Earth Planets Space, Vol. 55 (No. 10), pp. e17-e20, 2003
Yukihito Osada1, Hiromi Fujimoto2, Satoshi Miura2, Aaron Sweeney2, Toshihiko Kanazawa1, Shigeru Nakao1, Shin-ichi Sakai1, John A. Hildebrand3, and C. David Chadwell3
1Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
2Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan
3Scripps Institution of Oceanography, University of California San Diego La Jolla, CA 92093-0205, USA
(Received September 19, 2003; Revised November 3, 2003; Accepted November 5, 2003)
A GPS/Acoustic experiment on the southeastern slope of Hawaii Island presented precise seafloor positioning in the condition of large water depth (2.5-4.5 km) and large velocity variations. We estimated sound velocity variations from acoustic ranging, and found that temperature variation can well explain the velocity variation. The effect of daily variation in the sound velocity amounted to +/- 0.7 m on acoustic ranging of 4-7 km with a fixed velocity structure. CTD data observed about every 3 hours could decrease the range residuals to +/- 0.4 m. These large residuals were fairly well canceled in the positioning of the array center of three acoustic transponders. The estimated precision of the array center positioning was about 3 cm in latitude and longitude.
Key words: GPS/Acoustic, seafloor positioning, acoustic ranging, sound velocity, Hawaii Island.