Swallow Hybrid Underwater Glider
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Sample records for autonomous underwater gliders
Underwater Gliders: A Review Directory of Open Access Journals (Sweden) Javaid Muhammad Yasar 2014-07-01 Full Text Available Underwater gliders are a type of underwater vehicle that transverse the oceans by shifting its buoyancy, during which its wings develop a component of the downward motion in the horizontal plane, thus producing a forward force. They are primarily used in oceanography sensing and data collection and play an important role in ocean research and development. Although there have been considerable developments in these gliders since the development of the first glider concept in 1989, to date, no review of these gliders have been done. This paper reviews existing underwater gliders, with emphasis on their respective working principles, range and payload capacity. All information on gliders available in the public domain or published in literature from the year 2000-2013 was reviewed. The majority of these gliders have an operational depth of 1000 m and a payload of less than 25 kg. The exception is a blend-body shape glider, which has a payload of approximately 800 kg and an operational depth around about 300 m. However, the commercialization of these gliders has been limited with only three know examples that have been successfully commercialized. Ocean Research Enabled by Underwater Gliders Science.gov (United States) Rudnick, Daniel L. 2016-01-01 Underwater gliders are autonomous underwater vehicles that profile vertically by changing their buoyancy and use wings to move horizontally. Gliders are useful for sustained observation at relatively fine horizontal scales, especially to connect the coastal and open ocean. In this review, research topics are grouped by time and length scales. Large-scale topics addressed include the eastern and western boundary currents and the regional effects of climate variability. The accessibility of horizontal length scales of order 1 km allows investigation of mesoscale and submesoscale features such as fronts and eddies. Because the submesoscales dominate vertical fluxes in the ocean, gliders have found application in studies of biogeochemical processes. At the finest scales, gliders have been used to measure internal waves and turbulent dissipation. The review summarizes gliders' achievements to date and assesses their future in ocean observation. Underwater Glider: Its Applicability in the East/Japan Sea Directory of Open Access Journals (Sweden) Jong Jin Park 2013-06-01 Full Text Available The underwater glider is an autonomous vehicle that can glide through the ocean interior by using a pair of wings attached to its body and can move up and down through the water column by changing its buoyancy. As of now, there are three widely-used gliders, namely, the Spray that was codeveloped by Scripps Oceanographic Institution and Woods Hole Oceanographic Institution, the Slocum produced by the Webb Research Cooperation, and the Seaglider that was produced by the University of Washington. In this paper, I will introduce these three gliders and discuss the principles and procedures related to glider operation as well as the application and extendability of modern physical and biogeochemical sensors to gliders. My experiences in developing a glider for measuring ocean turbulence and testing it 7 times during 12 days are shared in this paper. On the basis of my experiences and knowledge, different kinds of aspects that should be considered for successful glider operation are discussed. In addition, a suggestion is made as to what would be the ideal way to operate underwater gliders in the East/ Japan Sea. At the end, the current status of active glider operation teams is presented and the efforts to proceed toward future gliders are briefly introduced. Dissipation measurements using temperature microstructure from an underwater glider OpenAIRE Peterson, Algot Kristoffer; Fer, Ilker 2014-01-01 Microstructure measurements of temperature and current shear are made using an autonomous underwater glider. The glider is equipped with fast-response thermistors and airfoil shear probes, providing measurements of dissipation rate of temperature variance, χχ, and of turbulent kinetic energy, εε, respectively. Furthermore, by fitting the temperature gradient variance spectra to a theoretical model, an independent measurement of εε is obtained. Both Batchelor (εBεB) and Kraichnan (εKεK) theore... Parametric geometric model and shape optimization of an underwater glider with blended-wing-body OpenAIRE Sun Chunya; Song Baowei; Wang Peng 2015-01-01 Underwater glider, as a new kind of autonomous underwater vehicles, has many merits such as long-range, extended-duration and low costs. The shape of