The Transient Electromagnetic Characteristics of Multitarget Unexploded Ordnance (UXO)

Multitarget unexploded ordnance (UXO) areas are often unavoidable during field exploration. However, most geoelectric models focus only on single targets and are not always reliable for the "detection" and "identification" of multidensity UXO. In this article, we first compare the numerical simulation results with the analytical solution to verify the correctness of the 3-D geoelectric forward modeling procedure based on the finite element (FE) method. Next, the results of time-domain attenuation signals, measurement line responses, and apparent depth inversions for non-, single-, and multiple-UXO at different burial depths are shown. The results show that the time-domain attenuation signals allow a simple identification of the type of UXO, the metal fragments, and the attitude of the UXO in the subsurface. Then, the effects of the variation of distance parameters on the electromagnetic (EM) response of multitarget UXOs of different combination types are explored in detail through a large number of geoelectrical forward modeling, and the laws are summarized. The results show that the size of the low-resistance range induced by multiple targets is not only related to the depth of burial, but also to the shape of the anomaly. The field experiment results show that the changing trend of numerical simulation results is basically consistent with the measured results, and the multitarget anomalies in different scenarios can be identified very clearly. Reasonable geoelectric modeling combined with field experiments can not only improve the exploration efficiency but also provide some reference for the selection of instrument parameters and data interpretation.