Presentation of magnetic anomaly map data by stereo projection of magnetic shadowgrams

Abstract

Coloured magnetic maps published at the 1:1 000 000 scale by the Geological Survey of Canada have been found to be useful aids in support of regional geological mapping and compilation projects. However, because of the quantization into colour intervals, some of the fine detail contained in the original magnetic data is lost. These smaller features can be brought out quite effectively with the shaded relief technique, although there is an attendant loss of amplitude information, which can be recovered by means of stereo-shadowgrams. A second shadowgram is produced by offsetting the original shadowgram by an amount proportional to the magnetic intensity of each data point and then the offset and original shadowgrams are viewed as a stereo pair. An example of the effectiveness of these techniques is the detail that can be seen on the shadowgrams and stereo-shadowgrams for the Lockhart River (IMW NP 12/13) and the Thelon River (IMW NQ 12/13/14) map sheets.