Demonstrating Calibrated Phase-Measuring Sidescan Sonar for Rapid Wide-Area and Detailed Mapping of UXO Shallower than 5 m
Dr. Kenneth Foote | Woods Hole Oceanographic Institution
This project will demonstrate an acoustic method for rapid, wide-area mapping of proud underwater unexploded ordnance (UXO) in the form of mortar shells (calibers 60 and 81 mm) and projectiles (calibers 105 and 155 mm) at depths shallower than 5 meters and in the presence of clutter objects. This is expected to yield detection, classification, and localization (DCL) data sufficient for Department of Defense (DoD) remediation of such UXO, thus contributing to the removal of conspicuous hazards to human life and avoidance of environmental degradation effects due to the inevitable release of hazardous materials from long-term submerged metallic objects. One or more members of the National Association of Ordnance Contractors (NAOC) are expected to observe the field demonstration. It is anticipated that they will advise on preparation of a technology transition tool in the form of a training course, with supervised instruction and practice, for personnel who map live underwater UXO. This project aims to incorporate the technology in a robotic system consisting of a high-frequency phase-measuring sidescan sonar, ancillary instruments to measure motion, heading, and position of the sonar, and an electric-powered autonomous surface vehicle (ASV), which would be transportable on a trailer.
A commercial off-the-shelf (COTS) high-frequency phase-measuring sidescan sonar (PMSS) will be the principal sensor. This operates at two frequencies, 520 and 1610 kHz, generating co-registered backscattering data at both frequencies and bathymetric data at the lower frequency. This sonar will be pole-mounted on the bow of a small, shallow-draft vessel. It will be used for UXO DCL by adapting and applying methods for sonar calibration, in-situ beam pattern estimation, and compensation for transducer nearfield effects. A motion-reference unit MRU will be mounted on the sonar for very precise and accurate measurement of the sonar orientation. Absolute position will be determined through the Global Positioning System (GPS), with antennas mounted on the vessel. The system will be tested and demonstrated on three readily accessible intertidal-subtidal zones in Cape Cod Bay, with respective sand, mud, and cobble bottoms, each seeded with government-furnished equipment in the form of mortar shells (calibers 60 and 81 mm) and projectiles (calibers 105 and 155 mm), at depths shallower than 5 meters and in the presence of clutter objects. These UXO will be surveyed using a Real Time Kinetic (RTK)-GPS instrument, supplemented at least by ground-based photogrammetry in the intertidal zone shallower than 3 m. These position data will enable presence-absence testing and cross correlation with sonar-derived UXO localization data, including both position and orientation.
At present, rapid, wide-area, shallow-water mapping of UXO with sufficient resolution for remediation lacks demonstration. It is believed that the adaptation of a COTS high-frequency PMSS for centimeter-scale resolution of bottom objects at depths shallower than 5 meters, with demonstration on UXO, will constitute essential, enabling technology for DoD-supported remediation of underwater UXO.