Data

Marine Gravity, Magnetic and Bathymetry Levelled Line Data in the Australian Region

Australian Ocean Data Network
Petkovic, P. ; Hackney, R. ; PoudjomDjomani, Y.
Viewed: [[ro.stat.viewed]] Cited: [[ro.stat.cited]] Accessed: [[ro.stat.accessed]]
ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rfr_id=info%3Asid%2FANDS&rft_id=https://pid.geoscience.gov.au/dataset/ga/74656&rft.title=Marine Gravity, Magnetic and Bathymetry Levelled Line Data in the Australian Region&rft.identifier=https://pid.geoscience.gov.au/dataset/ga/74656&rft.publisher=Commonwealth of Australia (Geoscience Australia)&rft.description=This compilation of gravity, magnetic and bathymetry ship-track line data, derived from the Geoscience Australia marine geophysical survey database 'Mardat', has been levelled in preparation for gridding. Data are included from Geoscience Australia geophysical surveys acquired since the 1970's as well as surveys from other institutions. The levelling process reduces mis ties between intersecting surveys of various vintages so that they can be integrated and represented as continuous surfaces. The compilation consists of time-indexed ASCII fixed format files organised by survey with a record spacing approximately 150m. Each survey file contains geographic coordinates and the potential field and bathymetry data, both unlevelled (source data as in Mardat) and levelled. The compilation does not include shot-indexed data as may be recorded on seismic reflection surveys. Note: The marine data was levelled by Desmond FitzGerald & Associates from 1998-2001, and Ron Hackney in 2009-2011. The final data were further reviewed by Yvette Poudjom Djomani prior to the release.Maintenance and Update Frequency: asNeededStatement: Lineage Data were sourced from Geoscience Australia (GA) unpublished database Mardat, which is a compilation of navigation files of geophysical marine surveys acquired by GA and other institutions from 1963 to 2011. Mardat files contain observations of bathymetry, and the Earth's gravity and magnetic fields as well as latitude and longitude of these observations. The observations from many surveys were integrated by a process of levelling in order to reduce the discrepancies at intersections of survey lines (which are due to use of different technologies over time, and observation errors). The data processing was done using Intrepid software by Intrepid Geophysics, Melbourne. Data Quality POSITIONAL ACCURACY The positional accuracy is variable according to the navigation systems used at the time each survey was acquired. For many surveys, particularly those obtained for this work from foreign institutions, the navigation system used is unknown. The surveys from the 1970's used dead reckoning tied to Transit satellite fixes several hours apart. Position at fixes has an accuracy of approximately 50m, while between fixes in deep water the error can be as high as 2000m. Positions are within approximately 50m for surveys which used radio navigation, such as long-range VLF. For surveys since the late 1990's using differential GPS or GPS without selective availability the positions are within approximately 20m. The geodetic datum for most surveys is WGS84, though the Transit system used APL72. The levelling process did not adjust horizontal positions of observations to minimise misties between surveys at line intersections, even though positioning errors will have contributed to mis-ties. Data Quality 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, or AAGD07 from 2008 onwards), but sometimes to reference stations in other countries that are in turn tied to the International Gravity Standardisation 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. The accuracy of bathymetry data is generally within 5% of the water depth. Data Quality LOGICAL CONSISTENCY Data are generally uniformly sampled (every 60 seconds of ship time, or approximately 150m) along individual lines, but some data gaps do exist. Data Quality COMPLETENESS The dataset includes all available processed bathymetry, gravity and magnetic data for all ship-tracks within the dataset coordinate limits (at the time of preparation, i.e. mid 2011). Excluded are bathymetry data acquired by swath or multibeam systems. Ship survey lines are variably distributed 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.&rft.creator=Petkovic, P. &rft.creator=Hackney, R. &rft.creator=PoudjomDjomani, Y. &rft.date=2018&rft.coverage=westlimit=102; southlimit=-52.00; eastlimit=172; northlimit=-8.00&rft.coverage=westlimit=102; southlimit=-52.00; eastlimit=172; northlimit=-8.00&rft_rights= https://creativecommons.org/licenses/by/4.0/&rft_rights=Creative Commons Attribution 4.0 International Licence&rft_rights=CC-BY&rft_rights=4.0&rft_rights=Any&rft_rights=Any&rft_rights=(c) Commonwealth of Australia (Geoscience Australia) 2024&rft_rights=Australian Government Security ClassificationSystem&rft_rights=https://www.protectivesecurity.gov.au/Pages/default.aspx&rft_rights=WWW:LINK-1.0-http--link&rft_rights=Creative Commons Attribution 4.0 International Licence http://creativecommons.org/licenses/by/4.0&rft_subject=geoscientificInformation&rft_subject=Data Package&rft_subject=gravity&rft_subject=magnetics&rft_subject=bathymetry&rft_subject=marine survey&rft_subject=data&rft_subject=marine&rft_subject=EARTH SCIENCES&rft_subject=Published_External&rft.type=dataset&rft.language=English Access the data

