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WAVE-POWERED AUTONMOUS SURFACE VESSELS AS COMPONENTS OF OCEAN OBSERVING SYSTEMS Roger Hine1 and Philip A. McGillivary2 1 2 Liquid Robotics Inc. U.S. Coast Guard PACAREA Science Liaison INTRODUCTION AND BACKGROUND New and transformative technologies are required to meet the growing needs for ocean observing systems internationally. A novel wave powered autonomous surface vehicle currently under test and development in Hawaii has potential to enable new types of ocean observation as well as cost savings over existing systems. Marine environments are key components of national and international economies as an everincreasing percentage of the global populace depends on trade moving through international ports. Security of ports, harbors, and maritime trade routes continues to be an important concern. The importance of marine fisheries as a source of food and food security for many countries also continues to increase, and changing climate and rainfall patterns are expected in the near-term to further increase dependence on the sea for global protein supplies. However in many countries, including the United States, there is a recognized crisis in policies for managing coastal, regional and adjacent global marine ecosystems (Young et al., 2007). To a large degree this crisis stems from a lack of data specific to the areas which must be managed in relation to the time-space scales of ocean hydrodynamics and ocean climate responses critical for intelligent and sustainable ocean management. This is true for developed nations throughout Europe and the U.S., as well as for developing nations such as China (Prandle et al., 2005; Robinson and Brink, 2005; Li, 2006). A series of national and international plans have therefore been developed to put in place a framework for ocean observing systems to address the need for improved spatial and temporal data from the sea to improve understanding and management of the oceans (Ocean.US, 2002; UNESCO, 2003; Ocean Action Plan, 2004; U.S. Commission on Ocean Policy, 2004; Ocean.US, 2006). Within the international framework, Ocean.US was established under the US Global Ocean Observing System (GOOS) management structure to coordinate efforts of nine federal agencies tasked with various aspects of marine ecosystem management as part of the National Ocean Partnership Program (NOPP). The charge for this organization was to develop the infrastructure to provide information on marine ecosystems that would not only be useful for oceanographic, ocean climate and scientific research, but also for operational ocean observations, which generally require data in near-real time. The Ocean Observing Initiative (OOI) plan has as its goal providing data for seven major purposes: 1) ocean climate studies; 2) maritime operations; 3) national security; 1 4) 5) 6) 7) sustainable resource management; preservation and restoration of marine systems; natural hazard mitigation; and, maintenance of public health (Ocean.US, 2002). The science plan that has developed for the OOI calls for a network of fixed sensors that provide near-real time data at high sampling rates, and mobile sensors with more restricted real-time data telemetry capabilities (Ocean Research Interactive Observatory Networks [ORION], 2005). The Science Summary Plan calls for a focus on the collection of ocean data to improve understanding of ocean ecosystems in five key science areas: 1) ocean climate studies, including improving data on ocean and atmospheric fluxes of heat and climate-critical gases such as CO2; 2) coastal dynamic studies, including improving data on conditions affecting fluxes of nutrients, and biological responses of the coastal ocean ecosystem, including shifts in species composition that affect fisheries and outbreaks of harmful algal blooms; 3) geodynamics, providing data on geological activity in the marine environment; 4) turbulent mixing and the biological responses to such mixing; and, 5) seafloor fluid-rock interactions (ORION, 2005). The temporal and spatial scales for data collection in these five key science areas for the proposed Ocean Observing Systems (OOSs) can be met partially by fixed data collection systems, but also require mobile data collection platforms. To date progress has been made using autonomous surface systems such as the GOOS drifters (http://www.aoml.noaa.gov/phod/dac/gdp.html), and ARGO floats (http://www.argo.ucsd.edu/Acindex.html). These relatively inexpensive autonomous systems have been supplemented in several spatially and temporally focused studies by more expensive, and therefore more numerically limited glider and propeller driven autonomous underwater vehicles (AUVs). Both kinds of vehicles have proven highly useful in focused studies where the relatively long endurance (months or more) but limited speed (at 0.5 knot) capabilities of gliders complements the higher speed (usually 2-4 knots) but shorter endurance (usually < a few weeks) endurance of most propeller type AUVs. Development of solar-powered AUVs (http://www.ausi.org/publications/SeaTechSolar.pdf) can improve the endurance of AUVs in environments where extended periods of sunlight are an option, but cannot be relied on in all circumstances. Other surface autonomous vehicles have also recently been developed which can potentially play a role