underwater glider is an important factor in determining the hydrodynamic efficiency. In this paper, a high lift to drag ratio configuration, the Blended-Wing-Body (BWB), is used to design a small civilian under water glider. In the parametric geometric model of the BWB underwater glider, the planform is defined with Bezier curve and linear line,... Parametric geometric model and shape optimization of an underwater glider with blended-wing-body Science.gov (United States) Sun, Chunya; Song, Baowei; Wang, Peng 2015-11-01 Underwater glider, as a new kind of autonomous underwater vehicles, has many merits such as long-range, extended-duration and low costs. The shape of underwater glider is an important factor in determining the hydrodynamic efficiency. In this paper, a high lift to drag ratio configuration, the Blended-Wing-Body (BWB), is used to design a small civilian under water glider. In the parametric geometric model of the BWB underwater glider, the planform is defined with Bezier curve and linear line, and the section is defined with symmetrical airfoil NACA 0012. Computational investigations are carried out to study the hydrodynamic performance of the glider using the commercial Computational Fluid Dynamics (CFD) code Fluent. The Kriging-based genetic algorithm, called Efficient Global Optimization (EGO), is applied to hydrodynamic design optimization. The result demonstrates that the BWB underwater glider has excellent hydrodynamic performance, and the lift to drag ratio of initial design is increased by 7% in the EGO process. Modeling and Simulation of A Novel Autonomous Underwater Vehicle with Glider and Flapping-Foil Propulsion Capabilities Institute of Scientific and Technical Information of China (English) TIAN Wen-long; SONG Bao-wei; DU Xiao-xu; MAO Zhao-yong; DING Hao 2012-01-01 HAISHEN is a long-ranged and highly maneuverable AUV which has two operating modes:glider mode and flapping-foil propulsion mode.As part of the vehicle development,a three-dimensional mathematical model of the conceptual vehicle was developed on the assumption that HAISHEN has a rigid body with two independently controlled oscillating hydrofoils.A flapping-foil model was developed based on the work done by Georgiades et al.(2009).Effect of controllable hydrofoils on the vehicle stable motion performance was studied theoretically.Finally,a dynamics simulation of the vehicle in both operating modes is created in this paper.The simulation demonstrates that:(1) in the glider mode,owing to the independent control of the pitch angle of each hydrofoil,HAISHEN travels faster and more efficiently and has a smaller turning radius than conventional fix-winged gliders; (2) in the flapping-foil propulsion mode,HAISHEN has a high maneuverability with a turning radius smaller than 15 m and a forward motion velocity about 1.8 m/s; (3) the vehicle is stable under all expected operating conditions. Parametric geometric model and shape optimization of an underwater glider with blended-wing-body Directory of Open Access Journals (Sweden) Sun Chunya 2015-11-01 Full Text Available Underwater glider, as a new kind of autonomous underwater vehicles, has many merits such as long-range, extended-duration and low costs. The shape of underwater glider is an important factor in determining the hydrodynamic efficiency. In this paper, a high lift to drag ratio configuration, the Blended-Wing-Body (BWB, is used to design a small civilian under water glider. In the parametric geometric model of the BWB underwater glider, the planform is defined with Bezier curve and linear line, and the section is defined with symmetrical airfoil NACA 0012. Computational investigations are carried out to study the hydrodynamic performance of the glider using the commercial Computational Fluid Dynamics (CFD code Fluent. The Kriging-based genetic algorithm, called Efficient Global Optimization (EGO, is applied to hydrodynamic design optimization. The result demonstrates that the BWB underwater glider has excellent hydrodynamic performance, and the lift to drag ratio of initial design is increased by 7% in the EGO process. Environmental data collection using autonomous Wave Gliders OpenAIRE Hermsdorfer, Kathryn M. 2014-01-01 Approved for public release; distribution is unlimited The Sensor Hosting Autonomous Remote Craft (SHARC), also known as Wave Glider, is an autonomous ocean vehicle powered by wave motion. This slow-moving platform makes long-term deployments and environmental data collection feasible, especially in data sparse regions or hazardous environments. The standard SHARC hosts a meteorological station (Airmar PB200) that samples air pressure, temperature, wind speed and wind direction at 1.12 m. ... Undersea gliders OpenAIRE Griffiths, G.; Jones, C.; Ferguson, J; N Bose 2007-01-01 Undersea gliders offer an