Short-period geomagnetic variations recorded concurrently with an aeromagnetic survey across the Bendigo area, Victoria

Abstract

A high-resolution aeromagnetic survey was undertaken by the Australian Geological Survey Organisation (AGSO) across the Bendigo 1:250 000 map sheet area during February to April 1994. For part of this period, high-resolution ground magnetometers were also deployed to test for the way that short-period variations of the geomagnetic field (including micropulsations) affect data recorded by the aircraft. These ground instruments consisted of the newly developed Helium base-station for AGSO aeromagnetic surveys, and two ring-core fluxgate magnetometers developed by the School of Earth Sciences at The Flinders University of South Australia. The Helium instrument was deployed at the Bendigo airport, in the south-west corner of the area, and the ring-core instruments were buried in the north-west and north-east corners of the area. Preliminary results indicate that while the phases of continuous Pc3 micropulsations of about 20 s period change little across the map sheet area, the amplitudes can vary significantly. For longer period geomagnetic variations (60 s to 600 s), there are significant differences in the amplitudes and phases of the total-field values measured at different sites. Induction vectors indicate a shallow zone of higher conductivity between the east and west measurement sites. Data from a single base-station magnetometer subtracted from airborne survey data will not adequately remove the short-period geomagnetic variations of the total field recorded during this survey period ? they are an additional noise source in the survey data.