Empirically Derived Response Variability for Munitions Items Using EM61 Towed Arrays

The depth at which UXO can be reliably detected using EM61 based arrays is not well<br>understood. Most remedial actions use the empirically derived standard of 11 x diameter of a<br>cylindrical munitions item as detection criteria. Unfortunately, the physics for forward modeling<br>discrete, non-spherical conducting object responses to Time-Domain EM systems are very<br>complex, especially for ganged arrays. There are no forward modeling algorithms available that<br>can resolve this problem. Further, field experience and familiarity with the physics indicate this<br>is a highly non-linear problem, where slight changes to the initial conditions can have a major<br>impact on instrument response.