alternative propulsion paradigm to the propeller-driven autonomous underwater vehicle by using buoyancy change and wings to produce forward motion. By operating at slow speed ( Embedded Control System for Underwater Glider based on PSoC5LP Directory of Open Access Journals (Sweden) Manoj Nair 2014-05-01 Full Text Available The conventional sonar designed for blue water operations present sub-optimal performance in the littorals, due to site specific behaviour of the underwater channel. The tropical waters in the Indian Ocean Region (IOR further degrade sonar performance due to random fluctuations in the surface parameters like temperature, wind, etc. There exists a requirement to gather credible oceanographic and ambient noise data at specific locations for neutralizing the impact of underwater channel distortions and ambient noise thereby achieving effective sonar performance. Underwater gliders are a class of Autonomous Underwater Vehicles (AUVs that do not use conventional propeller for propulsion, significantly minimizing their self noise. They are propelled by change in buoyancy to follow a “Saw-tooth†pattern of motion in sea. Underwater gliders are characterized by small size, long endurance, low speed and low cost. These characteristics make gliders extremely valuable for long term oceanographic sensing missions. During the saw-tooth evolutions of glider, the onboard sensor and data acquisition systems constantly record oceanographic data. Due to the ability to glide at slow speeds, gliders have longer deployment capabilities than standard powered autonomous underwater vehicles, making gliders extremely valuable for long term oceanographic sensing missions. An underwater glider design, development and deployment effort with an appropriate payload of sensors will be able to effectively address all important aspect of improving sonar performance for our military as well as non-military sonars in the IOR. The appropriate selection of the sensors, the data acquisition system, power supply modules, processors, system controllers, memory, etc, requires careful study and shortlisting. The interfacing of the multiple components and devices along with the programming of the controllers to manage precise functioning of the entire system requires meticulous Exploring Titan with Autonomous, Buoyancy Driven Gliders Science.gov (United States) Morrow, M. T.; Woolsey, C. A.; Hagerman, G. M. Buoyancy driven underwater gliders are highly efficient winged underwater vehicles which locomote by modifying their internal shape. The concept, which is already well-proven in Earth's oceans, is also an appealing technology for remote terrain exploration and environmental sampling on worlds with dense atmospheres. Because of their high efficiency and their gentle, vertical take-off and landing capability, buoyancy driven gliders might perform long duration, global mapping tasks as well as light-duty, local sampling tasks. Moreover, a sufficiently strong gradient in the planetary boundary layer may enable the vehicles to perform dynamic soaring, achieving even greater locomotive efficiency. Shape Change Actuated, Low Altitude Robotic Soarers (SCALARS) are an appealing alternative to more conventional vehicle technology for exploring planets with dense atmospheres. SCALARS are buoyancy driven atmospheric gliders with a twin-hulled, inboard wing configuration. The inboard wing generates lift, which propels the vehicle forward. Symmetric changes in mass distribution induce gravitational pitch moments that provide longitudinal control. Asymmetric changes in mass distribution induce twist in the inboard wing that provides directional control. The vehicle is actuated solely by internal shape change; there are no external seals and no exposed moving parts, save for the inflatable buoyancy ballonets. Preliminary sizing analysis and dynamic modeling indicate the viability of using SCALARS to map the surface of Titan and to investigate features of interest. Enabling Persistent Autonomy for Underwater Gliders with Ocean Model Predictions and Terrain Based Navigation Directory of Open Access Journals (Sweden) Andrew eStuntz 2016-04-01 Full Text Available Effective study of ocean processes requires sampling over the duration of long (weeks to months oscillation patterns. Such sampling requires persistent, autonomous underwater vehicles, that have a similarly long deployment duration. The spatiotemporal dynamics of the ocean environment, coupled with limited communication capabilities, make navigation and localization difficult, especially in coastal regions where the majority of interesting phenomena occur. In this paper, we consider the combination of two methods for reducing navigation and localization error; a predictive approach based on ocean model predictions and a prior information