network of seafloor observatories will help provide the means to accomplish this goal.

In this report, seafloor observatories are defined as unmanned, fixed systems of instruments, sensors, and command modules connected either acoustically or via a seafloor junction box to a surface buoy or a fiber optic cable to land. These observatories will have power and communication capabilities and will provide support for spatially distributed sensing systems and mobile platforms. Sensors and instruments that are used at seafloor observatories will potentially collect data from above the air-sea interface to below the seafloor and will provide support for in situ manipulative experiments. Seafloor observatories will also be a powerful complement to satellite measurement systems by providing the ability to collect vertical measurements within the water column for use with the spatial measurements acquired by satellites while also providing the capability to calibrate remotely sensed satellite measurements.

Ocean observatory science has already had major successes. For example, the Tropical Atmosphere-Ocean (TAO) array has enabled improved detection, understanding, and prediction of El Niño events and is an example of the achievements that can be accomplished with simple systems. TAO consists of approximately 70 moored ocean buoys in the tropical Pacific Ocean that telemeter oceanographic and meteorological data to shore in real-time via the ARGOS satellite system. TAO Autonomous Temperature Line Acquisition System (ATLAS) buoys (Figures 1-1 and 1-2) measure surface winds, air temperature and relative humidity, and ocean temperatures in the upper 500 m of the ocean, whereas TAO Equatorial Current Meter buoys include additional instruments to measure ocean currents and variables, such as shortwave radiation and rainfall.

Another success is the SOund SUrveillance System (SOSUS), which is a fixed component of the U.S. Navy's Integrated Undersea Surveillance Systems network used for deep-ocean surveillance during the Cold War. SOSUS consists of bottom-mounted hydrophone arrays connected by undersea communication cables to facilities on . The combination of location within the oceanic sound channel and the sensitivity of large-aperture hydrophone arrays allows the system to detect radiated acoustic power of less than a watt at ranges of several hundred kilometers. SOSUS is an important tool for both continuous monitoring of low-level seismicity around the northeast Pacific Ocean and real-time detection of volcanic activity along the northeast Pacific spreading centers, and has provided a useful means to track whale migrations (Plate I).

Although traditional seagoing investigations will continue to be prominent in oceanographic research, the question posed to this Committee was whether there is scientific justification for the establishment of a major coordinated seafloor observatory effort and whether such an effort is technically



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