Magnetic Anomaly Grid of the Australian Region

Note: This metadata describes the dataset in accordance with the ANZLIC (Australia New Zealand Land Information Council) Core Metadata Guidelines Version 2.

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Dataset citation

ANZLIC unique identifier: ANZCW0703004321

Title: Magnetic Anomaly Grid of the Australian Region

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Custodian

Custodian: Geoscience Australia

Jurisdiction: Australia

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These data represent the January 2002 edition of the Magnetic Anomaly Grid of the Australian Region. This version is the first integrated onshore/offshore magnetic anomaly grid for the complete Australian margin extending across 8S - 52S, 106E - 172E. The grid cell size is 0.01 degree (approx. 1 km). Earlier releases were restricted to portions of NW and SW Australia.

Magnetic anomaly unit is nanoTesla (nT). Appropriate IGRFs have been removed. Horizontal datum is GDA94 (which is equivalent to WGS84).

The marine data were levelled independently of the onshore data in three sectors (see below). The NNW and SSW sectors were released as grids previously. The eastern sector was levelled in 2000 in collaboration with Intrepid Geophysics (Melbourne, Australia). The three levelled sectors, together with the unlevelled sectors were combined with the onshore grid to give the present grid. Altogether, 3,022,656 data points are in the database from which the marine grid was created.

Unlevelled sectors: (-8 -25 160 172), (-39 -52 156 172), (-46 -52 106 140)

Levelled sectors: (-37 -52 140 156), (-25 -39 143 172), (-8 -25 143 160), (-24 -46 106 140), (-8 -24 106 143)

There are several places at the join between onshore and offshore grids where the two grids do not match. The problem exists because the onshore grid was developed earlier, and there was poor control on the grid merging process at the margins. Future work will attempt to address this issue and improve the continuity between the onshore and offshore grids.

ANZLIC search words:

GEOSCIENCES Geophysics Mapping

Spatial domain:

locality map

Geographic extent name: AUSTRALIA EXCLUDING EXTERNAL TERRITORIES - AUS - Australia - Australia

Geographic extent polygon: 106 -8, 172 -8, 172 -52, 106 -52, 106 -8,

Note: The format for each Geographic extent name is: Name - Identifier - Category - Jurisdiction (as appropriate) See GEN Register

Geographic bounding box:: North bounding latitude: -8 °; South bounding latitude: -52 °; East bounding longitude: 172 °; West bounding longitude: 106 °

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Data currency

Beginning date: 1963-01-01

Ending date: 2002-01-01

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Dataset status

Progress: In Progress

Maintenance and update frequency: Not Known

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Access

Stored data format:: DIGITAL - bil Band interleaved by line (BIL) image WGS84; DIGITAL - ers ER Mapper raster dataset ER Mapper WGS84

Available format type:: DIGITAL - bil Band interleaved by line (BIL) image WGS84; DIGITAL - ers ER Mapper raster dataset ER Mapper WGS84; DIGITAL - bil Band interleaved by line (BIL) image Geographic WGS84; DIGITAL - ArcGIS-coverage ArcInfo coverage Geographic WGS84

Access constraints:

You can purchase these data in a 2 CD set from the Sales Centre. The reference is:

Petkovic, P. and Buchanan, C. 2002. Australian bathymetry and topography grid. [CDROM]. Canberra: Geoscience Australia.

or download a selection for free from the National Geoscience Datasets downloads area : http://www.ga.gov.au/general/technotes/20011023_32.jsp

Free Data Download

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Data quality

Lineage:

The magnetic anomaly grid is a combination of the Magnetic Anomaly Map of Australia (3rd edition, derived from aeromagnetic data) and levelled ship-track data.

The onshore grid has been released separately and is available digitally in a higher resolution format with a cell size of 15 seconds of arc (approx. 400 m)(see GEOMET record 4381), and also in 1:5,000,000 and 1:25,000,000 scale hardcopy form as enhanced images. Geoscience Australia gratefully acknowledges the contribution of aeromagnetic data and assistance by the following organisations:Northern Territory Geological Survey; Department of Primary Industries and Resources South Australia; Department of Infrastructure, Energy and Resources Tasmania; New South Wales Department of Mineral Resources; Department of Natural Resources and Environment Victoria; Geological Survey of Queensland; Geological Survey of Western Australia

The offshore portion of the grid is derived from data in Geoscience Australia database GA-Mardat which has over 900 surveys acquired since 1963 by GA and foreign institutions.GA gratefully acknowledges the contribution of marine data and assistance by the following organisations: Bundesanstalt fur Geowissenschaften und Rohstoffe; Dept. Science, Industry and Resources (NZ); Geoscience Australia; Institut Francais de Recherche pour l'Exploitation de la Mer; Institut Francais pour la Recherche et la Technologie Polaires; Lamont Doherty Geophysical Observatory; Mobil Corporation; Division of National Mapping (Australia); National Geophysical Data Centre (USA); National Oceanic and Atmospheric Administration; Institut de Recherche pour le Developpement; Scripps Institution of Oceanography, U California; School of Ocean and Earth Science and Technology; South Pacific Applied Geoscience Commission; Texas A and M University; Institute of Oceanographic Sciences, UK; United States Geological Survey; US Navy; Woods Hole Oceanographic Institute

Positional accuracy:

The grid incorporates data from surveys acquired since 1963. Modern surveys which used GPS have a positional accuracy of 5 - 30 m depending on several factors, while earlier surveys which used dead reckoning and Transit satellite fixes had positions accurate to 50 - 2000 m depending upon the water depth and strength of currents. These surveys overlap in an irregular distribution. The grid cell size is 0.01 deg (close to 1 km), and it is estimated that 90% of cells give values within 1 cell of their measured position.

Attribute accuracy:

The ship-track data have been levelled to reduce crossover errors, but this process has introduced a shift in the measured values. The mean absolute difference between levelled and unlevelled values is about 9 nT (nano-Tesla) in the NW sector, 13 nT in the SW sector and 50 nT in the eastern sector. The overall mean absolute difference for all levelled data is 30 nT.

Logical Consistency:

The marine magnetic anomaly grid models data from surveys acquired since 1963, and as a consequence there are a variety of systems and methods used in the collection and processing of data. These surveys overlap in an irregular distribution of lines, and the values recorded in the principal facts databases are not necessarily unique at intersection points. The ship-track data were therefore put through a levelling process where the observed values were adjusted to minimise crossover errors. The horizontal position of points was not adjusted. The levelling has reduced but not eliminated the cross-over errors and artefacts due to these errors are still evident in the grid.

Other artefacts occur in sparse data areas where ship-track 'trails' occur due to the high along-line resolution and the grid cell size being too small. The gridding algorithm attempts to deal with this using a multi-pass method which uses a coarse cell size on the first pass.

All areas in the vicinity of line intersections and along solitary tracks should be interpreted with caution. The grid is accompanied by data distribution information, which should be used in conjunction with the magnetic anomaly grid, especially when assessing the reliability of small-scale features.

Completeness:

All of the data were acquired during the last century. The GA magnetic anomaly database and derived grids will be updated as new surveys are completed, older surveys are obtained from archival sources, or improved methods are devised for merging datasets of disparate vintages. Refer to the data distribution grid included with this product for an assessment of completeness of coverage.

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