HR: 1340h
AN: G13B-1233    [Abstracts]
TI: Development of the seafloor acoustic ranging system
AU: * Osada, Y
EM: osada@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, 6-6 Aramaki, Aoba-ku, Sendai, 9808578, Japan
AU: Kido, M
EM: kido@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, 6-6 Aramaki, Aoba-ku, Sendai, 9808578, Japan
AU: Fujimoto, H
EM: fujimoto@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, 6-6 Aramaki, Aoba-ku, Sendai, 9808578, Japan
AB: We have developed a seafloor acoustic ranging system, which simulates an operation with the DONET (Development of Dense Ocean-floor Network System for Earthquake and Tsunami) cable, to monitor seafloor crustal movement. The seafloor acoustic ranging system was based on the precise acoustic transponder (PXP). We have a few problems for the improvement of the resolution. One thing is the variation of sound speed. Another is the bending of ray path. A PXP measures horizontal distances on the seafloor from the round trip travel times of acoustic pulses between pairs of PXP. The PXP was equipped with the pressure, temperature gauge and tilt-meter. The variation of sound speed in seawater has a direct effect on the measurement. Therefore we collect the data of temperature and pressure. But we donft collect the data of salinity because of less influence than temperature and pressure. Accordingly a ray path of acoustic wave tends to be bent upward in the deep sea due to the Snellfs law. As the acoustic transducer of each PXPs held about 3.0m above the seafloor, the baseline is too long for altitude from the seafloor. In this year we carried out the experiment for the seafloor acoustic ranging system. We deployed two PXPs at about 750m spacing on Kumano-nada. The water depth is about 2050m. We collected the 660 data in this experiment during one day. The round trip travel time show the variation with peak-to-peak amplitude of about 0.03msec. It was confirmed to explain the majority in this change by the change in sound speed according to the temperature and pressure. This results shows the resolution of acoustic measurements is +/-2mm. Acknowledgement This study is supported by gDONETh of Ministry of Education, Culture, Sports, Science and Technology.
DE: 1222 Ocean monitoring with geodetic techniques (1225, 1641, 3010, 4532, 4556, 4560, 6959)
DE: 1294 Instruments and techniques
DE: 3050 Ocean observatories and experiments
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
SC: Geodesy [G]
MN: 2007 Fall Meeting