Authors / CoAuthors
Geophysical Acquisition & Processing Section
Abstract
Gravity data measure small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This National Gravity Compilation 2019 includes airborne CSCBA 1VD image is a first vertical derivative of the complete spherical cap Bouguer anomaly grid for the 2019 Australian National Gravity Grids. These gravity data were acquired under the project No. 202008. The national grid has a cell size of 0.00417 degrees (approximately 435m). This gravity anomaly grid is derived from ground observations stored in the Australian National Gravity Database (ANGD) as at September 2019, supplemented with offshore data sourced from v28.1 of the Global Gravity grid developed using data from the Scripps Institution of Oceanography, the National Oceanic and Atmospheric Administration (NOAA), and National Geospatial-Intelligence Agency (NGA) at Scripps Institution of Oceanography, University of California San Diego. Airborne gravity and gravity gradiometry data were also included to provide better resolution to areas where ground gravity data was not of a suitable quality. Out of the approximately 1.8 million gravity observations, nearly 1.4 million gravity stations in the ANGD together with Airborne Gravity surveys totaling 345,000 line km and 106,000 line km of Airborne Gravity Gradiometry were used to generate this grid. The grid shows complete Bouguer anomalies over Australia and its continental margins. The ground gravity data used in this grid has been acquired by the Commonwealth, State and Territory Governments, the mining and exploration industry, universities and research organisations from the 1940's to the present day. Station spacing varies from approximately 11 km down to less than 1 km, with major parts of the continent having station spacing between 2.5 and 7 km. Airborne surveys have a line spacing ranging from 0.5 km to 2.5 km. Terrain corrections to gravity were calculated using both offshore bathymetry and onshore topography data. A first vertical derivative was calculated by applying a fast Fourier transform (FFT) process to the complete spherical cap Bouguer anomaly grid of the 2019 Australian National Gravity Grids to produce the grid shown on this image.
Product Type
dataset
eCat Id
144767
Contact for the resource
Point of contact
Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
ACT
2601
Australia
Keywords
- theme.ANZRC Fields of Research.rdf
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- EARTH SCIENCES
- ( Data centre )
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- NCI
- ( Discipline )
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- Earth sciences
- ( Discipline )
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- geophysics
- ( Feature type )
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- image
- ( Place )
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- Australia
- ( Place )
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- None
- ( Project )
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- survey 202008
- ( Theme )
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- GADDS2.0
- ( Theme )
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- gravity
- ( Theme )
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- spherical cap
- ( Theme )
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- Bouguer
- ( Theme )
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- complete
- ( Theme )
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- B series
- ( Theme )
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- digital data
- ( Theme )
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- ground
- ( Theme )
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- marine
- ( Theme )
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- satellite
- ( Theme )
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- airborne
- ( Theme )
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- gradiometry
- ( Theme )
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- geophysical survey
- ( Theme )
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- grav
- ( Theme )
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- image
- ( Theme )
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- grid
- ( Theme )
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- raster
- ( Theme )
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- 1vd
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- Published_External
Publication Date
2020-11-09T00:00:00
Creation Date
2020-11-09T00:00:00
Security Constraints
Legal Constraints
Status
completed
Purpose
Maintenance Information
notPlanned
Topic Category
geoscientificInformation
Series Information
Lineage
