The primary objective of this project is to demonstrate and validate the ability of the U.S. Naval Research Laboratory’s autonomous underwater vehicle (AUV)-based structural acoustic sonar to detect, classify, and localize proud and buried unexploded ordnance (UXO) at real-world munitions response sites as an integral partner in generating the necessary site investigation information that confirms or excludes the presence of munitions and explosives of concern at the site. Two example sites considered to be candidates for demonstrating this technology are Vieques, Puerto Rico and the San Diego Harbor in California. Further, in carrying out these demonstrations, incorporated objectives are to evaluate the system capabilities, develop operational concepts, develop quality metrics, and expedite technology transition. The ability of this system technology to prosecute proud and buried UXO has been demonstrated in blind tests in the Boston Harbor and at Sequim Bay. The expected information provided by the application of this new technology to site inspection activities at on-going remediation sites includes the detection (PD ~ 1), classification (PC ≥ 0.9), and localization (~1m) of both proud and buried UXO.

The technology includes two complementary AUV-based structural acoustic systems: a side-look configuration used in wide area coverage against proud or partially-buried UXOs and a down-look configuration capable of detecting fully buried UXO. The AUV platform is a synthetic aperture (SA) sonar system in which a large virtual aperture is formed in the along-track direction designed to enhance the performance and imaging resolution of the sonar. The novel down-look configuration contains a pair of retractable receiver wings capable of looking deeply into the sediment and forming three-dimensional volumetric images of fully buried objects. The relatively low frequencies of the sonar penetrate the sediment providing access to targets buried meters beneath the seafloor. In both systems, echo data collected over multiple flight paths allows the construction of the target’s acoustic color spectrum, i.e. its spectral content versus observation angle, which contains the classifying features shown to be effective in discriminating between UXO and clutter. The current SA sonars developed under previous SERDP and ESTCP projects are implemented on a 21-inch diameter Bluefin AUV, and an ongoing ESTCP Program MR23-7753 is currently focused on adapting this SA sonar technology for implementation on a smaller man-portable AUV while maintaining equivalent performance.

High detection and classification performance against proud and buried UXO has been demonstrated in blind tests in the Boston Harbor and at the Sequim Bay Test Range. At the latter site, a P_d P_c = 0.95 was achieved with only two false alarms for UXO calibers larger than 60mm. Further, the AUV-based sonar successfully found UXO targets that went missing at the Sequim Bay Test Range, detecting and localizing the UXO 100 meters from their original location. The successful prosecution of deeply buried targets as demonstrated especially in the Boston Harbor has not been demonstrated by other technologies such as side scan and high-resolution imaging sonars and magnetic induction detectors since these do not penetrate the sediment sufficiently. The deployment costs of the technology will be significantly reduced with the planned successful implementation of the sonar on small AUVs in ESTCP project MR23-7753 saving money for the Department of Defense and civilian applications of this technology. (Anticipated Project Completion - 2028)