Differential Global Positioning System (DGPS) is a technology used to increase the accuracy of a GPS position and validate the integrity of the GPS signal. Relying on GPS, DGPS provides a corrective augmentation signal via a Medium Frequency broadcast (285 to 325 KHz). DGPS works by reducing the natural and man-made errors impacting the GPS signals within a geographic area. Maritime pilots have typically used DGPS receivers to precisely navigate large vessels in and out of congested ports and harbors.

Within the last year, the nationwide DGPS system has undergone a substantial reduction in the number of operational sites. In 2016, the number of sites was reduced from 84 to 45. The remaining DGPS sites are concentrated in coastal areas and along the Western Rivers. All sites are operated from the USCG Navigation Center (NAVCEN), located in Alexandria, Va. Most of the sites are owned and maintained by USCG, but a few are owned and maintained by the U.S. Army Corps of Engineers (USACE).

The USCG initially designed DGPS in the mid-1990s with a primary mission to provide sub-10 meter accuracy for the harbor and harbor approach phase of marine navigation. USACE and others found the DGPS service to be beneficial for purposes beyond navigation. Hydrographic surveying, dredging and coastal construction projects were a few innovative ways USACE found to utilize DGPS.

As the DGPS architecture and equipment aged, its maintenance and operating costs have become a burden for USACE operating budgets. With increased competition from private DGPS providers, high accuracy Real-Time Kinematic systems, and the Federal Aviation Administration’s Wide Area Augmentation System, USACE has come to the decision that its inventory of DGPS sites are no longer worthwhile.

USACE began a phased shutdown of its five remaining DGPS sites May 31, 2017 when the Louisville, Kentucky site permanently shutdown. On June 30, 2017 three more sites will be permanently shut down; St. Paul, Minnesota, Miller’s Ferry, Alabama, and Rock Island, Illinois. The final USACE owned DGPS site, Reedy Point, Delaware, will be permanently shut down July 31, 2017. The 39 USCG owned and operated DGPS sites will continue to transmit.

All DGPS operations are, and will continue to be, remotely monitored 24/7 by USCG NAVCEN. To learn more about DGPS or the Navigation Center, please visit their website at https://www.navcen.uscg.gov/.

Current DGPS

DGPS without USACE sites

This blog is not a replacement or substitute for the formal posting of regulations and updates or existing processes for receiving formal feedback of the same. Links provided on this blog will direct the reader to official source documents, such as the Federal Register, Homeport and the Code of Federal Regulations. These documents remain the official source for regulatory information published by the Coast Guard.