GPS

GPS Augmentations

To meet the specific user prerequisites for positioning, navigation, and timing (PNT), a number of augmentations to the Global Positioning System (GPS) are obtainable. 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 comprise, but are not limited to:

Nationwide Differential GPS System (NDGPS): The NDGPS is a ground-based augmentation system ran and maintained by the Federal Railroad Administration, U.S. Coast Guard, and Federal Highway Administration, that furnishes 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 all through 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 control by the U.S. Federal Aviation Administration (FAA), furnishes 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 extra 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 supervised by the National Oceanic & Atmospheric Administration, records 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 very accurate GPS augmentation system, developed by the Jet Propulsion Laboratory (JPL) to support the real-time positioning, timing, and orbit finding 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 broadcast 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 leading organizations in 80 countries. Its mission is to deliver the uppermost 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. Just about 100 IGS stations transmit their tracking data within one hour of collection.

There are other augmentation systems obtainable worldwide, for 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 highlight the importance that all global navigation satellite systems and their augmentations be well-matched with GPS.

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

The United States has a long supportive 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 looking up 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 various countries to ensure that GPS provides military space-based PNT service and practical user equipment to its alliance 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 constant worldwide basis, freely accessible 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.