Gravity's strong attraction at Geoscience Australia
•Download as PPT, PDF•
3 likes•1,494 views
The document discusses Geoscience Australia's work with gravity data, including airborne and satellite gravity. It aims to improve national gravity databases by expanding coverage and enhancing modeling capabilities. Key efforts include supporting airborne gravity surveys, developing a test site to evaluate new technologies, maintaining fundamental gravity networks, and improving 3D modeling through national and international collaborations.
Recommended
Recommended
More Related Content
What's hot
What's hot (20)
Viewers also liked
Viewers also liked (20)
Similar to Gravity's strong attraction at Geoscience Australia
Similar to Gravity's strong attraction at Geoscience Australia (20)
Recently uploaded
Recently uploaded (20)
Gravity's strong attraction at Geoscience Australia
- 1. The strong attraction of gravity at Geoscience Australia Richard Lane ( richard.lane@ga.gov.au ) Geoscience Australia 22nd ASEG International Conference & Exhibition 2012 © Commonwealth of Australia (Geoscience Australia) 2012
- 2. Gravity at GA ... More than just a ground gravity database • Significant scope to improve The quality and extent of the coverage By providing better support to help interpret and integrate gravity with other geoscientific information • Monitoring developments in AG and AGG • Expanding and improving the AFGN and the ANGD • Developing the Kauring test site Analysing test results Working towards a Deed-Of-Standing-Offer for service providers • Assisting State and Territory geoscience agencies, and other government groups with proposals calling for AG and AGG • Enhancing the rock properties database and web delivery application • Improving 3D modelling capabilities © Commonwealth of Australia (Geoscience Australia) 2012
- 3. The Long Term (Ideal) Objective Base coverage: Global Satellite or Satellite+Shipborne +Ground gravity models Coastal zone, offshore (EEC) and Antarctic coverage: Airborne gravity data at 2 km spacing © Commonwealth of Australia (Geoscience Australia) 2012 Global Satellite or Satellite+Shipborne+Ground data Airborne Gravity (AG) Airborne Gravity Gradiometry(AGG) Onshore coverage: Airborne gravity gradiometer data at 1 km line spacing
- 4. Airborne Gravity Gradiometry (AGG) Ideal requirement: 1 Eo/√(Hz) with 100 m resolution Status: Typically 5 Eo/√(Hz) with 400 m resolution Outlook: Several systems with desired specifications set for flight © Commonwealth of Australia (Geoscience Australia) 2012 trials Recommendation: Hold off on systematic surveying Consider special instances on a case-by-case basis Airborne Gravity (AG) Ideal requirement: 0.1 mGal with 1 km resolution Status: Typically 1 mGal with 3 km resolution Outlook: No breakthroughs in sight Recommendation: Pursue opportunities in coastal and marine settings, and in Australian Antarctic Territory Consider onshore usage on a case-by-case basis Satellite Gravity Recommendation: Pursue opportunities with GRACE and GOCE projects
- 5. Satellite Gravity © Commonwealth of Australia (Geoscience Australia) 2012
- 6. GRACE - Gravity Recovery and Climate Experiment (Courtesy of NASA and DLG) © Commonwealth of Australia (Geoscience Australia) 2012
- 7. GOCE - Gravity Field and Steady-State Ocean Circulation Explorer © Commonwealth of Australia (Geoscience Australia) 2012 (Courtesy of ESA)
- 8. © Commonwealth of Australia (Geoscience Australia) 2012 http://icgem.gfz-potsdam.de/ICGEM/ Global model GGM03C Combined GRACE, ground and satellite altimetric gravity model (Courtesy of ICGEM - IAG)
- 9. Airborne Gravity © Commonwealth of Australia (Geoscience Australia) 2012 (AG)
- 10. Gippsland Nearshore Airborne Gravity Survey Victorian Department of Primary Industries (DPI) • Consistent mapping of Survey outline geological structure between onshore and offshore • Sander AirGRAV © Commonwealth of Australia (Geoscience Australia) 2012 120 x 70 km area 10,500 km 1 km spacing RMS of 1.6 μms-2 for 3 km half wavelength • Kauring Test Site in WA also flown ( http://www.dpi.vic.gov.au/energy/sustainable-energy/carbon-capture- and-storage/the-carbonnet-project/airborne-gravity-survey )
- 11. Airborne Gravity Gradiometry (AGG) © Commonwealth of Australia (Geoscience Australia) 2012
- 12. Status update on existing AGG systems • ARKeX – FTG Adding a GMA Gz sensor to an existing FTG system • Bell Geospace – Air-FTG Testing a combination of Air-FTG and ZTEM AEM (an ambient EM system – Geotech) • Fugro – FALCON Latest system (#5, “Cavendish”) delivered HeliFALCON in commercial use since early 2011 Successful test flight of FALCON and TEMPEST AEM systems © Commonwealth of Australia (Geoscience Australia) 2012
