HR: 0800h
AN: G21A-0147    [Abstracts]
TI: Spatial variations in Acoustic velocity at Kuroshio region for the accurate ocean-bottom positioning
AU: * Yada, K
EM: yada@eps.nagoya-u.ac.jp
AF: Graduate School of Environmental Studies, Nagoya University, Furo-tyo, Tikusa-ku, Nagoya, 464-8602 Japan
AU: Ikuta, R
EM: ryoya@seis.nagoya-u.ac.jp
AF: Graduate School of Environmental Studies, Nagoya University, Furo-tyo, Tikusa-ku, Nagoya, 464-8602 Japan
AU: Ando, M
EM: ando@seis.nagoya-u.ac.jp
AF: Graduate School of Environmental Studies, Nagoya University, Furo-tyo, Tikusa-ku, Nagoya, 464-8602 Japan
AU: Okuda, T
EM: okuda@seis.nagoya-u.ac.jp
AF: Graduate School of Environmental Studies, Nagoya University, Furo-tyo, Tikusa-ku, Nagoya, 464-8602 Japan
AU: Tadokoro, K
EM: tad@seis.nagoya-u.ac.jp
AF: Graduate School of Environmental Studies, Nagoya University, Furo-tyo, Tikusa-ku, Nagoya, 464-8602 Japan
AU: Kuno, M
EM: yada@eps.nagoya-u.ac.jp
AF: Fisheries Research Division, Mie Prefectural Science and Technology Promotion Center, 3564-3, Hamajima, hamajima-tyo, Shima-gun, 517-0404 Japan
AU: Sugimoto, S
EM: sugimoto@eps.nagoya-u.ac.jp
AF: Graduate School of Environmental Studies, Nagoya University, Furo-tyo, Tikusa-ku, Nagoya, 464-8602 Japan
AU: Takatani, K
EM: kazunori@eps.nagoya-u.ac.jp
AF: Graduate School of Environmental Studies, Nagoya University, Furo-tyo, Tikusa-ku, Nagoya, 464-8602 Japan
AB: We have developed a system for observing seafloor crustal deformation. This system combines GPS and acoustic techniques. One of the main errors in this system is heterogeneity of acoustic velocity in sea water. In this talk we discuss effects of lateral heterogeneity of the velocity in sea water on the location of a seafloor station. We evaluated lateral heterogeneity of the velocity in sea water for accurate determination of the ocean-bottom position. If we carry out CTD (Conductivity Temperature Depth profiler) measurements with a single ship, we cannot distinguish spatial and temporal variations from the measurement results. We therefore made simultaneous CTD measurements with two ships at the Kuroshio region (Kumano Basin). The distances between two ships are 2, 1, 0.6, 0.3, and 0.15 nautical miles (nm). The two ships were aligned parallel or orthogonal to the direction of ocean current. The CTD profilers used are SBE-19, SBE-25, and SBE-911plus of Sea-Bird Co., Ltd. The spatial variation is large at depths above 600 meters. It increases with the ship separation; and it is negligible at 0.15 nm separation. The spatial variation is up to 2.3 m/s when the two ships were aligned parallel to the direction of ocean current, and up to 6.6 m/s for the orthogonal direction at outside of Kuroshio region. At Kuroshio region, the variation is up to 2.8 m/s for parallel direction, and up to 7.0 m/s for the orthogonal direction. In addition, the spatial variation is long-period variation at Kuroshio region. We estimated the location error in ocean-bottom positioning caused by the spatial variation of the velocity structure using the CTD data. The data used in this calculation are five simultaneous CTD measurements inside of the Kuroshio region and eight measurements at outside of Kuroshio region. We modeled a 3-D velocity structure from the above dataset. Then we obtained the location of transmission from the travel time data. We searched the location of seafloor station which explains the travel time data assuming a homogeneous velocity structure. The difference is defined as lateral error between the true location and the estimated location. Results as follows: (1) Inside of the Kuroshio region The lateral error was negligible for parallel direction, and up to 50 cm for the orthogonal direction. (2) Outside of the Kuroshio region The lateral error was 20 cm for the parallel and orthogonal directions. On the basis of the results, we evaluate the effects of the spatial variations on the location error of a sea-floor position.
DE: 4512 Currents
DE: 1709 Geodesy
DE: 1724 Ocean sciences
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting