Technical Papers - Airborne Magnetics

Model-Independent Depth Estimation with the SPI^TM Method

Jeffrey B. Thurston and Richard Smith, Fugro Airborne Surveys
2060 Walkley Road, Ottawa, Ontario, Canada, K1G 3P5 
Jean-Claude Guillon

Abstract

Two improvements have been made to a model-independent method of depth estimation using local wavenumbers. A new wavenumber is defined for use in computing depths of 2-D thick dykes and 2-D sloping steps. This quantity, and a previously defined model-independent wavenumber (that is applicable to horizontal cylinders, thin sheets and contacts), is then incorporated into a new depth-estimation algorithm based on automatic curve matching. The new algorithm has three appealing features: the most appropriate of these five models is selected automatically; the automatic curve matching is robust, using a least-squares technique to reject noisy data and responses that do not conform to the model assumptions; and interference from distant sources can be accounted for as a shift in the base level of the model-independent wavenumber curves.

Although the method is based on the assumption of 2-D sources, it has been adapted to gridded data, and thus does not rely on profiles perpendicular to strike. The depths computed from a grid of synthetic data are within 15% of the correct values. A depth image from aeromagnetic data in western Canada is consistent with a published structural interpretation based on drill intersections of the crystalline basement and overlying sediments.

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