- 13. Status update on new AGG systems • Rio Tinto – VK1 – 1 Eo per root Hz “Active period of airborne testing at the Kauring Test Site” • Lockheed Martin - Enhanced FTG - 2 Eo per root Hz “The system build and initial test will be completed in July 2012” • ARKeX - EGG Exploration Gravity Gradiometer – 1 Eo per root Hz “2 instruments built, ongoing flight trials” • Gedex - High Definition Airborne Gravity Gradiometer HD-AGG™ - 1 Eo per root Hz “Upgrades are being implemented (following initial flight trials), and the flight testing will resume in April 2012” © Commonwealth of Australia (Geoscience Australia) 2012
- 14. “Certainly the benchmark for airborne gravity.” (GW – University of Utah / TechnoImaging) “… the most comprehensive resource for this rapidly evolving technology. I believe that this is an important contribution by GA to the exploration and geological mapping community.” (CF – CSIRO) “… the proceedings was a very professionally put together document and will be an important resource for years to come.” (DH – Gedex Inc.) “I think it is terrific that Geoscience Australia supports such initiatives, and produces the record of proceedings.” (GW – BHP Billiton) “… the GA publication of the workshop proceedings is of the highest quality.” (DDF – Lockheed Martin) ( https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&catno=70673 ) © Commonwealth of Australia (Geoscience Australia) 2012
- 15. AFGN and ANGD © Commonwealth of Australia (Geoscience Australia) 2012
- 16. LaCoste Romberg Model G Scintrex CG-5 AUTOGRAV Land relative gravimeters © Commonwealth of Australia (Geoscience Australia) 2012
- 17. Land absolute gravimeter © Commonwealth of Australia (Geoscience Australia) 2012 Micro-g LaCoste A10 (Photographs courtesy of Ray Tracey - GA)
- 18. AFGN absolute gravity observations © Commonwealth of Australia (Geoscience Australia) 2012 (Courtesy of Ray Tracey, GA)
- 19. Absolute and relative gravity measurements in Antarctica • Absolute gravity reference points • Relative gravity observations to tie existing survey data to the absolute reference points (http://www.ga.gov.au/ausgeonews/ausgeo (Photograph of Ray Tracey - GA) news201006/inbrief.jsp ) © Commonwealth of Australia (Geoscience Australia) 2012
- 20. AAGD07 and revised processing equations and procedures • Absolute gravity observations for ~ 60 stations in the Australian Fundamental Gravity Network (AFGN) define AAGD07 © Commonwealth of Australia (Geoscience Australia) 2012 New datum replaces the Isogal84 datum Linked by relative observations to the IGSN71 global datum (Approximately) Supported by sparse, older absolute gravity observations • g(AAGD07) = g(ISOGAL84) – 0.78 μms-2 • Applied to >1.4 M observations in the Australian National Gravity Database (ANGD) • Also implemented revised processing equations and procedures More accurate equations Ellipsoid height datum and GDA94 horizontal datum
- 21. Observation uncertainty • Australian National Gravity Database (onshore) • Uncertainty estimates Standard deviation assuming a Gaussian error distribution © Commonwealth of Australia (Geoscience Australia) 2012 Horizontal location Vertical location Observed vertical gravity (Terrain corrections) • Combined uncertainty estimate for simple Bouguer vertical gravity values • 0.2 μms-2 to more than 20 μms-2
- 22. Sources of uncertainty values 1. Operations/Acquisition Report 2. Processing Report 3. Typical performance of reported method/equipment used 4. Typical performance of assumed method/equipment 5. Estimated from the date of the survey by reference to other surveys of a similar vintage 6. Analysis of the external network adjustment errors 7. Unknown source © Commonwealth of Australia (Geoscience Australia) 2012
- 23. Observation uncertainty – example of estimation from supplied uncertainties h uncertainty in horizontal position in © Commonwealth of Australia (Geoscience Australia) 2012 metres v uncertainty in vertical position in metres εobs vertical gravity observation error in μms-2 φ latitude in degrees north εht vertical gravity error in μms-2 associated with uncertainty in horizontal positioning εvfa error in μms-2 for free-air corrected vertical gravity due to uncertainty in vertical positioning εv error in μms-2 for simple Bouguer anomaly vertical gravity due to uncertainty in vertical positioning, given a correction density of 2670 kg/m3 εtc uncertainty in the accuracy of terrain corrections in μms-2 e ht » 0.01× h × sin 2j e vfa » -3× v e v » -2 × v ( 2 2 2 ) e FA = e ht +e vfa +e obs ( 2 2 2 2 ) e CBA = e ht +e v +e obs +e tc
- 24. Kauring Test Site © Commonwealth of Australia (Geoscience Australia) 2012