approach derived from terrain-based navigation. The motivation for this work is not only for real-time state estimation, but also for accurately reconstructing the actual path that the vehicle traversed to contextualize the gathered data, with respect to the science question at hand. We present an application for the practical use of priors and predictions for large-scale ocean sampling. This combined approach builds upon previous works by the authors, and accurately localizes the traversed path of an underwater glider over long-duration, ocean deployments. The proposed method takes advantage of the reliable, short-term predictions of an ocean model, and the utility of priors used in terrain-based navigation over areas of significant bathymetric relief to bound uncertainty error in dead-reckoning navigation. This method improves upon our previously published works by 1 demonstrating the utility of our terrain-based navigation method with multiple field trials, and 2 presenting a hybrid algorithm that combines both approaches to bound navigational error and uncertainty for long-term deployments of underwater vehicles. We demonstrate the approach by examining data from actual field trials with autonomous underwater gliders, and demonstrate an ability to estimate geographical location of an underwater glider to 2 Autonomous Underwater Vehicle control OpenAIRE Vidal Morató, Jordi; Gomáriz Castro, Spartacus; Manuel Lázaro, Antonio 2005-01-01 In this paper the system control design stages for an autonomous underwater vehicle are presented. The vehicle must be able to sail on sea surface, following a path without losing its route and once a position is reached, a dive following a perpendicular path to the surface is carried out. A two level system control are proposed. The primary level will control the navigation of the vehicle where a linear controllers are proposed. Whereas in secondary level guidance system, collision system, s... Dynamic Modeling and Motion Simulation for A Winged Hybrid-Driven Underwater Glider Institute of Scientific and Technical Information of China (English) WANG Shu-xin; SUN Xiu-jun; WANG Yan-hui; WU Jian-guo; WANG Xiao-ming 2011-01-01 PETREL,a winged hybrid-driven underwater glider is a novel and practical marine survey platform which combines the features of legacy underwater glider and conventional AUV(autonomous underwater vehicle).It can be treated as a multi-rigid-body system with a floating base and a particular hydrodynamic profile.In this paper,theorems on linear and angular momentum are used to establish the dynamic equations of motion of each rigid body and the effect of translational and rotational motion of internal masses on the attitude control are taken into consideration.In addition,due to the unique external shape with fixed wings and deflectable rudders and the dual-drive operation in thrust and glide modes,the approaches of building dynamic model of conventional AUV and hydrodynamic model of submarine are introduced,and the tailored dynamic equations of the hybrid glider are formulated.Moreover,the behaviors of motion in glide and thrust operation are analyzed based on the simulation and the feasibility of the dynamic model is validated by data from lake field trials. RuCool Operational Oceanography: Using a Fleet of Autonomous Ocean Gliders Science.gov (United States) Graver, J.; Jones, C.; Glenn, S.; Kohut, J.; Schofield, O.; Roarty, H.; Aragon, D.; Kerfoot, J.; Haldeman, C.; Yan, A. 2007-05-01 At the Rutgers University Coastal Ocean Observation Lab (RU-COOL), we have constructed a shelf-wide ocean observatory to characterize the physical forcing of continental shelf primary productivity in the New York Bight (NYB). The system is anchored by four enabling technologies, which include the international constellation of ocean color satellites, multi-static high frequency long-range surface current radar, real-time telemetry moorings, and long duration autonomous underwater vehicles (AUVs). Operation of the observatory is through a centralized computer network dedicated to receiving, processing and visualizing the real-time data and then disseminating results to both field scientists and ocean forecasters over the World Wide Web. The system was designed to conduct cutting edge research requiring the addition of rapidly evolving technologies, and to serve society by providing sustained data delivered in real-time. Rutgers COOL continues to work closely with Webb Research Corporation (WRC) in testing and development of the Slocum underwater gliders and continues to apply Slocum gliders in field operations spanning the globe. The continued strong collaboration between WRC and Rutgers has led to advances in glider operations and applications. These include deployment/recovery techniques, improvements in durability and