Transient electromagnetic detection of unexploded ordnance buried in underwater sediments

In this paper, we study the electromagnetic scattering of conducting targets buried in sea sediments. We adopt vector finite element technique to compute solutions for three dimension background and scattered fields under horizontal electric dipoles. The corresponding transient scattering responses to causal step waveform are computed through the digital sine transform. The derived fundamental solutions provide an easy and intuitive way to perform the three dimension underwater UXO modeling. The numerical simulation demonstrates that the influence of water depth is mainly in the shallow water area and at the late times of scattered responses. The shallow sea response is affected by altitudes of the in-loop system for the seafloor. The closer the source is, the easier it is to detect the target. On this basis, we calculated several 3D models. The scattering responses of the modeling results that well agree with the design models, and the shape and location of the abnormal bodies was outlined. In order to quantify the detecting effects of the TEM method, we have design a loop source configuration towing device and performed controlled underwater experiments to compare with the simulation model. This case study illustrates the capability of the TEM method for detecting the underwater buried UXO.