The goal of this project was to build a ship-deployed towbody instrumented with multiple acoustic sensors for detection, classification, and geolocation of munitions on and in ocean sediments. Then to formally demonstrate its capabilities via operation over a region of Sequim Bay, Washington State, where an unknown number of inert unexploded ordnance (UXO) and clutter objects were placed within a 50 meter radius circle at unknown locations.

The baseline Multi-Sensor Towbody (MuST) system comprises a FOCUS-3 towbody manufactured by MacArtney Underwater Technology, two towbody-mounted sonar systems manufactured by EdgeTech, a suite of towbody orientation and motion sensors, a shipboard handling system and shipboard data acquisition and analysis hardware and software. Together, the sonars can image the top 1-2 meter of the sediment with resolution voxels of 2.5 cm x 2.5 cm x 2.5 cm (when operated 5 meters above the water/sediment interface) and image the water/sediment interface with sub-cm pixel resolution.

During the demonstration in Sequim bay in September 2021 there were 42 detections that were subsequently classified as a target of interest or clutter via a Convolutional Neural Network (CNN) classifier. 18 of 23 UXO were correctly classified. MuST geolocation results were within 2 meters of ground truth measurements for 87.5% of the objects for which both MuST and ground truth measurements existed. Per day costs were O ($20,000) as operated during the demonstration. Actual daily operation costs and area coverage rate may be tailored to the mission parameters.

Use of underwater acoustics will always be subject to environmental assessment. However, the source levels of EdgeTech Buried Object Scanning System (eBOSS) are low and the other acoustic systems on MuST operate above 200 kilohertz. MuST is not an off-the-shelf technology that can be purchased and immediately operated by survey companies. There is significant training required. After that training, however, MuST is no more complicated to operate than other sonar system platforms. The purchase cost O ($2,000,000) of a fully instrumented MuST will be a barrier for smaller survey companies. An option to lease instead of buy could be viable for those smaller companies if supported by the stakeholder community.

Publications:

K. L. Williams, T. M. Marston, T. McGinnis, “Multi-Sensor Towbody”, Sea Technology, Sept. 2021, 8- 11.

K. L. Williams, T. Marston, D. Woodruff, S. Cazares, “Results from an informal demonstration of a buriedUXO detection, classification, geo-location system”, Underwater Acoustics Conference and Exhibition (UACE) 2021.

K. L. Williams, T. M. Marston, “Multi-Sensor Towbody (MuST): an expandable platform for detection, classification, and geolocation of UneXploded Ordnance,” Oceans 22, Virginia Beach, Virginia, Oct. 2022.