Scalar magnetic anomalies of Canada and northern United States derived from Magsat data

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Abstract
The total magnetic field of the earth over Canada and the northern United States is sampled along individual orbits (passes) of the magnetometer satellite (Magsat) on the basis of data extracted from the Magsat chronicle tapes. The main magnetic field at a given sample point is calculated using the main field model by Langel et al. (1982a) and then subtracted from the sampled value. The external magnetic field contribution is partially removed by a quadratic function fitted to each individual pass. The resulting magnetic residuals are resampled at 55 by 55 km grid points on an equal‐area projection and subsequently contoured. The dawn passes yield a magnetic map that is different than the dusk passes, implying that the remaining external magnetic field component has a dawn‐dusk asymmetry. The component is further suppressed by applying a band‐pass filter in the frequency domain. The magnetic anomaly map derived by averaging the dawn and the dusk band‐pass‐filtered maps shows the main features seen on the aeromagnetic maps of Canada and the United States. The map also shows that the Appalachian and the Cordilleran orogens and the Grenville‐Superior suture zone are magnetically low regions, whereas the craton basins such as the Michigan, the Thelon, and the NE British Columbia Basin are magnetically high areas.