October 04, 2005

AUVs for mine countermeasures shine at UUVS 2005

October, 03 2005

Small, manually launched AUVs were very much in evidence at the 7th UUVS, most conspicuously the little Gavia, a 1.7 m long, torpedo-like vehicle weighing about 44 kg in air and made by Hafmynd Gavia in Reykjavik, Iceland. On the first run on Wednesday, the Hafmynd people had clearly angered the god of demonstrations somehow because the AUV disappeared into the waters of Southampton Docks and refused to communicate despite efforts to contact it with an acoustic modem linked to the ruggedized laptop control station and anxious monitoring of the Iridium satellite phone it calls when it surfaces. Operator error, it turns out, was the cause: the pre-programmed mission plan had somehow combined a high-speed surface run with a steep dive angle. The inevitable consequence was a nose-first entry into the mud about 9 m down. They recovered the fully-functional Gavia and corrected the problem in time for a successful demo the following day.

Make your own modules

Gavia has a pressure hull divided into modules, each machined from aluminium alloy which is gold-anodized for extra corrosion resistance, held together with the proprietary QuickLock mechanism and sealed with double o-rings. From front to rear the module sequence runs: nose cone, battery, control and communication, propulsion and actuators. Payloads can be installed in the nose cone, C2 module (and in a variety of additional modules that can go between the C2 module and the propulsion section.) Customers can specify their own payload modules.

Existing customers include the US Navy's Space and Naval Warfare Systems Centre (SPAWAR) in San Diego and the National Research Council of Canada. SPAWAR ordered one for testing in mine countermeasures applications, and has an option for up to 10 more. The SPAWAR vehicle is equipped with a dual frequency MSTL 900/1800 kHz Side Scan Sonar, camera and strobe, and collision avoidance sonar. Navigation is provided by GPS on the surface and high-precision DVL-aided INS while underwater. An Iridium link, WLAN, and the acoustic modem provide communication.

The NRC's Gavia will be used for inspection of potable water pipes, testing of new sensors and actuators, free-swimming experiments and hydrographic mapping in lakes and oceans.

Hafmynd has also been working with EADS Deutschland GmbH Defence and Communications Systems to integrate Gavia into the mine countermeasures module of EADS's Advanced Naval Combat System (ANCS).

With 10 years of development behind it, Gavia has the feel and smell of a well-developed product and certainly looks the part in its gold anodized finish. It will need to be because it has to compete with the market-leading Remus vehicle developed over several years by the Woods Hole Oceanographic Institution and now manufactured by Pocasset, MA company Hydroid. More than 60 Remus vehicles have been delivered to customers and they have built up thousands of operational hours.

Remus speeds MCM ops

NATO now regards Remus as a viable commercial off-the-shelf system. The vehicle has taken part in NATO mine countermeasures exercises conducted between the Autumn of 2002 and the Spring of 2004 in La Spezia (Italy) Strenraer (Scotland) Rotterdam, (the Netherlands) and Olpenitz (Germany). Along with the larger experimental Ocean Explorer (OEX) AUV from Florida Atlantic University, Remus helped demonstrate convincingly that AUVs can dramatically speed up mine hunting operations in shallow water when used with MCM vessels and EOD divers.

Michael Rothenbach from the NATO Undersea Research Centre (NURC) in La Spezia told the audience at UUVS '05 that 'a gain of at least one order of magnitude in time was demonstrated in all experiments.'

He went on to say that although Remus can easily achieve the positioning accuracy required for EOD divers to re-aquire mines, confined areas may impose restrictions on the best placing of LBL transponders and therefore reduce the vehicle's navigation accuracy, and that obstacles such as piers, navigation buoys and moorings might limit its ability to manoeuvre. He recommended that other navaids such as GPS and INS be used to overcome the limitations of LBL transponders in confined spaces.

Partially buried mines are hard to classify with HF side-scan sonar, but they are detectable and can be classified using multiple images from different angles, a technique that demands very precise navigation to help ensure that the various images really are of the same target, said Rothenbach. Completely buried mines, however, are not detectable with current sonars.

Improvised bombs present particular problems because they come in a wider variety of shapes and sizes than military mines, most of which resemble the kind of objects that typically litter the bottom of commercial ports.

