Multimegameter-range acoustic data obtained by bottom-mounted hydrophone arrays for measurement of ocean temperature

Acoustic signals transmitted from the ATOC source on Pioneer Seamount off t he coast of California have been received at various sites around the Pacif ic Basin since January 1996, We describe data obtained using bottom-mounted receivers, including U.S. Navy Sound Surveilance System arrays, at ranges up to 5 Mm from the Pioneer Seamount source. Stable identifiable ray arriva ls are observed in several cases, but some receiving arrays are not well su ited to detecting the direct ray arrivals. At 5-Mm range, travel-time varia tions at tidal frequencies (about 50 ms peak to peak) agree well with predi cted values, providing verification of the acoustic measurements as well as the tidal model. On the longest and northernmost acoustic paths, the time series of resolved ray travel times show an annual cycle peak-to-peak varia tion of about 1 s and other fluctuations caused by natural oceanic variabil ity. An annual cycle is not evident in travel times from shorter acoustic p aths in the eastern Pacific, though only one realization of the annual cycl e is available. The low-pass-filtered travel times are estimated to an accu racy of about 10 ms. This travel-time uncertainty corresponds to errors in range- and depth-averaged temperature of only a few millidegrees, while the annual peak-to-peak variation in temperature averaged horizontally over th e acoustic path and vertically over the upper 1 km of ocean is up to 0.5 de grees C.