Remediating underwater unexploded ordnance (UXO) sites remains an emerging environmental issue that requires studies on the fundamental science of detection and discrimination, sensor modality, and deployment platform. This project developed an underwater electromagnetic sensor and data processing technologies to support characterization and clearance actions for underwater UXO.

The objective of this project was to advance the current state of the art in broadband electromagnetic sensor technology for underwater detection and discrimination of UXO, extending the sensor detection range so as to widen the sensor footprint.

Broadband discrimination methods applicable to underwater UXO were developed based on the electromagnetic induction spectroscopy (EMIS) technology pioneered by Geophex. A promising phenomenon, called the current-channeling effect, was investigated to extend the underwater detection range, and extensive field experiments were conducted to verify such effects. Required sensor parameters and configuration to maximize the detection range were determined. Signal processing algorithms for underwater UXO detection and discrimination also were developed.

The project team developed and deployed an operational underwater GEM-3 sensor, which has shown promise as a surface boat-towed, sled-mounted, or bottom-dragged system, and UXO detection capability was demonstrated. Results indicate that characterization of UXO and clutter for discrimination with EMI is possible and, specifically, EMIS-based discrimination with GEM-3 data is viable. Distortion of the intrinsic target spectra as measured in free-air arises out of current-channeling response (CCR). Propagation effects related to currents induced in the seawater increase with frequency and distance. For targets within a meter with lateral offset, these effects are generally weak, suggesting the use of a narrower frequency band than normally used on land.

Clearing underwater UXO poses technical challenges in detection, discrimination, survey platform, navigation, and logistics. This research in underwater EMI detection and discrimination will have an impact on the development of detection strategies for underwater UXO by providing a new sensor technology not only for remediating underwater UXO sites but also for many other applications in marine geotechnical engineering. (Project Completed – 2005)