DOI: 10.4225/25/561c7ce032eab
title: Total Magnetic Intensity (TMI) Colour Composite Image 2015

description: Total Magnetic Intensity colour composite image 2015

The image is created from the magmap_v6_2015 is a composite TMI grid of the Australian region with a grid cell spacing 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 fifth edition was released in 2010 data from 41 new surveys have been added to the database, acquired mainly by the State and Territory Geological Surveys. It is estimated that 
31 500 000 line-kilometres of survey data were acquired to produce the grid data, 4 500 000 line-kilometres more than for the previous edition. 

Details of the specifications of individual airborne surveys can be found in the Fourteenth Edition of the Index of Airborne Geophysical Surveys (Percival, 2014), which is included with the grid as a PDF document called magmap_v6_2015.pdf. This Index is also available online at http://www.ga.gov.au/metadata-gateway/metadata/record/gcat_f3ad4f15-96bc-0cf3-e044-00144fdd4fa6/Index+of+airborne+geophysical+surveys%3A+14th+edition. Further up to date information about individual surveys can also be obtained online from the Airborne Surveys Database at http://www.ga.gov.au/oracle/argus/.


Matching of the grids in the database was achieved using a program called Gridmerge, which was originally developed within Geoscience Australia and has now been commercialised. This program was used to merge 41 new surveys to the 5th Edition Total Magnetic Intensity Anomaly Grid of Australia (Milligan et al., 2010). The 5th Edition merged 795 individual grids to create the compilation and to constrain long wavelengths, an independent data set, the Australia-wide Airborne Geophysical Survey (AWAGS) airborne magnetic data, was used to control the base levels of those survey grids which overlapped the AWAGS data (Milligan et al., 2009). As the 5th Edition was used as a base grid for the Gridmerge operation the new 6th Edition is essentially levelled to AWAGS. 

Grid downloads:  The Magnetic Map of Australia grid can be downloaded using the Geophysical Archive Data Delivery System (GADDS) on the Australian Government's Geoscience Portal at http://www.geoscience.gov.au/gadds


File size:  At full resolution, the Magnetic Map of Australia grid has 41884 rows and 50592 columns and has a file size of approximately 8.3 Gb in ERMapper format.  Note that, because of GADDS file size limits, it is not possible for clients to download very large areas of the grid at full resolution. Clients wishing to do so should contact Geoscience Australia to make special arrangements to have the complete grid dataset provided on a user-supplied portable hard drive.
 
References

Milligan, P.R., Minty, B.R.S., Richardson, M. & Franklin, R., 2009. The Australia-wide Airborne Geophysical Survey � accurate continental magnetic coverage. Preview, 138, 70.

Milligan, P.R., Franklin, R., Minty, B.R.S., Richardson, L.M. and Percival, P.J., 2010. Magnetic Anomaly Map of Australia (Fifth Edition), 1:5 000 000 scale, Geoscience Australia, Canberra.

Percival, P.J., 2014. Index of airborne geophysical surveys (Fourteenth Edition). Geoscience Australia Record 2014/014.