Boreholes provide access to the magnetic field proximal to a subsurface magnetization, but inversion of a single string of TMI measurements provides only weak capability to vector towards source. Multicomponent measurements would provide vectoring capability, but require extreme precision in orientation. The magnetic gradient tensor provides vectoring capability with managable orientation requirements. However, the rapid decay of gradients from compact sources, and the trajectory of boreholes towards a source, introduce novel inversion challenges. Measurements made adjacent to a magnetization are unduly dominated by that local magnetization, and should not be allowed to contribute towards mapping of the more remote parts of the,magnetization, to which they have little or no sensitivity. Algorithms to invert borehole magnetic gradient tensor data therefore require self-adaptive capabilities to manage which parts of the data contribute to inversion of which parts of the model.


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