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The U.S. Army Corps of Engineers (USACE) and the U.S. Navy have identified more than 400 underwater sites that are potentially contaminated with munitions. The majority of these areas are in shallow water (0-35 meters [m]) where the munitions pose a threat to human health and the environment. Acoustics represents one viable means of detecting and classifying these munitions. The Navy uses acoustics as one of its primary modalities under its mine countermeasure programs. Though the sensors used are similar in Navy and remediation systems, the operational requirements differ. Whereas the Navy problem points toward the use of autonomous underwater vehicles (AUVs) with automated target recognition, the operational scenario of munitions cleanup lends itself to lower cost towbody-deployed instrumentation and post-mission operator in-the-loop analysis. Furthermore, the availability of continuous global positioning system (GPS) fixes for the host ship and complementary on-ship tracking of the towbody affords the use of commercial systems for geolocation of munitions that have been detected and classified.
The first objective of this project is to build, test and demonstrate the performance of a system that uses a Multi-Sensor Towbody (MuST) to deploy detection, classification and geolocation hardware from a surface vessel. The hardware and software systems on the surface vessel leverage relatively low-cost, commercial off-the-shelf (COTS) components to reduce the number and complexity of expensive in-water components as well as the level of expertise and training required in the operators.
A second, complementary objective is to assist in the development of underwater testbeds. Test bed development has been identified as a key effort in the overall success of demonstrating the MuST (and indeed any ESTCP-funded) system capability. As part of the present work we will help develop an integrated strategy that incorporates the realities of underwater operations (as compared to land-based operations) while meeting the requirements of the stakeholder community.
The baseline system comprises a FOCUS-3 towbody manufactured by MacArtneyUnderwater 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 m of the sediment with resolution voxels of 10 cm x 10 cm x 10 cm and image the sediment/water interface with sub-cm pixel resolution. The system also has power and data communications and auxiliary ports to add other sensor modalities. The demonstration goals are to: 1) classify proud and buried munitions at a performance level of Pc>0.94 @ Pfa<0.1 (Pc is the fraction of correct classifications and Pfa is the fraction of false alarms), 2) to geolocate the classified munitions to less than +/- 2m, and 3) perform the remediation surveys at a rate of 0.1 km2/h.
Relative to the second demonstration goal, a Greensea INSpect GS4 - Fiber Optic Gyro [FOG] INS will be purchased and integrated it into MuST. This includes software development, integration, and testing to assimilate that hardware into the MuST system.
Relative to AUV solutions, a towbody system offers lower system cost, operational simplicity, 24/7 operational capability, strap on sensors with low integration cycles, and surface based power and data handling. Of particular importance is that the high-risk, in-water assets for a towbody are about half the cost of the equivalent AUV-based solution (1 million dollars vs. 2 million dollars). The operational envelope of the full towbody/sensor system is primarily in the 6-40 m water depth range. However, from a sensor standpoint, much of the detection, classification and geolocation strategy can be easily adapted to shallower water using a surface vehicle (e.g., a towed sled). In these shallower water scenarios combining acoustics with magnetics has the potential to enhance performance without increasing remediation timelines.