AusMT / surveys / AWAGS 1989-90

AWAGS 1989-90 GDS

Geomagnetic depth sounding survey · Australia-wide · Flinders University

Part of the Australia legacy GDS collection

The Australia-Wide Array of Geomagnetic Stations was the first array experiment to cover an entire continent.

About this survey

The Australia-Wide Array of Geomagnetic Stations was the first array experiment to cover an entire continent. Led by Francois Chamalaun of Flinders University with Charlie Barton of the Bureau of Mineral Resources, soon to become the Australian Geological Survey Organisation, and run jointly by the two, it put fifty-four portable three-component fluxgate magnetometers across mainland Australia and added the four permanent observatories at Canberra, Charters Towers, Gnangara and Learmonth, an average spacing of 275 km over 26 degrees of latitude and 39 of longitude. Two decades of regional arrays had found the Flinders, Southwest Queensland, Canning Basin, Eyre Peninsula, Tamar and Otway anomalies one at a time. AWAGS was built to measure the inductive response of the whole continent at once. AWAGS was also meant to serve aeromagnetic surveying: high-resolution surveys needed to know how uniform the fluctuating field is across the continent, and the six permanent observatories then operating were too sparse to say.

The portable instruments were the three-component digital fluxgate magnetometers developed at Flinders by Francois Chamalaun and Bob Walker. Each was a sealed unit with three orthogonal fluxgate sensors and a microprocessor, resolving one nanotesla, built to the design they published in 1982 with the tape recorder replaced by a two-megabyte memory unit, and calibrated at Flinders before it went out. Buried a metre down with their sensors levelled and their azimuth found afterwards from quiet nights, they recorded once a minute into memory, and all of them started together at 01:19 UT on 18 November 1989. Deployment, servicing and recovery ran on four-wheel-drive vehicles and a chartered light aircraft across the north. Most stations ran for about eight months in two runs, and a north-south line of seven through the centre of the continent for twelve, the last data being recorded on 17 December 1990. Chamalaun and Barton's analysis of a twenty-day stretch found the induction dominated by a coast effect around the western, southern and eastern coasts, detectable up to 500 km inland from the 200 m isobath. The east and west coasts behaved so alike that the east-west difference in the coast effect proposed by J. E. Everett and R. D. Hyndman in 1967 was not evident. Albany showed a particularly large effect, and the northern margin a smaller and more complicated response. Contouring the transfer functions revealed a conductive zone sweeping through the sedimentary basins that separate the cratonic blocks and linking several of the conductors mapped before, which they named the Intercratonic Conductive Zone. They also identified a new Gulf of Carpentaria Anomaly as the northward extension of the Southwest Queensland conductor, which the 1995 Queensland arrays then confirmed. The data has since gone into thin-sheet and three-dimensional conductivity models of the continent, into studies of the daily variation, and into the aeromagnetic work the array was partly built to support.

The one-minute series were compensated for clock error and cleared of spikes, steps and drift, then levelled to a common reference. In 2026 they were reprocessed for AusMT with a robust remote-reference workflow to give a consistent set of vertical-field transfer functions at every station from 180 to about 28,800 s. No response of any kind had been published for four of the sites before. At the longest periods the source field is not a plane wave, so the transfer-function directions there should be read with caution.

The served values are vertical-field transfer functions for all 58 stations, computed in 2026 with a robust remote-reference workflow from the corrected one-minute X, Y and Z series the array recorded between 18 November 1989 and 17 December 1990. Those series were compensated for clock error, cleared of spikes and steps, corrected for instrument drift and levelled to a common reference by W. D. Welsh and Barton, a pass documented in AGSO Record 1996/54, Appendices A, D, F and G, and they are published by Geoscience Australia as eCat 116283, doi:10.4225/25/5aab48d653fb1. Each estimate carries its own variance and the variances travel with the values. The coordinates are AGSO's own station positions, taken from the station table published with the series and printed in Appendix A of the Record, and the original one-minute recordings are held at Geoscience Australia in that published dataset.

Data and downloads

Stations (58)

Contributors and organisations

Organisation

Flinders University

Licence

CC BY 4.0

Instruments

Flinders University Chamalaun three-component digital fluxgate magnetometer

Processing

Aurora

Publications

Welsh WD, Barton CE, Chamalaun FH (2018). The Australia-Wide Array of Geomagnetic Stations (AWAGS). Geoscience Australia, Canberra. 10.4225/25/5aab48d653fb1

Chamalaun FH, Walker R (1982). A microprocessor based digital fluxgate magnetometer for geomagnetic deep sounding studies. Journal of Geomagnetism and Geoelectricity 34(8), 491-507. 10.5636/jgg.34.491

Chamalaun F, Barton C (1990). Comprehensive mapping of Australia's geomagnetic variations. Eos, Transactions American Geophysical Union 71(51), 1867-1873. 10.1029/90EO00376

Chamalaun FH, Barton CE (1993). Electromagnetic induction in the Australian crust: results from the Australia-Wide Array of Geomagnetic Stations. Exploration Geophysics 24(2), 179-186. 10.1071/EG993179

Chamalaun FH, Barton CE (1993). The large-scale electrical conductivity structure of Australia. Journal of Geomagnetism and Geoelectricity 45(10), 1209-1212. 10.5636/JGG.45.1209

Lilley FEM, Corkery RW (1993). The Australian continent: a numerical model of its electrical conductivity structure, and electromagnetic response. Exploration Geophysics 24(3), 637-643. 10.1071/EG993637

Wang LJ, Lilley FEM (1999). Inversion of magnetometer array data by thin-sheet modelling. Geophysical Journal International 137(1), 128-138. 10.1046/j.1365-246x.1999.00780.x

Wang L, Hitchman AP, Ogawa Y, Siripunvaraporn W, Ichiki M, Fuji-ta K (2014). A 3-D conductivity model of the Australian continent using observatory and magnetometer array data. Geophysical Journal International 198(2), 1143-1158. 10.1093/gji/ggu188

Koch S, Kuvshinov A (2015). 3-D EM inversion of ground based geomagnetic Sq data. Results from the analysis of Australian array (AWAGS) data. Geophysical Journal International 200(3), 1284-1296. 10.1093/gji/ggu474

Stening R, Reztsova T, Le Huy M (2005). Day-to-day changes in the latitudes of the foci of the Sq current system and their relation to equatorial electrojet strength. Journal of Geophysical Research: Space Physics 110(A10). 10.1029/2005JA011219

Stening R, Reztsova T, Le Huy M (2007). Variation of Sq focus latitudes in the Australian/Pacific region during a quiet sun year. Journal of Atmospheric and Solar-Terrestrial Physics 69(6), 734-740. 10.1016/j.jastp.2006.12.002

Stening RJ (2008). The shape of the Sq current system. Annales Geophysicae 26(7), 1767-1775. 10.5194/angeo-26-1767-2008

Wang L, Greenhalgh S, Barton C, Heinson G, Hitchman A (2024). Vale: Francois Chamalaun (1937-2024). Preview 2024(232), 15-18. 10.1080/14432471.2024.2412324

Identifiers and provenance

Machine-readable survey record · catalogue schema mtcat 2.0