Defense, Security & Acoustic Research

Passive Acoustical Target DCLT

The Jetyak provides the Defense, Security and Intelligence community an autonomous vessel platform capable of passive detection, classification, localization, tracking and interception of acoustic targets.

Two Jetyaks were deployed in Great Harbor off Woods Hole, MA each equipped with a line array of eight HTI-96-MIN hydrophones sampled at 19.2 kHz using a Measurement Computing USB-1608FS-Plus-OEM data acquisition board, with data stored and processed on an inexpensive Raspberry Pi 3 Model B Single Board Computer running propretary signal propcessing software. The target was a single Lubell LL916C underwater acoustic source emitting a continuous 1kHz tonal and both the source and the hydrophone array were operating under 1m of water.

Jetyaks were able to track and intercept a stationary target on the dock with a single vehicle and stationary target in the harbor with two vehicles. This was performed without exposing personnel to risks of being on the water, with the passive sensors being immune to counter-measure detection.

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UXO Detection

Many coastal areas around the world have Unexploded Explosive Ordnance hazards, left over from past military exercises or campaigns. Buried for years, many of these UXOs are active and can be exposed and even mobilized by high energy storms. Understanding mobility, burial and reexposure rates is essential to planning remediation efforts. It involves modeling the complex interactions of sediment type, seafloor morphology, hydrodynamic conditions and munition density to name a few, and is often carried out using UXO surrogates in energetic near-shore environments.

One of the most important measurements for any study of UXO mobility is bathymetry, and the Jetyak is the ideal vehicle for surveying small-scale seafloor morphology and rapidly changing bathymetry. A Jetyak equipped with a a 200 kHz downward-aimed echo sounder and Post-Processed Kinetic (PPK) GNSS was deployed off the cost of Martha's Vineyard, MA in two separate study areas with distinct environments (strong tidal currents vs an energetic surf zone). These areas are known to contain munition hazards, many dating back to WWII.

The study resulted in newly discovered knowledge on the parameters required for UXO migration over moderate distances (100 m) previously not available. The mobile nearshore bathymetry data collected directly enabled further development of deterministic predictive models can be used as inputs to statistical models for operation over longer time periods and larger spatial domains. With refined models, remediation efforts become much more effective as it can predict objects migration into areas that have been previously cleared, and objects that have been detected and located can be removed before they migrate or become buried.

The challenging surf conditions also contributed to continued design refinements to improve vessel stability and overall mission efficiency.

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Port and Harbor Acoustic Modeling

Modeling acoustic propagation in enclosed or confined basins is an important element of port and harbor security. It enables the generation of distinct acoustically complex signatures in environments that contain a challenging mix of both natural and engineered features. Developing or improving underwater sound propagation models begins with the collection of accurate spatial data as a foundation element to describe the interaction of sound with all harbor features.

A Jetyak is the ideal collection platform for carrying out bathymetric surveys in these environments. Rapid data collection is required for minimal disruption to traffic in active ports, and accurate data collection over wide (3m) tidal range is a fundamental requirement to generate a true model. In surveys of the Quincy Fore River Shipyard area adjacent to Boston Harbor, MA, a monostatic swath bathymetric sidescan sonar (Ping DSP 3DS-DX-450) was carried approx. 60 cm below the waterline at the base of a centerline keel. Additionally the Jetyak carried a bistatic acoustic transducer (GTI M18-C-2.5) mounted 2 m below the waterline on a swinging ballasted stainless steel rod. To achieve the needed accuracy, the Jetyak carried a Novatel precision navigation system, which includes a real time kinetic GPS unit (RTK GPS) and an inertial measurement unit (IMU).

In this configuration, the accuracy of the gridded product is on the order 10 cm; the scatterer-detecting sonar system could localize reflections, from object or seabed, to a precision of 10 cm or better and comparisons of post-processed co-located seabed profiles from different passes were also found to agree to within 10 cm.

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