Investigations Into Inversion Of Magnetic And Gradient Magnetic Data For Detection And Discrimination Of Metallic Objects

We have extended our three-dimensional magnetic modeling capabilities to simulate TMI,<br>magnetic vector and gradient measurements for both permanent magnetization and strong induced<br>effects. We have developed capabilities to model quite general 3D shapes including conical and<br>cylindrical objects both solid and hollow. These general shapes can be combined to represent projectile<br>shells with quite general shapes having varying internal magnetic properties.<br>With these simulation capabilities, we investigated the use of inversion algorithms to determine<br>the internal magnetization vector of buried objects. Our objectives are to understand the limitations of<br>recovering the location of the magnetization vector as well as its magnitude and vector orientation.<br>Determining the strength and orientation of the internal magnetization can help in the discrimination of<br>material properties. Our experiments include examination of data sampling, data noise and combinations<br>of TMI, vector and gradient measurements to resolve the magnetization. As an example, we determined<br>that with adequate data sampling one could determine, extremely accurately, the location and orientation<br>of the internal magnetization vector only if the volume of the object is known. This was accomplished<br>by non-linear inversion combined with iterative grid volume modification. In addition, we have<br>experimented with the use of a modified Euler deconvolution technique for depth estimation. At present,<br>we are working with combining the two techniques.