Mitigating Geomagnetic Noise in Airborne Magnetic Surveys using GPS

Susan Skone

Abstract:	Magnetic Anomaly Detection (MAD) is an application in which airborne magnetometers are used to detect small magnetic variations against the Earth’s background magnetic field. This technique is used in aeromagnetic surveys, to detect mineral deposits, and applications such as antisubmarine warfare. The magnetic signals of interest typically have periods of 1-100 s and amplitudes of 0.001- 1 nT. In order to isolate and detect such signals, all other sources of magnetic noise in this frequency band must be modeled, or measured, and mitigated. Despite reduction of many error sources for MAD, a limiting factor remains – the small-amplitude variations caused by geomagnetic pulsations arising from ionospheric processes. In the frequency band of interest for MAD (0.01-1Hz), Pc 3 pulsations represent a significant error source. These continuous pulsations are apparent as pulse trains in magnetic time series for intervals as long as several minutes. These pulsations arise from resonant oscillations in the Earth’s environment driven by solar processes. For compressional Pc 3, electron density variations occur in the Earth’s ionosphere. Such fluctuations may be observed in GPS total electron content (TEC) observations. Using GPS to independently detect the presence of Pc 3 pulsations alleviates the necessity for closely-spaced ground reference magnetometers in aeromagnetic surveys, and allows long-range airborne operation without expensive ground infrastructure. Such survey operations already have dual frequency GPS capabilities onboard the airborne platform for estimation of precise aircraft trajectories. It is a natural extension to make use of such data in a novel manner to improve geophysical surveying capabilities. In previous studies we have demonstrated limited cases where Pc 3 pulsations were observed in GPS TEC variations. In some cases, results agreed very well with theory. In many cases, however, the TEC variations did not match theoretical predictions. In this paper we analyse additional data sets to clearly define the potential of Pc 3 detection using GPS. Analyses are conducted using 1 Hz data available from Canadian and Australian GPS reference stations and co-located magnetometers. Relative TEC variations are derived from the precise dualfrequency GPS carrier phase observations and bandpass filtered. Dominant TEC variations at Pc 3 frequencies are then correlated with local magnetic time series from the ground reference. Results indicate potential for statistically identifying periods of pulsation activity using GP
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	837 - 842
Cite this article:	Skone, Susan, "Mitigating Geomagnetic Noise in Airborne Magnetic Surveys using GPS," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 837-842.
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