The Acoustic Thermometry of Ocean Climate (ATOC) Project: Towards depth-averaged temperature maps of the North Pacific Ocean
Brian D. Dushaw and the ATOC Group* (Applied Physics Laboratory, College of Ocean and
Fisheries Sciences, University of Washington, Seattle, WA 98105)
e-mail: dushaw@apl.washington.edu
ABSTRACT
The ATOC Project has aquired trans-Pacific acoustic data from two acoustic sources: one located on Pioneer Seamount off the coast of Califomia, the other located north of Kauai, Hawaii. Transmissions from these sources are detected by U.S. Navy SOSUS arrays located throughout the North Paclfic. The time series of acoustic travel times from the Pioneer Seamount and Kauai transmissions are about 1 1/2 and 1 year long, respectively. Both time series have highly irregular sampling because of marine mammal protocols and temporary cable failures; the timeseries derived from the two acoustic sources overlap by about 75 days. These acoustic data are used to accurately estimate ocean temperature. The overlapping time series for the first time allow estimates of temperature maps of the North Pacific basin using long-range acoustics because the acoustic paths from these sources criss-cross the North Pacific. Maps of depth-averaged temperature of the North Pacific Ocean are derived using the time series collected through 1998.
INTRODUCTION
The Acoustic Thermometry of Ocean Climate (ATOC) program has achieved its original goal of acquiring time series of acoustic travel time over basin-scale paths (Figure 1) and using that data to accurately determine range- and depth-averaged ocean temperature [1-3]. Acoustic sources were deployed on Pioneer Seamount near San Francisco in October 1995 and on the north slope of the Hawaiian island of Kauai in July 1997. The Pioneer Seamount and Kauai sites, were selected to allow much of the acoustic energy to leave the source without interaction with the ocean bottom. To date several time series of acoustic data of about 15 months duration have been obtained from acoustic transmissions from the Pioneer Seamount acoustic source to receiving arrays located throughout the North Pacific ocean, including two moored vertical line arrays of hydrophones (VLAs) and U.S. Navy SOund SUrveilance System (SOSUS) bottom-mounted horizontal line arrays. The data have been collected since about 1 January 1996. The travel time data are obtained in near real time, and estimates of range-averaged temperature are obtained within a few days after the data are collected.
* The Acoustic Thermometry of Ocean Climate (ATOC) Group is : A.B. Baggeroer, D. Mene-memlis [now at JPL], and C. Wunsch (MIT); T.G. Birdsall, K. Metzger (U. Mich.); C. Clark (Cornell U.); J.A. Colosi (WHOI); B.D. Cornuelle, M. Dzieciuch, W. Munk, P.F. Worcester (SIO); D. Costa (U. Calif., Santa Cruz); B.D. Dushaw, B.M. Howe, J.A. Mercer. R.C. spindel (APL-U. Wash.); A.M.G. Forbes (CSIRO, Hobart).
