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Oceanography in 2025: Proceedings of a Workshop
Oceanography in 2025
Dana R. Yoerger*
Underwater vehicles and related in situ sensors will advance significantly in the next 16 years in terms of operating range, endurance, and in the types of measurements they can make. By vehicles, I am referring to powered autonomous underwater vehicles, remotely operated vehicles, gliders, and floats.
While AUVs are presently operational, the vehicles in everyday use today do not use their limited energy supplies to best effect, with the possible exception of gliders. As a result their range and operating speeds are limited. Vehicle drag is often dominated by external appendages such as hydrophones, antennas, and recovery aids rather than the hull form itself. Significant gains in the practical efficiency of propulsors and significant reductions in “hotel” loads (control system, sensors, etc.) are also possible. Many of these improvements can be obtained through hard-nosed, competent engineering rather than fundamental invention. AUV research and development groups around the world are actively involved in such developments, and we can expect that new or improved vehicles taking advantage of these efforts will be coming online in the next few years and will be very mature by 2025. A several-fold improvement in power consumption is nearly certain.
In the next 16 years, our present energy sources (lithium primary cells, lithium-ion secondary cells, for example) will most likely be completely surpassed by new developments. Possible near-term energy
*
Woods Hole Oceanographic Institution
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Oceanography in 2025: Proceedings of a Workshop
sources include lithium-seawater batteries and several types of fuel cells. These developments will be driven by applications outside oceanography. Our present battery technologies available for AUVs were driven by the needs of relatively small devices such as laptop computers and cell phones; the next generation of energy sources will be driven by the storage needs of systems with much larger energy requirements in response to larger societal needs such as distributed power generation (solar, wind, etc.) and electric vehicles. A developer of lithium-seawater batteries projects nearly a factor of 10 increase in energy density over present lithium primary cells. These improvements would totally reshape our use of both powered AUVs as well as gliders, where the power needs of the sensor packages impose fundamental limitations.
To take advantage of the combination of reduced power usage and increased energy supplies, the vehicles must be reliable, be able to localize their position without aid from a vessel or mission-specific seafloor beacons, and have sufficient intelligence to deal with unanticipated events during the mission. No doubt our capabilities in these areas will be substantially improved by 2025. While methodological breakthroughs are likely, pragmatic engineering progress will allow consistent progress on all these fronts.
These developments, properly assembled into well-designed operational systems, will permit a revolutionary new approach to many oceanographic problems. The combination of improved power use and significantly improved energy sources can increase the present range of vehicles (presently on the order of 100s of km) many fold, perhaps by a factor of 20 to 50. Can we imagine how we would take advantage of an AUV with 5000 km range?
In situ sensing technologies are on the brink of a revolution that can fundamentally change our understanding of a variety of important ocean processes. As an example, compact, low-powered mass spectrometers that can make laboratory-grade measurements even at great depth are coming online now. Likewise newly emerging in situ genomic sensors can assess the presence and even abundance of specific organisms. These powerful instruments can allow us to measure many quantities in situ for which we must presently secure samples for analysis in the laboratory. The change from laboratory analysis to in situ sensing not only dramatically lowers the cost per measurement, it also enables vastly improved spatial coverage as well as long-term time series observations that conventional sampling and laboratory analysis cannot possibly accommodate.
AUVs with such capabilities will enable fundamentally new operational paradigms. Present-day operational AUV costs are dominated by the cost of the vessel and the support personnel that must accompany the vehicle. But AUVs with reliable long range capabilities could operate with
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Oceanography in 2025: Proceedings of a Workshop
full autonomy provided other technical issues such as localization could be solved, greatly reducing costs since the vessel and support crew could go “off the clock” shortly after the vehicle is launched, either returning to port or go to work on a different task. The combination of increased range and new in situ sensors will allow spatial coverage and data densities unthinkable today. Likewise, multiple-vehicle operations using cooperative control schemes will further enable us to capture dynamic features over large areas.
A recent paper by Davis and McGillicudy (2006) illustrates the power of in situ sensing operating on a submerged platform with long range. They towed the Video Plankton Recorder (VPR), an in situ microscope, behind a research vessel in an undulating pattern between the surface and 130 meters along a continuous track over 5500 km in length. The resulting images, classified using automated techniques amenable to on-vehicle processing, showed unexpected widespread populations of the N2-fixing colonial cyanobacterium Trichodesmium, leading to a fundamental revision of our understanding of nitrogen fixing in the world’s oceans and resolving a conundrum that had not been resolved by conventional sampling methods. By 2025, we could have multiple long-range AUVs operating over such ranges in cooperating teams, each equipped with suites of in situ sensors such as the VPR, mass spectrometers, and a variety of genomic sensors. Such observations, combined with our improving ocean modeling capabilities, have the potential to fundamentally rewrite our understanding of many ocean processes.
Remotely operated vehicles are likely to evolve significantly in the near future as well. Taking advantage of many AUV technologies, self-powered remotely operated vehicles communicating with light optical fiber tethers, acoustic communications, or optical links will enable direct human control or at least human supervision without the heavy cables required to transmit power. By eliminating heavy winches, these vehicles will be more portable, will be able to work from smaller vessels, and may not require dynamic positioning. These qualities will increase the pool of candidate vessels and make the new vehicles applicable to event response or for cruises that require intervention or sampling capabilities but don’t require a full ROV spread.
Despite the advances with AUVs and gliders, our success will always depend on ships. Expanded AUVs equipped with new in situ sensors will not eliminate the need for sampling, and many types of sampling will remain in the domain of human-occupied vehicles, remotely operated vehicles, and specialized facilities (such as the new long core system on Knorr) that require capable vessels. Many of these sampling efforts are crucial elements of programs where oceanography is most relevant to pressing societal needs such as understanding past and present cli-
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Oceanography in 2025: Proceedings of a Workshop
mate variability. Undoubtedly laboratory instrumentation will continue to evolve and the resulting capabilities will always exceed those of in situ sensors. For example, in situ mass spectrometers will enable many new types of investigations; but they will not have sufficient performance to replace accelerator mass spectrometer facilities to determine the ventilation age of seawater. AUV capabilities will certainly improve for some types of sampling, but for the foreseeable future the most demanding types of sampling (gathering hydrothermal fluids, retrieving fossil corals, or taking cores, for example) will require skilled human intervention. The role of our ships may change, as their capabilities as tenders for launching vehicles, floats, and gliders will become much more important. But new ships well matched to this role will certainly be required in my view.
REFERENCE
Davis, C.S. and D.J. McGillicuddy, Jr. 2006. Transatlantic Abundance of the N2-Fixing Colonial Cyanobacterium Trichodesmium. Science. 312:1517-1520.