- 25. Kauring Test Site, Western Australia © Commonwealth of Australia (Geoscience Australia) 2012 ~ 110 km (Courtesy of David Howard)
- 26. © Commonwealth of Australia (Geoscience Australia) 2012 Kauring reference gravity data • Continental data Variable spacing • Regional data 150 x 150 km @ 2 km spacing • Airborne Gravity site 20 x 20 km @ 500 m spacing • Airborne Gravity Gradiometer site 5 x 6 km area at variable spacing 50 x 50 m; 100 x 50 m; 250 x 100 m Plus LiDAR DEM with 1 m grid cells Pe*rth
- 27. © Commonwealth of Australia (Geoscience Australia) 2012 FALCON AGG data • Flown July 2011 • Height ~70 m • Line spacing 50 m • Noise 1.9 Eo RMS • Bandwidth 0.18 Hz GDD from ground gravity GDD from FALCON (Courtesy of Mark Dransfield, FAS)
- 28. CSM CGEM synthetic studies Ground reference gravity Equivalent source model Invert data simulated for various systems Compare inversion models © Commonwealth of Australia (Geoscience Australia) 2012 Recovered inversion model Simulate data for various systems (Courtesy of Cericia Martinez and Yaoguo Li, CSM)
- 29. Simulated data and inversion models Low noise next- VK1a 60°heading © Commonwealth of Australia (Geoscience Australia) 2012 generation FTG system VK1c 60°heading vkc Eo (Courtesy of Cericia Martinez and Yaoguo Li, CSM)
- 30. AAAnnnooommmaaallilieieesss + + 1 1 E0ö Eö (400 m wavelength) 1 km Tunnel North Sphere East (NiS Dipping body) Dyke 3 50 At m surface m 8 225 14 000 Million m3 m3 34 0.02 4.5 MT MT @ @ 0.15 0.3 -2.67 g/g/cc cc g/contrast cc contrast contrast 30 0.8 12 Eö 4 75 150 m m m square thick, radius dipping tunnel, 500 at 45° m long © Commonwealth of Australia (Geoscience Australia) 2012 “Kauring Challenge” • Simulated the AGG response for known bodies beneath the Kauring terrain Gzz, 80 m clearance, 1 Hz sampling • Added noise 1 Eö or 10 Eö • Data available for inversion studies Deep Kimberlite Slab 150 3.5 Million 1.5 -0.4 Depth below ground 500 m Volume 48 Million m3 Excess mass 10 MT @ 0.2 g/cc contrast Peak response 2.5 Eö Comments Broad wavelength, Low response Truncated cone, 100 m upper rad 1 km (Courtesy of Theo Aravanis, Rio Tinto)
- 31. ( http://www.ga.gov.au/minerals/projects/current-projects/kauring.html) © Commonwealth of Australia (Geoscience Australia) 2012 Kauring Test Site, WA • www.ga.gov.au Search for “Kauring” • Reference data sets Magnetic, radiometric, elevation, gravity and digital geology • Simulated data sets • Bibliography • Test flight protocols • Observed AG and AGG data sets
- 32. Rock Properties © Commonwealth of Australia (Geoscience Australia) 2012
- 33. Geoscience Australia rock properties web delivery application • Very simple database © Commonwealth of Australia (Geoscience Australia) 2012 structure • Basic search and download application on our website • And now ... • Populating the database Existing density and magnetic property observations • Hoping to expand the scope of the database Additional property types Access to the data via a Web Feature Service (WFS) ( http://www.ga.gov.au/geophysics-rockpropertypub-web/rockproperties/search.htm )
- 34. Modelling © Commonwealth of Australia (Geoscience Australia) 2012
- 35. CBA as a response compensated for various model elements • GADDS Primary observations Plus residual gravity - excluded defined source features © Commonwealth of Australia (Geoscience Australia) 2012 • Tides Sun and the Moon • Theoretical gravity (including free air correction) Earth as a point mass or source with spherically symmetric density • Bouguer cap ~ 167 km radius Simple Bouguer anomalies (SBA) • Terrain correction ~ 167 km radius Complete Bouguer anomalies (CBA)
- 36. © Commonwealth of Australia (Geoscience Australia) 2012 CBA extensions • Distant relief correction The rest of the globe Beyond the (arbitrary) ~167 km radius used for Bouguer anomaly values • Isostatic correction Various models for isostatic compensation • Crustal models - v1, v2, v3, etc e.g., CRUST2 global seismic-based model GA regional models Semi-regional models District models Prospect models etc ... • Make available as options via GADDS
- 37. Ptolemy Magellan’s Expedition Apollo 17 Spherical mesh elements © Commonwealth of Australia (Geoscience Australia) 2012
- 38. Australia's maritime jurisdiction © Commonwealth of Australia (Geoscience Australia) 2012
- 39. CUG-CSM-GA International Project - Spherical mesh geometry gravity and magnetic modelling © Commonwealth of Australia (Geoscience Australia) 2012
- 40. Synthetic result for gravity modelling with a spherical mesh © Commonwealth of Australia (Geoscience Australia) 2012 Model resolution: 6°×6°× 10km # of cells: 60×30×10=18000 Data resolution: 6°×6° # of data points: 60×30=1800 (Courtesy of Qing Liang, CUG and CSM)
