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TitleA three-component airborne magnetometer
AuthorSerson, P H; Mack, S Z; Whitham, K
SourcePublications of the Dominion Observatory vol. 19, no. 2, 1957, 83 pages, (Open Access)
PublisherCanada Department of Mines and Technical Surveys
Mediapaper; on-line; digital
File formatpdf
Subjectsgeophysics; magnetometers; magnetism; magnetic properties; geophysical surveys; aeromagnetic surveys; magnetic surveys, airborne; geophysical interpretations; magnetic interpretations; magnetic anomalies; instrumentation; error analysis
Illustrationsphotographs; schematic diagrams; tables; schematic representations; flow diagrams; graphs; geophysical profiles; location maps; histograms
Released1957 01 01; 2018 11 13
AbstractA three-component airborne magnetometer has been designed and built at the Dominion Observatory. The magnetometer is mechanically linked to a gyro-stabilized platform which is maintained horizontal, independent of the motions of the aircraft. The gyroscopes are precessed at a rate proportional to the time integrals of signals from accelerometers mounted on the platform. The system acts basically as a pendulum with a six-minute period. Damping is provided by phase-advance networks in the control loops. Forced oscillations of the platform are reduced by the addition of automatically computed signals proportional to the aircraft accelerations. The accuracy of the platform is 2 or 3 minutes of arc under normal survey conditions. The azimuth reference for the instrument is provided by a directional gyroscope mounted on the platform, whose drift is determined to an accuracy of 0.2° by astronomical measurements with a periscopic sextant stabilized in azimuth.
The magnetometer head contains three orthogonal magnetic detectors of the saturated transformer type, which give direct currents proportional to the fore-and-aft and transverse horizontal components and the vertical component. These and the heading of the aircraft are fed into an analog computer which displays continuously the declination in degrees, and the horizontal and vertical field components in gauss. An alternative display presents automatically the average values of these quantities over successive five-minute intervals. The accuracy of measurement of field components referred to the reference axes established by the stabilization system is estimated to be 0.1° in declination, and 20 gammas in the other components.
Sources of error in survey operations are discussed and the reduction of survey results and the determination of the corrections for the magnetic field of the aircraft described. It is concluded that the probable error of a survey observation as plotted on a chart is about 100 gammas in any component, and is principally due to errors in navigation and plotting.