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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

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

collaboration via naref

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
nad83 background
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
nad83 realizations in canada
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
nad83 csrs issues
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
naref itrf densification
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
slide9

NAREF Horizontal Velocities

w.r.t. ITRF2005 plate motion

canadian campaign solutions
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
gps velocity grid for canada
GPS Velocity Grid for Canada

Based on NAREF+CBN

Vertical Velocities

(some outliers removed)

snarf
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