AUSGeoid09: a more direct and more accurate model for converting ellipsoidal heights to AHD heights
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In an absolute sense, AUSGeoid09 is an order of magnitude more accurate than AUSGeoid98 at converting ellipsoidal heights to Australian Height Datum (AHD) heights and vice versa. Results of this study show AUSGeoid09 can be used to compute AHD heights from Global Navigation Satellite System (GNSS) ellipsoidal heights with an uncertainty of less than +/-0.03 m (one sigma). The improvement is largely due to the inclusion of a geometric component in AUSGeoid09 that accountsfor the spatially varying offset between a gravimetric quasigeoid model and the AHD. This geometric component was calculated using least squares collocation in cross validation mode and then added to the gravimetric quasigeoid. Although previous AUSGeoid models were used to convert GNSS ellipsoidal heights to the AHD and vice versa, none until now have accounted for the gravimetric quasigeoid to AHD offsets. This offset is a consequence of how the AHD was realised and has commonly resultedin misfits of ~0.5 m or more. When used with GNSS technology, AUSGeoid09 can replace the need for traditional third-order levelling (Class LC; 12 roo k) in many situations. Relative tests of AUSGeoid09 over a continent-wide set of over 20 million baselines showed that it can deliver better than Class LC tolerances in 99 percent of cases. The model accepts a user?s GDA94 latitude, longitude and ellipsoidal height and returns an AHD height and deviations of the vertical. AUSGeoid09 is now availablefree-of-charge on the Geoscience Australia website (http://www.ga.gov.au/geodesy/ausgeoid/nvalcomp.jsp).
The attached document is the author's version of an article published as: Brown, N.J. and Featherstone, W.E. and Hu, G. and Johnston, G.M. 2011. AUSGeoid09: a more direct and more accurate model for converting ellipsoidal heights to AHD heights. Journal of Spatial Science. 56 (1): pp. 27-37. Journal of Spatial Science is available online at: www.tandfonline.com.
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Featherstone, Will; Kirby, Jonathan; Hirt, Christian; Filmer, Michael; Claessens, Sten; Brown, N.; Hu, Guorong; Johnston, G. (2011)AUSGeoid09 is the new Australia-wide gravimetric quasigeoid model that has been a posteriori fitted to the Australian Height Datum (AHD) so as to provide a product that is practically useful for the more direct determination ...
Featherstone, Will (2008)Ellipsoidal heights, i.e., w.r.t. a geometrical Earth figure, determined from Global Navigation Satellite Systems (GNSS) are inherently their least accurate coordinate, due mainly to satellite geometry and atmospheric ...
Filmer, Michael Shaun (2010)The Australian Height Datum (AHD) was established in 1971, and is the basis for all physical heights in Australia. However, a complete revision of the AHD has never occurred, despite problems that, although not always ...