- 41. © Commonwealth of Australia (Geoscience Australia) 2012 Theoretical data with noise Predicted data (Courtesy of Qing Liang, CUG and CSM)
- 42. Synthetic Synthetic © Commonwealth of Australia (Geoscience Australia) 2012 Synthetic Inverted Inverted Inverted (Courtesy of Qing Liang – CUG and CSM)
- 43. Gravity at GA ... More than just a ground gravity database • Significant scope to improve • Monitoring developments in AG and AGG • Expanding and improving the AFGN and the ANGD • Developing the Kauring test site Analysing test results Working towards a Deed-Of-Standing-Offer for service providers • Assisting State and Territory geoscience agencies, and other government groups with proposals calling for AG and AGG • Enhancing the rock properties database and web delivery application • Improving 3D modelling capabilities © Commonwealth of Australia (Geoscience Australia) 2012
Editor's Notes
- © Commonwealth of Australia (Geoscience Australia) 2012 This material is released under the Creative Commons Attribution 3.0 Australia Licence. 22nd ASEG International Conference & Exhibition 2012 20120229 Day 2 Session 2 Stream 5 – Minerals – Gravity and magnetic gradiometry – Keynote Address 11:00-12:00 “The strong attraction of gravity at Geoscience Australia” (Richard Lane, Geoscience Australia, richard.lane@ga.gov.au, rjllane@gmail.com) *** Abstract In the context of gravity, Geoscience Australia (GA) is probably best known as the custodian of the Australian National Gravity Database (ANGD). This has long been one of the “Crown Jewels” of the organisation. With more than 1 million ground gravity stations, the ANGD is a valuable resource for both internal and external clients, and the envy of many of our sister organisations around the world. We are not resting on this achievement, and gravity continues to exert a strong influence on our thinking and our work programs. I will use this opportunity to describe some of our activities that are relevant to the topic of gravity in its very broadest sense. I will highlight some resources that you may be able to use but may not have been aware of or may have forgotten about. This is also an excellent opportunity for me to get your feedback and use this to adjust our work programs. At GA, we frequently look at what we can do to improve the fundamental geoscientific knowledge of the Australian region. Of immediate relevance to the geophysical community at this conference would be aspirations to have data sets that would provide complimentary knowledge of a whole suite of rock properties. Our high resolution and coherent airborne magnetic coverage is the most detailed of the existing data sets. In an academic sense, we would like to have data sets with similar resolution that relate to seismic velocity, electrical conductivity, and mass density properties. This would clearly be an immense undertaking. In relation to the improvement to our knowledge of the gravity field, and hence information related to mass density, I shall be mentioning the following items; (a) Expansion and improvements to the high precision network of ground vertical gravity observations in both the Australian Fundamental Gravity Network (AFGN) and the ANGD. (b) Recognition of the need to move to airborne technologies, both airborne gravity (AG) and airborne gravity gradiometry (AGG), to obtain the uniformity and detail in high resolution gravity field observations for the entire Australian region. We are working towards a “Deed of Standing Offer” for suppliers of these services to help us to manage large AG and AGG surveys, both internally funded and those carried out in close collaboration with the State and Territory geoscience agencies. A test site to support this activity has been established in WA. We monitor and support developments in AG and AGG technologies, and the GA Records of the "Airborne Gravity 2004" and "Airborne Gravity 2010" forums held at previous ASEG Conferences are tangible, published items of global significance in this context. (c) We are also pushing forward in the quest to extract knowledge of rock properties from the geophysical data sets. We have recently established a coordinated database of rock properties that can be accessed in a very basic fashion by the public through our website. We have also formed a collaborative relationship with several international groups to advance the tools for modelling larger regions in a spherical rather than Cartesian frame of reference. This will enable us to model large regions far more accurately, and to provide clients with new gravity and magnetic products that have compensation for a variety of "regional effects" removed in a rigorous fashion through modelling.