reliability, integrated sensors suites, salinity spike removal, and adaptive controls utilized to optimize mission goals and data return. The gliders have gathered numerous data sets including salt intrusions as seen off of New Jersey, plume tracking, biological water sample matching, and operation through Hurricane Ernesto in 2006. This talk will detail recent oceanographic experiments in which the fleet has been deployed and improvements in the operation of these novel robotic vehicles. These experiments, in locations around the world, have resulted in significant new work in operation of underwater gliders and have gathered new and unique data Design of Autonomous Underwater Vehicle OpenAIRE Tadahiro Hyakudome 2011-01-01 There are concerns about the impact that global warming will have on our environment, and which will inevitably result in expanding deserts and rising water levels. While a lot of underwater vehicles are utilized, AUVs (Autonomous Underwater Vehicle) were considered and chosen, as the most suitable tool for conduction survey concerning these global environmental problems. AUVs can comprehensive survey because the vehicle does not have to be connected to the support vessel by tether cable. Whe... Design of Autonomous Underwater Vehicle Directory of Open Access Journals (Sweden) Tadahiro Hyakudome 2011-03-01 Full Text Available There are concerns about the impact that global warming will have on our environment, and which will inevitably result in expanding deserts and rising water levels. While a lot of underwater vehicles are utilized, AUVs (Autonomous Underwater Vehicle were considered and chosen, as the most suitable tool for conduction survey concerning these global environmental problems. AUVs can comprehensive survey because the vehicle does not have to be connected to the support vessel by tether cable. When such underwater vehicles are made, it is necessary to consider about the following things. 1 Seawater and Water Pressure Environment, 2 Sink, 3 There are no Gas or Battery Charge Stations, 4 Global Positioning System cannot use, 5 Radio waves cannot use. In the paper, outline of above and how deal about it are explained. Insurance for autonomous underwater vehicles OpenAIRE Griffiths, G; N Bose; Ferguson, J.; Blidberg, D.R. 2007-01-01 The background and practice of insurance for autonomous underwater vehicles (AUVs) are examined. Key topics include: relationships between clients, brokers and underwriters; contract wording to provide appropriate coverage; and actions to take when an incident occurs. Factors that affect cost of insurance are discussed, including level of autonomy, team experience and operating environment. Four case studies from industry and academia illustrate how AUV insurance has worked in practice. The p... Autonomous underwater riser inspection tool Energy Technology Data Exchange (ETDEWEB) Camerini, Claudio; Marnet, Robson [Petrobras SA, (Brazil); Freitas, Miguel; Von der Weid, Jean Pierre [CPTI/PUC-Rio, Rio de Janeiro, (Brazil); Artigas Lander, Ricardo [EngeMOVI, Curitiba, (Brazil) 2010-07-01 The detection of damage on the riser is a serious concern for pipeline companies. Visual examinations by remotely operated vehicle (ROV) are presently carried out to detect the defects but this process has limitations and is expensive. This paper presents the development of a new tool to ensure autonomous underwater riser inspection (AURI) that uses the riser itself for guidance. The AURI, which is autonomous in terms of control and power supply, is equipped with several cameras that perform a complete visual inspection of the riser with 100 % coverage of the external surface of the riser. The paper presents the detailed characteristics of the first AURI prototype, describes its launching procedure and provides the preliminary test results from pool testing. The results showed that the AURI is a viable system for autonomous riser inspection. Offshore tests on riser pipelines are scheduled to be performed shortly.
Ocean Circulation And Climate Isbn 0126413517
Copyright © 2001 Academic Press All rights of reproduction in any form reserved in-situ current measurements. At the time, direct current observations in the deep ocean were very limited, being restricted to about 20 locations in the Atlantic. Most were made by recording instruments suspended from anchored ships for durations between several hours and a few days. Bowden concluded there was great 'need for continuing the measurements at one station for a period of the order of a week...to derive a satisfactory value for the mean current'. In a Letter to the Editor, Henry Stommel (1955) suggested the visionary construction of Lagrangian alternatives to the Eulerian current measurements favoured by Bowden. Two devices came to Stommel's mind: (1) floats that sink to a predetermined