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4.0

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(c) Commonwealth of Australia (Geoscience Australia) 2024

Australian Government Security ClassificationSystem

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WWW:LINK-1.0-http--link

Access:

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Contact Information

clientservices@ga.gov.au

Brief description

This compilation of gravity, magnetic and bathymetry ship-track line data, derived from the Geoscience Australia marine geophysical survey database 'Mardat', has been levelled in preparation for gridding. Data are included from Geoscience Australia geophysical surveys acquired since the 1970's as well as surveys from other institutions. The levelling process reduces mis ties between intersecting surveys of various vintages so that they can be integrated and represented as continuous surfaces.

The compilation consists of time-indexed ASCII fixed format files organised by survey with a record spacing approximately 150m. Each survey file contains geographic coordinates and the potential field and bathymetry data, both unlevelled (source data as in Mardat) and levelled. The compilation does not include shot-indexed data as may be recorded on seismic reflection surveys.

Note: The marine data was levelled by Desmond FitzGerald & Associates from 1998-2001, and Ron Hackney in 2009-2011. The final data were further reviewed by Yvette Poudjom Djomani prior to the release.

Lineage

Maintenance and Update Frequency: asNeeded
Statement: Lineage
Data were sourced from Geoscience Australia (GA) unpublished database "Mardat", which is a compilation of navigation files of geophysical marine surveys acquired by GA and other institutions from 1963 to 2011. Mardat files contain observations of bathymetry, and the Earth's gravity and magnetic fields as well as latitude and longitude of these observations. The observations from many surveys were integrated by a process of "levelling" in order to reduce the discrepancies at intersections of survey lines (which are due to use of different technologies over time, and observation errors).

The data processing was done using "Intrepid" software by Intrepid Geophysics, Melbourne.

Data Quality POSITIONAL ACCURACY
The positional accuracy is variable according to the navigation systems used at the time each survey was acquired. For many surveys, particularly those obtained for this work from foreign institutions, the navigation system used is unknown. The surveys from the 1970's used dead reckoning tied to Transit satellite fixes several hours apart. Position at fixes has an accuracy of approximately 50m, while between fixes in deep water the error can be as high as 2000m. Positions are within approximately 50m for surveys which used radio navigation, such as long-range VLF. For surveys since the late 1990's using differential GPS or GPS without selective availability the positions are within approximately 20m. The geodetic datum for most surveys is WGS84, though the Transit system used APL72.

The levelling process did not adjust horizontal positions of observations to minimise misties between surveys at line intersections, even though positioning errors will have contributed to mis-ties.

Data Quality 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, or AAGD07 from 2008 onwards), but sometimes to reference stations in other countries that are in turn tied to the International Gravity Standardisation 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.

The accuracy of bathymetry data is generally within 5% of the water depth.

Data Quality LOGICAL CONSISTENCY
Data are generally uniformly sampled (every 60 seconds of ship time, or approximately 150m) along individual lines, but some data gaps do exist.

Data Quality COMPLETENESS
The dataset includes all available processed bathymetry, gravity and magnetic data for all ship-tracks within the dataset coordinate limits (at the time of preparation, i.e. mid 2011). Excluded are bathymetry data acquired by "swath" or multibeam systems. Ship survey lines are variably distributed 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.

Issued: 24 04 2024

This dataset is part of a larger collection

Click to explore relationships graph

172,-8 172,-52 102,-52 102,-8 172,-8

137,-30

text: westlimit=102; southlimit=-52.00; eastlimit=172; northlimit=-8.00

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Other Information
Download Levelled data (zip) [311.8 MB]

uri : https://d28rz98at9flks.cloudfront.net/74656/74656_00_0.zip

Download Grids (zip) [932.6 MB]

uri : https://d28rz98at9flks.cloudfront.net/74656/74656_01_0.zip

Download Reports (zip) [47.0 MB]

uri : https://d28rz98at9flks.cloudfront.net/74656/74656_02_0.zip

Download Metadata Statement (pdf) [269 KB] (Download Metadata statement (pdf) [269 KB])

uri : https://d28rz98at9flks.cloudfront.net/74656/74656_03_0.pdf

Identifiers