- Australia has a land area of 7,617,930 km2 (http://en.wikipedia.org/wiki/Australia), but we have direct interest in a further 8,148,250 km2 that falls within our Exclusive Economic Zone (http://en.wikipedia.org/wiki/Exclusive_Economic_Zone#Australia). AGG onshore coverage @$100/line km and line spacing of 1 km = A$750 M AG coastal and offshore coverage @$50/line km and line spacing of 2 km = A$250 M Total coverage costs = A$1 B
- GRACE - Gravity Recovery and Climate Experiment US and German space agencies (NASA and DLG) Launched March 2002. Orbiting at an approximate altitude of 485 km. Two satellites separated by approximately 220 km (“Tom” and “Jerry”). Separation monitored by microwave ranging to an accuracy of approximately 10 microns. Position of the satellites monitored using GPS navigation. Accelerometers onboard each satellite provide total acceleration, simply as a cross-check on the gravity determinations. Providing both mean global gravity fields and monthly estimates of the temporal variations in the force of gravity. Approximately 400 km horizontal spatial resolution. Applications Global mean gravity field maps Geoid determination Temporal variations in the Earth’s mass distribution (e.g., water storage changes – surface, groundwater, ice sheets and glaciers; sea level changes; tectonic movements) 10 nms-2 change in gravity is approximately equivalent to 24 mm of water. Opportunities for GA Custodian of national gravity information Long wavelength mean gravity fields for the Australian region Temporal changes in gravity for accurate corrections to gravity measurements Support for users of temporal gravity variations Support for geodetic applications (e.g., coastal regions, Antarctica) http://www.csr.utexas.edu/grace/ http://en.wikipedia.org/wiki/Gravity_Recovery_and_Climate_Experiment
- GOCE - Gravity Field and Steady-State Ocean Circulation Explorer European Space Agency (ESA) Launched March 2009. Orbiting at an approximate altitude of 260 km. Gravity gradients measured by an EGG (Electrostatic Gravity Gradiometer) Repeat orbit every 61 days. Position of the satellite monitored using GPS navigation. Providing both mean global gravity fields and monthly estimates of the temporal variations in the force of gravity. Approximately 100 km horizontal spatial resolution. Anticipated accuracy of ~ 1 mGal with 100 km resolution c/f GRACE – lower altitude and gradient measurement = superior spatial resolution First preliminary global models released June 2010 – currently being analysed http://earth.esa.int/GOCE/ http://en.wikipedia.org/wiki/GOCE
- The GGM 03S solution is a Grace only solution, which is complete to degree and order 180. The GGM 03C solution is obtained by combining the information arrays from the GGM 03S solution with surface gravity data to obtain a solution complete to degree and order 360. The higher resolution detail in the 03C solution represents the contribution of the surface gravity data ti the very accurate long and mid wave length GRACE data. THE COMBINATION GRAVITY FIELD MODEL GGMO3C Reference: B. Tapley, J. Ries, S. Bettadpur, D. Chambers, M. Cheng, F. Condi, S. Poole, 2007, The GGM03 Mean Earth Gravity Model from GRACE: Eos Trans. AGU 88(52), Fall Meet. Suppl., Abstract G42A-03, 2007. GGMO3C is a combination of GRACE gravity information from GGMO3S) with land and ocean gravity information, complete to degree and order 360. GGMO3S was determined from 47 months of GRACE K-band intersatellite range-rate data, GPS tracking and GRACE accelerometer data spanning the period from January 2003 through December 2006 (January 2004 excluded). The terrestrial gravity information was a combination of the NINA surface gravity anomalies, the CSR mean sea surface (MSS95), and the Arctic Gravity Project (ArcGP) gravity anomalies. GGM031 was used to fill where no terrestrial gravity information was available. The GRACE atmosphere-ocean de-aliasing product (A0D1B) was used, but the mean of the A0D1B for the 47 months has been restored. Please Note: the reference epoch of this mean gravity field model is 1 January 2005. Terms for which rates were modeled have been mapped to this epoch; these include C20, C30, C40, C21 and S21. For additional details on the background modeling, see the CSR RL04 processing standards document available at ... ftp://podaac.jpl.nasa.govipubigraceidoc/L2-CSR0004_ProcStd_v3.1.pdf Product type: gravity field Model name: GGMO3C Earth gravity constant: 0.3986004415E+15
- https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&catno=70673
