U.S. DEPARTMENT OF COMMERCE | National Oceanic and Atmospheric Administration | National Ocean Service

The National Geodetic Survey (NGS) computes orbits for the Global Positioning System (GPS) satellites in the Global Navigation Satellite System (GNSS) using 24 hour data segments observed at a global network of GNSS receivers and antennas. The global tracking network is coordinated by the International GNSS Service (IGS). The current reference frame used in the computation is the IGS05 reference frame, a GPS-only realization of the latest International Terrestrial Reference Frame (ITRF2005). An informational summary file documenting the computation of NGS orbits and containing other relevant information about the observed satellites can be viewed by clicking the "Analysis Strategy Summary" link below or by navigating to http://igscb.jpl.nasa.gov/igscb/center/analysis/noaa.acn.

NGS is currently one of eight IGS Analysis Centers contributing to the IGS precise products. Each day, NGS, and the other Centers, submit their computed daily orbits to the IGS for inclusion in the IGS Rapid Orbit product (igrWWWWD.sp3). Each week, NGS, and the other Centers, submit their final, precise orbits to the IGS for inclusion in the IGS Final Orbit product (igsWWWW7.sp3). This final orbit is considered the international standard and should be used when there is need for precision. The Final Orbit is made available after analysis of a full GPS week is complete. For example, Sunday through Saturday's orbits will be made available between 10 and 14 days after the end of the GPS week.

In addition to the Final and Rapid orbit products, the IGS supplies the Ultra Rapid Orbit, which is available every 6 hours.

1. GPS Orbit File Naming Convention
2. Other Information
3. Analysis Strategy Summary
4. NGS Orbits
• NOTICE – On February 24, 2007, NGS orbits attained cm-level precision.
• NOTICE – Beginning Nov. 5, 2006 NGS adopted the IGS05 reference frame, defined by 130 continuously operating sites in a global tracking network. The IGS05 reference frame is a GPS-realized version of the most recent International Terrestrial Reference Frame (ITRF05). Thus, starting with GPS Week 1410, NGS orbits are computed in IGS05.
• NOTICE – Beginning Dec. 26, 2004 NGS begun producing the precise orbits in a new and improved manner. Along with this improvement the orbit files no longer have the overlap (in time) on each end. Without this overlap the EF18 binary files should not be joined. To join daily orbits, you should use the program cat_sp3 (source code) to join the sp3 files. The NGS orbit (rapid or final) is only one of several orbits used to create the IGS (rapid or final) orbit; it is recommended that you use the IGS orbit.
• NGS Rapid Orbits (ngrWWWWD.sp3)
• 13-hour latency
• constrained (all fiducial sites fixed to their IGS05 coordinates) 24 hour file - sp3
• file named by GPS Week number and Day of Week
• also available at NASA’s CDDIS
• NGS Final Orbits (ngsWWWWD.sp3)
• 8 to 10 day latency
• minimally constrained (no-net rotation) 24-hour file – sp3
• file named by GPS Week number and Day of Week
• also available at NASA’s CDDIS
5. IGS Orbit Availability
• IGS Product Information
• Ultra-rapid (iguWWWWD.sp3 and igaWWWD.sp3)
• 6-hour latency
• constrained (no-net rotation, no-net translation) 24-hour file – sp3
• Rapid (igrWWWWD.sp3)
• 13-hour latency
• constrained (no-net rotation, no-net translation) 24-hour file – sp3
• Final (igsWWWWD.sp3)
• 12 to 14 day latency
• minimally constrained (no-net rotation) 24 hour file - sp3
• files named by GPS Week number and Day of Week
6. Orbit Utilities
7. SP3 Format
• SP3 version a
• SP3 version c
8. GPS Calendar
9. USCG Navigation Center

GPS Links:

GPS Bibliographies

National Geodetic Survey's Continuously Operating Reference Stations (CORS)
Related Geodetic Resources

Transform between height systems with GEOID99

NOAA's Forecast Systems Lab (GPS derived precipitable water vapor)

U.S. Coast Guard's Navigation Center

U.S. Naval Observatory's GPS Data & Information

Univ. of California's Scripps Orbit and Permanent Array Center
Southern California Integrated GPS Network

Jet Propulsion Lab

International GPS Service

Goddard Space Flight Center's Crustal Dynamics Data Information System

Canadian Active Control System

International Earth Rotation Service (IERS)

University NAVSTAR Consortium (UNAVCO)

Geography and Environment Gateway (GEsource)

Physical Sciences Information Gateway (PSIgate)

Orbiteers

Bill Kass
Bob Dulaney
Jake Griffiths

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CORS | NGS | NOS | NOAA | U.S. Dept. of Commerce

	Last updated by jake.griffiths on Thursday, 30-Apr-2009 12:22:58 EDT