1. A method for characterizing a ferromagnetic material, comprising: providing a plurality of magnetometers arranged in an at least one-dimensional array, the array being positionable at a standoff distance along a z axis from the ferromagnetic material and translatable along an x axis, perpendicular to the z axis, to a plurality of scan positions along the ferromagnetic material, wherein at least three magnetometers of the plurality of magnetometers are mutually spaced apart and disposed within the array along a first axis, perpendicular to the x and z axes; storing, in a memory, data representing a deterministic physics-based model for missing metal; for each scan position of the plurality of scan positions, calculating, by a processor, respective differences between a plurality of respective select pairs of the magnetometers, wherein at least one select pair of the plurality of respective select pairs of the magnetometers comprises two non-adjacent magnetometers of the at least three magnetometers disposed along the first axis, and each select pair of at least two other select pairs of the plurality of respective select pairs of the magnetometers comprises two adjacent magnetometers of the at least three magnetometers disposed along the first axis, and wherein each difference of the respective differences is calculated by dividing by a distance separating the respective select pair of magnetometers; and comparing, by the processor, respective differences between the plurality of respective select pairs of the magnetometers with the data representing the deterministic physics-based model for missing metal to identify metal missing from the ferromagnetic material.