Authors / CoAuthors
Geophysical Acquisition & Processing Section
Abstract
Total magnetic intensity (TMI) data measures variations in the intensity of the Earth's magnetic field caused by the contrasting content of rock-forming minerals in the Earth crust. Magnetic anomalies can be either positive (field stronger than normal) or negative (field weaker) depending on the susceptibility of the rock. The data 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 Magnetic Anomaly Map of Australia, Seventh Edition, 2020 - Enhanced Products Package - TMI RTP AS grid is a analytic signal of the Total Magnetic Intensity grid for the Magnetic Anomaly Map of Australia, Seventh Edition, 2019. The 2019 Total magnetic Intensity (TMI) grid of Australia has a grid cell size of ~3 seconds of arc (approximately 80 m) and only includes airborne-derived TMI data for onshore and near-offshore continental areas. Since the sixth edition was released in 2015, data from 234 new surveys have been added to the database, acquired mainly by the State and Territory Geological Surveys. The 2019 grid was derived from a re-levelling of the national magnetic grid database. The survey grids were levelled to each other, and to the Australia Wide Airborne Geophysical Survey (AWAGS), which serves as a baseline to constrain long wavelengths in the final grid. It is estimated that 33 500 000 line-kilometres of survey data were acquired to produce the 2019 grid data, about 2 000 000 line-kilometres more than for the previous edition. The VRTP processing followed a differential reduction to pole calculation up to 5th order polynomial. Magnetic inclination and declination were derived from the IGRF-15 geomagnetic reference model using a data representative date and elevation representative of the survey. An analytic signal was calculated by applying a fast Fourier transform (FFT) process to the Total Magnetic Intensity grid of the Magnetic Anomaly Map of Australia, Seventh Edition, 2019 to produce this grid. The Analytic Signal is the square root of the sum of the two horizontal derivative and the vertical derivative. This analytic signal grid has a cell size of 0.00083 degrees (approximately 88m) and units of nanoTesla per km (or nT/km).
Product Type
dataset
eCat Id
144750
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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- grid
- ( Place )
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- Australia
- ( Place )
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- None
- ( Project )
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- survey 1324
- ( Theme )
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- AWAGS
- ( Theme )
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- GADDS2.0
- ( Theme )
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- magnetics
- ( Theme )
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- analytic signal
- ( Theme )
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- magnetism
- ( Theme )
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- palaeomagnetism
- ( Theme )
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- airborne digital data
- ( Theme )
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- geophysical survey
- ( Theme )
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- mag
- ( Theme )
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- AS
- ( Theme )
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- RTP
- ( Theme )
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- VRTP
- ( Theme )
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- grid
- ( Theme )
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- raster
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- Published_External
Publication Date
2020-10-31T00:00:00
Creation Date
2020-10-31T00:00:00
Security Constraints
Legal Constraints
Status
completed
Purpose
Maintenance Information
notPlanned
Topic Category
geoscientificInformation
Series Information
Lineage
This Magnetic Anomaly Map of Australia, Seventh Edition, 2020 - Enhanced Products Package - TMI RTP AS grid is an analytic signal grid of the Total Magnetic Intensity (TMI) variable reduced to the pole (VRTP) anomaly for the Magnetic Anomaly Map of Australia, Seventh Edition, 2019. The data were acquired under the project No. 1324. The 2019 Total magnetic Intensity (TMI) grid of Australia (Poudjom Djomani et al., 2019) has a grid cell size of ~3 seconds of arc (approximately 80 m). This grid only includes airborne-derived TMI data for onshore and near-offshore continental areas. Since the sixth edition was released in 2015, data from 234 new surveys have been added to the database, acquired mainly by the State and Territory Geological Surveys. The new grid was derived from a re-levelling of the national magnetic grid database. The survey grids were levelled to each other, and to the Australia Wide Airborne Geophysical Survey (AWAGS) (Milligan et al., 2009), which serves as a baseline to constrain long wavelengths in the final grid. The levelling and grid-merging procedure was described in detail in Minty et al. (2003). It is estimated that 33 500 000 line-kilometres of survey data were acquired to produce the 2019 grid data, about 2 000 000 line-kilometres more than for the previous edition. The VRTP processing followed a differential reduction to pole calculation up to 5th order polynomial. Magnetic inclination and declination were derived from the IGRF-15 geomagnetic reference model using a data representative date and elevation representative of the survey. An analytic signal was calculated by applying a fast Fourier transform (FFT) process to the Total Magnetic Intensity grid of the Magnetic Anomaly Map of Australia, Seventh Edition, 2019 survey to produce this grid. The Analytic Signal is the square root of the sum of the two horizontal derivative and the vertical derivative. This grid was calculated using an algorithm from the INTREPID Geophysics software package. The processed data are checked by GA geophysicists using standard methods for assessing quality to ensure that the final data are fit-for-purpose. The analytic signal grid is independent of the inclination of the magnetic field. It's advantage is in locating the centre and boundary of magnetised bodies. The analytic signal grid has a cell size of 0.00083 degrees (approximately 88m) and units of nanoTesla per km (or nT/km). Details of the specifications of individual airborne surveys can be found in the Fourteenth Edition of the Index of Airborne Geophysical Surveys (Percival, 2014). This Index is also available online at http://pid.geoscience.gov.au/dataset/79134. References: Intrepid Geophysics, http://www.intrepid-geophysics.com; Milligan, P.R., Minty, B.R.S., Richardson, M. and Franklin, R., 2009. The Australia-wide Airborne Geophysical Survey accurate continental magnetic coverage. Preview, No. 138, p. 1-128. Minty, B.R.S., Milligan, P.R., Luyendyk, A.P.J. and Mackey, T., 2003. Merging airborne magnetic surveys into continental-scale compilations. Geophysics, 68 (3), 988-995. Percival, P.J., 2014. Index of airborne geophysical surveys (Fourteenth Edition); Poudjom Djomani, Y., Minty, B.R.S., Hutchens, M., Lane, R.J.L. 2019, Total Magnetic Intensity (TMI) Grid of Australia 2019 - seventh edition - 80 m cell size. Geoscience Australia, Canberra. http://dx.doi.org/10.26186/5e9cf3f2c0f1d, eCat record number 131505.
Parent Information
Geophysical Data Collection - Airborne Geophysics
UUID - c6b58f54-102c-19e9-e044-00144fdd4fa6,
eCat ID - 74512
Extents
[-43.9301, -9.0265, 105.9996, 154.6635]
Reference System
GDA94 (EPSG:4283)
Spatial Resolution
Service Information
Associations
Downloads and Links
File available for download in various formats from the GADDS2 portal
/g/data/iv65/Geoscience_Australia_Geophysics_Reference_Data_Collection/national_geophysical_compilations/Magmap2019/Magmap2019-grid-tmi_rtp_as-AWAGS_MAG_2019.nc file at NCI
/g/data/iv65/Geoscience_Australia_Geophysics_Reference_Data_Collection/national_geophysical_compilations/Magmap2019/Magmap2019-grid-tmi_rtp_as-AWAGS_MAG_2019.nc file download
Source Information
This Magnetic Anomaly Map of Australia, Seventh Edition, 2020 - Enhanced Products Package - TMI RTP AS grid includes airborne-derived TMI variable reduced to the pole (VRTP) data for the Magnetic Anomaly Map of Australia, Seventh Edition, 2019.