Journal of Oceanography, Vol. 53 (No. 2), pp. 117-127, 1997
Hong Zheng1, Noriaki Gohda1, Hideaki Noguchi2, Toshimichi Ito3, Haruhiko Yamaoka1, Tadashi Tamura4, Yoshio Takasugi2 and Arata Kaneko1
1Faculty of Engineering, Hiroshima University, Higashi-Hiroshima 739, Japan
2Chugoku National Industrial Research Institute, 2-2-2 Suehiro, Hiro, Hiroshima 731-01, Japan
3Japan Atomic Energy Research Institute, 4-24 Minato-machi, Mutsu, Aomori 035, Japan
4Sanyo Techno Marine, Inc., 1-3-17 Horidome-cho, Nihonbashi, Chuo-ku, Tokyo 103, Japan
(Received 18 April 1996; in revised form 12 August 1996; accepted 20 August 1996)
Abstract: A reciprocal sound transmission system has been designed to measure currents over a long term in the coastal sea with heavy ship traffic and fishing activities. The system was composed of two stations spaced with a distance of 5.7 km on both sides of a channel in the Seto Inland Sea, Japan. Each station was equipped with a transmitter, hydrophone and GPS receiver. Reciprocal sound transmission experiments between the two stations were successfully completed for 5 hours, using a carrier of 10.6 kHz modulated with the M sequence of 10th order. Time coordinates at both the stations was synchronized with the accuracy of 0.1 ms by 1 Hz and 1 kHz time signals received by GPS. Range-averaged current velocities, estimated from travel time data obtained reciprocally, were in good agreement with the results of ADCP measurement obtained along the sound transmission line. It is suggested that reciprocal sound transmission is applicable to velocity measurement in the inland sea with heavy ship traffic and fishing activities.