Merging fluxgate and induction coil data collected from Eskdalemuir geophysical observatory to produce low-noise, one-second data

Wang, Guanren ORCID:; Beggan, Ciaran D. ORCID:; Turbitt, Christopher ORCID: 2022 Merging fluxgate and induction coil data collected from Eskdalemuir geophysical observatory to produce low-noise, one-second data. Edinburgh, UK, British Geological Survey, 23pp. (IR/22/020) (Unpublished)

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This report describes the use of one-second MFS-07 induction coil and DMI FGE89J fluxgate magnetometer magnetic field data recorded at Eskdalemuir Geophysical Observatory in order to compute an "improved" one-second time series for frequencies higher than specified fluxgate operating band. The DMI instrument is a true one-minute system though it can produce one-second data which are relatively noisy in the 0.2 - 0.5 Hz band. The induction coils are sensitive for periods between 0.1 Hz and 50 Hz allowing their high frequency response to complement the low frequency to DC response of the DMI instrument. A numerical technique is adapted from published algorithms developed for merging one-second data recorded at Niemegk observatory in Germany. Our goal is to combine the long-term stability of the DMI fluxgate magnetometer with the low-noise of the induction magnetometer to capture the natural magnetic field for frequencies down to 0.5Hz. Magnetic field data with long-term stability in the low frequency end and also providing information at high frequencies are useful in the study of space weather storms. We have determined the improvement by examining the merged time series, computing the coherence and phase of the one-second merged data with that of the induction coil and fluxgate magnetometer data for the two horizontal components as well as plotting the spectrograms of fluxgate and merged frequencies of interest. We repeated our analysis using data from an instrument capable of meeting the INTERMAGNET one-second definitive data standard, the LEMI-025 fluxgate magnetometer, to compute a separate merged one-second time series as an independent check. We find that a high coherence exists between the two merged time series (LEMI-025/induction coil and FGE89J/induction coil), without phase difference. Spectrograms of the merged time series reveal micro-pulsations that are otherwise masked by the inherent noise from either fluxgate instruments at the frequency band where Pc1 pulsations occur (0.2-0.5Hz). The Pc1 pulsation in the one-second merged time series from Eskdalemuir observatory is also identified in the equivalent spectrogram of the Niemegk observatory from the same day. This proves that the numerical technique created to capture natural field variations in the 0.2-0.5Hz band can be applied effectively for this UK observatory.

Item Type: Publication - Report (Technical Report)
Funders/Sponsors: British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed but not externally peer-reviewed. Report made open by author in June, 2023.
NORA Subject Terms: Earth Sciences
Date made live: 30 Jun 2023 17:19 +0 (UTC)

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