An automatic method has been developed for compilation of digital aeromagnetic data. This method has been applied to the data obtained during a high-sensitivity aeromagnetic survey over an area in the Precambrian shield of north-eastern Ontario in Canada. With this method, all points of intersection between traverse and base lines are determined automatically and adjusted within the limits of positional error for minimizing differences in magnetic values at the intersections. Then the data are corrected for diurnal variation and leveled to tie the magnetic measurements together. Next, the resulting total field values are contoured with a machine method at a scale of 1:25,000. For such a scale, the minimum contour interval that can be used in the present area is two gammas. However, because of the accuracy of the method of compilation, with a larger scale, it is possible to trace one-gamma contours.The maps thus compiled have been compared with published aeromagnetic maps of data obtained with conventional flux-gate and proton-precession magnetometers. The new maps are vastly superior to the old ones for delineating trends, patterns, and fine features of available detailed geological maps. This superiority is mainly due to the excellent definition of small amplitude anomalies, some of only a few gammas in magnitude, on the high-resolution magnetic maps.

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