Improved AHD71 height determination from GNSS using AUSGeoid09 in New South Wales, Australia

In October 2010, Geoscience Australia released the latest beta version of AUSGeoid09 (beta 0.7), providing an improved geoid model to relate GNSS-derived ellipsoidal heights to the Australian Height Datum (AHD71) and vice versa. This paper quantifies the expected improvement of replacing the current geoid model, AUSGeoid98, with AUSGeoid09 in New South Wales (NSW). Four tests were performed to investigate 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. The first two tests showed the root mean square (RMS) of residuals improved by factors of 2.7 and 4.1 respectively. The magnitude of N values in NSW will change by up to 0.5 m when AUSGeoid09 is introduced. The adjustment tests confirmed these findings, evidenced by improved variance factors and reduced numbers of flagged residuals. The adjusted height observations showed an improved RMS of the residuals, generally by a factor of about 1.5, but reaching 4.6. In most cases the RMS of the AUSGeoid09-derived height results falls within the expected ±0.05 m accuracy stated by Geoscience Australia.