Geophysical Data Release
Magnetic Anomaly Map of Australia (Fourth Edition)

Release Date: 29 November 2004

Hardcopy Maps

Geoscience Australia (GA) is releasing the fourth edition of the "Magnetic Anomaly Map of Australia" at both 1:5 000 000 and 1:25 000 000 scales.

Two important revisions distinguish this new edition of the map from the third edition. Firstly, this edition is underpinned by the concept of a database of matched Total Magnetic Intensity (TMI) grids, from which any map at any resolution can be extracted. This differs significantly from previous editions, in which the emphasis was on the final map product. Secondly, this edition results from a completely new compilation of TMI grid data via a new method of matching the individual survey grids and the use of independent data to help constrain long wavelengths. A total of 684 individual grids have been matched and merged into the composite grid to produce the image for the map. The resolution of each grid is optimal for the specifications of the source survey line data.

Since the third edition map was released in December 1999, data from many new surveys have been added to GA's National Airborne Geophysical Database. This database contains data from the following sources:

• Surveys flown by Geoscience Australia;
• Surveys carried out by airborne geophysical companies operating under contract to GA and State and Territory Geological Surveys, either separately or in joint projects; and
• Surveys carried out for the private sector, which have been purchased or acquired by GA.

Most of the new data incorporated into this new edition of the map were acquired by the State and Territory Geological Surveys. It is estimated that 19 million line-kilometres of survey data were acquired to produce the grid data, 10 million line-kilometres more than in the previous edition.

The map image was generated from the natural colour palette (magenta high, blue low) and the application of histogram equalisation has maximised the available colour range. To emphasize the expression of anomalies attributable to near-surface geology, a Horn filter was used to produce an artificial sun-angle 'illumination' from the north-east.

[back to top]

Grids

Two composite grids of Total Magnetic Intensity (TMI) data are available in ERMapper format, with a Geodetic (longitude/latitude) projection and GDA94 datum:

• A grid of airborne survey data at 7.2 seconds-of-arc (approx. 250 m cell size) and
• A grid of airborne and marine survey data at 15 seconds-of-arc (approx. 400 m cell size).

[back to top]

Availability of Grids and Maps

The data can be downloaded for free using the Geophysical Archive Data Delivery System (GADDS), or alternatively may be purchased on two CD-ROMs from the Sales Centre at a cost of A$99.00 per CD (including GST; postage and packing extra).

Colour, gradient enhanced TMI pixel image maps are available for free from the Sales Centre. The maps include a 1:5 000 000 scale map (approx. A0 in size) and a 1:25 000 000 scale map (approx. A4 in size). Please note that although the maps are free, there is a nominal charge for the cost of postage and packaging.