Realization of the world height system in New Zealand: Preliminary study

We utilize the geopotential value approach to determine the average offsets of 12 major local vertical datums (LVDs) in New Zealand (NZ) relative to the world height system (WHS). The LVD offsets are estimated using the EGM2008 global geopotential model coefficients complete to degree 2159 of spherical harmonics and the GPS-levelling data. WHS is defined by the adopted geoidal geopotential value W0= 62636856 m2s-2. Our test results reveal that the average offsets of 12 major LVDs situated at the South and North Islands of NZ range from 0.01 m (Wellington 1953 LVD) to 0.37 m (One Tree Point 1964 LVD). The geopotential value of the tide-gauge station used as the origin for the LVD Wellington 1953 is thus almost the same as the geoidal geopotential value W0. EGM2008 and GPS-levelling data are further used to compute the differences between the NZGeoid05 regional quasigeoid model and the EGM2008 global quasigeoid model. The same analysis is done for NZGeoid2009 which is the official national quasigeoid model for NZ. The systematic bias of about 0.56 m is found between NZGeoid05 and EGM2008. A similar systematic bias of about 0.51 m is confirmed between NZGeoid2009 and EGM2008.