Geospatial Framework and Earth Dynamics
The goal of the geospatial component of AuScope to establish and operate a comprehensive national geodetic infrastructure with greater time and spatial resolution and increased accuracy. This geospatial infrastructure generates a significant quantity of data that being used to improve the accuracy of Australias Geospatial reference frame, as well as allowing Australian scientists to investigate pressing questions such as sea-level variation and earthquake hazard.
AuScope’s key geospatial infrastructure investment under NCRISincludes new and upgraded:
- Very Long Baseline Interferometry (VLBI) array
- Satellite Laser Ranging (SLR) facilities
- Global Navigation Satellite Systems (GNSS) ground stations and receivers, and
- Gravity measurement (GM) instruments.
VLBI and SLR are the key techniques to provide the long-term accurate determination of the fundamental components of a reference frame. VLBI is the most accurate technique available to define the scale and orientation of a reference frame, whereas SLR is the best technique to determine the origin of the reference frame and can also make a contribution to the scale. GNSS is the primary means by which the users can access the reference frame, and is the most effective way to accurately model of crustal deformation. Gravity provides a link that is needed between the satellite derived coordinate system and height systems defined by water surfaces including the ocean.
The VLBI array comprises three 12 metre radio-telescopes at Mt Pleasant near Hobart, Yarragadee in Western Australia and Katherine in the Northern Territory. The AuScope VLBI array underpins all space based observation, navigation and timing applications, and research in Australia because positioning relies on the VLBI enabled calibration of the global coordinate system.
VLBI observations in the Southern Hemisphere are particularly important because they directly support a large variety of Australian science endeavours. Indeed the positioning system underpins all science endeavours reliant on accurate spatial positioning.
The VLBI program completed the construction and implementation of the planned infrastructure in 2011. The emphasis has now shifted to operations with the VLBI array observing for more than 150 days each year. System tuning and optimisation is ongoing to improve the quality of data received, with a factor of two improvement in accuracy achieved over previous years. The University of Tasmania operates the AuScope VLBI array with all data being provided to the International VLBI Service (IVS) to support the maintenance of the International Terrestrial Reference Frame. This will improve the International Celestial Reference Frame, make regular measurements of Earth Orientation Parameters and develop associated products.
The Yarragadee and Mount Stromlo SLR stations are ranked first and third in the ranking of all SLR stations. Collectively they contribute 25 percent of the global data volume collected from 37 stations.
The upgrade of components at the Mt Stromlo SLR site, included larger power modules and increased laser pulse fire rates to enhance the ability of the system, by increasing the distance it can range to high-orbit satellites, permitting the GNSS system to be calibrated. This power upgrade significantly improved ranging to the GNSS constellations (GPS, Glonass, Beidou and the Galileo System) allowing both optical ranging via SLR and radiometric ranging via GNSS to the same satellites; this allows for direct technique inter-comparisons and system calibrations.
During 2007 a French mobile SLR system was used in a pilot study which enabled a continued presence in international altimeter programs at Burnie, Tasmania. The mobile system also allowed for further co-location experiments with VLBI and GNSS sites.
The new GNSS network was distributed across continental Australia. NCRIS funds combined with State funding built approximately 100 new stations; 55 of which were funded by AuScope. Each site has one instrument package include GNSS receiver, antenna and meteorology equipment.
The new stations have complimented the existing Australian Regional Geodetic Network and State networks providing higher resolution to crustal deformation monitoring. This has a direct beneficial impact on the refinement of Australia’s Geospatial reference frame.
Receivers installed have the ability to track all the constellations and their new signals (i.e. L). They also stream data in real-time and are combined with meteorological stations that support atmospheric sceince and weather forecasting in Australia.
The Gravity Program included procuring an FG5 absolute gravimeter, three gPhone Earth tide metres and the establishment of the instrument calibration facility in the Reynolds Dome at Mt Stromlo. This included the renovation of the Reynolds Dome and the commissioning of the facility as the new gravity building.
The new absolute and relative gravimeters acquired, permit regular gravity measurements to be made at strategic sites across the country. The upgrades to the gravity building at Mt Stromlo, the purchase of a relative gravimeter for the ANU and the purchase of a portable FG5 absolute gravimeter allowed ANU in collaboration with Geoscience Australia to establish the National Gravity Observation Program. This program is designed to provide national gravity data with national network observations at distributed observatories around Australia.
The initial planned build of four remote gravity huts ended up delivering seven gravity observation huts completed late in 2013. gPhone observations have been successfully undertaken at Jabiru, Katherine, Tennant Creek, Broome, Karratha and Warakurna (Giles).
AuScope’s Australian Geophysical Observing System augmented existing NCRIS AuScope infrastructure with new capability that focused particularly on emerging geophysical energy issues. AuScope AGOS infrastructure is used to enable collection of new baseline data including surface geospatial and subsurface imaging and monitoring data, thereby providing for better long-term management of crustal services, particularly in Australia’s energy-rich sedimentary basins.
