Precise measurement of travel time difference for reciprocal transmission of Central Equatorial Pacific tomography

• Published in: The Journal of the Acoustical Society of America 2006-11, Vol.120 (5_Supplement), p.3019-3020
• Main Authors: Hachiya, Hiroyuki, Nakamura, Toshiaki, Fujimori, Hidetoshi, Nakano, Iwao
• Format: Article
• Language: English
• Subjects: Oryza sativa
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4787089

We present the estimation results of the travel time difference in reciprocal transmission data collected during the tomography experiment performed by Japan Agency for Marine-Earth Science and Technology (JAMSTEC) in the Central Equatorial Pacific. A precise estimation of travel time is essential for measuring ocean current using ocean acoustic tomography. We estimate the variation of the correlation of reciprocal propagated sound transmissions. Generally, reciprocal propagation sound waveforms that are transmitted at the same time are similar mutually, and it is considered that their correlation is high. However, it is found that reciprocal sound waveforms sometimes become different in the experiment. The vertical arriving angle of ray is measured using the phase differences between the receivers of a 30-m-long receiving array. The theoretical analysis of phase deviation using the Rice distribution is presented. From the ray identification results, the travel time difference between corresponding rays of reciprocal transmissions can be estimated. Since the phase of a ray signal is very stable, the precision of the travel time difference using phase difference is 6 times higher than the conventional estimation. The combination of the amplitude and phase information is effective for observing the ocean structure change.