Comparison Of Emi Measurements On Large Projectiles And On Exploded Projectile Fragments

A seeded test site of large inert projectiles was set up on a former artillery range with real<br>exploded clutter and measured by EM61 and EM61 MkII electromagnetic induction (EMI) sensors. The<br>major source of non-ordnance signatures was clusters of exploded shell fragments. When fitted to a<br>simple dipole response model, the ordnance signatures were characterized by a large primary dipole<br>response and two smaller secondary dipole responses. The ratio of primary to secondary was typically<br>less than two. The fragment clusters were characterized by two large responses and a much smaller third<br>response with a primary to secondary ratio greater than two. While only limited MkII data was collected,<br>comparison of EM61 and MkII signatures over the same object show little difference in signal shape or<br>signal-to-noise levels. EM63 data was collected with inert rounds and a simulated cluster on a test stand.<br>This data indicates that the early MkII time gates do not cover the full range of the time decay curves for<br>large ordnance items. The MkII gates cover only the inverse power law of the decay. After several<br>milliseconds, the decay rolls over into an exponential decay. In these later time gates, the ratio of<br>primary to secondary betas grows much larger for the projectiles. It stays constant for the clusters.