The Australian Bureau of Mineral Resources (BMR) is responsible for the National Airborne Magnetic Database. This data base consists of results from approximately 3 500 000 line‐km of regional survey flying carried out over 35 years, recording total magnetic intensity. The magnetic data base is one of the most important geophysical data bases for Australia and is used extensively by the minerals and petroleum exploration industries. First‐pass coverage of onshore Australia is aimed for completion in 1992. This coverage contains data from surveys with a wide range of specifications, resulting in a wide range of data quality; some of the areas covered by poorer quality data may be reflown later. For the most part, the intention has been to acquire data at a continuous ground clearance of 150 m and with a line spacing of 1500 m. However, over some sedimentary basins, the line spacing is in excess of 3200 m. New color and grey‐scale (image processed type) digital magnetic maps (pixel maps) are in preparation; these will supersede the 1976 digital magnetic map of Australia, which was gridded on a 1.2 minute mesh (2000 m) mostly by digitizing contours on maps. The new map, produced from flight‐line data, will have a grid size of 0.25 minutes. Initially, a series of maps will be produced with each one covering a block of 4 degrees latitude by 6 degrees longitude, coinciding with standard 1 : 1 000 000 map sheets. An example included for the Adelaide 1 : 1 000 000 map sheet in Southern Australia shows a dramatic increase in the number of anomalies over those that were evident in earlier contour presentations.
In areas of extensive surficial cover regional geological maps are limited principally by the lack of outcrop, and it is useful to take advantage of airborne magnetics to see through cover.
The Bureau of Mineral Resources (BMR) has begun producing and releasing a series of standard 1 : 1 000 000 sheet pixel maps of gridded airborne magnetic data for various parts of Australia. The new series is based on a standard mesh size of 0.25 min. The first of these maps are being produced for those areas where digital data exists; other areas will follow as analogue data are converted to digital form.Maps produced on high resolution pixel plotters are superior to contour maps and are the only practical means of displaying gridded data over large areas. Over small areas, machine contouring may be viable because of the ease with which a hard copy with desired projection and scale can be produced.Grids of magnetic data are warped to accommodate projection, annotated, and displayed on a pixel plotting device, which can accommodate up to 4000 X 4000 pixels on a photographic negative in black and white or colour. The negative is then enlarged linearly by photographic means to produce a hard copy with the required scale.Examples are shown here of magnetic pixel maps of the Roper River 1 :1 000 000 sheet. They include total intensity in black and white, colour, and two gradient presentations. These maps reveal new information in the form of magnetic dykes, volcanic extrusions, and deep-seated, possibly granitic, bodies.
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