A microcomputer program for transformation of two-dimensional magnetic anomalies

The BASIC computer program described here performs reduction to the equator and orthogonal reduction as used in the interpretation of magnetic survey data, whereby a total field magnetic intensity profile due to a two-dimensional (2D) body with known dip and remanence directions observed at any magnetic latitude is converted to one that would have been observed at the equator or at a magnetic latitude of 45°, respectively, had the body been situated at these locations. Since field data are necessarily of short length, the program provides the option of applying windows of the Hanning or Hamming types to smooth the spectrum of the data, therby minimizing the instability of the edges of the output anomaly observed for short lengths of data. The principal use of the techniques is to determine the position of the sources of magnetic anomalies on the ground surface, thereby facilitating the selection and siting of exploratory drill holes. The calculation of apparent susceptibility distribution via reduction to the pole or equator is also possible (Gunn 1975; Silva and Hohman 1984). An advantage of the methods is that they are independent of the body geometry of the magnetic sources. Other techniques are either based on models which idealize particular geological situations (e.g. Parasnis 1986, p. 44) or utilize some involved geometric construction procedures. The program is based on convolution in the space domain. It is illustrated on field data from Botswana.