One of the challenges in potential field (magnetic and gravity) data interpretation is to determine the depth of different superimposed sources. Until now there is no effective method to distinguish them. Based on the spectrum theory, we deduced a mathematical formula to express the relationship between the depth of the source of the magnetic anomaly and the wave-number of the maximum power, and then developed a depth imaging method. The method has high spatial resolution for a horizontal distribution of sources. For vertical superimposed bodies, higher accuracy is obtained for the estimation of their depth when the depth increases. When a small body overlays on larger body, we can easily separate them by the discontinuity of power spectrum at the depth; however, when the bigger body hides a small body, the top depth of the deepest body can be clearly determined only if they are separated by a certain distance.;We then analyzed the impact of noise on the depth imaging method. The noise can cause a gross distortion to the result of Fourier transform as the NSR increases, also the DC components become more significant.;As regarding the problem of equivalent source, we conclude that several similar bodies having different geometries can generate similar magnetic anomalies but they are at the same depth. This sort of equivalence does not cause problems in the interpretation of magnetic or gravity because the source location is the same. If we try to find some equivalent bodies that are deeper than the causative body, to compensate for the attenuation of the magnetic anomaly the magnetic susceptibility must be at least 8 times higher than that of the causative body in our example, this which is not realistic in nature. Finally, we applied the method to an actual geological case---Gallen massive sulphide deposit in Abitibi region. The depth imaging results from the airborne magnetic data did not only show some known geological features but also gave some new information about underground structure according to the amplitude of power spectrum, its spacing and continuity.;Keywords: Magnetic anomaly, Spectrum analysis, Depth imaging method, 3D geological model.
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