Underwater Acoustic Positioning Systems for MEC Detection and Reacquisition Operations
There have been few advances in commercially available, high-precision underwater positioning systems to support munitions and explosives of concern (MEC) detection needs. Though the basic technologies for detecting underwater unexploded ordnance (UXO) are the same as those on land, the underwater environment poses a distinct challenge to positioning geophysical measurements, particularly when the need exists to compensate for current, wave action, and wind when calculating accurate sensor positions. The objective of this project is to modify two long baseline (LBL) positioning systems, AquaMap Seafloor and RangeNav, for use in high-precision underwater MEC detection and reacquisition operations. Both are acoustic positioning systems manufactured by Desert Star Systems, LLC.
AquaMap Seafloor is a wireless LBL positioning system consisting of four self-contained baseline transponders, a tow-fish mountable mobile station (analogous to a global positioning system [GPS] antenna mounted on a land-based sensor), and surface station software. This LBL system uses time-of-flight between baseline transponders and the mobile station to compute the mobile station's position. When integrated with diver operations, up to 10 divers can use mobile dive stations, which are similar to a personal digital assistant (PDA) to record custom-defined observations that are automatically associated with their location. The system also can be used to navigate divers to predetermined locations on the sea floor, and it allows two-way communication between divers and top-side personnel.
RangeNav is a cabled system that consists of any number of seafloor-mounted listening stations linked by a cable to each other and a surface station. RangeNav tracks a pinger that is mounted on the object (or array) to be positioned. The cabled approach scales to cover any desired area, using more listening stations and cables to provide increased coverage as needed. The system also produces a higher position update rate of under one per second, as compared to 2-4 seconds for AquaMap Seafloor. While deployment is simple by the standards of cabled systems, it is still more involved than for AquaMap Seafloor.
It is anticipated that the AquaMap Seafloor and RangeNav systems will be comparable in price to survey-grade, real-time kinematic differential global positioning system (DGPS) or robotic total stations and will generate simple coordinate strings that are output via RS232, which can be recorded by any data acquisition system commonly used today. The systems also can benefit the UXO community in providing a means to reacquire anomalies, with at least 30-centimeter accuracy, and record anomaly findings using the dive station, similar to many land-based DGPS/PDA combination systems in use today. (Anticipated Project Completion - 2009)
Points of Contact
Mr. Andrew Schwartz
U.S. Army ESCH
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