Interpolation artifacts as a result of spatial aliasing: A case study of the airborne magnetic data set of southeastern Minas Gerais, Brazil

Linear features at an acute angle with the flight direction are imaged as a series of aligned circular anomalies in the images of Area 15 aeromagnetic survey, which covered part of the Brazilian southeastern region. These features are interpolation artifacts, a recurring problem found in airborne magnetic images that cause problems for qualitative and quantitative geophysical-geologic interpretation. This imaging problem is attributed to spatial aliasing. By running simulations of magnetic data on a synthetic model, we have physically demonstrated that the interpolation artifacts from Area 15 are due to inappropriate survey design. Besides the most common expression of artifacts, we described a geologically noncoherent linear pattern as a new type of artifact. Supported by spectral analyses, we found that the Area 15 aliased spectrum is similar to geologic high-frequency magnetic features, which constitutes a motive for unearthing the correct geophysical signal. Thus, we made use of four techniques for removing the artifacts. The trend enforcement method partially improved the images, whereas the inverse interpolation method was ineffective, apparently because Area 15 data are severely aliased. The constrained coherence diffusion and multitrend gridding methods were able to significantly reduce the presence of artifacts. Despite the highfrequency attenuation, these tools adequately enhanced the magnetic trends and minimized the artifacts. Therefore, the improved images are better suited for reliable geologic interpretation.