The ocean is tremendously under-observed, largely as a consequence of the high cost of making measurements in its interior. The objective of this project is to develop new technologies for characterizing the ocean, and to merge these tools into a coherent operational paradigm which offers: extended presence, reactivity, and multiscale observational capability.
This project has three distinct stages. The first is to develop autonomous survey platforms capable of unattended deployments over periods of months, as well as supporting communications and power management technologies. Second, we will demonstrate the system's capability in a science driven deployment in Labrador Sea. Finally, we will merge the observational system with ocean modeling and data assimilation systems and demonstrate the combined capability in a experiment on the continental shelf. The system so created is referred to as an Autonomous Ocean Sampling Network (AOSN).
The components of AOSN under development are: fast survey AUVs (Odyssey class vehicles), buoyancy driven gliders, moorings, and the software environment which binds the system together. While some of the instruments had been developed under prior ONR support, many new capabilities are required for long-term unattended deployment. These include: reliable autonomous docking including efficient power transfer and high-bandwidth communications, gliders capable of extended low-speed operations, acoustic communications, and satellite communications for surfaced vehicles and moorings. New techniques, such as acoustically focused sampling, in which AUVs are employed interactively within an acoustic tomographic array are evolving from the synergistic use of usually independent capabilities.
Significant progress has been made on mobile platforms in the last year. Prototypes of two different buoyancy driven vehicles are nearing readiness for field experiments. Two way satellite communication capability is being tested to provide a data/command link with the gliders and moorings. The Odyssey class vehicles have been employed in a large field experiment for mapping ocean fronts, generating unique observations of tidal mixing processes. AUVs were used independently, under surface control, in pairs, under surface control in coordination with a drifter (IOS Seascan platform), and within an acoustic tomography network. Capabilities necessary for docking have been demonstrated with a variety of homing sensors and capture strategies.
These advances are being driven by the demands of a three month deployment of the full AOSN in Labrador Sea in support of the Deep Oceanic Convection ARI. While deep convection plays an important role in global heat transport between low and high latitudes, it is not well understood, in part because it has been poorly observed. Challenges to measurement of deep oceanic convection stem partly from the hostile conditions of the North Atlantic during February through April, the period in which convection reaches its peak, and partly from the episodic nature of the process. Thus the AOSN deployment in Labrador Sea, while extremely challenging, provides a previously unavailable ability to obtain both spatially and temporally distributed observations of convection events in a reactive, repetitive manner.
Following the Labrador Sea deployment in early 1998, the focus will shift to coupling the AOSN observational capability with established modeling and data assimilation packages to create a coupled observation/modeling system. The vision is to assimilate AOSN measurements into the model and then use the model to generate the sampling plan which makes optimal use of scarce oceanographic assets. Thus the model both represents the optimal use of the measurements, and provides the guidance to optimize the next set of observations. Concrete steps towards demonstrating this capability have already been made, working with both the Harvard group (originators of HOPS, the Harvard Ocean Prediction System), and with collaborators at the MIT Earth and Planetary Science Department.
The next several years will see MURI efforts focused on pursuing the long term goal of a fully integrated observational and modeling system. However, an additional goal will be to integrate intermediate results of the project, for example the autonomous platforms, into broader use by the oceanographic community. This process is being pursued by participating in various ONR initiatives, for example Primer activities, the National Ocean Technology Program and proposed efforts under the National Ocean Partnership Program. Thus the legacy of this effort will go far beyond mere proof of concept; the intent is to create a fully operational capability available to the entire community.