Realization and Unification of NAD83 in Canada and the U.S. via the ITRF

  • M. Craymer
  • R. Ferland
  • R. Snay
Part of the International Association of Geodesy Symposia book series (IAG SYMPOSIA, volume 120)


A more unified realization of the North American Datum of 1983 (NAD83) was recently implemented by Canada and the U.S. to provide more accurate and convenient access to this reference system. In both countries, NAD83 is the adopted datum for spatial positioning. It was initially realized in the mid-1980s by adjusting primarily classical geodetic observations that connected a network of monumented control points spanning North America. Although the new NAD83 realization is compatible with the original one within the accuracies of those classical observations, the wide use of high precision GPS surveys since then have required a more rigorous definition of NAD83 in terms of network scale, ellipsoidal heights and crustal motion. In an effort to provide a more precise realization of a 3D NAD83 common to both countries, and to comply with LAG resolutions recommending that reference systems be tied to the ITRS, Canada and the U.S. have collaborated in the determination of a common transformation between the ITRF and the fundamental 3Ddatum of NAD83. This conformal similarity transformation is based upon ITRF96, the latest realization of ITRF. Through the use of continuously operating GPS stations (CACS in Canada and CORS in the US) forming part of the ITRF, this transformation also provides more accurate and convenient access to the NAD83 reference frame. It also allows for the conversion of IGS precise GPS ephemerides from ITRF to NAD83, thereby enabling high accuracy GPS surveys to be performed entirely within NAD83.


Very Long Baseline Interferometry North American Plate Ellipsoidal Height Convenient Access International Terrestrial Reference Frame 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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  1. Demets C., Gordon R.G., Argus D.F., Stein S. (1994). Effect of recent revisions to the geomagnetic reversal time scale on estimates of current plate motions. Geophysical Research Letters, Vol. 21, No. 20, pp. 2191–2194.CrossRefGoogle Scholar
  2. International Association of Geodesy (1992). IAG Resolutions adopted at the XXth IUGG General Assembly in Vienna. The Geodesist’s Handbook. Bulletin Geodesique, Vol. 66, No.2, pp. 132–133.Google Scholar
  3. Larson K.M., Freymueller J.T., Philipsen S. (1997). Global plate velocities from the Global Positioning System. Journal of Geophysical Research, Vol. 102, No. B5, pp. 9961–9982.CrossRefGoogle Scholar
  4. Mccarthy D.D. (ed.) (1996). IERS Conventions (1996). Technical Note 21, International Earth Rotation Service, Paris Observatory, Paris.Google Scholar
  5. Soler T., Love J.D., Hall L.W., Foote R.H.(1992). GPS Results from Statewide High Precision Networks in the United States. Proceedings of the 6th International Geodetic Symposium on Satellite Positioning, The Ohio State University, Columbus, OH, March 17–20, pp. 573–582.Google Scholar

Copyright information

© Springer-Verlag Berlin · Heidelberg 2000

Authors and Affiliations

  • M. Craymer
    • 1
  • R. Ferland
    • 2
  • R. Snay
    • 3
  1. 1.Geodetic Survey Division, Natural Resources CanadaOttawaCanada
  2. 2.Geodetic Survey Division, Natural Resources CanadaOttawaCanada
  3. 3.National Geodetic Survey, N/NGS5, National Oceanic and Atmospheric AdministrationSilver SpringUSA

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