Active Source Electromagnetic Methods for Marine Munitions

The detection of munitions targets obscured in coastal and marine settings has motivated the need for advanced geophysical technologies suited for underwater deployment. Building on conventional marine electromagnetic theory and based on the use of existing electric and magnetic field sensing designs, we analyze the electromagnetic fields emitted from excited targets in the frequency range between 1 kHz and 1 MHz. We present evidence that employing electromagnetic modes that are higher in frequency relative to those typically used in ground-based sensing yields greater range and sensitivity for underwater surveys. We develop potential design strategies for implementing both magnetic (B) and electric (E) field sources and sensors in the marine environment, and determine optimal arrangements for a potential combined E-and B-field sensing system. The implementation of both 1D analytical and 3D numerical simulations yields the primary and secondary field distributions in representative underwater settings for various source-receiver arrangements. We study the electromagnetic field distributions from both electric (voltage-fed dipole) and magnetic field (encased and submerged induction coil) active sources. Application of these concepts provide unique and useful information about targets from the addition of electric field sensing alone as well as through the combination of electric and magnetic field sensing.