GPS Augmentations

To meet the specific user requirements for positioning, navigation, and timing (PNT), a number of augmentations to the Global Positioning System (GPS) are available. An augmentation is any system that aids GPS by providing accuracy, integrity, reliability, availability, or any other improvement to positioning, navigation, and timing that is not inherently part of GPS itself. Such augmentations include, but are not limited to:

Nationwide Differential GPS System (NDGPS): The NDGPS is a ground-based augmentation system operated and maintained by the Federal Railroad Administration, U.S. Coast Guard, and Federal Highway Administration, that provides increased accuracy and integrity of the GPS to users on land and water. Modernization efforts include the High Accuracy NDGPS (HA-NDGPS) system, currently under development, to enhance the performance and provide 10 to 15 centimeter accuracy throughout the coverage area. NDGPS is built to international standards, and over 50 countries around the world have implemented similar systems.

Wide Area Augmentation System (WAAS): The WAAS, a satellite-based augmentation system operated by the U.S. Federal Aviation Administration (FAA), provides aircraft navigation for all phases of flight. Today, these capabilities are broadly used in other applications because their GPS-like signals can be processed by simple receivers without additional equipment. Using International Civil Aviation Organization (ICAO) standards, the FAA continues to work with other States to provide seamless services to all users in any region. Other ICAO standard space-based augmentation systems include: Europe's European Geostationary Navigation Overlay System (EGNOS), India's GPS and Geo-Augmented Navigation System (GAGAN), and Japan's Multifunction Transport Satellite (MTSAT) Satellite Augmentation System (MSAS). All of these international implementations are based on GPS. The FAA will improve the WAAS to take advantage of the future GPS safety-of-life signal and provide better performance and promote global adoption of these new capabilities.

Continuously Operating Reference Station (CORS): The U.S. CORS network, which is managed by the National Oceanic & Atmospheric Administration, archives and distributes GPS data for precision positioning and atmospheric modeling applications mainly through post-processing. CORS is being modernized to support real-time users.

Global Differential GPS (GDGPS): GDGPS is a high accuracy GPS augmentation system, developed by the Jet Propulsion Laboratory (JPL) to support the real-time positioning, timing, and orbit determination requirements of the U.S. National Aeronautics and Space Administration (NASA) science missions. Future NASA plans include using the Tracking and Data Relay Satellite System (TDRSS) to disseminate via satellite a real-time differential correction message. This system is referred to as the TDRSS Augmentation Service Satellites (TASS).

International GNSS Service (IGS): IGS is a network of over 350 GPS monitoring stations from 200 contributing organizations in 80 countries. Its mission is to provide the highest quality data and products as the standard for Global Navigation Satellite Systems (GNSS) in support of Earth science research, multidisciplinary applications, and education, as well as to facilitate other applications benefiting society. Approximately 100 IGS stations transmit their tracking data within one hour of collection.

There are other augmentation systems available worldwide, both government and commercial. These systems use differential, static, or real-time techniques.

U.S. Policy on International Cooperation

The U.S. Space-Based Positioning, Navigation, and Timing Policy underscores the importance that all global navigation satellite systems and their augmentations be compatible with GPS.

The agreement in 2004 between the United States and the European Union (E.U.) on GPS and Galileo recognized the benefits of interoperable systems. The parties agreed to pursue a common, open, civil signal on both Galileo and future GPS satellites, in addition to ongoing cooperation on the GPS-based EGNOS augmentation system.

The United States has a long cooperative relationship with Japan on GPS. In addition to the Multifunction Transport Satellite (MTSAT) Satellite Augmentation System (MSAS), the parties are working towards developing a GPS-compatible regional satellite "mini-" constellation known as the Quasi Zenith Satellite System (QZSS).

The United States is also consulting closely with India on its development of its GAGAN space-based augmentation system, and with the Russian Federation on compatibility and interoperability between GPS and Russia's satellite navigation system, GLONASS.

The U.S. Department of Defense also cooperates with numerous countries to ensure that GPS provides military space-based PNT service and interoperable user equipment to its coalition partners around the world.

Space-based PNT services must serve global users with transparent interfaces and standards. The U.S. policy is to provide space-based PNT services on a continuous worldwide basis, freely available to all for civil, commercial, and scientific uses, and provide open, free access, to information necessary to develop and build equipment to use these services.

Source:gps.gov