Performance of AUSGeoid09 in NSW

Abstract

In March 2011 Geoscience Australia released AUSGeoid09, an improved geoid model for Australia to relate GNSS-derived ellipsoidal heights to the Australian Height Datum (AHD71) and vice versa. This paper briefly reviews the theory of GNSS-based height determination and illustrates that the absolute accuracy of N values is increasingly important for users of Global Navigation Satellite System (GNSS) Continuously Operating Reference Station (CORS) networks. In order to quantify the expected improvement of replacing the current geoid model, AUSGeoid98, with AUSGeoid09 in New South Wales (NSW), four tests were performed. These tests investigated how well the two geoid models fit known AHD71 heights, based on (1) about 500 AUSPOS solutions, (2) 38 CORSnet-NSW sites, (3) several GNSS-based adjustments, and (4) numerous height control points from these adjustments. It was found that AUSGeoid09 provides a considerably improved fit to AHD71 for GNSS-based height transfer in NSW. In most cases the AUSGeoid09-derived height results fall within the expected ±0.05 m accuracy stated by Geoscience Australia. It is also shown that the magnitude of N values in NSW will change by up to 0.5 m when AUSGeoid09 is introduced in order to provide a better fit to AHD71. The NSW Land and Property Management Authority (LPMA) has adopted AUSGeoid09 for all operations and urges all spatial professionals to do the same.