1. Canada’s Natural Resources – Now and for the Future 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. Canada’s Natural Resources – Now and for the Future Collaboration via NAREF IAG Commission 1 Reference Frames Sub-Commission 1.3 Regional Reference Frames Regional Sub-Commission 1.3c for North America (NAREF) Regional Sub-Commission 1.3a for Europe (EUREF) Working Group 1 Regional Dense Velocity Fields ITRF Densification Reference Frame Transformations SNARF

3. Canada’s Natural Resources – Now and for the Future 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. Canada’s Natural Resources – Now and for the Future NAD83 Realizations in Canada Version (epoch)FrameAdoptedDescription v0(n/a)Original1986-1993Horizontal adjustments v1(?)CSRS96*1996Based on ITRF94? v2 (1997.0)CSRS98**1998Based on ITRF96 v3 (1997.0)2000Based on ITRF97 v4 (2002.0)2002Based 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. Canada’s Natural Resources – Now and for the Future 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 !  h NAD83 – h WGS84/ITRF = -0.5 to >1 m ! ⇒ Replace NAD83 with an ITRF-based frame

6. Canada’s Natural Resources – Now and for the Future 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. Canada’s Natural Resources – Now and for the Future Regional Contributions

8. NAREF Horizontal Velocities

9. w.r.t. ITRF2005 plate motion

10. NAREF Vertical Velocities

11. Canada’s Natural Resources – Now and for the Future 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. Canada’s Natural Resources – Now and for the Future GPS Velocity Grid for Canada Based on NAREF+CBN Vertical Velocities (some outliers removed)

15. Canada’s Natural Resources – Now and for the Future 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