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USVs Find Use in Shallow-, Deepwater Applications

By Don Darling

The USV-2600 deployed in the Arctic.

Developments in unmanned systems technology, data telemetry systems, remote sensing and automation have provided a new set of tools for inland and offshore tasks, including survey, intervention, inspection and monitoring. Unmanned surface vehicles (USVs) can be applied to shallow- and deepwater operations.

SeaRobotics (Stuart, Florida) has developed a family of reconfigurable USVs allowing adaptation to various operational scenarios and payloads. Along with other hull forms, catamaran-type USVs offer a high degree of stability, a substantial payload capacity, moon pool-like equipment deployment capability and a large open-deck area to accommodate survey equipment.

These USVs utilize DC battery systems, AC/DC generator sets, renewable power sources or a combination of several energy sources. Communication with the USV is achieved by means of line of sight using a wireless telemetry system or high-bandwidth satellite networks that allow for extended endurance, long-range remote operation and operations from nearshore to far offshore.

When combined with other robotic devices and sensor payloads, USVs can operate 24/7 and minimize costs of inland, coastal and offshore tasks through the reduction of day rates and involvement of fewer personnel, as compared to vessel work.

USVs utilize standard commercial off-the-shelf (COTS) sensor suites that can be easily integrated. With the USV's large deck areas, power availability and communication bandwidth, payload integration can be as simple as plugging into the appropriate 'user ports' and securing the payload. Some of the sensors integrated include forward-looking and down-looking multibeam sonars, scanning sonars, single-beam echosounders, magnetometers, sub-bottom profilers, side scan sonars and pipeline pulse induction survey systems, as well as sampling systems and sensors used to detect obstructions and hazards to navigation. Many COTS sensor suites can be integrated during the design process or by the end user's reconfiguration of the payload deck to satisfy mission objectives.

USV missions range from simple bathymetric surveys, volume flow rate measurements in rivers or stream gauging to more challenging missions that involve cast sensor suites, towed sensors, ROV operations, or mine countermeasures (MCM) and autonomous mine neutralization.

Riverine and Coastal Surveys
Numerous systems are in use to quantify estuary, riverine and coastal environments. The Naval Postgraduate School has conducted riverine and coastal surveys to study the environment and quantify the statistical accuracy for USV-deployed sensors and the efficacy of USV operations.

These surveys deployed a SeaRobotics USV-2600, outfitted with a Teledyne RDI (Poway, California) 1,200-kilohertz acoustic Doppler current profiler (ADCP), a Tritech International Ltd. (Westhill, Scotland) PA200 altimeter, an AQUAscat (Hartley Wintney, England) 1000 acoustic backscatter sensor and a WetLabs (Philomath, Oregon) spectrophotometer. The system incorporated an Ashtech (Santa Clara, California) real-time kinematic GPS. The payload sensors acquired water quality, sediment transport and volume flow rate data in the Kootenai River of Idaho and the Elkhorn Slough in California. Extensive missions were performed to quantify data taken with both USVs and a YSI Inc. (Yellow Springs, Ohio) EcoMapper AUV.

The USV-2600 performed successfully due to its ability to station keep for extended periods within 1 meter of the desired location. The study used a station-keeping period of 10 minutes, but post-processing with Kalman algorithms indicated a four-minute dwell would have been sufficient.

The operation concluded that the USV's ability to precisely hold station in both time and space exceeded the ability of humans, showing it could effectively study parameters associated with the riverine flow environment.

Similarly, USVs used in studies performed by the U.S. Geological Survey and others in shallow waters have quantified oyster beds and gathered water quality data. The agency utilized EdgeTech (West Wareham, Massachusetts) FS-4200 dual-frequency side scan sonar (120 and 410 kilohertz) and sub-bottom profiler, Teledyne RDI 600-kilohertz Workhorse Rio Grande ADCP and Ashtech RTK GPS from Thales (Paris, France) to map current and acquire side scan sonar data and sub-bottom profiles to locate current and ancient oyster beds to track bed health and migration over time in Apalachicoloa Bay, Florida. CSA International Inc. (Stuart, Florida) performed a similar survey with a SeaRobotics USV-1000 trimaran in 1 meter of water to assess oyster beds in the St. Lucie River, Stuart, Florida.

The National Institute of Ocean Technology of India began conducting a survey in December 2011 with a USV-2600 to map current flows and acquire water quality data in the Gulf of Khambhat in northwest India. The gulf experiences 10-meter tidal swings with tidal currents ranging to 8 knots.

Using a Teledyne RDI 1,200-kilohertz ADCP and a YSI Inc. (Yellow Springs, Ohio) multifunction sensor, the USV continues to map water currents in the gulf during full tide cycles. The USV is outfitted with a 4-kilowatt, water-cooled, electric-start DC generator designed by SeaRobotics.

Survey tasks requiring hull-mounted bathymetric and side scan surveys, as well as those requiring towed sensor platforms, have been performed with similar USVs. To continue this article please click here.

Don Darling, president of SeaRobotics, received a master's in mechanical engineering from the Massachusetts Institute of Technology. He has 30 years of experience developing ROVs (Perry Triton System), AUVs, USVs, ocean sampling systems and autonomous hull-cleaning systems.

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