Geoscience Australia?s Geomagnetism Program ? Assisting geophysical exploration

Abstract

The Geoscience Australia Geomagnetism Program monitors the changing geomagnetic field using a network of nine geomagnetic observatories and fifteen repeat stations. The observatories collect calibrated vector data with 1-second sample interval and scalar data with 10-second samples which are sent to Geoscience Australia in near real-time. Among their many uses, these data have excellent application as base station data for magnetic surveys or remote reference data for magnetotelluric (MT) surveys, and for monitoring geomagnetically induced currents (GIC). These data also contain the subtle signal of the slowly changing main magnetic field that originates in Earth?s outer core. An understanding of the scalar main field is essential for main-field removal from magnetic survey data sets. Geomagnetic inclination and declination are required for reduction to the pole techniques. Across Australia, the scalar field is 40% stronger in southern Australia than in the north, the angle of inclination is 50% steeper in the south than the north, and the declination angle varies from about -3 degrees in Western Australia to +15 degrees in Tasmania. Additionally, the rates of change of these field components also differ across the country. This temporal and spatial dependence of the main field is represented in Australian and international geomagnetic reference field models. In Australia, both the Australian Geomagnetic Reference Field model (AGRF), produced by Geoscience Australia, and International Geomagnetic Reference Field model (IGRF), produced by an international group of modellers, are available to users. Each has its pros and cons and users may select the model most appropriate to their needs.