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Enhanced gravity and magnetic grids for Northern Australia

<p>Geoscience Australia (GA) generated a series of gravity and magnetic grids and enhancements covering Northern Australia. Several derivative gravity datasets have been generated 1) for the North-West Shield Western Australia region (approximately between latitudes 7‒26⁰ S and longitudes 110‒130⁰ E), 2) for the Northern Territory (approximately between latitudes 7‒26⁰ S and longitudes 125.5‒141⁰ E) and for Queensland (approximately between latitudes 7‒30⁰ S and longitudes 135‒160⁰ E). The magnetic dataset has been generated only for the North-West Shield Western Australia region (approximately between latitudes 7‒26⁰ S and longitudes 110‒130⁰ E). The magnetic and gravity data were downloaded from the Geophysical Archive Data Delivery System (GADDS), website ( http://www.geoscience.gov.au/cgi-bin/mapserv?map=/nas/web/ops/prod/apps/mapserver/gadds/wms_map/gadds.map&mode=browse). Satellite Free-air (FA) gravity v27.1 (released March 11, 2019) and Satellite Topography v19.1 (released January 14, 2019) data were sourced from Sandwell et al. (2014) and downloaded from the Scripps Institution of Oceanography (SIO), National Oceanic and Atmospheric Administration (NOAA), U.S. Navy and National Geospatial-Intelligence Agency (NGA) (SIO Satellite Geodesy, website, http://topex.ucsd.edu/WWW_html/mar_grav.html). The Satellite Bouguer gravity grid with onshore correction density of 2.67 gcm-3 and offshore correction density of 2.20 gcm-3 was derived from the Free-air gravity v27.1 and Topography data V19.1. This Bouguer gravity grid was used for filling areas of data gaps in the offshore region.


<p>Data evaluation and processing of gravity and magnetic data available in the area of interest resulted in the production of stitched onshore-offshore Bouguer gravity grid derived from offshore satellite Bouguer gravity grid and GA’s onshore ground and airborne gravity survey data and a stitched Total Magnetic Intensity (TMI) grid derived from airborne and shipborne surveys (Tables 1 and 5). A Reduction to the Pole (RTP) grid was derived from the stitched TMI grid. The TMI, RTP, FA and terrain corrected Bouguer gravity anomalies are standard datasets for geological analysis. The free-air gravity anomaly provides the raw and basic gravity information. Images of free-air gravity are useful for first-pass interpretation and the data is used for gravity modelling. Magnetic anomalies provide information on numerous magnetic sources, including deep sources as arising from the structure and composition of magnetic basement and shallow sources such as intra-sedimentary magnetic units (e.g. volcanics, intrusions, and magnetic sedimentary layers). A standard TMI image will contain information from all these sources. Geosoft Oasis montaj software was used throughout the data processing and enhancement procedure and the montaj GridKnit module was used to generate the stitched gravity and magnetic grids.


<p>Enhancement techniques have been applied to the final processed Bouguer gravity and RTP magnetic grids to highlight subtle features from various sources and to separate anomalies from different source depths. These enhancement techniques are described in the next section.


<p>Enhancement processing techniques and results

<p>A summary of image processing techniques used to achieve various outcomes is described in Table 1.

<p>Data type Filter applied Enhancement/outcome

<p>Gravity/Magnetic First vertical derivative (1VD) Near surface features (e.g. intrabasinal)

<p>Gravity/Magnetic Upward continuation Noise reduction in data

<p>Gravity/Magnetic Low pass filter, or large distance upward continuation Enhancement of deep features (e.g. basement)

<p>Gravity/Magnetic High pass filter Enhancement of shallow features (e.g. surface anomalies)

<p>Gravity/Magnetic Tilt filter and 1VD Enhancement of structure (e.g. in basement)

<p>Gravity/Magnetic ZS-Edgezone and ZS-Edge filters Enhancement of edges

<p>Gravity/Magnetic horizontal modulus / horizontal gradient Enhancement of boundaries

<p>Magnetic RTP (reduction to the pole), Compound Anomaly, and Analytic Signal filter Accurate location of sources

Simple

Identification info

Date (Creation)
2019-08-14T10:00:00
Date (Publication)
2019-09-02T00:45:00
Citation identifier
Geoscience Australia Persistent Identifier/https://pid.geoscience.gov.au/dataset/ga/130720

Citation identifier
Digital Object Identifier/http://dx.doi.org/10.26186/5d6c66a1a075e

Cited responsible party
Role Organisation / Individual Name Details
Author

Shi, Z.

Author

Rollet, N.

Purpose

Digital grids for public use

Status
Completed
Point of contact
Role Organisation / Individual Name Details
Point of contact

Commonwealth of Australia (Geoscience Australia)

Voice
Point of contact

Rollet, N.

