The objective of this project is to investigate the impacts of environmental aging on acoustic scattering from unexploded ordnance (UXO) that have been submerged in the underwater environment for long periods of time. This effort aims to characterize long-term underwater aging related to corrosion and biofouling of UXO, linking changes in microstructure, morphology, cross-section, and surface characteristics to the acoustic response of underwater UXO.
It is expected that as UXO spend long periods of time (years or decades) in an underwater environment, accumulated biofouling layers and corrosion will lead to increasingly larger deviation of the acoustic scattering signature from the baseline pristine state. The relationship between corrosion/biofouling and changes to the acoustic signature are not well understood. Quantifying these linkages is the core focus of this project. To achieve this aim, this study will characterize the free-field frequency and aspect dependent acoustic scattering response of UXO that have been subjected to decades of natural environmental exposure. Additionally, the acoustic response of pristine, but otherwise identical, UXO that were not exposed to environmental conditions will be measured. Through comparison of the pristine and aged targets, this work will investigate potential shifts in the environmentally exposed UXO’s resonance frequencies, aspect variation, or overall target strength level that may have occurred due to corrosion-biofouling effects. By looking at the free-field acoustic scattering response, other environmental effects, such as sediment burial or seabed roughness scattering, will be isolated from exposure-induced changes to the UXO baseline acoustic response. Analytical material characterization and high-resolution imaging techniques will be employed to determine whether shell material loss or formation of specific biofouling-corrosion products (oxides, sulfides, organics, calcium-based, etc.) correlate to the modified acoustic signature.
This research will enhance the scientific understanding of the acoustical effects of biofouling, calcification and corrosion of manmade objects, which could have a broader range of application to fields within underwater acoustics outside of sonar-based target detection. Furthermore, the experimental results obtained in this effort will provide input to the target physics modeling community for better understanding of impacts of environmental aging on the acoustic scattering response of UXO. The current state of scientific knowledge is lacking on corrosion and biofouling effects on the acoustic response of submerged targets. The long-term goal of this study is to benefit the Department of Defense by increasing the understanding on this topic, ultimately improving and facilitating sonar detection and classification of UXO and other targets that have been in the water environment long enough for degradation to occur due to biofouling or corrosion.