in OOSs as well, including the Robo-kayak and the OASIS platform (Curcio, et al., 2006; http://www.isd.gsfc.nasa.gov/Allhands/12-16-04/ASF.ppt), but their routine use remains to be fully evaluated. For research in spatially limited areas where underwater moorings are present to receive data from gliders and AUV vehicles via acoustic modems, near-real time data can be provided by these arrangements. However for most regional and global ocean studies data telemetry for such underwater vehicles is more restricted (ORION, 2005). Moreover, currently the deployment and retrieval of gliders and AUVs usually involves the use of relatively expensive research vessels, and to date has often included the additional cost of the loss of a certain portion of these relatively expensive vehicles. Plans for a network of OOSs that meet science needs of the ocean community are now well developed, with a Conceptual Network Design (CND) plan and Conceptual Design Review 2 (CDR) completed in 2006 following a series of workshops addressing both OOS infrastructure and costs requirements. However, one critical problem has arisen in that funding of the planned OOSs has stalled at a small percentage of the estimated funding needed to deploy and maintain the planned systems into the future. Insofar as the need for proceeding with a system of ocean observatories is clearly critical for understanding climate, resource management, national security and other concerns, a review of plans for proceeding with OOS deployment is ongoing. This review is intended to re-evaluate costs and requirements with a goal of reducing costs as long as six goals for the OOSs can still be met, namely that any cost-reducing methods: 1) involve new and transformative technology that provides interactive controls and realtime data; 2) new technologies must address priority research questions noted above; 3) new technologies must be useful at all three spatial scales, i.e. coastal, regional and global; 4) new technologies must balance high risk and low risk components to provide a reasonably high probability of success; 5) new technologies must balance fixed and mobile assets to avoid spatial or temporal aliasing of data collection; and, 6) new technologies must be capital expenditures that reduce life cycle costs (ORION, 2005). We here describe a new technology which meets all six of the ORION requirements for inclusion as a component of ocean observing systems, providing continuous real-time data on the ocean surface mixed layer. WAVEGLIDER, A NEW AND TRANSFORMATIONAL TECHNOLOGY Figure 1: An early wave glider prototype and one of the authors 3 Why a Wave Powered Vehicle? A large range of ocean observing goals require light equipment to be positioned at the sea surface for long durations. In many cases it is preferable to have a large number of small, low cost, observing systems rather than a few large systems. Without an anchor, keeping station at sea is fundamentally an energy problem. Currents and weather effects will tend to pull a surface vehicle off target and energy is required to resist this. Whether it is in batteries, fuel cells, or fuel tanks, energy stored on the vehicle will eventually run out. The problem worsens as vehicle size decreases due to the increasing ratio of drag area relative to the volume available for energy storage. Thus any small vehicle that is to autonomously maintain station at the sea surface for indefinite duration must harvest energy from the environment. Wind, sun and wave energy are the three primary sources available for mechanical energy harvesting at the ocean surface. Wind energy can be effectively converted to thrust through sails, or rigid wings that function like sails. However a sailing vessel must tack to advance into the wind, and this involves moving at high speeds relative to the water surface. As wind increases, so do wind waves, and these waves will obstruct a small vehicle from moving effectively at high speed. Solar power can be converted to electricity using commercial solar panels, but will be unavailable when needed most; during prolonged storm periods. Worse, large solar panels become a liability in these situations. Wave energy is ubiquitous in the ocean environment and has the attractive attribute of increasing during storm periods when it will be needed most. Harvesting Wave Energy As a waves move horizontally across the water surface, the water itself moves in approximately circular orbits. The diameter of the orbit decreases logarithmically with depth such that it is near zero at a depth of approximately ½ the wave length. A vehicle with a component at the surface and a component at depth can harness energy from this relative motion. Figure 2. Wave Motion and WaveGlider. Water particles move in approximately circular orbits of decreasing diameter as depth increases. The float will pull the glider upward with a rising wave crest but the water around the glider will remain relatively stationary. (Items in figure not to scale.) 