3-D inversion of magnetic data

Abstract

We present a method for inverting surface magnetic data to recover 3-D susceptibility models. To allow the maximum flexibility for the model to represent geologically realistic structures, we discretize the 3-D model region into a set of rectangular cells, each having a constant susceptibility. The number of cells is generally far greater than the number of the data available, and thus we solve an underdetermined problem. Solutions are obtained by minimizing a global objective function composed of the model objective function and data misfit. The algorithm can incorporate a priori information into the model objective function by using one or more appropriate weighting functions. The model for inversion can be either susceptibility or its logarithm. If susceptibility is chosen, a positivity constraint is imposed to reduce the nonuniqueness and to maintain physical realizability. Our algorithm assumes that there is no remanent magnetization and that the magnetic data are produced by induced magnetization only. All minimizations are carried out with a subspace approach where only a small number of search vectors is used at each iteration. This obviates the need to solve a large system of equations directly, and hence earth models with many cells can be solved on a deskside workstation. The algorithm is tested on synthetic examples and on a field data set.

3D joint inversion of gravity gradiometry and magnetic data in spherical coordinates with the cross-gradient constraint

“…A radial weighting similar to the depth weighting (e.g., Li and Oldenburg, 1996) is also used to deal with the natural decay of the kernel. The same approach is used by Du et al (2013) in the inversion of magnetic data in spherical coordinates.…”

“…There have been many efforts in this area by formulating the modelling and inversion in the spherical coordinates. In particular, Liang et al (2014) develop a method for 3D inversion of gravity data in spherical framework by extending the work of Li and Oldenburg (1996) in the Cartesian coordinates. Du et al (2013) develop a spherical magnetic inversion algorithm using a similar formulation.…”

Aeromagnetic survey using an unmanned autonomous helicopter over Tarumae Volcano, northern Japan

“…The uniform model reconstructed the overall characteristics of the dipolar anomaly, although detailed anomalies in the summit atrio were not reproduced. Further 3D magnetisation modelling by introducing horizontal and vertical variations would be possible (e.g., Li and Oldenburg, 1996). However, we are not going to discuss here the detailed internal inhomogeneity of the volcanic edifice owing to the lack of other constraining data such as drilled cores.…”

Improving modelling of AEM data affected by IP, two case studies

“…The EM data were inverted using Cole-Cole model in order to extract IP information, including chargeability of the subsurface using SCI concept (Viezzoli et al, 2013). Further, the Magnetica data TMI data were inverted using UBC-GIF approach (Li and Oldenburg, 1996). From geological evidence the Mt.…”