Using GPS TEC measurements to detect geomagnetic Pc 3 pulsations

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 in 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. In the frequency band of interest for MAD (0.01-1 Hz), 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 dayside magnetosphere driven by the solar wind. Such fluctuations may be observed in GPS total electron content (TEC) observations. In this paper, analyses are conducted using 1 Hz data available from GPS reference stations and colocated magnetometers in Canada and Australia. Relative TEC variations are derived from the precise dual-frequency GPS carrier phase observations and band-pass-filtered. Dominant TEC variations at Pc 3 frequencies are then correlated with local magnetic time series from the ground reference. Results are analyzed as a function of solar wind parameters, and the potential for exploiting standalone GPS to derive Pc 3 pulsation indices is investigated.