Rothenbach recommends that sensitive areas be surveyed regularly and any new objects noted with the aid of evolving automated change detection techniques. As yet, these are limited to finding objects that can be detected by standard Computer Aided Detection (CAD) algorithms and are susceptible to false alarms, but: 'We do believe that this is the only viable option until better quality and higher frequency sonar are used.'
He also calls for future studies of sensors that might be able to classify mines buried in soft mud, magnetic sensors and chemical sniffers for example.

Towards a 3D future?

Lawrence Langebrake from the University of South Florida's Center for Ocean Technology gave a presentation that concentrated on an innovative sensor suite that a USF team has developed using a mix of its own and commercially available sensors. The Mobile Inspection Package (MIP) contains an 3D imaging sonar from CodaOctopus called the EchoScope Mk II, the USF's own digital video system and 3D Laser Line Scanner (LLS), an image scaling system from Tritech that uses a laser scaling video camera and a DIDSON 2D imaging sonar.

USF developed the MIP under the guidance of the US Office of Naval Research and the US Coast Guard's Research and Development Center (Groton, Connecticut), and tested it on a pole mount from a boat, an ROV and a Blue Fin 32 (32 cm/12.75 in diameter) AUV. Langebrake showed some excellent 3D, geo-referenced images of mine like objects attached to ship hulls, harbour walls, bottoms and jetty structures. Some were single-sensor images taken on one occasion, while others were composite mosaics of output from different sensors at different times, showing the flexibility of the system. The laser scaling camera produced a particularly clear image of a Walmart Christmas tree stand that was doing a very good impression of a limpet mine attached (with permission, of course) to the hull of a Coast Guard cutter. This instrument also provides very accurate size information on objects.

HUGIN in service

Exciting and promising though they are, the events described so far have been trials and experiments. In contrast, Nils Storkensen from the Norwegian Defence Research Establishment presented some lessons learned in the Royal Norwegian Navy's mine hunting operations with the HUGIN family of larger AUVs built by Kongsberg.

Experiments with HUGIN 1 led to an order from the RNoN for a dedicated military HUGIN 1000 vehicle and the installation of the infrastructure needed to run missions aboard the mine hunter KNM Karmøy in the summer of 2002. During 2002 and 03, Karmøy and HUGIN 1 performed several route surveys in key areas around Norway.

In the run-up to NATO Exercise Northern Light 03, the vehicle surveyed a corridor 500 metres wide and 12 nautical miles long in the shallow waters and 3 kt currents of Luce Bay, Scotland, completing four missions successfully in 48 hours, each in the six hours of highest tide, recharging batteries at low tide. The vehicle performed its pre-programmed missions by itself with Karmøy standing off a few miles but the two were able to communicate acoustically at ranges of 2 to 3 nm. Once processed, the data became a set of AML (Additional Military Layers) files for MCMVs to use in clearance operations.

Less than two weeks later, Karmøy and HUGIN 1 were demonstrating route survey, mine mapping and covert Rapid Environmental Assessment (REA) operations outside Hanko, Finland, for the Finnish Navy. Change detection software was used to find mine-like objects laid between missions. The AUV completed some of these missions completely on its own. In one it mapped a 3 km2 area in six hours while the crew slept.

Six weeks after the delivery of the military HUGIN 1000, Karmøy and its new AUV completed 13 missions (mainly covert REA and MCM work) off Norway in NATO Exercise Joint Winter 04, then harbour surveys around Arendal, Norway in Blue Game 04.

In the autumn and winter of 04, the two were deployed as part of NATO's Standing MCM Force North, participating in mine clearance operations in the Baltic off Lithuania, Latvia, Germany and Denmark in waters littered with tens of thousands of mines and unexploded ordnance from the last century.

On 20 April this year, HUGIN 1000 was operating off Bergen, Norway. Thanks to acoustic modem communications with Karmøy and a satcom system on the ship, its data was shown in real time at the annual Azalea Festival in Norfolk, Virginia. The two-way link enabled commands to be sent to the AUV from the other side of the Atlantic. On this mission, HUGIN found a US submarine that sank in 1931. By May/June, the two were back in the Baltic off Latvia, where they discovered a couple of live mines that were then neutralised by divers.

