GPS AUGMENTATION SYSTEMS
The U.S. Government operates and maintains two nation-wide GPS augmentation systems that are usable and free of any charge for users with the correct equipment. The augmentation systems, typically, are used to increase the accuracy of the basic GPS signal. Both systems are developed to international standards to promote seamless navigation around the world.
Differential GPS (DGPS)
The US Coast Guard operates the DGPS (Differential GPS) System for surface users. The primary users of the DGPS system are mariners, surveyors, and agricultural users. The system is terrestrial-based with local transmitters broadcasting correctional data. The system operates in the Medium Frequency spectrum (285 -325 KHz). DGPS coverage is provided to 92% of the continental US and 100% coverage of Puerto Rico and Hawaii. The DGPS System reached Full Operating Capability (FOC) on 15 March 1999. Specifics on DGPS, including status and technical background information are located within the Navigation Center website DGPS section.
Wide Area Augmentation System (WAAS)
The Federal Aviation Administration operates the WAAS system for aviation users. WAAS is a satellite based augmentation system (SBAS) serving North America. WAAS is a critical component of the Federal Aviation Administration's strategic objective of a seamless satellite navigation system for civil aviation. On 11 July 2003, the FAA commissioned WAAS for instrument flight use. WAAS enhances the accuracy and reliability of the global positioning system (GPS) and transmits horizontal and vertical guidance capability. Real-time coverage a can be seen at: http://www.nstb.tc.faa.gov/RT_VerticalProtectionLevel.htm. For more information on WAAS, please visit the FAA website.
Other GPS Augmentation Systems
LAAS (Local Area Augmentation System)
LAAS is a ground-based augmentation system (GBAS) to GPS that focuses its service on an airport area (approximately a 20-30 mile radius) for precision approach, departure procedures, and terminal area operations. It broadcasts correction messages via a very high frequency (VHF) radio data link from a ground-based transmitter. The worldwide community has adopted GBAS as the official term for this type of navigation system. To coincide with international terminology, the FAA is also adopting the term GBAS to be consistent with the international community. For more information on WAAS, please visit the FAA websiteCommercial Augmentation Systems
There are many different commercial entities who provide GPS augmentation to users to increase accuracy or usefulness of the basic GPS signal. We recommend users contact their equipment vendor to determine if a fee or subscription cost is required to use their system.
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