Options for Modernising the Geocentric Datum of Australia

Instantaneous, reliable and fit-for-purpose positioning and time services across Australia are the aims of the National Positioning Infrastructure policy. Indeed, it is already possible to achieve centimetre-level positioning almost anywhere (outdoors) and anytime, following advances in positioning technologies over the last few decades. Not surprisingly, this capability has highlighted limitations and distortions in the current Geocentric Datum of Australia 1994 (GDA94) which was not designed to support positioning at this level of accuracy. A ‘next-generation’ datum or ‘Australian Terrestrial Reference Frame’ is currently being prepared which will remove the known distortions of the current datum realisation, create a homogenous 3-D datum across Australia based on permanent GNSS datum stations, be adaptable and flexible by incorporating new measurements and technologies as they become available, and assign realistic uncertainties to coordinates. Importantly, this datum will include a comprehensive deformation model to account for real-world dynamics which GDA94 currently ignores, such as the metre-level differences between our maps and mobile positioning devices due to tectonics, earthquakes, ground subsidence and localised deformation. This paper presents the technological progress towards this new datum, reports on recent user-needs assessments across Australia, discusses several options for the final realisation of the modernised datum, and discusses future research required to achieve a fully dynamic datum. While focused on the Australian datum, much of what is presented is also applicable to the modernisation of national and international datums across the globe.