475 research outputs found
Challenges of using an AUV to find and map hydrothermal vent sites in deep and rugged terrains
No full textIn March 2010, the Autosub6000 AUV embarked on a cruise to discover, locate and map hydrothermal vent sites in an active spreading centre, the Cayman trough in the Caribbean sea. The environment provided the challenge of steep and rugged terrain together with deep water (in places greater than 5000 m). Autosub6000 is a flight class, hydrodynamically shaped AUV, with good endurance capability, making it well suited for searching for plume signals and mapping terrain over the required moderately large areas. However, it must fly at a forward speed greater than 0.8 ms-1 to achieve control, and so it requires a capable forward look collision avoid capability. Another potential challenge is navigation. To make best use of ship time, Autosub6000 missions are commonly conducted with neither the support ship in attendance, nor an acoustic transponder long baseline network. Hence positioning is dependent upon the AUV autonomous navigation (aided by a position fix after the AUV’s descent to within ADCP bottom tracking range of the seabed). For the cruise on the UK research ship RRS James Cook, the AUV was equipped with sensors for EH (redox potential), turbidity, CTD, tri axis magnetometer, and an EM2000 multibeam sonar. The paper describes the Autosub6000 vehicle, its systems, capabilities, the missions it undertook in the deep Caribbean sea, and the discoveries it made. The missions, although ultimately very successful, were not without problems, with, for example, the steep seabed slopes, at times affecting the accuracy for the navigation system. The paper will also discuss these issues and how they might be addressed in the future. <br/
Autonomous underwater vehicle collision avoidance for under-ice exploration
No full textOn 22 August 2004 the Autosub-2 autonomous underwater vehicle (AUV) was on its return leg of a 144 km, 24 h under-ice mission in the Arctic sea over the Northwind Shoal off the northeast Greenland coast when it found its path blocked by a deep ice keel that had drifted across its planned mission route. After three attempts, the Autosub found a way around the keel and continued on its way to rendezvous with its mother ship. This paper reports the development, testing, and operation of collision and obstacle avoidance techniques used in the Arctic and Antarctic under-ice expeditions of the Autosub-2 AUV.<br/
Low-altitude terrain following and collision avoidance in a flight-class autonomous underwater vehicle
No full textAn autonomous underwater vehicle (AUV), Autosub6000, has been shown to operate safely at altitudes as low as 3?m above rugged and complex sea floor environments. This capability is essential for future AUV missions in such environments, e.g. high-resolution surveys using colour photography or multi-beam sonar bathymetry. This was achieved through the development of an obstacle avoidance system for the AUV, incorporating relatively low-cost off-the-shelf components and simple algorithms. This paper details the specification, design, and testing at sea of Autosub6000's obstacle avoidance system. It describes how the specification of the system was influenced by the need to retrofit it into the existing control architecture, together with the pragmatic need to minimize overall complexity. The sensor used in the obstacle avoidance system is a mechanically scanned forward-looking sonar, and the control algorithm is based upon the detection of the range and elevation of the horizon relative to the AUV. The avoidance behaviour is by default to fly over obstacles but, if this is not possible, a turn-around and retry collision avoidance algorithm is invoked. Results are presented of the system's performance during recent deep-water trials of the AUV over the Casablanca Seamount region of the Atlantic Ocean
Range-only positioning of a deep-diving Autonomous Underwater Vehicle from a surface ship
No full textThis paper describes a method for the precise postprocessed
positioning of a deep-diving autonomous underwater vehicle
(AUV) using only a set of acoustic ranges from a surface ship
while the AUV executes a closed path under the ship. This approach
avoids the use of either a precisely calibrated (and consequently
expensive) ultrashort baseline (USBL), or a long baseline
(LBL) system (which is expensive in ship time to deploy). Results of
Monte Carlo simulation and field results from the first trials of the
Autosub6000 AUV are presented to support the hypothesis that an
AUV at 6000-m depth can be positioned to an accuracy commensurate
with global positioning system (GPS) quality or better, within
a period of 1 h
Autosub6000: its first deepwater trials and science missions
No full textIn September 2007 on RRS Discovery, theAutosub6000 autonomous underwater vehicle (AUV)completed its first deepwater engineering trials and,fitted with a multibeam bathymetric mapping sonar,carried out its first science missions less than a yearlater as part of a geology and geophysics sciencecruise onboard the RRS James Cook. This paperdescribes how the issues of energy storage, navigationand buoyancy control were tackled that specificallyaffect a deep-diving AUV, capable of operating withtrue autonomy independently of the mother ship
Collection of water samples from an autonomous underwater vehicle for tracer analysis
No full textA compact water sampler rated to full ocean depth has been deployed from an autonomous underwater vehicle (AUV) to enable oceanographic tracer measurements. Techniques developed to allow the instrument to collect up to 49 samples of sufficient purity for tracer measurement without the need for extensive flushing have increased its sampling frequency, allowing a 200-mL seawater sample to be collected in 10 min. This is achieved by flushing the instrument and sample containers before deployment with a fluid of known properties that can be detected after recovery using salinity analysis. A deployment in which water samples were collected for oxygen isotope ratio analysis is presented as an example. Factors limiting the reliability of the instrument when deployed from an AUV are identified and procedures are developed to address critical problems.<br/
Pneumococcal carriage in United Kingdom families: Estimating serotype-specific transmission parameters from longitudinal data
No full textRepeated observations of pneumococcal infection in 121 United Kingdom families (October 2001-July 2002) were used to explore the transmission properties of five highly prevalent pneumococcal serotypes (6A, 6B, 14, 19F, 23F). A family-based Markov model was developed, and maximum likelihood estimates were produced for model parameters. The authors found higher community acquisition rates among preschool children for all serotypes and higher within-household transmission for 6A and 14. Significant differences in the spontaneous clearance rate were estimated between age categories and serotypes, with 6B being carried for almost 4 months in children. Different mechanisms of competition between serotypes were investigated, and a complete exclusion model (i.e., the resident strain cannot be outcompeted by challengers) was discarded in favor of a competing mechanism that leaves a resident serotype partially or fully susceptible to challengers. Large variation was found in the challenging strength, which was low for 19F and 23F and high for 6A and 6B. Serotype 6B was the only one characterized by high resistance capacity. Only small differences in the transmission characteristics were found when vaccine and nonvaccine serotypes were grouped, suggesting that a serotype-specific analysis is needed to detect distinctive serotype behavior. © The Author 2007. Published by the Johns Hopkins Bloomberg School of Public Health. All rights reserved
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