In this paper, we present the stability estimation results of the data collected during the sound transmission experiment performed by Japan Marine Science and Technology Center (JAMSTEC) in 1996 at the western equatorial Pacific. The amplitude and the phase of a correlated signal were very stable within 50 s. There was a small component of the acoustic changes with a period of less than 50 s due to the ocean-structure change. The amplitude and phase, changed significantly within about 3 h. The travel time could be estimated with an error of less than 0.3 ms. The combined information of the amplitude and phase was effective for identifying a ray and observing the ocean-structure change.