Duncan R. Cowan

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Measures of the local phase of potential fields can be a useful aid to their interpretation. There are several variations in use, such as the tilt angle, tilt derivative and the Theta map. This paper compares the results of these filters, and introduces some new phase-based filters which show improved performance as edge detectors in different ways. The(More)
Vertical derivatives of aeromagnetic and gravity datasets are routinely used as an aid to the interpretation process because they enhance detail and sharpen geophysical anomalies. Since they are a form of high-pass filter they also have the undesirable property of enhancing noise. Traditionally, the second order vertical derivative of a dataset would be(More)
Similarity measures are becoming increasingly commonly used in comparison of multiple datasets from various sources. Semblance filtering compares two datasets on the basis of their phase, as a function of frequency. Semblance analysis based on the Fourier transform suffers from problems associated with that transform, in particular its assumption that the(More)
Geophysical potential field data are usually interpolated onto a regular grid before data enhancement and interpretation. Unfortunately the inherent smoothing in the gridding process can be sufficient to distort or even hide small-amplitude anomalies that are nevertheless of economic importance. Circular features may correspond to anomalies from Kimberlite(More)
Large-scale compilations of airborne geophysical data are an important part of regional-scale mineral exploration and in most cases, the compilation involves merging datasets of varying quality, acquired over a long period of time. Merging radiometric datasets involves the additional complication that many older surveys were flown with uncalibrated(More)
Horizontal directional derivatives and sunshading are two commonly used gradient-based filters for enhancing linear features in potential field data. The Tilt angle is a useful filter that produces an amplitude-balanced vertical derivative. The disadvantage of the Tilt angle-based filters is that they require the computation of the vertical derivative of(More)
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