Australia is a large continent with a relatively low population which is highly dependent on the mining, agricultural and transport industries for economic prosperity. These industries are themselves increasingly dependent on having access to high-quality geodetic infrastructure, especially when seeking operating efficiencies. Australia is also surrounded to the north and east by some of the most seismically active zones in the world, and is geographically isolated by the Indian, Pacific and Southern Oceans. This combination of characteristics creates some interesting challenges for the Australian Government in maintaining, developing and delivering a stable reference frame as a platform upon which a precise positioning capability can be established for science and society more generally. This presentation will detail recent GGOS related efforts in Australia to improve the accuracy of the International Terrestrial Reference Frame (ITRF). It will also discuss crustal deformation monitoring programs that allow ITRF based precise positioning services to be used in areas where localized deformation is not detected by existing GGOS infrastructure. Lastly, the presentation will also summarise efforts currently underway to enhance the provision of access to the ITRF anywhere, anytime across the Australian landmass in real time.

This research utilises metadata from GA's centralised metadata store containing the history of the equipment changes which have taken place at all GNSS stations; such as antenna or receiver swaps, firmware upgrades and removal/ alteration of antenna domes and cables. Several change detection algorithms have been implemented for automatic detection of discontinuities in the coordinate time series. Once offsets are detected, their position in time is correlated with equipment changes or earthquake occurrences nearby the station. If a correlation is found and the offset is visibly evident, the offset is introduced into a database. This information is used in the routine combination of weekly SINEX solutions using the CATREF software to produce an enhanced set of coordinates and velocities. It is shown that after cleansing the offsets in time series using this approach, the quality of the combined APREF solution is improved in terms of WRMS. By analysing time series coordinates at a few stations using CATS software, it is shown that the uncertainty of velocity estimates is improved after offsets are detected and removed from the time series.

Tide gauge data forms the basis for determining global or local sea level rise with respect to a global geocentric reference frame. Data from repeated precise levelling connections between the tide gauge and a series of coastal and inland benchmarks, including a Continuous GPS (CGPS) benchmark, is used to determine the stability of tide gauges at 12 locations in the South Pacific. The method for determining this is based on a constant velocity model which minimises the net movement amongst a set of datum benchmarks surveyed since the installation of the tide gauges. Tide gauges were found to be sinking, relative to the CGPS benchmark, in Pohnpei (FSM), Samoa, Vanuatu, Tonga, Nauru, Tuvalu, Fiji and Cook Is; listed in order of the sinking rate, with a maximum of -1.01 - 0.63 mm/yr at Pohnpei (FSM) and a minimum of -0.03 - 0.81mm/yr at Cook Is. The tide gauge was rising, relative to the CGPS benchmark, in Solomon Is, Manus Is (PNG), Kiribati and Marshall Is, with a maximum of 3.12 - 0.49mm/yr in Solomon Is and a minimum of 0.01 - 0.91mm/yr in Marshall Is. However, these estimates are unreliable for the Solomon Is and Marshall Is, which have recently established CGPS benchmarks and have been surveyed less than 3 times. In Tonga and Cook Is, the tide gauge was found to be disturbed or affected by survey errors whereas the Vanuatu results were affected by earthquakes. It was also found that the constant velocity model did not fit the observations at the tide gauges in Tonga, Cook Is, Fiji, Marshall Is and Vanuatu, which had large variations in their velocities. This is an indicator of the high frequency (short period) motion of the tide gauge structure, which cannot be measured by the levelling method since these have a higher frequency than the time interval between levelling surveys.

Advice to National Measurement Institute regarding update to the recognized-value standard of measurement for position, June 2011

An increasingly important requirement for Australia's geodetic reference system is that the relationships between the International Terrestrial Reference Frame (ITRF) and the national horizontal and vertical datums are well understood. To support the development of improved geodetic infrastructure in Australia, we have analysed GPS data observed at 2310 survey marks. These data, observed between 1995 and 2009, across continental Australia were processed with consistent standards to generate a combined solution with an estimated uncertainty of better than 5 and 20 mm (1 sigma) in the horizontal and vertical components, respectively. Our combined solution, which was mapped to ITRF2005 at the reference epoch of 2000, is the first unified single-epoch solution with sufficient resolution to support datum modernisation in Australia. We review the considerable work undertaken to determine the optimum analysis procedure, including comparisons of solutions using different antenna phase centre variations (PCV) calibration models, and find that the heights determined using relative PCV models differ from those determined using absolute PCV models by a maximum of 27 mm and an average of 6 mm. Also, we assess the impact of both observation session lengths and crustal velocity modelling. There will be two important applications for this new GPS solution. First, will be the development of an improved model for the estimation of Australian Height Datum (AHD) values from GNSS observations, and the solution will be an important input into the Australian Height Modernisation Project. Second, will be its use as constraining dataset for the readjustment of the terrestrial geodetic observations used in GDA94 as part of the creation of the Geodetic Model of Australia, and will potentially lead to a new national datum.

