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Levelled gravity and magnetic data covering the Capel and Faust basins, offshore eastern Australia

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


Dataset citation

ANZLIC unique identifier: ANZCW0703014435

Title: Levelled gravity and magnetic data covering the Capel and Faust basins, offshore eastern Australia


Custodian

Custodian: Geoscience Australia

Jurisdiction: Australia


Description

Abstract:

This dataset contains levelled ship-track potential-field (gravity and magnetic) data covering the Capel and Faust basins offshore eastern Australia. The dataset combines ship-track data from various surveys obtained between 1967 and 1998 with data collected in 2006 and 2007 during Geoscience Australia surveys GA-302 and GA-2436. Line levelling is a key step in processing ship-borne gravity and magnetic data. This process minimises mis-tie errors at ship-track cross-overs. Without accounting for these cross-over errors, gridded data can be rendered un-interpretable by artefacts and distortions at line cross-overs.

Full details can be found in:

Hackney, R., 2010. Potential-field Data Covering the Capel and Faust Basins, Australia's Remote Offshore Eastern Frontier. Geoscience Australia Record 2010/34, 40pp.

ANZLIC search words:

  • GEOSCIENCES Geophysics Exploration
  • GEOSCIENCES Geophysics Surveys
  • MARINE Geology and Geophysics Exploration
  • MARINE Geology and Geophysics Surveys

Spatial domain:

locality map

Geographic extent name: PACIFIC OCEAN - SW - PACIFIC OCEAN - SW - Ocean and Sea Regions - Australia

Geographic extent name: TASMAN SEA - TASMAN SEA - Ocean and Sea Regions - Australia

Geographic extent polygon: 157 -24, 165 -24, 165 -31, 157 -31, 157 -24,

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

Geographic bounding box:
North bounding latitude: -24 °
South bounding latitude: -31 °
East bounding longitude: 165 °
West bounding longitude: 157 °

Data currency

Beginning date: 1967-04-01

Ending date: 2007-11-01


Dataset status

Progress: Complete

Maintenance and update frequency: Not Known


Access

Stored data format:
DIGITAL - VPF Vector Product Format Geographic WGS84
DIGITAL - XYZ Ascii Point file Geographic WGS84
Available format type:
DIGITAL - XYZ Ascii Point file Geographic WGS84
DIGITAL - VPF Vector Product Format Geographic WGS84

Access constraints:

No restrictions

Free Data Download

Data quality

Lineage:

The source data used to generate a levelled dataset for the Capel and Faust basins includes:

1) a dataset of gravity and magnetic data for the Australian region sourced internally from Geoscience Australia holdings of ship-track data and levelled by Desmond Fitzgerald and Associates Pty Ltd (now Intrepid Geophysics) in the late 1990s under contract to the Australian Geological Survey Organisation (now Geoscience Australia);

2) gravity and magnetic data from Geoscience Australia seismic survey GA-302 (2006/2007); and

3) gravity and magnetic data from Geoscience Australia marine survey GA-2436 (2007).

The data for the GA-302 and GA-2436 surveys were provided to Geoscience Australia in mid-2008 by Fugro Robertson LCT Gravity and Magnetics Division (Job Numbers 4640 and 4731), the contractor used by Geoscience Australia to process gravity and magnetic data from these surveys.

The processing steps applied to this dataset include: 1) re-computation of free-air gravity anomalies to ensure consistent computation of gravity anomalies between the different datasets; 2) splitting ship-tracks into relatively straight line segments to avoid multiple cross-overs between any pair of lines; 3) line filtering of the previously-levelled Australia-wide dataset to reduce noise and improve cross-over computations; 4) merge the individual datasets into a single master dataset for levelling; 5) editing to remove lines or line segments with spurious data - lines that were too short or too close to other line segments were also removed in order to improve levelling results; 6) line levelling - gravity data were levelled using a polynomial levelling technique referenced to a satellite radar altimetry-derived dataset, magnetic data were loop levelled (minmising misclosures around closed loops formed by ship tracks); 7) computation of simple Bouguer gravity anomalies (ie. without terrain corrections) using a spherical-cap Bouguer correction and a density contrast between water and sediment of 970 kilograms per cubic metre and water depths interpolated at each data point from the 2009 Bathymetry and Topography Grid of Australia.

The data processing and levelling were conducted using the INTREPID software from Intrepid Geophysics (versions 4.2.756 and 4.2.1782). The resulting gravity and magnetic data for the Capel and Faust basins are contained in INTREPID vector databases and are also available in an ascii column-based file exported from INTREPID.

Positional accuracy:

Positional accuracy is variable and in some cases unknown.

Most older marine surveys (prior to the early 1990s) were positioned using dead reckoning tied to Transit satellite fixes. The satellite fixes are accurate to around 50m horizontally, but in deep water areas, positional errors could be as much as 1 to 2 km. Most surveys since the early 1990s used GPS navigation, either stand-alone GPS (subject to degradation by selective availability prior to 1 May 2000) or differential GPS using references receivers onshore.

The geodetic datum for all data is assumed to be WGS84. Some of the oldest surveys in the dataset are tied to the APL72 datum or have no information on coordinate datum. Newer surveys utilising GPS are tied to WGS84.

Attribute accuracy:

The accuracy of gravity anomaly data is estimated to be about 20 to 50 micrometers per second squared (i.e. 2 to 5 mGal). Gravity data are generally tied to reference stations of the Australian Fundamental Gravity Network (ISOGAL84 gravity datum), but sometimes to reference stations in other countries that are in turn tied to the International Gravity Stnadardisation Network of 1971.

The accuracy of magnetic anomaly data is estimated to be of the order of 5 nano Tesla (nT). Anomaly computation is achieved through subtraction of appropriate International Geomagnetic Reference Field values, though the generation of the IGRF used for individual surveys is not preserved in this dataset.

Logical Consistency:

The dataset of ship-track gravity and magnetic anomalies is separated into 379 uniquely identifiable lines from 25 different marine surveys. Data are generally uniformly sampled (every 10 seconds for older surveys and every 1 second for newer surveys) along individual lines, but some data gaps do exist.

Completeness:

The dataset includes all available gravity and magnetic data for all ship-tracks within the dataset coordinate limits (at the time of preparation, i.e. late 2009). Ship-tracks are variably spaced and do not provide complete coverage of the area. Not all ship-tracks contain both gravity and magnetic data at every coordinate location, but separate coordinate sets for data points associated with either gravity or magnetic data alone are included in the dataset.


Contact information

Contact organisation: Commonwealth of Australia (Geoscience Australia) (GA)
Contact position: Manager Client Services
Mail address: Cnr Jerrabomberra Ave and Hindmarsh Dr
Mail address: GPO Box 378
Locality: Canberra
State: ACT
Country: Australia
Postcode: 2601
Telephone: 02 6249 9966
Facsimile: 02 6249 9960
Electronic mail address: sales@ga.gov.au

Metadata information

Metadata date: 2013-03-08


Additional metadata

Metadata reference XHTML: http://www.ga.gov.au/meta/ANZCW0703014435.html

Metadata reference XML: http://www.ga.gov.au/meta/ANZCW0703014435.xml

.

Authors:Hackney, R.
SPATIAL INFORMATION FOR THE NATION