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Magnetic Anomaly Images of the Australian RegionNote: This metadata describes the dataset in accordance with the ANZLIC (Australia New Zealand Land Information Council) Core Metadata Guidelines Version 2. Dataset citationANZLIC unique identifier: ANZCW0703004421 Title: Magnetic Anomaly Images of the Australian Region CustodianCustodian: Geoscience Australia Jurisdiction: Australia DescriptionAbstract: These images are derived from the January 2002 edition of the "Magnetic Anomaly Grid of the Australian Region" (GEOMET Record : 4321). That grid 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. ANZLIC search words:
Spatial domain:
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
Data currencyBeginning date: 1963-01-01 Ending date: 2002-01-01 Dataset statusProgress: In Progress Maintenance and update frequency: Not Known Access
Access constraints: Licence required. Download these data for free from the National Geoscience Datasets downloads area : http://www.ga.gov.au/general/technotes/20011023_32.jsp Free Data DownloadData qualityLineage: Using an ER Mapper algorithm associated with the "Magnetic Anomaly Grid of the Australian Region" (GEOMET Record : 4321) a colour geo-referenced TIF with a cell size of 0.01 degrees was generated using the elevation palette and manipulated so as to appear to be illuminated from the north-east. A compression ratio of 27 was used, utilising ER Mapper's ECW compression algorithm, to compress the TIF image to an adequate size for provision over the Internet. The geo-referenced TIF was then reprojected to Lambert Conformal Conic projection, with a cell size of approximately 1000 metres using ArcInfo. Georeferenced TIF images and ECW compressed images were then generated for this projection in the same process outlined above. Positional accuracy: Nominal Scale 1:1,000,000 Pixel sizes :- For datasets in LAMBERT CONFORMAL CONIC PROJECTION - 1000 metres For datasets in GEOGRAPHIC PROJECTION - 0.01 degrees The accuracy of these images is derived from the "Magnetic Anomaly Grid of the Australian Region" (GEOMET Record : 4321). The positional accuracy of that grid is as follows :- 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 accuracy of these images is derived from the "Magnetic Anomaly Grid of the Australian Region" (GEOMET Record : 4321). The attribute accuracy of that grid is as follows :- 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 consistency of these images is derived from the "Magnetic Anomaly Grid of the Australian Region" (GEOMET Record : 4321). The logical consistency of that grid is as follows :- 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: The completeness of these images is derived from the "Magnetic Anomaly Grid of the Australian Region" (GEOMET Record : 4321). The completeness of that grid is as follows :- 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. Contact information
Metadata informationMetadata date: 2013-03-08 Additional metadataMetadata reference XHTML: http://www.ga.gov.au/meta/ANZCW0703004421.html Metadata reference XML: http://www.ga.gov.au/meta/ANZCW0703004421.xml It is recommended to refer to these images as: Hatch, L and Kilgour, B. 2002. (compilers) Australian bathymetry and topography images. [Digital Dataset]. Canberra: Geoscience Australia. Authors:Kilgour, B. Hatch, L. |
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