| Title | Minimizing the effects of electromagnetic noise and auroral disturbance in the 2017 Kaskattama magnetotelluric data set, Manitoba |
| Download | Downloads |
| |
| Licence | Please note the adoption of the Open Government Licence - Canada
supersedes any previous licences. |
| Author | Ferguson, I J; Macleod, J; Clark, N; Craven, J A; Roberts, B R; Hodder, T; Nicolas, M P B |
| Source | Geological Survey of Canada, Open File 8964, 2023, 53 pages, https://doi.org/10.4095/331646  Open Access |
| Image |  |
| Year | 2023 |
| Publisher | Natural Resources Canada |
| Document | open file |
| Lang. | English |
| Media | on-line; digital |
| File format | readme
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| File format | pdf; rtf |
| Province | Manitoba |
| NTS | 53O/16; 53P/13; 53P/14; 53P/15; 53P/16; 54B; 54C/01; 54C/08; 54C/09; 54C/16 |
| Area | Kaskattama |
| Lat/Long WENS | -92.5000 -90.0000 57.0000 55.7500 |
| Subjects | Science and Technology; e m surveys; geomagnetism; magnetotelluric field; magnetotelluric interpretations; magnetotelluric surveys; magnetotelluric data; data collections |
| Illustrations | graphs; location maps; tables; spectra; models; magnetic profiles; bar graphs; plots |
| Program | GEM-GeoNorth: Geo-mapping for Energy and Minerals GEM Program Coordination |
| Released | 2023 03 21 |
| Abstract | (Summary)
The 2017 Kaskattama (KSK) Highland magnetotelluric (MT) dataset was collected in northeastern Manitoba in a quiet geomagnetic period (with geomagnetic disturbance index Kp values of
mostly <4), during which only one minor storm occurred. The high geomagnetic latitude of the survey, 65º N, resulted in the recorded MT data containing strong Pc1 micropulsation signals and auroral signals with a potential impact on the quality of MT
responses derived from the data. The survey area is within 250 km of hydroelectric facilities in the Gillam area and associated strong sources of electromagnetic noise. Initial computation of MT responses using standard processing methods, such as
magnetic field remote-references, yielded MT responses of only moderate quality. Poor long-period responses (periods >30-100 s, frequencies <0.01-0.03 Hz) were attributed to the effects of auroral electrojet signals. This report examines the signals
and noise in the KSK MT data, describes the reprocessing of the MT responses, and makes the MT responses publicly-available in Society of Exploration Geophysicist electrical data interchange (EDI) format. The relatively complicated mix of signal and
noise in the KSK dataset was examined using the MT data and geomagnetic recordings from the Geospace Observatory Canada CARISMA stations at Gillam and Churchill, Manitoba and Rabbit Lake, Saskatchewan. Methods used for defining the spatial, temporal,
and frequency distribution of the signal and noise included examination of timeseries, spectra, and spectrograms; examination of MT responses for different remote-reference recordings including magnetic and electric field recordings; examination of
MT responses as a function of recording time; and examination of MT responses for different robust processing parameters. There were several types of noise identified in the KSK and CARISMA recordings. At Gillam, two main forms of electromagnetic
noise were observed: 1. Time-varying broad-band noise present over several time intervals on all three magnetic components. 2. Narrow band noise centred on 4.8 s period (0.21 Hz frequency) and observed most strongly on the magnetic north and vertical
(Bx and Bz) components. The first form of noise was also recorded in the KSK horizontal magnetic field data at locations 240 km away from Gillam. It contributes to significant bias of MT and tipper responses at periods of 0.1- 20 s (frequencies of
0.05-10 Hz) calculated using local fields only, and to weaker bias of responses calculated using a magnetic-field remote reference from the Kaskattama area. Spike-like events occurring sporadically in individual magnetic field recordings caused
spatially-localized broad-band noise. The spike-like noise did not cause any bias in remote-reference MT responses. Pc1 micropulsation signals did not appear to cause significant bias and the higher signal levels during their occurrence improved the
signal to noise ratio. The MT responses for KSK data set were recomputed using the full length of recording available at each site and with remote-reference electric fields. The reprocessing removed local biases at intermediate periods caused by
spatially-corrected magnetic field noise, such as the broad-band noise noted at Gillam, and added at least one-half a decade of improved responses at the longest periods (lowest frequencies). |
| Summary | (Plain Language Summary, not published)
This report documents a ground geophysical dataset collected in 2017 to investigate an anomalous highland region in northern Manitoba. The dataset is
released as part of this report. Noise sources related to nearby power generating plants and auroral activity are documented. |
| GEOSCAN ID | 331646 |
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