A survey of underwater vehicle navigation: Recent advances and new challenges

The Arctic seafloor remains one of the last unexplored areas on Earth. Exploration of this unique environment using standard remotely operated oceanographic tools has been obstructed by the dense Arctic ice cover. In the summer of 2007 the Arctic Gakkel Vents Expedition (AGAVE) was conducted with the express intention of understanding aspects of the marine biology, chemistry and geology associated with hydrothermal venting on the section of the mid-ocean ridge known as the Gakkel Ridge. Unlike previous research expeditions to the Arctic the focus was on high resolution imaging and sampling of the deep seafloor. To accomplish our goals we designed two new Autonomous Underwater Vehicles (AUVs) named Jaguar and Puma, which performed a total of nine dives at depths of up to 4062m. These AUVs were used in combination with a towed vehicle and a conventional CTD (conductivity, temperature and depth) program to characterize the seafloor. This paper describes the design decisions and operational changes required to ensure useful service, and facilitate deployment, operation, and recovery in the unique Arctic environment.

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Deep sea underwater robotic exploration in the ice-covered Arctic ocean with AUVs

In this field note, we detail the operations and discuss the results of an experiment conducted in the unstructured environment of an underwater cave complex using an autonomous underwater vehicle AUV. For this experiment, the AUV was equipped with two acoustic sonar sensors to simultaneously map the caves' horizontal and vertical surfaces. Although the caves' spatial complexity required AUV guidance by a diver, this field deployment successfully demonstrates a scan-matching algorithm in a simultaneous localization and mapping framework that significantly reduces and bounds the localization error for fully autonomous navigation. These methods are generalizable for AUV exploration in confined underwater environments where surfacing or predeployment of localization equipment is not feasible, and they may provide a useful step toward AUV utilization as a response tool in confined underwater disaster areas.

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Toward Autonomous Exploration in Confined Underwater Environments

This paper presents experimental results from a number of performance verification sea tests of the MARPOS(R) Doppler-inertial navigation system jointly implemented by Maridan A/S, Denmark, and the Technical University of Denmark for use onboard the MARIDAN series of AUVs. MARPOS(R) is a dead-reckoning based navigation system, the core of which is a state-of-the-art ring laser gyro (RLG) and a Doppler velocity log (DVL). The system also integrates a very accurate CTD sensor suite and a high quality embedded differential GPS receiver used at the surface for position initialization, a priori sensor calibration and moving base alignment of the INS. A series of accuracy verification tests were performed at a sheltered shallow water test facility, using a small surface vessel to allow simultaneous logging of DGPS reference positions and Doppler-inertial based dead-reckoning navigation data. The proven accuracy was 0.10% of distance traveled for straight line trajectories and 0.02% for site surveys, where navigation was performed in a confined area, typically 1/spl times/1 km. Results from a number of surveys carried out by a MARIDAN 150 AUV have confirmed the operational efficiency and robustness of the system. Correlation of overlapping sidescan sonar imagery indicates that the operational performance of MARPOS(R) actually surpasses the outcome of the surface vessel tests. A probable cause is the inherently more stable platform provided by an AUV as opposed to a small surface vehicle which is subjected to wave induced motion and the often more extreme sound velocity variations of the surface water layers.

High performance Doppler-inertial navigation-experimental results

In March and April 2010, an International Submarine Engineering (ISE) Explorer Autonomous Underwater Vehicle (AUV), built for Natural Resources Canada (NRCan), was deployed to Canada's High Arctic. Its mission was to undertake under-ice bathymetric surveys in support of Canada's United Nations Convention on the Law of the Sea (UNCLOS) Outer Continental Shelf claim. During this deployment several under-ice records were broken and several new technologies were demonstrated. This achievement was in part the result of the development work that ISE and Defence Research and Development Canada (DRDC) undertook from 1993 to 1996 on the Theseus AUV during the Spinnaker program. During this program Theseus successfully completed two 200 km under-ice missions from CFS Alert on Ellesmere Island. NRCan's AUV is an ISE Explorer class vehicle, with several innovative additions to make it suitable for Arctic survey work. Most notable are a 4000 m depth rated variable ballast system, a 1500 Hz long range homing system, and under ice charging and data transfer capabilities. A Short Range Localization (SRL) system was also developed for close range positioning. The homing and SRL systems were developed by Canadian defense scientists and engineers at DRDC. The Explorer's range was extended to approximately 400 km by adding an additional hull section to accommodate extra batteries. The Main Camp near Borden Island (78°13.50'N, 112°38.87'W) was the launch site for the AUV. It was launched from an 8 m by 2.5 m ice-hole, cut through 2 – 3 m of thick ice. After several test dives its first mission was a transit to a Remote Camp, over 300 km to the northwest. The AUV autonomously homed into the Remote Camp and was successfully docked at the ice-hole where, without being removed from the water, it was charged and survey data was downloaded, all through a 1.5 m square ice hole. Subsequently, a second survey mission greater than 300 km in round trip length was undertaken, after which the AUV returned back to the Remote Camp. Finally, the vehicle embarked on a return mission to the Main Camp for recovery. From beginning to end, the AUV spent nearly 12 days under the ice before being successfully recovered. In total, close to 1000 km of under ice survey was accomplished between the AUV launch, Remote Camp mission, and recovery. The AUV reached depths of 3160 m and transited at an average speed of 1.5 m/s at an altitude of 130 m off the seabed. ISE and DRDC are now preparing for a 2011 deployment to collect additional data UNCLOS data. Aspects of the pre-deployment that will be presented include fail-safe provisions, mission planning, risk assessment, and mission logistics. Operational aspects to be discussed will include dealing with AUV operations in the extreme cold, initialization of the inertial navigation system, under-ice acoustics, acoustic homing to the recovery site and the procedures for recovery.

12 days under ice – an historic AUV deployment in the Canadian High Arctic

International submarine Engineering Research and the Esquimalt Defence Research Detachment of the Defence Research Establishment Atlantic have worked together to develop a large autonomous underwater vehicle, named Theseus, for laying optical fiber cables in ice-covered waters. It was able to lay a fiber optic cable in a completely autonomous mode for a distance of 200 km under Arctic sea-fee and then return to the launch station for recovery. It operates in either depth-keeping mode or bottom-following mode, was designed to operate at a maximum depth of 1000 m, and has operated at a depth of 425 m. The vehicle is equipped with an inertial navigation unit and Doppler sonar speed sensor for autonomous navigation, a forward-looking obstacle avoidance sonar, an acoustic homing system, and acoustic transponders for use with surface tracking stations. An acoustic telemetry system enables communication with Theseus from surface stations, and an optical telemetry system is used for system monitoring while Theseus is laying optical fiber cable. All sub-systems are controlled by an MC68030 based sensor integration and control computer. Theseus' qualities of covertness, long endurance and precise navigation make possible such tasks as long base-line oceanographic data collection, remote route surveys, remote mine hunting, the rapid deployment of acoustic and non-acoustic surveillance systems, and even the towing of mobile sensor arrays. The paper describes the vehicle and presents the results of the evaluation trials and its first cable laying mission.

A. Pope

Papers

The Theseus autonomous underwater vehicle. A Canadian success story