Classification of unexploded ordnance-like targets with characteristic response in transient electromagnetic sensing

Characteristic response parameterized in time-dependent target intrinsic polarizabilities can be used to discriminate unexploded ordnance (UXO) from harmless items. This study explains the measurement, analysis, and classification of UXO-like targets against data collected under laboratory-type conditions with a specially designed transient electromagnetic (TEM) system. After a brief description of the single dipole model and TEM system, the characteristic responses of all UXO-like targets have been measured with an improved long straight solenoid. The influence of the target shape and size on characteristic response is analyzed. Results show that targets of the same shape share similar power law function decay rate at an early time. The larger the target size is, the greater the response will be. The characteristic response for harmless targets decays faster than the UXOs, leading to a considerable difference in a later time, which can be used for target classification. When the characteristic response is parameterized as kt(-beta)e(-gamma) t in 100 ms, targets can be effectively separated with the fitted parameters k, beta and gamma. However, when fitted in 10 ms, the fitted parameter gamma may be thousands of times than the one fitted in 100 ms, resulting in classification failure. The normalized response combined with the fitting parameter beta can be used for target classification to overcome the instability of fitted parameter gamma in 10 ms. Finally, all UXOs are completely separated from harmless targets within 10 ms.