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| DGPS | |
|---|---|
| Name | Differential Global Positioning System |
| Type | Navigation augmentation |
| Introduced | 1970s |
| Manufacturer | Various |
DGPS
Differential Global Positioning System (DGPS) augments satellite navigation by providing corrections to improve location accuracy for users of the Global Positioning System and compatible constellations. DGPS systems combine corrections from fixed reference stations with satellite observations to reduce common-mode errors that affect users across regions. Prominent in maritime safety, surveying, and precision agriculture, DGPS links infrastructure and services from national agencies to private firms.
DGPS operates by comparing satellite-derived positions at precisely surveyed, stationary reference stations—such as those operated by the United States Coast Guard, the Ordnance Survey, or the National Oceanic and Atmospheric Administration—with the known coordinates of those stations. Corrections computed at reference stations are broadcast via radio beacons, satellite links, or internet protocols to users aboard vessels, aircraft, or land vehicles. Systems and institutions including the International Maritime Organization, the European Space Agency, and the Federal Aviation Administration have integrated DGPS concepts into navigation frameworks and service requirements. DGPS is related to concepts developed for Navstar GPS, GLONASS, Galileo, and BeiDou, and interoperates with augmentation schemes like SBAS and regional networks run by organizations such as the National Geospatial-Intelligence Agency and national hydrographic offices.
Early differential techniques emerged during experiments by research groups at institutions such as the Jet Propulsion Laboratory and universities like Massachusetts Institute of Technology and Ohio State University in the 1970s and 1980s. Maritime DGPS infrastructures expanded under initiatives by the International Maritime Organization and national services including the United States Coast Guard and the Canadian Coast Guard through the 1990s. Surveying and cadastral adoption was influenced by standards from bodies such as the International Association of Geodesy and national mapping agencies like the Ordnance Survey and Institut Géographique National. The proliferation of cellular and internet connectivity in the 2000s enabled real-time kinematic (RTK) and networked DGPS services run by commercial operators including firms like Trimble, Topcon, and Leica Geosystems.
DGPS relies on simultaneous reception of signals from navigation constellations including Navstar GPS and GLONASS at reference stations and user receivers. At each reference station, the difference between the computed satellite range and the known range yields correction terms for satellite clock, ephemeris, and atmospheric delays. Corrections are formatted per standards from organizations such as the Radio Technical Commission for Maritime Services and transmitted using mediums like terrestrial LF/MF radio beacons, satellite broadcast channels from entities like the Inmarsat network, or internet protocols standardized by the Open Geospatial Consortium. User receivers apply differential corrections in real time or post-processing, improving positional solutions and enabling integration with inertial navigation systems supplied by manufacturers such as Honeywell and Northrop Grumman.
DGPS implementations vary from single-station differential beacons run by national hydrographic services to wide-area networked solutions and commercial RTK networks. Maritime DGPS networks operated by agencies including the United States Coast Guard and the Australian Maritime Safety Authority commonly employ LF/MF transmissions compatible with user equipment from manufacturers like Furuno and Garmin. Land-based networked RTK and differential services provided by companies such as Trimble, Topcon, and Hexagon AB use internet-enabled protocols and real-time data streams from networks of reference stations. Other configurations include satellite-based augmentation and hybrid systems that combine DGPS corrections with precise point positioning from research projects at institutions like the European Space Agency and the National Aeronautics and Space Administration.
DGPS supports maritime navigation, where organizations such as the International Maritime Organization and national marine authorities require high-integrity positioning for port approach and pilotage. Surveying and cadastral mapping rely on DGPS in workflows used by the United States Geological Survey and national land registries. Precision agriculture employs DGPS-guided machinery from firms like John Deere and Case IH for field operations, while construction and civil engineering projects run by companies such as Bechtel use DGPS for machine control. Environmental monitoring projects at institutions like the Scripps Institution of Oceanography and Woods Hole Oceanographic Institution use DGPS for vessel-based data collection. Aviation applications integrate differential corrections through systems overseen by the Federal Aviation Administration and Eurocontrol for certain non-precision approaches.
DGPS reduces errors from satellite clock offsets, ephemeris inaccuracies, and atmospheric effects caused by the ionosphere and troposphere, but residual errors remain due to multipath, local interference, and user receiver noise. Accuracy depends on satellite geometry described by dilution of precision metrics used in receivers by companies like Garmin and Trimble, and on separation between reference stations and users: single-station DGPS performance degrades with distance from reference stations, prompting development of networked corrections by providers such as Leica Geosystems. Signal obstructions in urban canyons near landmarks like Statue of Liberty or dense infrastructure in cities such as New York City and Tokyo increase multipath and reduce availability. Jamming and spoofing threats studied at research centers like MIT Lincoln Laboratory and countermeasures developed by agencies including the National Institute of Standards and Technology represent ongoing challenges.
Regulatory bodies such as the International Maritime Organization, Federal Communications Commission, and European Union framework agencies define service expectations and spectrum use impacting DGPS beacon operations. Standards from the Radio Technical Commission for Maritime Services, the Open Geospatial Consortium, and the International Organization for Standardization shape correction message formats and interoperability. Implementation challenges include funding and maintaining dense reference networks, spectrum coordination with broadcasters and services like Amateur Radio and Digital Audio Broadcasting, and transitioning users to satellite-based augmentations promoted by the European Space Agency and International Civil Aviation Organization. National mapping agencies like the Ordnance Survey and Geoscience Australia coordinate modernization efforts to ensure legacy users of DGPS equipment from vendors such as SiRF Technology and u-blox continue to receive reliable positioning services.
Category:Satellite navigation