Analysis of spheroidal electromagnetic induction response as a model of unexploded ordnance

Identifying, detecting, classifying and separating unexploded ordnance (UXO) is one of the essential needs of countries and societies that have been involved in war. Marine mines submerged in seawater or buried in land are a common danger in many areas of the world. The majority of mines are composed of metal and explosive materials. There are many non-destructive schemes for detecting the location, orientation and depth of a metallic mine (modeled as a perfectly conducting sphere and spheroid). These methods of exploration of such materials, which are mainly based on geophysical methods, have a special importance and capability in terms of economy and safety. A major challenge of detecting a metallic object is to discriminate the object, such as an unexploded ordnance, from the noisy environment. It takes time and resources to identify the object, especially due to false signals from other metal objects and cultural features such as metal buildings, pipelines, and oil well casings. By measuring the secondary response of an electrically conductive object placed in a low frequency primary magnetic field, distinct spectral characteristics such as electrical conductivity, magnetic permeability, object geometry, and size can be obtained. Being one of the frequency domain methods, the Electromagnetic Induction method (EMI) is an efficient geophysical method that is used to identify land mines and sea mines. This technique takes into account Eddy-Current Response (ECR) induced on the conducting marine mines as well as Current-Channeling Response (CCR) associated with the perturbation of currents induced in the conductive marine environment. In the processing of the data obtained from geophysical surveys, especially in the EMI, such anomalies are modeled with simple geometric objects such as spheres or spheroids. In the first step of data interpretation and to determine the dimensions of the model that indicates the type of mine or bomb and also to determine its location, it is necessary for the interpreter to have a clear view of how the electromagnetic induction response depends on the geometrical and physical parameters of such materials. For this purpose, in this article, the changes and behavior of the received electromagnetic induction response in the receiver coil are investigated according to the depth, dimension and orientation of the abnormality. The graphs obtained are examined and analyzed using the mentioned variables. While qualitatively determining the state of abnormality to a large extent, the obtained results can be useful in numerical methods of calculation of geometrical and physical quantities of anomalies.