There are approximately one million acres of underwater lands at Department of Defense (DOD) and Department of
Energy (DOE) sites that are highly contaminated with unexploded ordnance (UXO) and land mines. The detection and
disposal of Underwater Military Munitions are more expensive than excavating the same targets on land.
Electromagnetic induction (EMI) sensing has emerged as one of the most promising technologies for underwater
detection. In order to explore the full potential of various EMI sensing technologies for underwater detection and
discrimination, to achieve a high (~100%) probability of detection, and to distinguish UXO from non-UXO items
accurately and reliably, first the underlying physics of EM scattering phenomena in underwater environments needs to be
investigated in great detail. This can be achieved by using an accurate 3D numerical code, such as the combined method
of auxiliary sources and thin skin depth approximation (MAS/TSA), the pseudospectral time-domain technique, finite
element methods or other approaches. This paper utilizes the combined MAS/TSA, originally developed for detection
and discrimination of highly conducting and permeable metallic objects placed in an environment with zero or negligible
conductivity. Here, first the theoretical basis of the MAS/TSA is presented for metallic objects placed in an electrically
conductive environment. Then numerical experiments are conducted for homogeneous targets of canonical (spheroidal)
shapes subject to frequency- or time-domain illumination. The results illustrate coupling effects between the object and
its surrounding conductive medium, particularly at high frequencies (early times for time-domain sensors), and the way
this coupling depends on the distance between the sensor and the object's center.