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Global Navigation Satellite System (GNSS) Ultra-Rapid Orbit Product (sub-daily files, generated 4 times/day) from NASA CDDIS

This derived product set consists of Global Navigation Satellite System Ultra-Rapid Orbit Product (daily files, generated daily) from the NASA Crustal Dynamics Data Information System (CDDIS). GNSS provide autonomous geo-spatial positioning with global coverage. GNSS data sets from ground receivers at the CDDIS consist primarily of the data from the U.S. Global Positioning System (GPS) and the Russian GLObal NAvigation Satellite System (GLONASS). Since 2011, the CDDIS GNSS archive includes data from other GNSS (Europe’s Galileo, China’s Beidou, Japan’s Quasi-Zenith Satellite System/QZSS, the Indian Regional Navigation Satellite System/IRNSS, and worldwide Satellite Based Augmentation Systems/SBASs), which are similar to the U.S. GPS in terms of the satellite constellation, orbits, and signal structure. Analysis Centers (ACs) of the International GNSS Service (IGS) retrieve GNSS data on regular schedules to produce precise orbits identifying the position and velocity of the GNSS satellites. The IGS Analysis Center Coordinator (ACC) uses these individual AC solutions to generate the official IGS ultra-rapid combined orbit products. The ultra-rapid orbit and clock combination is a sub-daily solution, released four times per day, at 03:00, 09:00, 15:00, and 21:00 UTC (prior to GPS week 1267 they were released twice daily). In this way the average age of the predictions is reduced to 6 hours (compared to 36 hours for the old IGS predicted products and 9 hours for the twice-daily ultra-rapid solutions). IGS ultra-rapid orbit files contain 48 hours of tabulated orbital ephemerides, and the start/stop epochs continuously shift by 6 hours with each update. The first 24 hours of each IGS ultra-rapid orbit are based on the most recent GNSS observational data from the IGS hourly tracking network. At the time of release, the observed orbits have an initial latency of 3 hours. The next 24 hours of each file are predicted orbits, extrapolated from the observed orbits. The orbits within each ultra-rapid product file are, however, continuous at the boundary between the observed and predicted parts. Normally, the predicted orbits between 3 and 9 hours into the second half of each ultra-rapid orbit file are most relevant for true real time applications. All orbit solution files utilize the extended standard product-3 (SP3c) format. The reduced latency on availability of these products allows for significantly improved orbit predictions and reduced errors for user applications.

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