ITRF to GDA94 coordinate transformations

Abstract

The Geocentric Datum of Australia 1994 (GDA94) is a static coordinate datum realised with respect to the International Terrestrial Reference Frame (ITRF) at the reference epoch of 1 January 1994. At this time GDA94 and ITRF were coinci- dent, however, as a consequence of the tectonic mo- tion of the Australian Plate, ongoing refinement of the ITRF and crustal deformation, the two reference frames have diverged and the absolute di¤erence between them is now approximately 1 m. Conse- quently, precise coordinate transformations between ITRF and GDA94 are required for many applica- tions, and in this study these transformations are reviewed, improved and extended. New transforma- tion parameters between ITRF and GDA94 are computed, including the specific ITRF realisations of ITRF1996, ITRF1997, ITRF2000, ITRF2005 and ITRF2008. The two most recent ITRF realisa- tions, ITRF2005 and ITRF2008, after transforma- tion have a root-mean-square di¤erence of less than 10 and 30 mm in the horizontal and vertical compo- nents, respectively, with respect to GDA94 at the Australian Fiducial Network (AFN) stations. How- ever, the magnitude of some residuals exceed 15 and 60 mm in the horizontal and vertical components, respectively, which reflects the accuracy limit of GDA94. Finally, the implications and future strat- egies for managing the di¤erences between GDA94 and ITRF are discussed, including novel coordinate transformation approaches and justifications for the modernisation of GDA.