DEWARPING THE COMPOSITE AEROMAGNETIC ANOMALY MAP OF AUSTRALIA USING CONTROL TRAVERSES AND BASE STATIONS

摘要

The composite aeromagnetic anomaly map of Australia, like similar maps of other continent-size regions, contains spurious trends, warps, and base-level shifts. These arise from the arbitrary nature of aeromagnetic data processing methods and edge matching of disparate surveys. Corrections have been applied to the Australian map based on long aeromagnetic control traverses flown around the country in January and February 1990. The control traverses were timed to coincide with a continent-wide magnetometer array study, thus enabling accurate corrections to be made for transient (diurnal) variations of the geomagnetic field. Magnetic observatory data spanning several months each side of the traverse interval were used to correct for long-term displacement of the total field from its normal value. The transient contribution to total field was modeled as a set of one-minute time slices over the whole country, and then used to reduce the control-traverse data to normal values. Absolute anomaly values were generated along traverses by subtraction of IGRF 1990, then compared with corresponding anomalies given by the uncorrected composite map. The resulting anomaly difference values were interpolated and extrapolated over the whole country and used to relevel the composite magnetic anomaly map. The corrections applied range typically between -200 and +200 nT, with a maximum of about +400 nT in the far western region and a minimum of about -450 nT in South Australia. These corrections are smaller than expected, but are still large compared with the amplitude of long-wavelength magnetic anomalies. [References: 19]