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Gravity Anomaly Image of the Australian Region - 2008Note: 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: ANZCW0703012115 Title: Gravity Anomaly Image of the Australian Region - 2008 CustodianCustodian: Geoscience Australia Jurisdiction: Australia DescriptionAbstract: These images are derived from the "Gravity Anomaly Grid of the Australian Region" (GEOMET record:12115 ). The grid combines accurate onshore gravity measurements with satellite data used in offshore areas. The cell values represent simple Bouguer anomalies at a density of 2.67 tonnes per cubic metre onshore and free-air anomalies offshore. The grid cell size is 0.5 minutes of arc, which is equivalent to about 800 metres. ANZLIC search words:
Spatial domain:
Geographic extent name: AUSTRALIA EXCLUDING EXTERNAL TERRITORIES - AUS - Australia - Australia Geographic extent polygon: 100 -8, 170 -8, 170 -52, 100 -52, 100 -8, Note: The format for each Geographic extent name is: Name - Identifier - Category - Jurisdiction (as appropriate) See GEN Register
Data currencyBeginning date: 1950-01-01 Ending date: 2008-05-01 Dataset statusProgress: Complete Maintenance and update frequency: Not Known Access
Access constraints: Please Note: These grids and images may be used internally in Geoscience Australia for research/interpretation purposes, but should not be distributed outside the Organisation. External clients can access the grid using the GADDS online facility. Free Data DownloadData qualityLineage: The gravity grid was derived from the complete onshore database as at May 2008 and marine gravity derived from satellite altimetry. A two-pass process was used to generate the grid from a composite file containing 1.4 Million land observations, 10.5 Million satellite values. For the satellite values refer to Sandwell, D.T. and W.H.F.Smith, Marine Gravity Anomaly from Geosat and ERS-1 Altimetry, J. Geophys. Research, 1997. The 0.5 minute grid is the finest mesh that is currently meaningful over the whole continent given that much of the data coverage is spaced at 4 or 11 km. The parameters of the grid are: Grid spacing: 0.5 minute = 0.0083333 degree (approx. 800 m) Projection: Rectangular in latitude and longitude Grid size: 8401 points longitude x 5276 points latitude Grid origin: 7 degrees 58.55 min south, 99 deg 57.35 min east (1,1) Scaling: Nil. Values are in decimal units (µms-² (micro metres per second squared)) Null value: -99999.0 Data accuracy: 5 units, maximum error 100 units onshore Data precision: 1 unit Gravity Datum: The gravity data as supplied are based on the AAGD07 datum. The gravity unit used is micrometres per second squared which is equivalent to 0.1 milligals. A filtered image was also created using a high-pass filter with a cutoff wavelength of 500 km. Images have a sunangle with illumination from the north east. Positional accuracy: Pixel size : 0.0083333 degrees (approx 800m) Highly variable depending on the age of the individual surveys that comprise this data set. Prior to 1995 (approximately), data were collected using various techniques such as manually scaling from base maps (100's m error), digitising from base maps derived from air photo station plots (100's m error), and using optical surveying methods (metre accuracy). More recent surveys were acquired using differential GPS with sub metre accuracy. Vertical accuracy is highly variable too, depending on the age of the survey. Prior to the use of differential GPS station heights were determined by picking off from a topographic map (10's metre error), using barometric techniques (metre errors) and optical surveying techniques (sub metre accuracy). Differential GPS gives centimetre accuracy. Attribute accuracy: Highly variable depending on the age of the individual surveys that comprise this dataset. Modern surveys using LaCoste and Romberg or Scintrex gravity meters have an accuracy of 0.01 micro metres per second squared. Earlier surveys using older style quartz spring meters have a lower accuracy ~ 1.0 micro metres per second squared. Logical Consistency: A geoscientist visually inspected the finished dataset to make sure the data were accurate and consistent with current scientific information. Completeness: Complete for the coverage of continental Australia and Australia's continental margins. Contact information
Metadata informationMetadata date: 2013-03-08 Additional metadataMetadata reference XHTML: http://www.ga.gov.au/meta/ANZCW0703012115.html Metadata reference XML: http://www.ga.gov.au/meta/ANZCW0703012115.xml . Authors:Bacchin, M. |
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