AUSGeoid09 performance in mountainous terrain: A case study in the Blue Mountains

AUSGeoid09 is the latest model used to convert Global Navigation Satellite System (GNSS) derived ellipsoidal heights to heights in the Australian Height Datum (AHD). While previous studies have evaluated the performance of the AUSGeoid09 model across Australia, such studies have not focused on mountainous regions in particular. This paper evaluates AUSGeoid09 in the Blue Mountains region of New South Wales from a practical user's point of view. Along a 90 km stretch of road incorporating flat to mountainous terrain, comparisons were undertaken between AUSGeoid09-derived heights and published AHD heights, using repeated Network Real Time Kinematic (NRTK) GNSS observations. The performance of AUSGeoid09 was also evaluated relative to its predecessor, AUSGeoid98, and the latest gravimetric model AGQG2009. It was found that AUSGeoid09 performs well across the study area and provides a significant improvement over AUSGeoid98. AUSGeoid09 generally allows AHD height determination at the ±0.03 m level (1 sigma) in flat terrain and at the ±0.06 m level (1 sigma) in mountainous terrain. However, across the entire study area, AUSGeoid09-derived AHD heights are consistently lower than the published AHD heights. Comparison of the results obtained with AUSGeoid09 against those using AGQG2009 in flat terrain illustrates the benefit that the introduction of the geometric component of AUSGeoid09 has had on the determination of AHD heights with satellite technology. However, for elevations above 500 m it appears that the geometric component degrades the fit to AHD in the study area, indicating that there is room for improvement in regards to future versions of the AUSGeoid model.