HR: 0800h
AN: G51B-0825    [Abstracts]
TI: Introduction of the Concept of the Transducer's Phase Center to the Seafloor Geodetic Station Positioning
AU: * Mochizuki, M
EM: moma@iis.u-tokyo.ac.jp
AF: Inst. of Industrial Science, Univ. of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8505 Japan
AU: Ishikawa, T
G51B-0825 AF: Hydrographic and Oceanographic Dept., Japan Coast Guard, 5-3-1 Tsukiji, Chuo-ku, Tokyo, 104-0045 Japan
AU: Narita, Y
G51B-0825 AF: 7th Regional Coast Guard Headquarter, Japan Coast Guard, 1-3-10 Nishi-Kaigan, Moji-ku, Kita-Kyushu, 801-0045 Japan
AU: Yoshida, Z
G51B-0825 AF: Inst. of Industrial Science, Univ. of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8505 Japan
AU: Matsushita, H
G51B-0825 AF: Hydrographic and Oceanographic Dept., Japan Coast Guard, 5-3-1 Tsukiji, Chuo-ku, Tokyo, 104-0045 Japan
AU: Matsumoto, Y
G51B-0825 AF: Hydrographic and Oceanographic Dept., Japan Coast Guard, 5-3-1 Tsukiji, Chuo-ku, Tokyo, 104-0045 Japan
AU: Kawai, K
G51B-0825 AF: Hydrographic and Oceanographic Dept., Japan Coast Guard, 5-3-1 Tsukiji, Chuo-ku, Tokyo, 104-0045 Japan
AU: Fujita, M
G51B-0825 AF: Hydrographic and Oceanographic Dept., Japan Coast Guard, 5-3-1 Tsukiji, Chuo-ku, Tokyo, 104-0045 Japan
AU: Asada, A
G51B-0825 AF: Inst. of Industrial Science, Univ. of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8505 Japan
AB: Institute of Industrial Science, University of Tokyo and Hydrographic and Oceanographic Department, Japan Coast Guard have been constructing the geodetic observation network on the seafloor around Japan. The observation network, which consists of eighteen seafloor geodetic reference stations, has been built along the ocean trench regions. The observation results were accumulated as the observations have been routinely repeated. Issues and knowledge that we have through the observations should be fed back to the system and further observation for improvement. One of such issues is one inherent in the acoustic transducers. Cylindrical acoustic transducers are employed both on the ship-board system and on the seafloor unit. Coded sinusoidal acoustic wave with 15 cm wave length is used as the ranging signal. This wave length is compatible to the dimension of the cylindrical transducer. This implies that possible ranging error is caused depending on the incident angle of the acoustic signal to the transducer. We are introducing new acoustic transducer which is designed so that same response is secured within some range of the incident angle to take measures against this issue. Tank tests were conducted to evaluate the phase responses of both new and old acoustic transducers. Ranging procedure has repeated by receiving a signal transmitted from the transducer with hydrophone at points keeping constant distance (150.0cm) from the transducer. The phase response curves against incident angle were deduced from the tank tests. Some corrections to retain continuity in the seafloor geodetic observation could be deduced from these comparisons. The phase response curves that we got were applied to the procedure of seafloor geodetic station positioning in order to make corrections to the ranging errors caused by incident angle dependent phase shift. However, it was difficult to do so, because we had no knowledge on attitudes of the seafloor acoustic units. Then we changed our policy of using the phase response curves for the correction. We derived the phase centers of the acoustic transducers from the phase response curves. The phase centers were determined on the points, 12 cm inside from the top center of the transducer for old one, 9 cm inside for the new one, respectively. The concept of the phase center of the acoustic transducer was introduced to the seafloor geodetic station positioning, instead of introduction of the phase response curve itself. We will report how much improvement on the seafloor unit positioning we can expect by the introduction of the concept of the transducer_fs phase center.
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 1294 Instruments and techniques
SC: Geodesy [G]
MN: Fall Meeting 2005