Magnetic Anomaly Map of Australia, Seventh Edition, 2020 - Enhanced Products Package - TMI RTP image (PGravThd)  


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 2019 Total magnetic Intensity (TMI) grid of Australia 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 2019 national 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 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 image (PGravThd) is a pseudocolour image of the TMI grid of the Magnetic Anomaly Map of Australia, Seventh Edition, 2019. This grid has a cell size of 0.00083 degrees (approximately 88m). This pseudocolour image shows the magnetic response of subsurface features with contrasting magnetic susceptibilities. The image can also be used to locate structural features such as dykes.

Product Type

dataset

eCat Id

144728

Contact for the resource

  Point of contact

Commonwealth of Australia (Geoscience Australia)  
Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
ACT
2601
Australia

Keywords

theme.ANZRC Fields of Research.rdf
  • EARTH SCIENCES
( Data centre )
  • NCI
( Discipline )
  • Earth sciences
( Discipline )
  • geophysics
( Feature type )
  • image
( Place )
  • Australia
( Place )
  • None
( Project )
  • survey 1324
( Theme )
  • GADDS2.0
( Theme )
  • TMI
( Theme )
  • magnetics
( Theme )
  • magnetism
( Theme )
  • palaeomagnetism
( Theme )
  • airborne digital data
( Theme )
  • geophysical survey
( Theme )
  • national
( Theme )
  • mag
( Theme )
  • total magnetic intensity
( Theme )
  • pseudocolour
( Theme )
  • image
( Theme )
  • reduced to the pole
( Theme )
  • pseudocolour image
( Theme )
  • raster
( Theme )
  • pseudo-gravity transformation
( Theme )
  • total horizontal derivative filter
( Theme )
  • pseudo susceptibility
( Theme )
  • tilt angle
( Theme )
  • total horizontal gradient
( Theme )
  • variable vertical gradient of TMI vertical component
( Theme )
  • VBzz
  • Published_External

Publication Date

2020-11-09T00:00:00

Creation Date

2020-11-09T00:00:00

Security Constraints

Australian Government Security ClassificationSystem    

Classification - unclassified

Legal Constraints

Creative Commons Attribution 4.0 International Licence    

Access - license

Use - license

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 image (PGravThd) includes an enhanced variable reduction to the pole (VRTP) of airborne-derived Total Magnetic Intensity (TMI) data for onshore and near off-shore continental areas (Poudjom Djomani et al., 2019). The Magnetic Anomaly Map of Australia, Seventh Edition, 2019 under project number 1324 was produced with a grid cell size of 0.00083 (approximately 88m), given in units dependent on the enhancement. It is estimated that 33 500 000 line-kilometres of survey data collected by State and Territory geological surveys and Geoscience Australia were acquired to produce the 2019 grid, about 2 000 000 line-kilometres more than for the previous edition. The 2019 magnetic grid was derived from a complete 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). The new 2019 map compilation is comprised of a merge of 1059 survey grids. The addition of almost a decade's worth of new high-quality surveys adds significantly to the 2010 and 2015 versions of the map. Further processing was applied to the original TMI grid to reduce the magnetic effect of the Portland Smelter Complex (PSC) (Poudjom Djomani et al., 2019). The anomaly associated with the complex can have erroneous effects on products created using Fourier domain processing of the grid. A subset of the TMI grid covering the area of the PSC was cut for easy processing. Filling of the grid was done in MATLAB using function 'inpaintn' from Garcia (2020), based on Wang et al. (2012). This procedure resulted in an anomaly of +100nT in the region of the PSC. Further, a cosine averaging filter was applied to the PSC and its edges to remove the short wavelength anomalies which may lead to misinterpretation of the data. The processed subset grid was then overlain onto the national TMI grid as a final product. The data has had a variable reduction to the pole applied to centre the magnetic anomaly over the magnetised body. 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 enhancement 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 enhancement is one of pseudo-gravity transformation, total horizontal derivative filter, pseudo susceptibility, tilt angle, total horizontal gradient, variable vertical gradient of TMI vertical component, VBzz. This image was calculated using an algorithm from the INTREPID Geophysics software package. 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. Refrences: Garcia, D., 2020. Inpaint over missing data in 1-D, 2-D, 3-D, ... nd arrays. Percival, P.J., 2014. Index of airborne geophysical surveys (Fourteenth Edition). Intrepid Geophysics http://intrepid-geophysics.com. https://www.mathworks.com/matlabcentral/fileexchange/27994-inpaint-over-missing-data-in-1-d-2-d-3-d-nd-arrays), MATLAB Central File Exchange. 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. 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; Wang, G., Garcia, D., Liu, Y., de Jeu, R. and Dolman, A.J., 2012, A three-dimensional gap filling method for large geophysical datasets: Application to global satellite soil moisture observations: Environmental Modelling Software, 30, 139-142, doi: 10.1016/j.envsoft.2011.10.015.

Parent Information

Geophysical Data Collection - Airborne Geophysics

UUID - ddeb0fc4-32e3-4913-80f2-f4249b17a925,

eCat ID -

Extents

[-43.9301, -9.0265, 105.9996, 154.6635]

Reference System

GDA94 (EPSG:4283)

Spatial Resolution

Service Information

Associations

Association Type - operatedOnBy

Magnetic Anomaly Map of Australia, Seventh Edition, 2020 - Enhanced Products Package - TMI RTP image (PGravThd) OPeNDAP    

Downloads and Links

File available for download in various formats from the GADDS2 portal  

Magnetic Anomaly Map of Australia, Seventh Edition, 2020 - Enhanced Products Package - TMI RTP image (PGravThd) file download  

Magnetic Anomaly Map of Australia, Seventh Edition, 2020 - Enhanced Products Package - TMI RTP image (PGravThd) OPeNDAP  

Source Information

This Magnetic Anomaly Map of Australia, Seventh Edition, 2020 - Enhanced Products Package - TMI RTP image (PGravThd) is a pseudocolour image of the TMI VRTP enhanced data for the Magnetic Anomaly Map of Australia, Seventh Edition, 2019 produced by Geoscience Australia.