Long-range tomography experiment in the western equatorial Pacific

Abstract

An ocean acoustic tomography experiment was performed with a pair of 200-Hz transceivers in the western equatorial Pacific along the longitudinal line of 147.5 °E during April–December 1996. Time series of reciprocal ray travel times were obtained at about the 700-km range for approximately 100 days between the transceivers. The one-direction, resolved-ray travel times were applied to obtain temperature, and differential resolved-ray travel times to obtain barotropic current velocity. The inversions derived from the stochastic inverse method gave a series of snapshots of two-dimensional temperature fields, which showed a pattern similar to that determined from CTD measurements during the transceiver deployment cruise. The range-averaged temperature anomaly, δT(z), agreed almost perfectly with that calculated from the difference between the CTD temperature profile and the NODC reference temperature profile within an estimated error of ±0.5 °C, except for the surface layer. The evolution of acoustically determined range-averaged temperature and temperature anomaly structures agreed well with the concurrent PMEL/TAO array data. A range-averaged barotropic current determined from the difference of the reciprocal ray travel times also agreed with the range- and depth-averaged meridional velocity determined from ADCP measurements during the transceiver deployment cruise in the same order.