NASA's New GDGPS
The National Aeronautics and Space Administration (NASA) is implementing a new Global Differential GPS (GDGPS) system, developed by Jet Propulsion Laboratory (JPL), that provides seamless global real-time positioning at sub-20-cm vertical accuracy and sub-10-cm horizontal accuracy for dual frequency GPS receivers. Such accuracy has previously been available only on a selected local basis, through real-time kinematic (RTK) techniques, which have enabled decimeter-level (and better) real-time GPS-based positioning on a few kilometers local scale.
Beginning in early 2001, even areas without RTK capability could access real-time positioning at the decimeter level, without performance degradation. Many applications require precise real-time, onboard knowledge of a platform's position and velocity as a critical component. For regional applications, wide-area differential systems such as the Federal Aviation Administration's (FAA) Wide Area Augmentation System (WAAS), the U.S. Coast Guard's Continuously Operating Reference Station (CORS), and various commercial differential systems have provided meter-level positioning. However, global (ground, airborne, and spaceborne) real-time positioning at the decimeter level has never been attempted nor achieved because of perceived technical and cost challenges. [GPS World, January 2001]