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CASSIAR GEOPHYSICAL SURVEY
Open File GSC 3198
1997 Aeromagnetic Total Field Map, British Columbia
(Parts of NTS 104P/NW)
The aeromagnetic survey was carried out by Geoterrex using a Titan 404 aircraft. A 0.005 nT sensitivity split-beam cesium vapour magnetometer was mounted in the tail boom of the survey aircraft.
The survey operations were carried out from August, 1995 to March, 1996. Sensor height was a smooth drape, to within 300 metres of the highest peaks; it was controlled by a computer assisted, real-time corrected Global Positioning System, which provided vertical, as well as horizontal guidance. This vertical guidance ensured correlation of elevation of traverse and control line intersections. The average traverse line spacing was 800 meters with control lines at 5 kilometre spacing. Flight path was recovered using a post flight differential Global Positioning System, combined with a vertically mounted video camera.
After editing the survey data, the intersections of control and traverse lines were established and the differences in the magnetic values were computer analyzed and manually checked to obtain the level network. Because short-period diurnal micropulsations will pass through standard control line levelling, a micro-levelling operation (Minty, B.R.S., 1991: Exploration Geophysics, 22, 591-592) was applied to the total field grid. Intensive manual intervention with the micro-levelling corrections prevented any significant alteration of real magnetic signal. Turbulence-induced altitude variations were examined by computer for correlative wavelengths in the magnetic data. Corrections of up to 0.022 nT/m were applied at correlative sites. The levelled total field values were then interpolated to a 100 m grid. The International Geomagnetic Reference Field has not been removed. The data were processed by Geoterrex.
Copies of this map may be obtained from the Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, K1A 0E8. It is also available online at the MIRAGE and at the Geoscience Data Repository. The geophysical data used to compile this map are available in digital form from the Geophysical Data Centre. Geological Survey of Canada, 1 Observatory Crescent, Ottawa. Ontario, K1A 0Y3.
Analogue and digital products include data for magnetic parameters in two projections: