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Reference Frames Panel Discussion

Reference Frames Panel Discussion. M. Craymer Geodetic Survey Division, Natural Resources Canada. IAG Workshop on Monitoring North American Geoid Change Boulder, CO, October 21-23, 2009. IAG Commission 1 Reference Frames. Sub-Commission 1.3 Regional Reference Frames.

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Reference Frames Panel Discussion

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  1. Reference Frames Panel Discussion M. Craymer Geodetic Survey Division, Natural Resources Canada IAG Workshop on Monitoring North American Geoid Change Boulder, CO, October 21-23, 2009

  2. IAG Commission 1 Reference Frames Sub-Commission 1.3 Regional Reference Frames Regional Sub-Commission1.3a for Europe (EUREF) Regional Sub-Commission1.3c for North America (NAREF) Working Group 1Regional Dense Velocity Fields ITRFDensification Reference FrameTransformations SNARF Collaboration via NAREF

  3. NAD83 Background • Original realization based on Doppler RF = WGS84 • Thought to be geocentric at the time • Now known to be offset by ~2 m and slightly misoriented • ~1.5 m difference at surface • Now realized as a best-fitting transformation from ITRF96 (IAG recommendation) • NAD83(CSRS) in Canada • NAD83(CORS96) in US • Frame kept aligned to N.A. using NUVEL-1A • Transformation updated to new ITRF’s using transformations between ITRF’s

  4. NAD83 Realizations in Canada Version (epoch) Frame Adopted Description v0 (n/a) Original 1986-1993 Horizontal adjustments v1 (?) CSRS96* 1996 Based on ITRF94? v2 (1997.0) CSRS98** 1998 Based on ITRF96 v3 (1997.0) 2000 Based on ITRF97 v4 (2002.0) 2002 Based on ITRF2000 v5 (2006.0) Based on ITRF2005 * Preliminary ITRF-NAD83 transformation (CSRS96) ** Adopted ITRF-NAD83 transformation (CSRS98=CSRS) • Difference between realizations primarily due to different epochs (crustal motion) • Reconciled with GPS velocity model/grid

  5. NAD83(CSRS) Issues • Not geocentric • Not compatible with modern global frames • Motion of N.A. in ITRF modelled by NUVEL-1A • NUVEL-1A biased by ~2 mm/y • Need to periodically update frame to more recent epoch (eg, v4 & v5) • Need better estimate of plate motion • Many users/software believe NAD83=WGS84 ! • hNAD83 – hWGS84/ITRF = -0.5 to >1 m ! • Replace NAD83 with an ITRF-based frame

  6. NAREF ITRF Densification • Contributed Regional Solutions • NRCan/GSD (GIPSY + Bernese) • NRCan/PGC WCDA (Bernese) • NGS CORS (PAGES) • SIO Preliminary PBO (GAMIT/GLOBK) • MIT Official PBO Combos (GLOBK) • Products • Weekly coordinate combinations • Periodic velocity solutions

  7. Regional Contributions

  8. NAREF Horizontal Velocities

  9. NAREF Horizontal Velocities w.r.t. ITRF2005 plate motion

  10. NAREF Vertical Velocities

  11. Canadian Campaign Solutions • Canadian Base Network (CBN) • Network of stable forced-centering pillars • Using 27 repeated campaign surveys 1994-2006 • Three main campaigns (1994-99, 2001-2, 2005-6) • Multiple 24 hr occupations/stations in each campaign • Processed with Bernese GPS Software • Same strategy as for continuous data

  12. CBN Vertical Velocities

  13. NAREF+CBN Vertical Velocities

  14. GPS Velocity Grid for Canada Based on NAREF+CBN Vertical Velocities (some outliers removed)

  15. SNARF • Stable North American Reference Frame • Based on ITRF • Fixed to stable North America • Estimating transformation that minimizes motion of “frame” sites • Includes model of GIA • Weighted assimilation of GPS + a priori GIA model • SNARF v1.0 released Dec 1996 • Based on NAREF & Calais velocity solutions • SNARF v2.0 still in preparation • Based on updated NAREF, Calais & MIT velocity solutions

  16. SNARF v1.0

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