Among many lessons learned, Nils Storkensen emphasised the importance of testing at sea and involving the end-user in the development programme as early and as much as possible. One of the main problems was in getting the control system and processor of the main sensor, an EdgeTech 4400-SAS (Synthetic Aperture Sonar), working properly. This system is now performing acceptably in the very challenging waters around the Norwegian coast, says Storkensen.

The RNoN has subsequently ordered a HUGIN 1000-MR AUV, which will be equipped with a 'more robust and capable' SENSORTEK SAS.

Seaglider odysseys

The most elegant vehicles discussed at the conference were undoubtedly the Seagliders presented by Charles C Eriksen from the University of Washington's School of Oceanography. These remarkable little AUVs (1.8 m long, 52 kg in air) can traverse the world's oceans in data gathering missions lasting many months with no obvious means of propulsion or control.

A Seaglider will glide on short wings down to a pre-set depth, then rise to the surface, where it will tip nose down to stick its tail-mounted antenna out of the water to get a GPS fix, then send data home and download new instructions over an Iridium satellite phone.
A Seaglider's propulsion system may not be immediately discernible, but it is effective. It propels itself through varying its buoyancy by pumping compressible oil between high- and low-pressure chambers that together act just like a swim bladder in a fish. Pitch and roll control come courtesy of the battery pack that can be slid back and forth and swung from side to side.

The battery powers the pump, the motor to tip and slide itself, the GPS and satellite phone and its sensors, which measure water temperature, salinity, electrical conductivity, dissolved oxygen, chlorophyll fluorescence and optical backscatter. Knowledge of the glider's hydrodynamics combined with GPS fixes allows researchers to calculate depth-averaged current speeds accurate to 0.01 m/sec over individual dives.
That propulsion system is remarkably efficient, the 10 kJ in the lithium thionyl chloride batteries being enough to power several hundred dives to 1 km. It cruises at 'half a knot on half a Watt,' says Eriksen.

The team at the University of Washington have built 22 gliders, eventually losing eight out of the first 10 built, but only two of the subsequent 12. One of the hazards is running out of battery power, which can happen if a glider gets caught in an eddy current for a long time, but Eriksen says that his team has now learned how to avoid such hazards most of the time.

Future developments include 'Deepglider' capable of diving to 6 km and an under-ice version of Seaglider equipped with an ice avoidance sensor.

AUVs coming of age?

While the ROV sector could be described as 'mature' thanks to the long-standing oil industry acceptance as ROVs as robust tools for tough jobs, the AUV sector is perhaps best thought of as 'adolescent' in that it is showing great promise and has growing real-world experience under its belt, but there are still important areas in which much development is still needed: collision avoidance behaviour, true autonomy, long range underwater communication, precise navigation and sensors capable of finding buried objects are among them.

European student AUV competition kicks off

While the US has the Grand Challenge for UGVs and AUV fest for the underwater robotics community, Europe has lacked a similar vehicle for attracting bright students and developing a base of expertise and enthusiasm to build the future AUVs – until now. The Student Autonomous Underwater Challenge --Europe (SAUCE) has secured support from the UK Defence Science and Technology Laboratory (DSTL), Edinburgh's Heriot Watt University and the National Oceanography Centre in Southampton and the first challenge for student teams 'target location' is set to take place at Pinewood Studios near Slough, Berkshire in July of next year. Industry support for individual teams is invited. Find out more.

Terminology v technology?

In current common use, the term UUV is generally used when people mean a free-swimming vehicle, but logically, the term 'Unmanned Underwater Vehicle' should encompass tethered Remotely Operated Vehicles and the free-swimming vehicles that are generally referred to as Autonomous Underwater Vehicles, whether they have true autonomy (very rare as yet) or whether they operate to a predetermined plan. Developments in sensors and control strategies based on artificial intelligence will lead to more and more 'autonomous' behaviour. Complicating the matter further, modern underwater acoustic communications allow an operator to control a vehicle directly without a cable, so a single vehicle could be an AUV and an ROV in the course of the same mission. Technology always outruns terminology!

Peter Donaldson


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