A new method for interpolating linear features in aeromagnetic data

Tomas Naprstek,Richard S. Smith

doi:10.1190/geo2018-0156.1

Abstract

When aeromagnetic data are interpolated to make a gridded image, thin linear features can result in “boudinage” or “string of beads” artifacts if the anomalies are at acute angles to the traverse lines. These artifacts are due to the undersampling of these types of features across the flight lines, making it difficult for most interpolation methods to effectively maintain the linear nature of the features without user guidance. The magnetic responses of dikes and dike swarms are typical examples of the type of geologic feature that can cause these artifacts; thus, these features are often difficult to interpret. Many interpretation methods use various enhancements of the gridded data, such as horizontal or vertical derivatives, and these artifacts are often exacerbated by the processing. Therefore, interpolation methods that are free of these artifacts are necessary for advanced interpretation and analysis of thin, linear features. We have developed a new interpolation method that iteratively enhances linear trends across flight lines, ensuring that linear features are evident on the interpolated grid. Using a Taylor derivative expansion and structure tensors allows the method to continually analyze and interpolate data along anisotropic trends, while honoring the original flight line data. We applied this method to synthetic data and field data, which both show improvement over standard bidirectional gridding, minimum curvature, and kriging methods for interpolating thin, linear features at acute angles to the flight lines. These improved results are also apparent in the vertical derivative enhancement of field data. The source code for this method has been made publicly available.

Highlights

An iconic aspect of many geophysical surveys is that the acquired data are spatially dense along traverse lines and entirely devoid of data between these lines
It is an aliasing issue, in which features that occur across lines need to be handled appropriately or artifacts may occur (Reid, 1980). One such type of artifact is the aeromagnetic response of thin, linear features, like those often produced by dikes and dike swarms (Pilkington and Roest, 1998). If these linear features are trending at nonperpendicular angles with respect to the flight lines, the response often manifests as a string of beads or boudinage artifact on the interpolated map (Keating, 1997; Smith and O’Connell, 2005; Guo et al, 2012; Geng et al, 2014)
This leads to effective interpolation of anomalies that are perpendicular to the flight lines; it can lead to these beading artifacts when a linear anomaly is at an acute angle to the line data

Summary

INTRODUCTION

An iconic aspect of many geophysical surveys is that the acquired data are spatially dense along traverse lines and entirely devoid of data between these lines. If these linear features are trending at nonperpendicular angles with respect to the flight lines, the response often manifests as a string of beads or boudinage artifact on the interpolated map (Keating, 1997; Smith and O’Connell, 2005; Guo et al, 2012; Geng et al., 2014) This is prone to occurring when data are interpolated using the most commonly used methods in mining geophysics, such as bidirectional splines (Bhattacharyya, 1969; Akima, 1970), minimum curvature (Briggs, 1974; Swain 1976; Smith and Wessel, 1990), and kriging (Hansen, 1993). The C# source code has been made available (see Data and Materials Availability)

METHOD

Findings

CONCLUSION