokole Point, Hawaii; Upolu Point, Hawaii; Driver, Virginia; Kensington, South Carolina; Cape Canaveral, Florida; Card Sound, Florida; Tampa, Florida; Wisconsin Point, Wisconsin; Mequon, Wisconsin.
In Fiscal Year 2020, the Coast Guard is planning to terminate the DGPS broadcast at the following sites: Penobscot, Maine; Acushnet, Massachusetts; Hudson Falls, New York; Moriches, New York; Sandy Hook, New Jersey; English Turn, Louisiana; Angleton, Texas; Annette Island, Alaska; Biorka, Alaska; Kenai, Alaska; Kodiak, Alaska; Gustavus, Alaska; Potato Point, Alaska; and Level Island, Alaska, Upper Keweenaw, Michigan; Cheboygan, Michigan; Detroit, Michigan; and Youngstown, New York.

Coverage Plots

NDGPS provides service for coastal coverage of the continental U.S, the Great Lakes,  portions of Alaska, and Hawaii. 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.