Brief description
Total magnetic intensity (TMI) data measures variations in the intensity of the Earth magnetic field caused by the contrasting content of rock-forming minerals in the Earth crust. Magnetic anomalies can be either positive (field stronger than normal) or negative (field weaker) depending on the susceptibility of the rock.The first vertical derivative (1VD) grid is derived from the 2019 Total magnetic Intensity (TMI) grid of Australia which has a grid cell size of ~3 seconds of arc (approximately 80 m). As the vertical derivative filter is essentially a high-pass filter, longer wavelengths are suppressed, and shorter wavelengths emphasized. The magnetic units of the data are in nT per metre.
Lineage
Maintenance and Update Frequency: notPlanned
Statement: The first vertical derivative (1VD) is derived from the 2019 Total Magnetic Intensity (TMI) grid of the Australian region. The TMI grid is the seventh edition with a cell size of ~3 seconds of arc (approximately 80 m). This grid only includes airborne-derived TMI data for onshore and near-offshore continental areas. Since the sixth edition was released in 2015, data from 234 new surveys have been added to the database, acquired mainly by the State and Territory Geological Surveys. It is estimated that 33 500 000 line-kilometres of survey data were acquired to produce the 2019 grid, about 2 000 000 line-kilometres more than for the previous edition.
The 2019 magnetic grid was derived from a complete re-levelling of the national magnetic grid database. The survey grids were levelled to each other, and to the Australia Wide Airborne Geophysical Survey (AWAGS) (Milligan et al., 2009), which serves as a baseline to constrain long wavelengths in the final grid. The levelling and grid-merging procedure was described in detail in Minty et al. (2003).
The first vertical derivartive (1VD) grid was produced in two steps. The TMI grid was first transformed to a Lambert Conic Conformal projection before applying a standard implementation of the vertical derivative process in the frequency domain, and then conversion back to a geodetic coordinate system. As the vertical derivative filter is essentially a high-pass filter, longer wavelengths are suppressed, and shorter wavelengths emphasized. The magnetic units of the data are in nT per metre.
References
Milligan, P.R., Minty, B.R.S., Richardson, M. and Franklin, R., 2009. The Australia-wide Airborne Geophysical Survey accurate continental magnetic coverage. Preview, No. 138, p. 1-128.
Minty, B.R.S., Milligan, P.R., Luyendyk, A.P.J. and Mackey, T., 2003. Merging airborne magnetic surveys into continental-scale compilations. Geophysics, 68 (3), 988-995.
The 2019 magnetic grid was derived from a complete re-levelling of the national magnetic grid database. The survey grids were levelled to each other, and to the Australia Wide Airborne Geophysical Survey (AWAGS) (Milligan et al., 2009), which serves as a baseline to constrain long wavelengths in the final grid. The levelling and grid-merging procedure was described in detail in Minty et al. (2003).
The first vertical derivartive (1VD) grid was produced in two steps. The TMI grid was first transformed to a Lambert Conic Conformal projection before applying a standard implementation of the vertical derivative process in the frequency domain, and then conversion back to a geodetic coordinate system. As the vertical derivative filter is essentially a high-pass filter, longer wavelengths are suppressed, and shorter wavelengths emphasized. The magnetic units of the data are in nT per metre.
References
Milligan, P.R., Minty, B.R.S., Richardson, M. and Franklin, R., 2009. The Australia-wide Airborne Geophysical Survey accurate continental magnetic coverage. Preview, No. 138, p. 1-128.
Minty, B.R.S., Milligan, P.R., Luyendyk, A.P.J. and Mackey, T., 2003. Merging airborne magnetic surveys into continental-scale compilations. Geophysics, 68 (3), 988-995.
Issued: 04 11 2019
Modified: 20 11 2019
text: westlimit=112.502532; southlimit=-43.928981; eastlimit=154.662516; northlimit=-9.025662; projection=GDA94 (EPSG:4283)
Subjects
Australia |
Earth Sciences |
Earth sciences |
GADDS2.0 |
Geophysics |
Magnetism and Palaeomagnetism |
NCI |
Published_External |
Vertical Derivative |
airborne digital data |
first vertical derivative |
geophysics |
geoscientificInformation |
grid |
magnetics |
national geophysical compilation |
raster |
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Other Information
Download the data (ers) [4.7 GB]
uri :
https://d28rz98at9flks.cloudfront.net/132275/132275.zip
Identifiers
- global : 77fccb44-c2d2-468b-bfb9-fd21b6030661
- URI : http://pid.geoscience.gov.au/dataset/ga/132275
- DOI : 10.26186/5dd48b1368ece
