Monday 22 August 2005

G4
1330-1500 hours

062
Limitations in the NZGD2000 deformation model
Beavan, John¹, Blick, Graeme²
1 Institute of Geological and Nuclear Sciences, Lower Hutt, New
Zealand
2 Land Information New Zealand, Wellington, New Zealand
Author email: gblick@linz.govt.nz
The New Zealand Geodetic Datum 2000 (NZGD2000) is a semi- dynamic datum, in that coordinates are fixed to their values at 1 Jan 2000 and velocities from a horizontal deformation model are used to transform the coordinates of data collected before or after that date. The deformation model was calculated from GPS campaign data collected between 1993 and 1998, and was aligned with ITRF96. We examine the performance of this model in 2005 from two points of view: (1) how different are the ITRF2000 velocities from ITRF96? (2) for new stations, and older stations where additional data have been collected, how well do the newly estimated velocities match those in the deformation model (after the ITRF96-ITRF2000 transformation)? We have calculated ITRF2000 velocities at about 50 points throughout New Zealand. The differences between ITRF96 and ITRF2000 velocities range from about 3.6 mm/yr at 97° in southernmost New Zealand to about 4.4 mm/yr at 97° in northernmost New Zealand. The differences between newly-calculated ITRF2000 site velocities and velocities from the deformation model transformed to ITRF2000 generally range between zero and about 4 mm/yr. Velocities of some continuous GPS stations installed in the past two years differ from the deformation model by more than this (in one case by 8 mm/yr), probably because the new velocities cannot be estimated reliably from such short spans of data. Significant vertical velocities up to a few mm/yr are estimated for continuous GPS stations established for at least 3 years; all vertical velocities were assumed zero in NZGD2000. These comparisons suggest that a new deformation model should be considered in the relatively near future. Alignment of the deformation model with ITRF2000 will have benefits in combining newly collected data with existing data, as the ITRF96-ITRF2000 transformation step will no longer be needed.

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