Characteristic response parameterized in time-dependent target intrinsic polarizabilities has been widely used to create feature libraries for unexploded ordnance (UXO) discrimination. This paper discusses the accurate measurement of characteristic response for UXOs with transient electromagnetic (TEM) system. First, a specially designed TEM system, which utilizes a modified solenoid and a pair of rectangular coils as transmitting coils to ensure the uniformity of primary field up to 96% throughout the target, is described. Then, the characteristic responses of 12 UXOs are measured from directions vertical or parallel to the axis at distances from 40 to 120 cm. The measured characteristic responses show a power law decay function at an early time and an exponential decay function at a later time. The characteristic responses parallel to the target axis are larger, and the decay is considerably slower than those vertical to the axis, leading to one to two orders of magnitude difference at a later time. Results also show that the characteristic response measured from the direction vertical to the axis of the target is more precise than that from the direction parallel to the axis at the same distance. The portion of the target that is close to the system accounts for a large proportion of the response. A target can be approximated as a single dipole only when it is located no less than twice its length from the system. Finally, the characteristic responses of 12 targets are parameterized with the Pasion–Oldenburg expression for feature library creation.

中文翻译：

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用瞬态电磁系统精确测量未爆弹药的特性响应

以时间相关的目标固有极化率参数化的特征响应已被广泛用于创建未爆炸弹药 (UXO) 鉴别的特征库。本文讨论了具有瞬态电磁 (TEM) 系统的 UXO 特性响应的准确测量。首先，描述了一种专门设计的 TEM 系统，该系统利用改进的螺线管和一对矩形线圈作为发射线圈，以确保整个目标的初级场均匀性高达 96%。然后，在 40 到 120 厘米的距离处，从垂直或平行于轴的方向测量 12 枚 UXO 的特征响应。测得的特征响应显示早期的幂律衰减函数和稍后的指数衰减函数。平行于目标轴的特征响应更大，衰减比垂直于轴的特征响应慢得多，导致稍后出现一到两个数量级的差异。结果还表明，从垂直于目标轴的方向测量的特征响应比在相同距离处平行于轴的方向测量的特征响应更精确。靠近系统的目标部分占响应的很大比例。只有当目标距离系统的长度不小于其两倍时，才能将目标近似为单个偶极子。最后，使用 Pasion-Oldenburg 表达式参数化 12 个目标的特征响应以创建特征库。导致以后出现一到两个数量级的差异。结果还表明，从垂直于目标轴的方向测量的特征响应比在相同距离处平行于轴的方向测量的特征响应更精确。靠近系统的目标部分占响应的很大比例。只有当目标距离系统的长度不小于其两倍时，才能将目标近似为单个偶极子。最后，使用 Pasion-Oldenburg 表达式参数化 12 个目标的特征响应以创建特征库。导致以后出现一到两个数量级的差异。结果还表明，从垂直于目标轴的方向测量的特征响应比在相同距离处平行于轴的方向测量的特征响应更精确。靠近系统的目标部分占响应的很大比例。只有当目标距离系统的长度不小于其两倍时，才能将目标近似为单个偶极子。最后，使用 Pasion-Oldenburg 表达式参数化 12 个目标的特征响应以创建特征库。结果还表明，从垂直于目标轴的方向测量的特征响应比在相同距离处平行于轴的方向测量的特征响应更精确。靠近系统的目标部分占响应的很大比例。只有当目标距离系统的长度不小于其两倍时，才能将目标近似为单个偶极子。最后，使用 Pasion-Oldenburg 表达式参数化 12 个目标的特征响应以创建特征库。结果还表明，从垂直于目标轴的方向测量的特征响应比在相同距离处平行于轴的方向测量的特征响应更精确。靠近系统的目标部分占响应的很大比例。只有当目标距离系统的长度不小于其两倍时，才能将目标近似为单个偶极子。最后，使用 Pasion-Oldenburg 表达式参数化 12 个目标的特征响应以创建特征库。