Effects of severe corrosion on acoustic signatures of underwater munitions

Sonar-based identification of underwater unexploded ordinance (UXO) is a potentially powerful technique for aiding in clean-up of former military sites, in which recovery of munitions is essential for public safety. We hypothesize that as UXO age for long periods of time in the underwater environment, accumulated effects of corrosion and material loss lead to increasingly larger deviation of the acoustic scattering signature from the pristine state, thus potentially confounding sonar-based target classification algorithm performance. To investigate this, a set of World-War-II-era miniature practice bombs (model AN-Mk 23), recovered from a brackish pond after about 80 years exposure, were obtained. Free-field acoustic color measurements were conducted on the samples, which exhibited a range of corrosion-erosion damage, in addition to clean, uncorroded samples and clutter objects for comparison. Analysis was conducted to isolate various corrosion effects on the acoustic signature. Additionally, we investigated impacts of corrosion on the performance of select classification algorithms. [Work sponsored by SERDP and DOD SMART Scholarship.]