This National Gravity Compilation 2019 includes airborne CSCBA 1VD image is derived from the 2019 Australian National Gravity Grids B series. These gravity data were acquired under the project No. 202008. The grid used to create this image has a cell size of 0.00417 degrees (approximately 435m). This gravity anomaly grid is derived from ground observations stored in the Australian National Gravity Database (ANGD) as at September 2019, supplemented with offshore data sourced from v28.1 of the Global Gravity grid developed using data from the Scripps Institution of Oceanography, the National Oceanic and Atmospheric Administration (NOAA), and National Geospatial-Intelligence Agency (NGA) at Scripps Institution of Oceanography, University of California San Diego. Airborne gravity and gravity gradiometry data were also included to provide better resolution to areas where ground gravity data was not of a suitable quality. Out of the approximately 1.8 million gravity observations, nearly 1.4 million gravity stations in the ANGD together with Airborne Gravity surveys totaling 345,000 line km and 106,000 line km of Airborne Gravity Gradiometry were used to generate this grid. The ground and airborne gravity data used in this grid has been acquired by the Commonwealth, State and Territory Governments, the mining and exploration industry, universities and research organisations from the 1940's to the present day. Station spacing varies from approximately 11 km down to less than 1 km, with major parts of the continent having station spacing between 2.5 and 7 km. Airborne surveys have a line spacing ranging from 0.5 km to 2.5 km. The image shows a first vertical derivative of the complete Bouguer anomalies (B series) over Australia and its continental margins. Three processes are required to correct the gravity observations for the effects of the surrounding topography: (1) a Bouguer correction (Bullard A), which approximates the topography as an infinite horizontal slab; (2) a correction to that horizontal slab for the curvature of the Earth (Bullard B); and (3) a terrain correction (Bullard C), which accounts for the undulations of the surrounding topography. The complete spherical cap Bouguer gravity anomalies were calculated by applying terrain correction (Bullard C) to the spherical cap Bouguer anomaly point data of 2019 Australian National Gravity Grids. These corrections were calculated using software that is based on a combination of the methods described by Nagy (1966) and Kane (1962). The adjustments were calculated to a radius of 166.7 km using a terrain density of 2670 kg/m3 and a sea water density of 1030 kg/m3. The terrain for onshore Australia was based on 3 second Shuttle Radar Topography Mission (SRTM) data (Gallant et al., 2011), whilst the bathymetry and the terrain data for other countries was based on AusBath09 (Whiteway, 2009) and ETOPO data. More information about the 2019 national gravity grids and the processing steps can be found in Lane et al. (2020a,b). Details of the specifications of individual surveys held in the Australian National Gravity Database (ANGD) can be found in the Second Edition of the Index of Gravity Surveys (Wynne and Bacchin, 2009). A first vertical derivative was calculated by applying a fast Fourier transform (FFT) process to the complete spherical cap Bouguer anomaly grid of the 2019 Australian National Gravity Grids to produce the grid shown by this image. This vertical derivative was calculated using an algorithm from the INTREPID Geophysics software package. References: Gallant, J.C., Wilson, N., Dowling, T.I., Read, A.M., and Inskeep, C., 2011. SRTM-derived 3 Second Digital Elevation Models Version 1.0. Geoscience Australia, Canberra. https://pid.geoscience.gov.au/dataset/ga/72760; Intrepid Geophysics, http://www.intrepid-geophysics.com; Kane, M. F., 1962, A comprehensive system of terrain corrections using a digital computer, 27, 455-462; Lane, R. J. L., Wynne, P. E., Poudjom Djomani, Y. H., Stratford, W. R., Barretto, J. A., and Caratori Tontini, F., 2020a, 2019 Australian National Gravity Grids: Geoscience Australia, eCat Reference Number 133023, https://pid.geoscience.gov.au/dataset/ga/133023; Lane, R. J. L., Wynne, P. E., Poudjom Djomani, Y. H., Stratford, W. R., Barretto, J. A. and Caratori Tontini, F., 2020b, 2019 Australian national gravity grids explanatory notes: Record 2020/22, Geoscience Australia, Canberra, http://dx.doi.org/10.11636/Record.2020.022; Nagy, D., 1966, The gravitational attraction of a right rectangular prism: Geophysics, 31, 362-371; Whiteway, T. G., 2009. Australian Bathymetry and Topograhy Grid, June 2009. Geoscience Australia, Canberra. http://dx.doi.org/10.4225/25/53D99B6581B9A 20170906; Wynne, P. and Bacchin, M., 2009. Index of Gravity Surveys (Second Edition). Geoscience Australia, Record 2009/07.
Parent Information
Geophysical Data Collection - gravity
UUID - c6b58f54-102c-19e9-e044-00144fdd4fa6,
eCat ID - 74512
Extents
[-48.0021, -7.9979, 107.9979, 164.0021]
Reference System
GDA94 (EPSG:4283)
Spatial Resolution
Service Information
Associations
Downloads and Links
Source Information
This National Gravity Compilation 2019 includes airborne CSCBA 1VD image includes ground, marine, airborne and gravity gradiometry data for the 2019 Australian National Gravity Grids B series