- Tracey R, Bacchin M & Wynne P. 2008. AAGD07: A new absolute gravity datum for Australian gravity and new standards for the Australian National Gravity Database. Extended Abstracts, 19th International Geophysical Conference and Exhibition. Australian Society of Exploration Geophysicists. Tracey R & Nakamura A. 2010. Complete Bouguer Anomalies for the Australian National Gravity Database: Extended Abstracts, 21st International Geophysical Conference and Exhibition. Australian Society of Exploration Geophysicists.
- First absolute gravity measurements in the Australian Antarctic Territory Geoscience Australia has recently conducted absolute gravity observations at Davis and Mawson stations in the Australian Antarctic Territory. These observations are the first such measurements undertaken at any of the Australian Antarctic stations to establish accurate gravity reference points for future gravity surveys. They will also enable gravity surveys that have already been conducted in the Australian Antarctic Territory to be tied to the same datum, thus allowing previous and future gravity surveys to be accurately merged and combined. Figure 1. Ties between existing gravity base stations and the new absolute gravity base stations were conducted using a relative gravity meter. Gravity reference points (or gravity base stations) have been established at the Australian Antarctic stations in the past but these were done with relative gravity meters. These instruments measure the difference in gravity from one point to another and were used to measure the difference between a reference point in Australia and the reference points that had been established in Antarctica. Unfortunately the length of time involved in travelling to Antarctica combined with 'instrumental drift' was not conducive to accurate readings so the accuracy of these older reference points was compromised. Figure 2. Map showing the location of Davis and Mawson in relation to Australia and the track of the RSV Aurora Australis during Voyage 3, 2009-10. The absolute gravity meter determines the actual acceleration of gravity by measuring the trajectory of a free-falling object in a vacuum. The surviving gravity base stations at Davis and Mawson were tied to the new absolute base stations using a relative gravity meter (figure 1). Gravity surveys that used these old reference points can now be adjusted to the new absolute datum. Transport to and from the Antarctic stations was onboard the Australian Antarctic Division's re-supply vessel RSV Aurora Australis, which departed Hobart on 25 January 2010 and returned on 28 February 2010. The ship's track for this voyage and the location of Davis and Mawson can be seen in figure 2. For more information Ray Tracey on +61 2 6249 9111 (email ray.tracey@ga.gov.au)
- 20081015 What's so fundamental about a gravity network? Presenter - Ray Tracey, OEMD Abstract The Australian Fundamental Gravity Network (AFGN) provides the datum for gravity surveys conducted in Australia and the surrounding oceans. It consists of more than 900 gravity stations at over 250 locations. The network was initially established in the early 1950s with stations added at various times up to the present. All of these stations were established using relative gravimeters to measure gravity differences between stations. Relative gravimeter ties to overseas gravity stations were used to establish the gravity datum prior to 1979 when five absolute gravity sites were established in Australia with a Soviet absolute gravimeter. These sites were tied to the network and used to constrain the Isogal84 datum, which was in use from 1984 until 2008. Between 2003 and 2006 Geoscience Australia conducted absolute gravity measurements with a portable absolute gravimeter at 60 AFGN stations. These measurements showed that there was a consistent difference between the Isogal84 datum and the absolute measurements. These measurements have been used to establish a new datum, the Australian Absolute Gravity Datum 2007 (AAGD07), and to adjust the Australian National Gravity Database (ANGD) to this new datum. Concurrent with implementing AAGD07, the standards used for reducing gravity data in the ANGD have been reviewed and updated. These changes include using the closed form of the 1980 International Gravity Formula, global horizontal and vertical datums, and a spherical cap Bouguer correction that accounts for the Earth's curvature. These new standards provide more accurate anomalies, particularly in longer wavelengths thus benefiting regional studies. This talk presents an abridged history of the AFGN explaining the new