The geospatial component complements the broader AGOS infrastructure platform that is focused on delivering the understanding of the physical state of the accessible crust of the Australian continent, which is crucial to meeting secure, sustainable future energy needs. Specifically, the capability has provided the research community with access to state-of-the-art geodetic instruments that support the highest precision measurement of deformation of the solid Earth. The AGOS geospatial infrastructure includes the following infrastructure investments.
The deployable pool of GNSS instruments for episodic campaign surveys in Australia includes 80 GNSS instruments, ten ionospheric receivers and three Real Time Kinematic (RTK) kits. The geospatial equipment is available for loan and is suitable for GNSS related geospatial and geophysical experiments. Whilst characterising the deformation of the Earths crust is the targeted application of the equipment, other novel uses are been encouraged.
This instrument pool is fully operational and well utilised. Users of the equipment include Geoscience Australia, Australian National University, The University of NSW, The University of Tasmania and the Australian Antarctic Division, with projects being undertaken in Australia, Indonesia and Antarctica. The GNSS instrument pool represents a significant new capability to measure subsidence caused by crustal services, particularly those in the energy sector.
A geodetic survey mark network including co-located radar corner reflectors enables precise measurement of surface deformation at a regional scale using Interferometric Synthetic Aperture Radar (InSAR) and GNSS techniques. Both the radar reflector array (40 sites) and survey mark networks (65 sites) in the Surat Basin in Queensland, were established to specification.
A broad scale experiment to measure subsidence related to CSG extraction has commenced and is expected to conclude within a decade. The reflector array is currently being used by five individual space agencies for satellite radar mission calibration and validation.
Four high precision GNSS CORS monuments were installed at Mitchell (Queensland), King Island (Tasmania), Blinman (South Australia) and at the Murchison Radio Observatory, Boolardy (Western Australia). These monuments supplement AuScope’s GNSS CORS funded through NCRIS. The data streams from these stations are full integrated into the AuScope GNSS array. Data from the stations is being used by the research community, government agencies and industry to support precision positioning applications.
AuScope’s robotic GNSS antenna calibration facility is the only one of its kind in the southern hemisphere. The facility includes two components: the outdoor robot facility located at Geoscience Australia in Canberra and, an indoor anechoic chamber located at the National Measurement Institute (NMI) in Sydney. The NMI component of the GNSS antenna calibration facility is highly complementary to the robotic GNSS calibration facility. The infrastructure has enabled inter-comparisons between the two systems and has confirmed the operations of the Canberra facility.
The instrumentation has resulted in significant improvement in the accuracy of crustal deformation measurements made by the GNSS instrument pool. A number of industry partners have already accessed or plan to access the infrastructure.
An open-access repository of Synthetic Aperture Radar (SAR) data acquired by the European Remote-sensing Satellite (ERS) satellites over the Australian continent is suitable for InSAR analysis to detect ground surface deformation. Data has demonstrated the value of satellite observations and significant interest in being generated in the capability. The NSW Government is currently constructing a GNSS and radar-monitoring network based on the AGOS design.
This Geospatial capability was established to provide the research community with access to state-of-the-art geodetic instruments that support the highest precision measurement of deformation of the solid Earth. The AGOS Geospatial equipment, which is available for loan, is suitable for Global Navigation Satellite System (GNSS) related geospatial and geophysical experiments. Access to the equipment is prioritised according to the AGOS Geospatial Selection Criteria.
AGOS Geospatial equipment is available to all researchers on the basis of merit, as judged by an Access Committee on the basis of a short proposal. Researchers have to meet the project operating costs but training is provided in the use of the portable equipment. Applicants for access to AGOS Geospatial equipment are encouraged to contact Dr John Dawson, Geoscience Australia, to discuss their needs for prospective projects and then prepare a formal proposal. The equipment pool presently comprises 80 geodetic Global Navigation Satellite System (GNSS) receivers and antennas as well as solar panels that support their operation. Applications to use AGOS equipment should be submitted to the AGOS Access Committee electronically by completing the AGOS Application Form which includes confirmation of institutional support (electronic signature is acceptable). The AGOS Geospatial Access Committee will deliberate periodically – normally four times per year in March, June, September, and December. The schedule of equipment allocations for successful proposals will be updated following the Access Committee deliberations. Successful applicants will be required to sign a project agreement. This is a simple form, confirming insurance arrangements and the liability of the proposer for losses and repairs. For more complex multi-party arrangements a formal Project agreement will be required to specify the nature of the project and the responsibilities of the parties.
The data produced from the new geospatial infrastructure will be central to research undertaken over the next decade in Australian geodesy. Estimates of the crustal deformation of the Australian plate at levels of accuracy previously unattainable can now be expected. Data will be used to develop a new national geospatial reference frame, which will be an order of magnitude more accurate than any currently used in Australia. This reference frame will include models for the continual deformation of the crust.
For more information on current and potential projects or accessing AuScope’s Geospatial framework and earth dynamics infrastructure component for a project please contact Program Leader Nicholas Brown, Geoscience Australia.