Determination of the parameters of compact ferrometallic objects with transforms of magnitude magnetic anomalies
Abstract
The transforms based on magnitude of the magnetic anomaly (MMA), or absolute value of anomalous magnetic intensity, are relatively insensitive to the direction of the source magnetisation vector and show high centricity. Obtaining them requires calculation of only firstorder horizontal derivatives of the component magnetic anomalies X, Y and Z, obtained through transformation of total magnetic anomalies Δ T (TMA). We studied the use of the magnetic transforms based on the MMA of a dipole source and that of their ratios for determining the geometric and physical parameters of compact environmental ferrometallic sources. Analytical formulas for all the parameters of the magnetic dipole based on calculation of MMAs, their gradients and Laplacian, and their ratios were obtained. The horizontal position of the dipole source is determined by the maximum of the Laplacian of the MMA, which is the transform with the highest centricity. We applied the approach on model data and on magnetic anomalies over environmental sources, represented by unexploded ordnance (UXO) and clutter from the Badlands Bombing Range, USA. The obtained parameter values were compared with those estimated through Euler deconvolution using unprescribed structural index and linear model of the background, and through inversion. The comparison showed that the proposed method produced similar depth results to that of the Euler deconvolution method for the objects with estimated structural index over and around 2.5, i.e., for the sources, which to a great extent can be approximated with a dipole. The inversion for the dipole parameters using as initial parameters the estimated with the MMA transform method ones confirmed the results of the MMA transform method for the dipole coordinates and magnetisation for all items.
 Publication:

Journal of Applied Geophysics
 Pub Date:
 March 2004
 DOI:
 10.1016/j.jappgeo.2003.10.001
 Bibcode:
 2004JAG....55..173G