Total Magnetic Intensity (TMI) greyscale Image of Australia 2019 with Variable Reduction to Pole (VRTP)

Brief description

This image is a greyscale image of the Total Magnetic Intensity (TMI) Anomaly Image of Australia with Variable Reduction to Pole (VRTP).
Total magnetic intensity (TMI) data measures variations in the intensity of the Earth magnetic filed 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.
A variable reduction to Pole is aimed at locating magnetic anomalies exactly above their source bodies and without any distortion. The image is created from the 2019 variable reduction to Pole of the TMI grid with a grid cell size of ~3 seconds of arc (approximately 80 m). This image only includes airborne-derived TMI data for onshore and near-offshore continental areas.
The image provides a better interpretation of the magnetic data by giving an accurate location of magnetic source bodies.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: The variable reduction to Pole (VRTP) grid of Australia is processed from the 2019 TMI grid of the Australian region. The TMI grid is the sixth edition magnetic grid 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 new 2019 map compilation is comprised of a merge of 1059 survey grids. The addition of almost a decade’s worth of new high-quality surveys adds significantly to the 2010 and 2015 versions of the map.
The VRTP processing followed Cooper and Cowan's (2005) differential reduction to pole up to 5th order polynomial. Magnetic inclination and declination were derived from the IGRF-11 geomagnetic reference model (Finlay et al., 2010) using a data representative date of January 2005 and elevation 300 m.

References:
Cooper, G.R.J., Cowan, D.R., 2005. Differential reduction to the pole, Computers & Geosciences, Vol. 31, Issue 8, pp. 989-999
Finlay, C.C., Maus, S., Beggan, C.D., Bondar, T. N., Chambodut, A., Chernova, T.A., Chulliat, A., Golovkov, V.P., Hamilton, B., Hamoudi, M., Holme, R., Hulot, G., Kuang, W., Langlais, B., Lesur, V., Lowes, F.J. Lühr, H., Macmillan, S., Mandea, M., McLean, S., Manoj, C., Menvielle, M., Michaelis, I., Olsen, N., Rauberg, J., Rother,M., Sabaka, T.J., Tangborn, A., Tøffner-Clausen, L., Thébault, E., Thomson, A.W.P., Wardinski, I., Wei1, Z. and Zvereva, T.I., 2010. International Geomagnetic Reference Field: the eleventh generation, Geophysical Journal International, vol. 183, pp. 1216-1230.
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.