datum and standards and showing why the AFGN is fundamental to Australian gravity. Biography Ray Tracey is a geophysicist in the Continental Geophysics Project in OEMD where he is responsible for the maintenance of the Australian Fundamental Gravity Network. He started work with BMR/AGSO/GA in 1975 as a Trainee Technical Officer and gained experience in a number of different areas of the Bureau during the traineeship. After completing his traineeship he conducted numerous gravity surveys in many out of the way parts of the country before being foolish enough to accept the pieces of silver on offer to join the crew on BMR's marine research vessel, Rig Seismic. After experiencing life on the high seas for a number of years, he jumped ship and returned to solid land and the more stable lifestyle of gravity surveying. Along the way, Ray has acquired a computing and remote sensing degree from the University of Canberra and a Master of Geoscience from Macquarie University
- Philosophers and seafarers in ancient Greek and Egyptian civilizations were aware of it from the 6th century BC onwards. The circumnavigation of the Earth in the early 16th century by members of Ferdinand Magellan’s voyage made it really difficult to ignore. Pilots and astronauts could see directly that it is true from high altitude and space in the 20th century. Here in the 21st century, few of us doubt that it is true. What am I talking about? We carry out our modelling using rectangular “flat Earth” coordinate systems. But the Earth is more like a sphere than a slab. So rather than simply continue to perform all of our gravity and magnetic modelling in Cartesian “flat Earth” coordinate reference frameworks, we are collaborating with a number of groups spread right across the globe to implement modelling options that use a spherical reference framework.
- 40 degrees E to 180 degrees E 0 degrees to 90 degrees S Australia's Maritime Jurisdiction spans nearly ¼ of the globe.
- CUG-CSM-GA International project for spherical mesh geometry gravity and magnetic modeling CUG – China University of Geosciences CSM – Colorado School of Mines GA – Geoscience Australia Our Memorandum-Of-Understanding (MOU) signed on 11-October-2011 ... "Our respective organizations acknowledge a commitment to pursue an agreement for international collaboration on the modeling and application of gravity and magnetic data in a spherical mesh geometry. We shall work together in good spirit and faith to finalize an agreement, and if this is successful, to then carry out the project. We commit to work to the benefit of the collective group, recognizing that this will produce the greatest overall benefit to the individual interests of each of the constituent parties over the full course of the collaborative project.“ Richard Lane (Geoscience Australia) Yaoguo Li (Colorado School of Mines) Chao Chen and Qing Liang (China University of Geosciences)
- (From a presentation prepared by Qing Liang titled “3-D inversion of gravity data in spherical coordinate: Modeling the density structure of planetary lithosphere”) Chen, C., Chen, B., and Ping, J. S., Liang, Q., Huang, Q., And Zhao, W. J., 2009, The interpretation of gravity anomaly on lunar Apennines: Science in China Series G: Physics, Mechanics & Astronomy, 52(12), 1824-1832, doi: 10.1007/s11433-009-0281-0. Du., J. S., Chen, C., Liang, Q., and Zhou, C., 2011, Lateral density variations on the surface and in the crust of the Moon: The 42nd Lunar and Planetary Science Conference, The Woodlands, Texas, USA, March 7–11, Abstract #1744. Liang, Q., 2010, Gravity anomaly features and 3D density imaging of the Moon: PhD dissertation, China University of Geosciences (Wuhan), Wuhan, China. Liang, Q., Chen, C., and Du, J., Chen, B., 2009, Calculation of lunar Bouguer gravity anomaly using Chang'E-1 topography data: Interpretation for mascons: Poster presented at the AGU Fall Meeting, San Francisco, California, USA. Liang, Q., Chen, C., Huang, Q., Chen, B., and Ping, J. S., 2009, Bouguer gravity anomaly of the Moon from CE-1 topography data: Implications for the impact basin evolution: Science in China Series G: Physics, Mechanics & Astronomy, 52(12), 1867-1875, doi: 10.1007/s11433-009-0278-8. Liang, Q., Chen, C., and Li, Y., 2010, 3D inversion of lunar gravity data and preliminary results: Poster presented at the AGU Fall Meeting, San Francisco, California, USA. Liang, Q., Chen, C., and Li, Y., 2011, 3-D inversion of the gravity data on the moon: The 42nd Lunar and Planetary Science Conference, The Woodlands, Texas, USA, March 7–11, Abstract #1729.
