Structural Mapping from High Resolution Aeromagnetic Data in Namibia using Normalized Derivatives

Abstract

Summary We generate a range of normalized derivatives for high resolution aeromagnetic data from Namibia, and illustrate their effectiveness for structural mapping. A rapid method of mapping the depth of cover is also applied to the study area. Introduction And Methodology Magnetic maps contain signals with a wide range of amplitudes, reflecting the varying depth, geometry and susceptibility contrasts of sources. Such maps are often dominated by large amplitude anomalies which can obscure more subtle anomalies. Modern methods of color display such as histogram color equalization and false shaded relief help to some extent to enhance these subtle anomalies. In the last few years there have been a number of methods proposed to help normalize the signatures in images of magnetic data so that weak, small amplitude anomalies can be amplified relative to stronger, larger amplitude anomalies. Examples of normalized derivatives discussed here include the Tilt derivative (Miller and Singh, 1994, Verduzco et al., 2004), Theta derivative (Wijns et al., 2005) and TDX derivative (Cooper and Cowan, 2006). These methods were reviewed and critically evaluated using geologically relaistic models by Fairhead and Williams (2006). Here, we apply the methodologies to high resolution aeromagnetic data from Namibia. We also use a range of local wavenumber methods to determine the depth to top of sources to investigate the variability of these estimates and determine which is best. These results will be presented and discussed.