During this project, White River Technologies, Inc. and the Woods Hole Oceanographic Institution investigated the application of marine electromagnetic sensing techniques for detecting and characterization underwater ordnance. The main motivation was to investigate the potential to use both magnetic and electric field information for detection, localization, and classification of underwater unexploded ordnance (UXO).

The overarching approach of this project was to utilize a combination of analytical modeling and experimentation to better understand the potential of adding electric field transmitters and/or receivers to the conventional architecture of electromagnetic induction sensing technology for underwater UXO. Electromagnetic propagation models were developed and applied to better understand the relative contribution of electric fields as part of the composite electromagnetic response in the marine environment. Two sets of open water experiments were conducted to develop a fundamental understanding of magnetic and electric field responses to varying marine environments, to metal targets of interest, and to proximity to the seafloor and air-sea interface. 

Building on established marine electromagnetic theory and based on the use of existing sensing designs, the electromagnetic fields emitted from excited targets were analyzed. Modeling and experimental studies supported potential design strategies for implementing both magnetic and electric field sources and receivers. Application of three-dimensional numerical simulations yield optimal arrangements for a potential advanced electromagnetic sensing system. Experiments have also revealed that the scattered magnetic fields generated by an electric dipole field source produce larger signals compared to those from magnetic field sources at greater range from targets. Both the model and the measurements indicate a crossover in the field intensity curves at distances of 2-5 m from the sources. After this point, the signals generated by the electric dipole are stronger than those produced by the magnetic dipole source (given both sources are carrying equal current).

In-water experiments conducted at the Waquoit Bay National Estuarine Research Reserve Facility in Massachusetts exercised a full-scale prototype mixed mode testbed. The detection capabilities of an electric-field transmitter source modality was assessed through a number of experiments and identified methods that exploited marine electromagnetic phenomenology to boost range performance for detection of seabed munitions targets.

The experiments provided insight into the range capabilities of the electric field modality and indicated its potential to exceed the performance of conventional induction coils in detecting underwater UXO. This directly benefits the emerging designs of marine UXO survey instrumentation being developed by SERDP and demonstrated under ESTCP. (Project Completion - 2025)