ABSTRACT

The concept of integrated acoustics systems to provide navigation and communications and to conduct acoustic measurements, all in support of science applications within the ocean's volume, is developed. The navigation function is analogous to the now-ubiquitous satellite based Global Positioning System (GPS), but because the ocean is opaque to electromagnetic waves and transparent to sound, acoustics systems are necessary. In the ocean, a series of nested systems are envisioned, from small-scales to regional to basin-scales as required. A small number of acoustic sources sending coded, low power signals can service unlimited numbers of inexpensive receivers. These sources can serve double duty by transmitting control data from users to remote instruments; if enabled as receivers, two-way acoustic communications links in large-scale networks can be established. Acoustic based instrumentation that shares the acoustic bandwidth with, and depends upon, the navigation and communications capabilities completes the concept of integrated acoustic systems.

This navigation and communications infrastructure is a prerequisite to the sustained presence of mankind in the ocean. Many applications require or are enabled by this infrastructure. Autonomous undersea vehicles (powered and gliding) can navigate themselves over the ocean bottom and through the water column without coming to the surface. They can obtain navigation fixes and communicate their data and status to users via acoustic modems to cabled or surface satellite telemetry systems without breaking away from their underwater missions. Profiling and drifting floats can more accurately measure the ocean's velocity structure, tagged fish and marine animals can be tracked with high precision, moorings can track their motion in ocean currents, and bottom-fixed instruments can measure seafloor motion.

The sources and receivers can serve multiple functions: sources as navigation and communications components as well as multi-static active transmitters, and receivers as communications components and as passive listening devices. With signal standards and protocols for managing the acoustic spectrum, the system will be an extensive multipurpose acoustics infrastructure, capable of supporting applications even beyond our present vision. Drawing a further analogy with GPS and its use for tomography of the atmosphere and ionosphere, the various acoustic sources and multitude of receivers can function similarly in the ocean. This has significant implications for observing the ocean's interior in real time, and measuring long-term climate variability. Receivers on globally distributed floats can also listen to ambient sound: wind and rainfall, seismic T-phases, marine mammals, and ships. Some of these natural sources of sound can in-turn be used as sources of opportunity for other purposes.

The provision of such a transformational infrastructure to the ocean community is expected to be one of the enabling technologies fueling a revolution in ocean observatories. This report examines the concept by addressing technical questions and implementation issues. The IASOO Committee is a newly formed specialty committee of the Acoustical Society of America. Broad community participation is encouraged.