Geodetic Systems

• International Committee on GNSS

  Working Group D, Saint Petersburg, Russia
• GPS Geodetic Reference System

  16 September 2009
• WGS 84


  World Geodetic System 1984
• Approved for Public Release 09-478
• GPS Reference Frame


  World Geodetic System 1984 (WGS 84)
• WGS 84


  • Reference for Positioning and Navigation
  • Aligned to International Terrestrial Reference Frame (ITRF)
  • Consistent with international standards
  • Supports GPS Operational Control Segment (OCS)
• GPS References WGS 84

  Interoperability requires relationship between WGS 84 and other GNSS reference systems
• WGS 84 Support for Positioning and Navigation

  • Safety of Navigation (Maps, Charts, Grids, Publications, Inertial Navigation System support)
  • Reference system (Network solution, Grids and coordinate system, Relationship to local datums, Gravity and magnetic models, Elevations and bathymetry)
  • GPS coordinates tie WGS 84 to physical Earth
  • Key component for interoperability
• Reference Frame


  Global network of control stations that binds an Earth-centered, Earth-fixed 3-D coordinate system to the earth
• Control Station Position Accuracy: Transit (1 - 2 m) Jan 1987, G730 (~10 cm) Jun 1994, G873 (~5 cm) Jun 1997, G1150 (~1 cm) Jan 2002
• Ensure the WGS 84 Reference Frame errors are negligible in the GPS ephemeris error budget
• WGS 84 Maintenance


  • Ensure scientific integrity (Align to ITRF, Use International standards and conventions)
  • GPS Monitor Station Coordinates (Next network adjustment 2011)
  • Earth Gravitational Model (EGM08 released)
  • World Magnetic Model (Next release Jan 2010)
  • NIMA Technical Report 8350.2 (Defines WGS 84 Reference System, Update publication in 2011)
  • Information available via internet
• NGA Monitor Station Coordinates

  • Next network adjustment 2011 (Ensure Geodetic quality, Equipment changes, Add Reference Markers, Align to IGS reference sites)
  • Interim adjustments ongoing due to antenna replacement
  • Plan to update NGA GPS operations to 2003 conventions
  • Changes to NGA processes are coordinated with GPS OCS
• WGS 84 aligned to ITRF
• WGS 84 aligned to ITRF

  • NGA and US Air Force site coordinates solved using NGA orbits, Solution constrained to ITRF network, Validation: Hold WGS 84 sites fixed and allow IGS sites to adjust, Direct comparison between NGA and IGS orbit solutions
• WGS 84 (G1150) aligned to ITRF2000
• NGA contributes its GPS observational data to IGS to support consistency between WGS 84 and ITRF
• WGS 84 used World-wide


  • Reference frame for maps, charts, and GPS, International Organization for Standardization (ISO) certified process

  
• Documents that reference WGS 84

  • US government (Department of Defense Master Positioning, Navigation and Timing Plan, Federal Radionavigation Plan, Technical manuals and Instructions)
  • International documents (North Atlantic Treaty Organization Standardization Agreement, Spatial Reference Model, International Civil Aviation Organization Adopted, International Hydrographic Organization Technical Resolution)
• Discussion of Standards


  • ITRF as the world standard proposed in multiple venues, A scientific standard is desirable (Best practices for constants, models, and methods), Practical applications have special needs (Frequent updates of constants and other values are undesirable), Interoperability requires relationships amongst reference systems
• Earth Gravitational Model 2008 (EGM08) has 5 min x 5 min resolution, 15 cm RMS accuracy, 2160 x 2160 error propagation, uses CHAMP and GRACE for long wavelengths, 54 million surface gravity values, SRTM, ICESAT for elevation, 4.7 M coefficients
• World Magnetic Model next epoch is 2010.0, has a Main Field Model (12) and a Crustal Model (720)