Resource provider

Resources Division

Spatial representation type

Spatial resolution

Level of detail

1000 m

Topic category
  • Geoscientific information

Extent

Temporal extent

Time period
2019-08-30

Extent

N
S
E
W


Maintenance and update frequency
As needed

Resource format

Title

Product data repository: Various Formats

Website

Data Store directory containing the digital product files

Data Store directory containing one or more files, possibly in a variety of formats, accessible to Geoscience Australia staff only for internal purposes

theme.ANZRC Fields of Research.rdf
  • GEOPHYSICS

  • EARTH SCIENCES

Keywords
  • Northern Australia

Keywords
  • Western Australia

Keywords
  • Northern Territory

Keywords
  • Queensland

Keywords
  • Gravity anomalies

Keywords
  • Magnetic anomalies

Keywords
  • Enhancement processing

Keywords
  • Enhancement images

Keywords
  • Published_External

Resource constraints

Title

Creative Commons Attribution 4.0 International Licence

Alternate title

CC-BY

Edition

4.0

Website

http://creativecommons.org/licenses/

Access constraints
License
Use constraints
License

Resource constraints

Title

Australian Government Security ClassificationSystem

Edition date
2018-11-01T00:00:00
Website

https://www.protectivesecurity.gov.au/Pages/default.aspx

Classification
Unclassified
Language
English
Character encoding
UTF8

Distribution Information

Distributor contact
Role Organisation / Individual Name Details
Distributor

Commonwealth of Australia (Geoscience Australia)

Voice
OnLine resource

Download the Gravity data package

Download the Gravity data package

Distribution format
  • various

OnLine resource

Download the Magnetic data package

Download the Magnetic data package

Distribution format
  • various

OnLine resource

Download the Metadata document

Download the Metadata document

Distribution format
  • docx

Resource lineage

Statement

Data were compiled for a series of grids and enhancements covering Northern Australia, extending roughly from -24° to -7° Latitude and 110° to 130° Longitude. The data were downloaded from the Geophysical Archive Data Delivery System (GADDS) and Sandwell and Smith (2014). The stitched Bouguer gravity grid (unit in mGal) has a cell size of 1 km (Figure 1). The stitched TMI grid has a grid cell size of 200 m (Figure 2). The TMI grid was reduced to the pole (RTP) and enhancement processing have been applied to the RTP grid (Figure 2). All colour shaded relief images of gridded magnetic and gravity data have been produced with a NE sun shade


The description of the input datasets used to construct the stitched grids covering the North-West Shield Western Australia region are as follows:


a) Input gravity datasets (downloaded from GADDS) for the stitched Bouguer gravity grid (Table 2):

1. Australia Onshore Complete Bouguer Anomaly July 2016;

2. Satellite Free-Air Gravity v27.1;

3. NE Canning Airborne Gravity Survey, Western Australia (WA), 2017

4. Tanami-King Leopold Airborne Gravity Survey, Western Australia (WA), 2017


The resolution of the gravity dataset varies from 500m (0.005 degrees) to 2000 m (0.01667 degrees) in grid cell size. In areas covered by datasets from different sources, only the best quality dataset has been selected to produce the stitched gravity grid.


b) Input magnetic datasets (downloaded from GADDS) for the stitched Total Magnetic Intensity (TMI) anomaly grid (Table 3):

1. Sixth Edition Total Magnetic Intensity (TMI) Anomaly Grid of Australia, GA; (magmap_v6_2015.ers, 2015)

2. Geological Survey of Western Australia (GSWA) WA marine TMI grid 2005 (WA_marine_TMIG.ers, 2005)

3. Fourth Edition Total Magnetic Intensity (TMI) Anomaly Grid of Australia, Offshore, GA; (Magmap04_off.ers, 2004)


Links to grids metadata are:

• Geophysical Archive Data Delivery System (GADDS) website – http://www.geoscience.gov.au/cgi-bin/mapserv?map=/nas/web/ops/prod/apps/mapserver/gadds/wms_map/gadds.map&mode=browse

• SIO Satellite Geodesy website ─ http://topex.ucsd.edu/WWW_html/mar_grav.html.

Reference System Information

Reference system identifier
EPSG/GDA94 (EPSG:4283)

Metadata constraints

Title

Australian Government Security Classification System

Edition date
2018-11-01T00:00:00
Website

https://www.protectivesecurity.gov.au/Pages/default.aspx

Classification
Unclassified

Metadata

Metadata identifier
urn:uuid/0e40695c-95b9-4275-a0da-5994cb5bbc5a

Title

GeoNetwork UUID

Contact
Role Organisation / Individual Name Details
Point of contact

Commonwealth of Australia (Geoscience Australia)

Voice
Point of contact

Rollet, N.

Type of resource

Resource scope
Dataset
Name

Gravity and magnetic enhancement grids for Northern Australia

Alternative metadata reference

Title

Geoscience Australia - short identifier for metadata record with

uuid

Citation identifier
eCatId/130720

Metadata linkage

https://ecat.ga.gov.au/geonetwork/srv/eng/catalog.search#/metadata/0e40695c-95b9-4275-a0da-5994cb5bbc5a

Date info (Creation)
2019-08-15T00:31:32
Date info (Revision)
2019-08-15T00:31:32

Metadata standard

Title

AU/NZS ISO 19115-1:2014

Metadata standard

Title

ISO 19115-1:2014

Metadata standard

Title

ISO 19115-3

Title

Geoscience Australia Community Metadata Profile of ISO 19115-1:2014

Edition

Version 2.0, September 2018

Citation identifier
https://pid.geoscience.gov.au/dataset/ga/130720

 
 

Spatial extent

N
S
E
W


Keywords

Enhancement images Enhancement processing Gravity anomalies Magnetic anomalies Northern Australia Northern Territory Queensland Western Australia
theme.ANZRC Fields of Research.rdf
EARTH SCIENCES GEOPHYSICS

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