The secular aberration drift caused by the acceleration of the Solar system barycentre with respect to the reference quasars could be estimated using the recent geodetic VLBI data. The practical approach of the secular aberration drift estimation is proposed. The general equation of group delays has been modified to incorporate the barycentre acceleration vector. More than four million of group delays observed between 1980 and 2008 were adjusted to obtain the secular aberration drift estimates by three approaches. All estimates of this effect amplitude are close (about 18 ± 2 -asec/year) and correspond to the magnitude of the barycentre acceleration vector of (9+/-1)*10(-13) km/sec.

AUSPOS, Geoscience Australia's online GPS positioning service, has now been in worldwide use since 2000 and has processed over 150,000 user data files. In 2011, the AUSPOS service was fully upgraded to use the Bernese Software as the processing engine together with more sophisticated GPS data analysis strategies, new ITRF to GDA transformations and the recently developed the AUSGEIOD09 model. In this presentation, we will briefly overview the AUSPOS2 system including the improved modelling and analysis strategies employed. Then, we will present test results for AUSPOS2 using 1, 2, 6, 12, 24 hours of data from 232 IGS2008 core stations as well stations from the Asia Pacific Reference Frame (APREF) network within mainland Australia using the IGS final, rapid and ultra rapid products, respectively. Preliminary tests using 24 hours data show that coordinate differences between AUSPOS solutions and APREF weekly solutions are within a millimetres level for all three components.

The new Australian geodetic VLBI network operated by the University of Tasmania (UTAS) started regular observations in October, 2010. Three 12-meter "Patriot" radio telescopes are dedicated to the improvement of the celestial and terrestrial reference frames in the southern hemisphere. We present first results from the analysis of an eight-month set of geodetic VLBI data. The data were processed within a global VLBI solution by the least squares collocation method using the OCCAM software. The geodetic positions of the AuScope radio telescopes were estimated with accuracy less than 10 millimetres, and the first sign of their motion due to tectonic plate movement was indicated.

Analysis of very long baseline interferometry (VLBI) records of distant radio source signals allows one to determine the proper motions of extragalactic objects with an accuracy of a few tens of microseconds of arc per year. Such an accuracy is sufficient to investigate the aberration in proper motions of distant bodies due to the rotation of the Solar system barycenter around the Galactic center, as well as higher degree systematics of the velocity field. We analyzed geodetic and astrometric VLBI data of 1979--2010 to produce radio source coordinate time series. The velocity field made up of the proper motions of 497 sources of good observational history is investigated by fitting the vector spherical harmonic components of degree 1 and 2. Within error bars, the magnitude and the direction of the dipole component agree with predictions made by using the most recent estimates of the Galactic parameters. The acceleration vector, estimated together with a non significant global rotation, has an amplitude of 5.8+/-1.4 microseconds of arc per year and is directed towards equatorial coordinates alpha = 266+/-8 deg and delta = -18+/- 18 deg. Degree 2 harmonics of the velocity fields appear to be less significant. It yields that the primordial gravitational wave density integrated over a range of frequencies less than 10^{-9} Hz is lower than 0.0031+/- 0.0002h^{-2}.

The GPS and Galileo systems are designed to transmit signals on three carrier frequencies, which are available freely to the GNSS user community. This provides an opportunity for users to form an optimal linear combination which has low noise, is free from ionospheric errors, has increased wavelength and will enable integer ambiguity resolution. This paper presents optimised linear combinations for GPS and Galileo which address all but the last of these factors. Based on the theoretical development, the optimal combination is free from first order ionospheric effects and has less noise than any of the other dual frequency ionosphere free combinations. The wavelength of the combination can be specified by the user at any desired length. The optimal combination was validated using authentic triple frequency data from the recently launched Block IIF GPS satellite, PRN 25. It is shown that the noise in the optimal combination is lower than the L1/L2 and L2/L5 dual frequency ionosphere free combinations and at about the same level as the L1/L5 combination. The optimal linear combination is ideal for undifferenced Precise Point Positioning (PPP) which requires an ionosphere free, low noise combination that does not necessarily have integer coefficients.