depth where they 'keep in "trim" in the manner of a submarine' and (2) the more elegant species of 'buoyant floats of a material less compressible than water . without any power-driven control'. Stommel imagined locating his freely drifting floats a single time using the time of arrival of explosive sound waves at three shore-based SOFAR (Sound Fixing And Ranging) stations. By expecting that 'currents as slow as 10~2cms_1 could be detected' he rated these current observations to be much more precise than the state-of-the-art vessel-based measurements. Stommel's plea for Lagrangian in-situ observations marks the birth date of a completely new generation of oceanic instruments. Practically all elements of Stommel's vision have become reality since his 1 i-page paper appeared in 1955: floats with active depth control and passive pre-ballast-ing have been constructed; oceanographers have learnt to utilize the acoustical transparency of the SOFAR channel for locating and data transmission; floats have been used in quantity to map ocean circulation and its fluctuations. The only thing missing is that Stommel's 'SOFAR time bombs' have been replaced by more peaceful and long-lived piezoelectric devices and sophisticated electronic instrumentation. The first report of a functional neutrally buoyant float appeared only a few months after Stom-mel's note when John Swallow (1955) introduced his ingenious invention of what later became known as a Swallow float (Fig. 3.2.1). This pioneering instrument represents the first passively ballasted drifter according to Stommel's second specification. At the surface these floats are slightly negatively buoyant but, owing to the choice of material that make them less compressible than the ambient water, gain buoyancy while sinking. Swallow's first test missions in the Iberian Basin lasted about 3 days and revealed deep clockwise M2-tidal currents superimposed on a steady drift. In contrast to Stommel's suggestion, Swallow's floats were located by a dual-hydrophone array Fig. 3.2.1 John C. Swallow preparing an early neutrally buoyant float on the RRS Discovery II in spring 1955.These 'Swallow' floats were constructed from readily available scaffolding tubing, whose physical properties were well established, and the wall thickness was reduced by etching in a solution of caustic soda (cf. Charnock, 1997). Courtesy J. Gould, Soc, Southampton, UK. Fig. 3.2.1 John C. Swallow preparing an early neutrally buoyant float on the RRS Discovery II in spring 1955.These 'Swallow' floats were constructed from readily available scaffolding tubing, whose physical properties were well established, and the wall thickness was reduced by etching in a solution of caustic soda (cf. Charnock, 1997). Courtesy J. Gould, Soc, Southampton, UK. under the keel of a research vessel within a range of about 200 m. Five years later Swallow and Hamon (1960) summarized their first experiences during the International Geophysical Year (IGY). They had observed deep currents of order 0-5 cms-1 with time scales of weeks and spatial scales of a few tens of miles. It was explicitly noted that a 'level of no motion' could not be detected in the eastern North Atlantic. Swallow and Hamon's observations of the wide range of variability, including the lack of a reference layer for geostrophic current calculation, were confirmed and extended later by joint British/ US (Aries) observations 350km west of Bermuda (Crease, 1962). In this frequently referenced article, Crease comes to two basic observational results: 1 float trajectories are 'contrary to the widely held view that the deep ocean is relatively quiescent with velocities of order 1 cms-1; and 2 the new observations 'raise the question of just how important the... mean circulation is... compared with the eddy transport of properties .' The discovery that the interior ocean was not quiescent led to the internationally coordinated Mid-Ocean Dynamics Experiment (MODE) during the early 1970s (MODE Gap, 1978). MODE, and its successor POLYMODE, gave impetus to development of a new float technology that fulfilled Stommel's dream of long-range tracking. Rossby and Webb (1970) developed a new generation employing large low-frequency sound projectors capable of being tracked in the SOFAR channel at ranges beyond 1500 km. The remarkable increase in size over a Swallow float of these instruments, which became known as SOFAR floats, is shown in Fig. 3.2.2. SOFAR floats were first tracked in the western North Atlantic by military facilities and later by self-recording moored sound receivers. By offering a multiyear life and a long tracking range, these floats made possible the first identification of mesoscale structures (Riser and Rossby, 1983) and their statistics (Freeland et al., 1975) and the discovery by McDowell and Rossby (1978) of tight coherent eddies in the North Atlantic, called Med-dies because their water properties disclosed their Mediterranean source. Over the years substantial improvements for tracking Swallow floats were made (Swallow et al., 1974) and their utility for observing small-scale processes continues. Fig. 3.2.2 The first neutrally buoyant float that could be tracked for long distances was the SOFAR float developed by Tom Rossby (left) and Doug Webb (right), who watch one being loaded for deployment in the Mid-Ocean Dynamics Experiment (MODE). Fig. 3.2.2 The first neutrally buoyant float that could be tracked for long distances was the SOFAR float developed by Tom Rossby (left) and Doug Webb (right), who watch one being loaded for deployment in the Mid-Ocean Dynamics Experiment (MODE). Rossby et al. (1986) introduced a fundamentally new step by reversing the principle of the SOFAR tracking and exchanging the location of sound sources and receivers. The principle of the reversed SOFAR technology, using roving receivers and fixed sound sources, was expressed by the acronym RAFOS, i.e. SOFAR spelled backwards. Former SOFAR floats were converted into moored sound sources and replaced by low-cost and lightweight RAFOS floats with acoustical receivers. These expendable instruments record times of sound arrival from moored sources, drop a ballast weight at the end of their mission and upload their data via satellite after surfacing. They are typically used on missions for 6-24 months to deliver eddy-resolving submerged trajectories and time series of temperature and pressure. Studies that depended on the relatively low-cost and well-resolved trajectories of RAFOS floats include the description of the transport of water across the axis of the Gulf Stream by Bower and Rossby (1989) and many studies discussed below. In some studies a high premium is placed on using floats to represent fluid-parcel trajectories. This dictated the uninterrupted current following that can be achieved only with acoustic tracking. It also requires a float with approximately the same compressibility as seawater, which can follow water parcels as they change depth. A technique for increasing a float's compressibility to approximate that of seawater by adding a spring-backed piston was developed by Rossby et al. (1985) and is used in many studies where quasi-Lagrangian properties are primary. In a sense the idea of autonomous (i.e. not requiring an acoustic tracking network) floats traces to Stommel's idea of current-followers that are located only occasionally. The first autonomous float (Davis et al., 1992), shown in Fig. 3.2.3, was the Autonomous LAgrangian Circulation Explorer Fig. 3.2.3 Jim Dufour holding the ALACE that his engineering improvements made into a reliable autonomous float. Fig. 3.2.3 Jim Dufour holding the ALACE that his engineering improvements made into a reliable autonomous float. (ALACE). A hydraulic pump enables this instrument, with a mass near 25 kg, to change its volume by moving oil between external and interior bladders. On an interval between a few days and a month, an ALACE cycles from depth to the surface, where it is located by satellite and uplinks collected data. Because autonomous floats operate independently of sound-source arrays, provide hundreds of cycles over a time up to 7 years and are easily deployed, they can operate economically on a truly global scale to provide the long records needed to isolate the general circulation from mesoscale variability. The autonomous mode of operation also allows data to be received continuously through multiyear missions, alleviating the difficulty with RAFOS floats that data is received only at a mission's end. The penalty for autonomous operation is a long time interval between known positions, which precludes resolving eddies unless cycling is rapid, and periodic surfacing that interrupts the quasi-Lagrangian trajectory. In addition to errors in positioning, a float's vertical motion through sheared currents introduces error into the estimates of the end positions of the at-depth period over which subsurface currents are measured. While descent and ascent velocities vary widely with depth, a float operating at 800 m passes through the upper 400 m in approximately an hour. In a uniform shear with 50cms-1 difference across 400m this corresponds to a position change during ascent/ descent of less than 1 km (less than the error in long-range acoustic tracking) and on a 20-day cycle time contributes an error of 1mms-1 to the mean current measurement. Outside western boundary currents, shears are generally smaller than this and variable, so the main effect of shear is to add velocity noise that adds little to the noise coming from mesoscale variability and is easily suppressed by averaging over time or multiple