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Gliders Evolving to Enhance Ocean Observation

Laurent Mortier,
Professor of Oceanography,
ENSTA ParisTech,
Member of Laboratoire d'Océanographie et du Climat
Université Pierre et Marie Curie, Paris

In his impressive science-fiction article published in Oceanography in 1989, Henry Stommel anticipated a revolution in ocean-observing capabilities due to the development of new mobile platforms and sensing systems. We can now marvel at how much his predictions came true. Thousands of profiling floats are drifting in all the oceans and underwater gliders are widely used by laboratories and navies, while propelled AUVs are handling complex missions near the bottom of the sea. In fact, modern AUVs allow both physical and biological characterization of the water column across a continuum of space and timescales, while real-time data transmission enables remote steering and efficient use of collected data. These new autonomous platforms, particularly gliders, have significantly changed the way experiments and observations in the coastal and open oceans are carried out.

Underwater gliders are intelligent and affordable platforms, useful for long-term, multiparameter marine observations. Because of their remotely controlled navigational capabilities and the high spatial and temporal resolution of their real-time measurements, gliders have been tapped to complete ocean-observing systems at global, regional and local levels. But for pure research and for monitoring activities, the academic and industrial communities still face several challenges.

In ocean observing systems, gliders have yet to fill knowledge gaps left by other in-situ platforms. The main infrastructure at present in the Global Ocean Observing System relies upon Argo profiling floats, which are freely drifting devices; hence the need for gliders that can be steered. The issues here are finding the optimal way to add gliders to the Argo array to maximize data gathered and minimize costs. Because gliders' versatility allows for a large number of parameters useful to managing the marine environment, entities in charge of this management, including those in the private sector, are now showing a great interest in gliders. In fact, the future needs are for information on geochemical and biological parameters, and all water-quality descriptors. The potential for industry to help develop gliders is high, and gliders will be used to collect and distribute data for an increasing number of environmental applications.

This is true for pure research. Gliders are now the cost-effective way to investigate the marine ecosystems in the upper and deep ocean when high spatial and temporal resolution are required. Many miniaturized sensors suitable for geochemical and biological observations have been successfully tested in the last few years. For example, nitrate concentration can now be measured by gliders and cameras, with onboard video signal analysis to aggregate marine particle information just around the corner. Laboratories and companies continue to create new sensors, such as microcytometers for plankton monitoring, and are looking to a lab-on-a-chip approach for chemical analysis and advanced passive acoustics, which will advance understanding of how marine ecosystems, from bacteria to large animals, behave.

Other needs for gliders include greater depth range, with an endurance of about one year. Active developments face incredible energy-consumption challenges, a problem being solved by the University of Washington's deep glider project, which is developing a 6,000-meter glider with one-year endurance for the Ocean Observatories Initiative.

Finally, the need for environmental information on offshore activities, including those for defense and security, is rapidly growing for routine use and in cases of accidental or intentional release of pollutants and toxins. Existing technologies could be adapted to fit these new needs for the hostile marine environment, e.g., lab-on-a-chip technologies for sensors. It is the sum of small improvements to present technologies that create progress. The versatility of gliders should also favor wider private sector involvement, for example, providing the platform itself, its sensors, and the communications and piloting services. Above all, today, an increased reliability of the gliders is critical to their evolution.

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