4 WaveGliders are comprised of two parts, a surface float and a submerged glider, connected by an umbilical cable. As the float rises on the surface of the water it pulls the glider upwards. Fin surfaces on the glider passively rotate to a positive angle of incidence so as to produce thrust. In a second stage of motion, the float sinks down into a wave trough and allows the glider to lower with it. The fin surfaces on the glider then rotate to a negative angle of incidence to produce thrust again. Through both upward and downward motion stages the glider produces thrust. This thrust generation is purely mechanical and continuous without the use of any electrical power or control Figure 3. Upward and downward motion phases Aside from thrust generation, a second, perhaps equally significant, benefit arises from the two part vehicle construction. This is the fact that the lower portion is sheltered from weather effects. Storm winds will have a strong effect on small surface vehicles and will rapidly generate currents in the very upper layers. These effects will be minimal slightly below the surface. The submerged portion of a wave glider acts similarly to a sea anchor by keeping hold in the relatively still waters below the surface. The result is that wave glider performance typically improves as wind picks up. The increase in wave energy is more significant than the effects of wind and surface currents on the float. Vehicle Design A wide variety of wing forms and vehicle architectures are possible and many have been tested. They hold in common the basic distribution of components between float and glider. While WaveGliders do not need electrical systems for propulsion, they do need them for navigation, communication and sensor payload. Solar panels on the float provide a means of 5 charging batteries, although depending on payload and desired mission duration single charge batteries may also be also a viable option. The float also supports communications and GPS antennae. Iridium satellite communication is being used for primary command and control while UHF is used for high bandwidth line of site transmissions such as hydrophone audio and still image surveillance. A variety of different communications options can be supported. The primary batteries are located in the glider where their weight is useful for generation of thrust during the down stroke of the vehicle. A compass and the steering controller are also located in the glider. The only actuator required in the system is used to drive the rudder for steering control. Payload may include a variety of observational equipment. Because they have no motor and no propeller and because they have a portion of the vehicle already at depth, wave gliders make good listening platforms. A connection for a hydrophone is placed at the tail of the glider. The length of the hydrophone cable may be selected to achieve the desired depth and separation. Cameras also may be placed at various locations on the vehicle. A look forward camera at the back of the float shows the float, and birds resting on the float, as well as the area ahead. A look down camera has been used to view the condition of the glider as well as the sea floor below. Cameras mounted on the glider are suitable for observation of wildlife and fish counts. WaveGlider prototypes have been developed to be portable by two people. They can be bundled and shore launched and recovered by two people. Significantly larger sizes are also feasible and may be desirable depending on payload and area of operation. Development and Testing Wave glider development and testing is being conducted by Liquid Robotics Inc. on the South Kohala coast of the Big Island of Hawaii. The first operational prototypes were built in 2005 and dozens of configurations have been tested. Multiple patent applications have been filed. A test area for unattended glider operations is near a boat ramp and within kayak distance from shore. Reliability and performance testing and continuous design improvement activities focus on achieving demonstrable results in this and other test areas. A web based user interface allows constant monitoring of location, status and sensor data. The interface uses Google Maps to display position on a satellite image or map background. Users can click on the map to create new waypoints and the gliders can be commanded to keep station or to follow a waypoint course. Gliders also may be piloted remotely either with direct rudder commands or desired heading commands. A common operating mode is for the glider to follow a square course around four waypoints. This reveals information about the glider performance as well as about environmental conditions. Competing designs then may be raced around the course. Various design alterations are evaluated empirically this way. 6 Figure 4. Screen capture of user interface showing 60 position reports from a WaveGlider on a test course Figure 5. Left: a glider was launched from shore and given command to proceed around the square course. Right: A second glider that had been waiting off shore was commanded to race the first on the same course. The relative performance was used to evaluate a design change. APPLICATION TO OCEAN OBSERVING SYSTEMS A number of capabilities which relate to OOS science areas are in formative stages of development. For ocean climate observations, a payload may include two ultrasonic anemometers at two and four meter heights to determine air-sea fluxes of heat and gases when combined with an onboard atmospheric CO2 sensors (eg LiCOR CO2 sensor), and other marine meteorology sensors. Such capabilities can be combined with water column thermistor chains or 7 small conductivity/temperature/depth (CTD) sensor packages which could be lowered through the upper water column using existing low power technologies. WaveGliders were originally developed and have been demonstrated with an acoustic hydrophone used to monitor whale sound. This capability could be expanded for use in assisting marine operations to provide data for whale collision avoidance along shipping and high speed ferry routes by distribution of this data in real time via the National Automatic Identification System (N-AIS) technology. Other possible uses for marine operations relating to shipping and fisheries are the capability of WaveGliders to be used as either fixed or mobile communications nodes to extend the range and reduce the cost of communications between ships and the shore, or between ships. These communication node capabilities can similarly prove useful for national security purposes, which can additionally make use of the capability of WaveGliders to acoustically detect ships or divers in restricted areas. WaveGliders may be particularly well suited to mapping applications, especially in remote areas. An acoustic bathymetry system may be supported to provide seafloor maps in remote areas. A similar system may be used for detection of suspicious objects in ship channels, as well as mapping shipping channels in port and harbors for bottom obstructions that may occur as a result of natural hazards such as tsunami or hurricane storm surge. For management of resources, preservation of marine ecosystems and maintaining public health, WaveGliders will be developed for monitoring of coastal pollution, and can be used in future for monitoring of water quality associated with offshore aquaculture facilities. The possibility also exists in the near future of including sensors on WaveGliders that detect harmful algal blooms, human and fish disease microorganisms. WaveGliders are already being developed for wider use in detection, tracking and preservation of protected marine mammals. Further, as noted above, WaveGlider acoustic detection systems can monitor vessel activities in marine protected areas to ensure conservation. CONCLUSION The novel energy harvesting and station keeping technology being demonstrated by Liquid Robotics in Hawaii represents an important new platform with cost saving capabilities that have not been available previously to the scientific community. With continuous surface presence, wave powered autonomous surface vehicles can offer unrestricted real-time data capabilities and blur the boundaries between traditional fixed and mobile assets. Small and low cost vehicles make redundant use practical to decrease mission risks and ensure continuous coverage. The ability to be remotely deployed from ship or shore, travel long distances to a mission area, and to return to port for maintenance significantly reduces operating costs associated with other systems that require expensive ship time. WaveGliders represent a new and transformative technology that is likely to play an important enabling role for achieving international ocean observing system goals. 8 REFERENCES Curcio, J.A., P.A. McGillivary, K. Fall, A. Maffei, K. Schwehr, B. Twiggs, C. Kitts and P. Ballou. 2006. Self-positioning smart buoys, the “Unbouy” solution: logistic considerations using autonomous surface craft technology and improved communications infrastructure. Proceedings Marine Technology Society, Boston, 2006, 4pp.. (Online) Li, H. 2006. The impacts and implications of the legal framework for sea use planning and management in China. Ocean and Coastal Management 49(9-10):717-726. Ocean.US. 2002. Building Consensus: Toward an Integrated and Sustained Ocean Observing System, Ocean.US Publication No.1, 174pp. (www.ocean.us/documents/) Oceans.US. 2002. Promoting and facilitating an integrated and sustained ocean observing system. (www.ocean.us.net) Ibid., 2006. The First U.S. Integrated Ocean Observation System Development Plan. Ocean.US Publication No.9, 86pp. (www.ocean.us/documents) Ocean Research Interactive Observatory Networks [ORION]. 2005. Ocean Observatories Initiative Science Plan Summary. Revealing the Secrets of Our Ocean Planet. 9pp. (www.orionprogram.org) Ibid., 2006. News from the Program Office. ORION Newsletter 3(2):1-2. (www.orionprogram.org) Prandle, D., H. Los, T. Pohlman, Y-H. de Roeck, and T. Stipa. 2005. Modeling in coastal and shelf seas – European challenges. European Marine Board Position Paper 7, 28pp. Robinson, A.R. and K. Brink. 2005. The Sea: The Global Coastal Ocean: Multiscale Interdisciplinary Processes. Harvard University Press, Boston, Mass.. UNESCO. 2003. The Integrated Strategic Plan for the Coastal Module of the Global Ocean Observing System. GOOS Report No. 125, 190pp. (http://ioc.unesco.org/goos/docs/doclist.htm) U.S. Commission on Ocean Policy. 2004. An Ocean Blueprint for the 21st Century: Final Report of the U.S. Commission on Ocean Policy. ww.oceancommission.gov/documents/welcome.html Young, O.R., G. Osherenko, J. Eckstrom, L.B. Crowder, J. Ogden, J.A. Wilson, J.C. Day, F. Douvere. C.N. Ehler, K.L. McLeod, B.S. Halpern, and R. Peach. 2007. Solving the crisis in ocean governance. Place-based management of marine ecosystems. Environment 49(4):20-32. WaveGlider is a trademark of Liquid Robotics Inc. Patent Pending All trademarks are the property of their respective owners. 9