The use of 'Automatic Gain Control' to display vertical magnetic gradient data

Abstract

Magnetic anomalies vary widely both in amplitude and in spatial frequency. As conventional methods of presenting total field data tend to highlight regional anomalies, vertical gradient (VG) data is often used to delineate high-frequency anomalies. While collecting gradient data as part of an aeromagnetic survey is becoming more common, it is also possible to approximate it by using high-pass filters or Fourier Transforms. However, presenting gradient data is more of a problem than computing it. Contour maps are difficult and expensive to produce. Significant, low-amplitude anomalies may not be clearly represented. In addition, the large number of closures characteristic of a VG contour map can make the choice of contour levels and the identification of trends difficult.