floats. During WOCE, the family of Lagrangian current-followers grew substantially. In France, Ollitrault et al. (1994) developed a hybrid of RAFOS and ALACE technology called MARVOR after the Celtic word for seahorse. It blends the vertical cycling and repeated data transmission functions of ALACE with the eddy-resolving properties of RAFOS floats. For the study of potential vorticity conservation, Sundermeyer and Price (1998) used a SOFAR float that included ALACE technology to cycle between a pair of isotherms in the main thermocline. While ALACEs are pre-ballasted to drift approximately at a selected depth, the more modern autonomous floats used toward the end of WOCE, such as the SOLO (Davis et al., 2000) and APEX, have full buoyancy control and can be programmed to follow the flow at a different depth than the bottom of their profiles, or even to track isotherms. These floats correspond exactly to the category of floats that 'keep in trim in the manner of a submarine' that Stommel had in mind in 1955. The aspect of float development that made possible the bold WOCE attempt to directly measure velocity fields on basin scales was the cost reduction made possible by the development of RAFOS and vertical cycling technologies that make it possible to measure velocity at a cost near two thousand dollars per year. A RAFOS float costs about $4500, autonomous floats twice this, and MARVOR floats about three times as much. RAFOS floats typically operate for 1-2 years, autonomous floats can report every 10 days for over 5 years, and Ollitrault (1999) has shown that 50% of his MARVOR floats were still alive after 5 years. Sound sources (approximately $22 000 each) and costs of analysis of acoustic time delays add to the cost of RAFOS and MARVOR operations. The scientific utility of ALACE floats has been significantly increased by adding temperature and conductivity sensors so that temperature and salinity profiles from transits between the surface and the target depth can be reported (cf. Davis et al., 2000). Because a Profiling ALACE (P-ALACE) executes 200 depth cycles, the per-profile cost is competitive with expendable probes so long as the conductivity sensor remains stable enough to yield good salinities. Even if the float's entire construction and communication cost is charged to profiling (neglecting the value of velocity observations), the full operational cost of a temperature profile is about $50, with $25 to add a salinity profile. To complete this historical perspective, let us note that the community is now implementing Henry Stommel's last vision for observing the ocean. He was aware that early autonomous floats could, in addition to tracking currents, be adept at measuring profiles, but that there were many reasons for wanting to control where these profiles were taken. A simple solution was to fit wings to a buoyancy-changing float to produce a simple autonomous underwater glider. In a visionary article, Stommel (1989) combined this with the revolutionary idea of generating the necessary buoyancy forcing from the ocean's thermal stratification to propose a new observational tool, which he called 'Slocum' in honour of the first global circumnavigator, Captain Joshua Slocum (1900) and enjoyed demonstrating a prototype thermal buoyancy engine in the workshop behind his Fal-mouth home. Technologists from University of Washington, Scripps Institution of Oceanography and Woods Hole Oceanographic Institution are adapting autonomous float technology to develop simple electric-powered underwater gliders, while Webb Research Corporation is implementing Stommel's full vision of thermal-powered gliders. In each implementation, wings are used to efficiently convert buoyancy into forward motion of the O(30cms-1) as the vehicle cycles between shallow and deep levels. This forward motion can be used to hold station to gather a time series of profiles (a virtual mooring) or to sample autonomously a hydrographic section of several thousand kilometres in length.
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中国水下滑翔机在南海30天航行1千公里创纪录
由中国自主研发的水下滑翔机近日在南海结束为期40天的海上试验。记者22日从中国科学院沈阳自动化研究所了解到，该水下滑翔机此次试验海上总航程达1022.5公里，持续30天，创下中国深海滑翔机海上作业航程最远、作业时间最长记录。 此次试验从9月5日开始至10月15日结束。据中国科学院沈阳自动化研究所研究员俞建成介绍，本次海上试验的内容主要包括两项，一项为多滑翔机同步区域覆盖观测试验，是指岸基监控中心通过控制2台滑翔机，在55公里见方的设定观测轨迹内，执行同步观测，验证水下滑翔机系统的远程控制和协同观测能力；另一项是长航程观测试验，目的在真实海洋环境条件下，考验滑翔机系统的续航能力和系统可靠性。 此次中国制造的水下滑翔机在长航程试验中，无故障工作30天，完成229个1000米深海剖面观测，水平航行距离达到1022.5公里，创下两项新的纪录。 此前，中国水下滑翔机的最远航行纪录为500多公里。此次所以创下两项新的纪录，主要原因为操控软件、设计指标等大幅改进。 水下滑翔机研制是中国“十二五”863计划海洋技术领域支持项目，主要目标是开展深海滑翔机工程技术研究，提高滑翔机系统的综合性能、可靠性和稳定性，解决滑翔机远程监控、海上应用及观测数据处理等问题。 中国水下滑翔机主载体长2米？，直径0.22米，翼展1.2米，重量65公斤，海洋航行深度1000米，呈锯齿状轨迹在海中滑翔探测。速度为0.5节到1节。 据悉，今年以来，中科院沈阳自动化所研制的水下滑翔机完成3次海上试验，海上累计工作80天，航程2400多公里，观测剖面数超过600个。通过多次海上试验，全面考核了水下滑翔机系统的可靠性和稳定性，使中国深海滑翔机达到实用化装备水平，预示将进入推广阶段。其主要应用于探测海洋环境、海水质量等有效参数。