- (From a presentation prepared by Qing Liang titled “3-D inversion of gravity data in spherical coordinate: Modeling the density structure of planetary lithosphere”) Chen, C., Chen, B., and Ping, J. S., Liang, Q., Huang, Q., And Zhao, W. J., 2009, The interpretation of gravity anomaly on lunar Apennines: Science in China Series G: Physics, Mechanics & Astronomy, 52(12), 1824-1832, doi: 10.1007/s11433-009-0281-0. Du., J. S., Chen, C., Liang, Q., and Zhou, C., 2011, Lateral density variations on the surface and in the crust of the Moon: The 42nd Lunar and Planetary Science Conference, The Woodlands, Texas, USA, March 7–11, Abstract #1744. Liang, Q., 2010, Gravity anomaly features and 3D density imaging of the Moon: PhD dissertation, China University of Geosciences (Wuhan), Wuhan, China. Liang, Q., Chen, C., and Du, J., Chen, B., 2009, Calculation of lunar Bouguer gravity anomaly using Chang'E-1 topography data: Interpretation for mascons: Poster presented at the AGU Fall Meeting, San Francisco, California, USA. Liang, Q., Chen, C., Huang, Q., Chen, B., and Ping, J. S., 2009, Bouguer gravity anomaly of the Moon from CE-1 topography data: Implications for the impact basin evolution: Science in China Series G: Physics, Mechanics & Astronomy, 52(12), 1867-1875, doi: 10.1007/s11433-009-0278-8. Liang, Q., Chen, C., and Li, Y., 2010, 3D inversion of lunar gravity data and preliminary results: Poster presented at the AGU Fall Meeting, San Francisco, California, USA. Liang, Q., Chen, C., and Li, Y., 2011, 3-D inversion of the gravity data on the moon: The 42nd Lunar and Planetary Science Conference, The Woodlands, Texas, USA, March 7–11, Abstract #1729.
- (From a presentation prepared by Qing Liang titled “3-D inversion of gravity data in spherical coordinate: Modeling the density structure of planetary lithosphere”) Chen, C., Chen, B., and Ping, J. S., Liang, Q., Huang, Q., And Zhao, W. J., 2009, The interpretation of gravity anomaly on lunar Apennines: Science in China Series G: Physics, Mechanics & Astronomy, 52(12), 1824-1832, doi: 10.1007/s11433-009-0281-0. Du., J. S., Chen, C., Liang, Q., and Zhou, C., 2011, Lateral density variations on the surface and in the crust of the Moon: The 42nd Lunar and Planetary Science Conference, The Woodlands, Texas, USA, March 7–11, Abstract #1744. Liang, Q., 2010, Gravity anomaly features and 3D density imaging of the Moon: PhD dissertation, China University of Geosciences (Wuhan), Wuhan, China. Liang, Q., Chen, C., and Du, J., Chen, B., 2009, Calculation of lunar Bouguer gravity anomaly using Chang'E-1 topography data: Interpretation for mascons: Poster presented at the AGU Fall Meeting, San Francisco, California, USA. Liang, Q., Chen, C., Huang, Q., Chen, B., and Ping, J. S., 2009, Bouguer gravity anomaly of the Moon from CE-1 topography data: Implications for the impact basin evolution: Science in China Series G: Physics, Mechanics & Astronomy, 52(12), 1867-1875, doi: 10.1007/s11433-009-0278-8. Liang, Q., Chen, C., and Li, Y., 2010, 3D inversion of lunar gravity data and preliminary results: Poster presented at the AGU Fall Meeting, San Francisco, California, USA. Liang, Q., Chen, C., and Li, Y., 2011, 3-D inversion of the gravity data on the moon: The 42nd Lunar and Planetary Science Conference, The Woodlands, Texas, USA, March 7–11, Abstract #1729.