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In the Swim
April 1, 2005 By: Marty Whitford GPS WorldGPS Guides Autonomous Underwater Vehicles
GPS-synchronized acoustic transponders and sensors create an underwater baseline acoustic net. Long-baseline scans can provide data on surveys covering up to 2,000 meters. Ultra-short baseline (USBL) is a single sensor (three or more elements) mounted, for instance, on a surface ship. USBL's range can be in order of 3,000 meters in deep water. In shallow water, dependent on the acoustic environment, USBL's range can be as short as 200 meters. With USBL, one does not need to deploy a number of transponders on the seafloor, but the USBL system must be within acoustic range of the AUV for position updates.
The AUV relies on the INS and an Acoustic Doppler Current Profiler (ADCP), specifically a DVL, a pressure sensor and sometimes a compass, to estimate position information underwater. By transmitting and receiving signals to and from the acoustic transponders, or "pingers," the AUV can estimate how far it is from each transponder, and therefore how far it has traveled and its likely location.
 Photonics, Buoy Upgrades |
In rare cases, a fiber-optic link may provide information to supplement acoustic-based communications. Radio contact with the "mother ship" — typically a deployed vessel, but sometimes a base station/AUV command-and-control center — is possible only at the start and completion of an AUV run, and upon each resurfacing if applicable.
Armed with advanced technologies, AUVs can deliver real-time remote control capabilities and the capturing of — and reacting to — mid-mission position, sonar surveying and other underwater information.
Software controllers can provide full autonomy, easy configuration and modification of mission plans, customizable fault responses, and a host of other features.
A vehicle control computer can provide guidance and control using both AUV sensors and actuators, supporting a well-defined communications protocol for interface with various payload computers. An Ethernet network can connect components onboard the AUV, with an "umbilical cable" used for network connectivity when the AUV is on deck.
 ISE's Explorer AUV features a telescoping GPS receiver/antenna, allowing the drone to capture constant GPS time and position data in certain underwater surveying applications. |
On the mother ship, a network of computers can provide AUV mission planning, monitoring, data analysis and access to shipboard positioning sensors. Sensor and system add-ons, when integrated, can add tens to hundreds of thousands of dollars to the cost of an AUV.
Field Tests
In fall 2003, the Finnish Navy hosted sequential sea trials in which six countries using different mine countermeasure technologies competed to see who could find the most mines most efficiently."A HUGIN I AUV, now used by the Norwegian Defense Research Establishment (FFI) and Kongsberg Maritime for scientific research and development, won the exercise hands down," said Bjorn Jalving, principal scientist with FFI. "Embedded with a 12-channel GPS receiver and a DVL-aided inertial navigation system, the HUGIN found every single mine. Competing countries deploying state-of-the-art mine countermeasure sonars on surface vessels, and tow fish, did not perform anywhere near as well."
FFI began developing AUVs in 1991. For the past ten years, the organization has partnered with Kongsberg Maritime, manufacturer of the HUGIN I, 1000, and 3000 AUV models.
 Naval Sorties with UUVs |
The HUGIN 1000 is designed primarily for military applications including mine detection, identification and classification, and rapid environmental assessment, root survey and detailed seabed mapping.
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