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Vertical Datums The predominant height datum in PNG is Mean Sea Level (MSL). Due to the rugged nature of the terrain and inaccesibility of much of the terrain, most of the country has not been connected by conventional levelling networks from a Tide Gauge. Most local realisations of MSL, especially in the Highlands and inland areas have been derived from trigonometric heighting or altimetry. Differences of up to 6 metres between true MSL and local MSL can occur. The recommended approach for height transfer in PNG is to use GPS or GNSS heighting in conjunction with a suitable geoid model. If GPS/GNSS heighting is used on a project where MSL has already been established then the offset between the geoid model and local MSL should be determined. PNG08 Geoid Model A new geoid model for PNG (PNG08) has been released on the 14th October 2011. The new geoid model is derived from the EGM2008 geoid model and was developed by Quickclose Pty Ltd. An offset plane approximating the Mean Dynamic Topography (MDT) of the oceans (the difference between observed MSL and a global geoid model) was applied to EGM2008 and validated by observed offsets between EGM2008 and MSL in PNG. This approach ensures that realistic MSL can now be obtained from WGS84, ITRF2008 and PNG94 ellipsoidal heights. The PNG08 model is a grid of N values (geoid ellipsoid separations) between Latitude 0 and 12 degrees South, and between 140 and 158 degrees East. The model spacing is 2.5 minutes of Latitude and Longitude in WGS84, ITRF and PNG94. Interpolation of the model is by Bi-linear interpolation. The accuracy of the model is 0.2 metres at 1 Standard Deviation. PNG08 in text format PNG08 in .csv format PNG08 in Leica GEM format (amended 24th August 2012) PNG08 in Trimble GGF format PNG08 in Topcon Sokkia GFF format PNG08 in Carlson SurvCE GSF format PNG08 in Agisoft TIFF format EGM2008 Geoid Model The EGM2008 2.5' geoid model is widely used in PNG, however for coastal engineering and hydrology studies a substantial offset is required to be applied to account for the effects of Mean Dynamic Topography (MDT) which is the elevation of Mean Sea Level (MSL) above the global geoid due largely to thermal expansion of the ocean in warmer equatorial zones. Observed offsets are -0.93 m at Port Moresby and Kerema, -1.12 m at Madang and -1.21 metres at Hansa Bay. These offsets are consistent with models of MDT. Local MSL = ITRF ellipsoid height - EGM2008 N value + offset EGM2008 with specified offsets are used (and may continue to be used) for the following resource projects in PNG: Note that some offsets are to fit established MSL height datums, and are not necessarily in agreement with MDT models. XStrata Frieda River Project, offset is -1.42 m Hidden Valley and Wafi Projects, offset is -0.63 metres Woodlark Island, offset is -0.75 metres Western Province Horizon and Talisman projects, offset is -3.00 metres Marengo Mining, Yandera, offset is -1.12 metres EGM2008 in text format EGM2008 in .csv format EGM2008 in Leica GEM format EGM2008 in Trimble GGF format EGM2008 in Topcon GFF format EGM2008 in Sokkia BIN format (not yet clipped for PNG) EGM96 Geoid Model EGM96 has been used in PNG as the geoid model for the PNG LNG Project and Interoil LNG projects. The following offsets are applied to obtain MSL: PNG LNG Project, offset is -0.87 metres Interoil Project, offset -1.58 metres PNG94 geoid model A geoid model for PNG was developed by Prof. Bill Kearsley in 1996. The binary executable only works on MS-DOS, Windows 3, Windows 95 and Windows 98 platforms. Windows XP, Windows Vista and Windows 7 cannot run the the model. |
Maintained by: Richard Stanaway, Quickclose Pty. Ltd.
Last Updated: 23rd June 2022