GPS Augmentation Systems
To meet the specific user requirements for PNT, a number of augmentations to GPS are available. A GPS augmentation is any system that aids GPS by providing accuracy, integrity, availability, or any other improvement to PNT that is not inherently part of GPS itself. Such augmentations include, but are not limited to, the following systems.
Nationwide Differential GPS System (NDGPS)
NDGPS is a ground-based augmentation system operated by the U.S. Coast Guard, Federal Railroad Administration, and Federal Highway Administration that provides increased accuracy and integrity of GPS information 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 10-15 centimeter accuracy throughout the coverage area. NDGPS is built to international standards, and similar systems have been implemented by 50 countries around the world. For more information about NDGPS, visit the websites of the Coast Guard Navigation Center and the Federal Highway Administration.
Wide Area Augmentation System (WAAS)
WAAS, a satellite-based augmentation system operated by the Federal Aviation Administration (FAA), supports aircraft navigation across North America. Although designed primarily for aviation users, WAAS is widely available in receivers used by other PNT communities. FAA is committed to providing WAAS service at the performance levels specified in the GPS WAAS Performance Standard. FAA is improving WAAS to take advantage of the future GPS safety-of-life signal to provide even better performance. Other similar space-based augmentation systems include Japan's Multi-functional Transport Satellite (MTSAT)-based Satellite Augmentation System (MSAS) and Quasi-Zenith Satellite System (QZSS), the European Geostationary Navigation Overlay Service (EGNOS), and India's GPS And Geo-Augmented Navigation (GAGAN) system. For more information about WAAS, visit the FAA website.
Continuously Operating Reference Stations (CORS)
The U.S. CORS network, managed by the National Oceanic and Atmospheric Administration, archives and distributes GPS data for precise positioning tied to the National Spatial Reference System. Over 200 private, public, and academic organizations contribute data from over 1,200 GPS tracking stations to CORS. The web-based Online Positioning User Service (OPUS) offers free post-processing of GPS data sets to the centimeter level using CORS information. CORS is also being modernized to support real-time users. For more information about CORS, visit the CORS website.
Global Differential GPS (GDGPS)
GDGPS is a high accuracy GPS augmentation system, developed by the NASA Jet Propulsion Laboratory to support the real-time positioning, timing, and determination requirements of 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). For more information about GDGPS, visit the GDGPS website.
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. For more information about IGS, visit the IGS website.
Other Augmentations
There are many other GPS augmentation systems available worldwide, both government and commercial. These systems use differential, static, or real-time techniques. There are also systems that augment other global navigation satellite systems. The United States is cooperating with many other nations to ensure the interoperability of international augmentation systems with GPS and U.S. GPS augmentations.