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Metadata : Northern Territory Statewide Geophysics - Magnetics |
Index:
Metadata Details:
Name:AS/NZS ISO 19115 Geographic Information - Metadata, ANZLIC Metadata Profile
Version:1.0
Date Metadata Extracted:2024-11-23
Date Metadata Last Updated:2023-09-14
Current URL (HTML format) : http://www.ntlis.nt.gov.au/metadata/export_data?type=html&metadata_id=FAD676B1836D327CE040CD9B2144232F
Current URL (XML format) : http://www.ntlis.nt.gov.au/metadata/export_data?type=xml&metadata_id=FAD676B1836D327CE040CD9B2144232F
Citation
ANZLIC Identifier:FAD676B1836D327CE040CD9B2144232F
Title: Northern Territory Statewide Geophysics - Magnetics
Citation Date:1950-12-31
Date Type:creation
Custodian:Department of Industry, Tourism and Trade
Description
On a background of pre-1980 GA-collected magnetic data, further airborne surveys by NTGS and exploration companies have been gridded, merged and imaged on the NT-wide scale. Grids and images are supplied on disk freely to the public, the images are served over the Internet through the Image Web Server and STRIKE, the NTGS' Internet GIS
- geoscientificInformation
Bounding Coordinates:
- North Bounding Coordinate:-11
- South Bounding Coordinate:-26
- East Bounding Coordinate:138
- West Bounding Coordinate:129
Dataset Status
Dataset ID:
Language:English
Character Set: Latin 1
Progress:completed
Maintenance and Update Frequency:annually
Data Currency Start Date:1950-01-01
Data Currency End Date:
Access Constraint:Copyright Northern Territory of Australia (Northern Territory Geological Survey)
With the exception of the Northern Territory of Australia logo, other government and corporate logos and where otherwise noted, all material in this publication is provided under a Creative Commons
Attribution 4.0 International licence (creativecommons.org/licenses/by/4.0/legalcode).
You are free to re-use the work under the licence, on the condition that you attribute the Northern Territory of Australia (Northern Territory Geological Survey) and comply with the other licence terms.
Disclaimer: While all care has been taken to ensure that information contained in this publication is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of its information. The Northern Territory of Australia gives no warranty or assurance, and makes no representation as to the accuracy of any information or advice contained in this publication, or that it is suitable for your intended use. You should not rely upon information in this publication for the purpose of making any serious business or investment decisions without obtaining independent and/or professional advice in relation to your particular situation. The Northern Territory of Australia disclaims any liability or responsibility or duty of care towards any person for loss or damage caused by any use of, or reliance on the information contained in this publication.
Data Quality
Lineage:The NT-wide geophysical grids and images are a compilation of NTGS, Geoscience Australia and industry geophysical surveys and are levelled to Geoscience Australia's Australia Wide geophysical grids and maps. See the Image Web Server for the metadata for the separate surveys.
Total Magnetic Intensity (TMI) coloured image is created with a sun filter from the northeast and equally assigned hues from the colour wheel from violet up to red.
Vertical derivative (1VD) image has an equally assigned greyscale, with no sunshade or reduction to pole.
TMI-1VD drape image assigns a spectrum pseudocolour to the TMI with 1VD replacing it in the intensity. The image is brightened by adding a translucent image of the shaded TMI.
Magnetic depths image has the Reduced to pole (RTP) vertical derivative (1VD) assigned to the red layer of an RGB image, with the green layer assigned to a reprocessed version of the same grid after a subsequent RTP at false inclination of 40 Deg and declination of 090. Red-green glasses are required to perceive structures at depth.
Magnetic Worms (aka: Strings) are a derived product and are described in the 'other comments' field below
Positional Accuracy:Reconnaissance data collected by BMR in the 60s and 70s appears to have been located on air photos, thus accurate to better than a kilometre, whereas the higher resolution (500 m) surveys of the 70s and 80s were located by radio beacons on the ground so are accurate to 100 m approx. Since 1996 GPS located the aircraft to accuracies of a few metres. See the separate surveys for details.
Processing can also produce location errors, such as a half-pixel error of 50 m shifted southeast by image processing software.
Attribute Accuracy:Cesium magnetometers are capable of precision to a few picotesla. Variations in the the earth's magnetic field during a survey can also produce errors of a fraction of a nanotesla, as the base station values subtracted do not fully measure the variation at the location of the aircraft. Levelling and decorrugation can shift longer wavelengths values by a few nanotesla.
Logical Consistency:Not applicable
Completeness:Dynamic datasets. Updated annually. New images may be added.
Contacts
Name Organisation Position Role Phone Fax Manager Geoscience Business Systems Department of Industry, Tourism and Trade Manager Geoscience Business Systems custodian (08) 8999 5448 (08) 8999 6824 geoscience.spatial@nt.gov.au
Data Dictionary
No data dictionary defined for this dataset
Supplementary Information
Search Words: Geophysics, magnetics, total magnetic intensity, vertical derivative, reduction-to-pole, magnetic depths.
Magnetic Worms (aka Strings):
The second horizontal derivative of the gravity or magnetic field reaches a maximum over the edge of an extensive body. Consequently this value can be
used to trace a "worm" automatically around an extensive magnetic or dense body.
The second horizontal derivative is sensitive to nearby objects, so some of the outlines are obtained by standing off further from the sample plane.
Upward continuation is obtained by smoothing in the Fourier domain.
NT's magnetic grid is composed of surveys of various flight line spacing, so some areas are particularly detailed and others particularly sparse.
The worms arising from sparse areas tend to smooth geological details.
When you use worms to delineate a body, it is important to check the implied boundary with other indications you have of the body of interest.
This record maintained using the NTLIS Metadata Tool