A Global Ocean Acoustic Observing Network

Abstract

Passive and active acoustic measurements are effective and unique approaches to ocean observation. Both approaches have techniques that are well-established and suitable for immediate deployment as part of an operational observing system.Many of these techniques exploit the remarkable ability of lowfrequency sounds to traverse great distances in the ocean. Passive acoustic measurements of natural or man-made sounds are made for diverse purposes ranging from assessing the environmental impact of human activities, to geophysics, to monitoring changes in biodiversity in response to climate change. Active acoustic systems are employed for tracking instruments and acoustic tomography. Tomography has a role in the ocean observing system that is complementary to altimetry and profiling floats, particularly in the context of data assimilation and ocean modeling. Modest systems of acoustic receivers and sources deployed across ocean basins can make cost effective, sustained observations of a variety of ocean processes.

Progressing Towards Global Sustained Deep Ocean Observations

“…Also, acoustic tomography may provide helpful data for temperature and salinity in the deep ocean. The role of acoustic tomography is discussed in a companion Community White Paper (CWP) [65].…”

“…Several different technologies for the remote retrieval of data from deep moored instruments are presently being developed around the globe or are proposed to be developed (e.g., CWP by [66], [65], [68], [69], [70] and [71]. The Woods Hole Oceanographic Institution system called "UltraMoor" is perhaps the furthest along, having been used in several deployments off the eastern seaboard of the United States.…”

Simulated tomographic reconstruction of ocean current profiles in a bottom‐limited sound channel

“…These experiments determined sound speed and current velocity. The results are well validated in the deep-sea environment and described, for example, by the review papers by Dushaw et al [1993Dushaw et al [ , 2001Dushaw et al [ , 2010 and the textbook by Munk et al [1995]. Recently, the OAT method using highfrequency sound has been applied to coastal seas.…”

Multipurpose Acoustic Networks in the Integrated Arctic Ocean Observing System

“…Through inversion techniques, internal ocean temperature can be retrieved with an accuracy of 0.01˚C over a 200 km distance (Munk et al, 1995;Dushaw et al, 2010). Average current velocities are determined from the differences between reciprocal travel times produced by simultaneously transmitting acoustic pulses in opposite directions along an acoustic path.…”

“…The development and implementation of the infrastructure for multipurpose acoustic networks in the Arctic Ocean would support in situ ocean observations with instrumented moorings, autonomous vehicles, and floats, as well as with acoustics (Dushaw et al, 2010;Sagen et al, 2010). The OceanObs'09 Conference Summary (Fischer et al, 2010) identifies active and passive ocean acoustics as a proven technology for in situ ocean observing.…”