Analysis of the effect of salt water on time domain electromagnetic induction sensing of submerged metallic objects

Relative to free-space or non-responsive media, salt water (SW) alters both primary and secondary electromagnetic induction (EMI) fields that pass through it. Effects appear distinctly in the frequency domain (FD), depending on both frequency and sensor-target distance, and may be distinctly quantified. Target signatures are distorted particularly over roughly the upper half log-space of the frequency range where distinctive response patterns may appear. This paper pursues the implications of those distortions when they are translated mathematically to the time domain (TD). Effects of sensor-target standoff, target composition and orientation are pursued. Within configurations of potential interest, SW effects appear strongly in very early time (< 0.1 ms); we investigate the extent to which these effects may spill over further into the early time (ET) range (~ 0.1 ms – 1 ms), which has been important for signal interpretation in sensing on land. Lastly, computations compare the relative magnitude of these SW effects in the secondary field (SF) with those from the SW background itself.