Comments from ONR's Ocean Acoustics Program
Jeff Simmen
Office of Naval Research
This presentation will briefly describe the ONR Ocean Acoustics Program, in particular as it relates to the topics and issues addressed at the SCOR symposium. Though the talk will include an outline of the overall goals and plans of the new Ocean Acoustics Program, the discussion will focus on the program's interest in long-range acoustic propagation, the inverse problem, and international collaboration. Upcoming and relevant ONR-sponsored field experiments and the need for international exchange/cooperation will be highlighted.
Application of the Acoustic Tomography to Velocity Measurement in Coastal Seas
H. Zheng, N. Gohda, H. Yamaoka, A. Kaneko and
(Faculty of Engineering, Hiroshima University, Japan)
T. Takano
(Asia Air Survey Co., Ltd, Japan)
The multi-station acoustic tomography system composed of five acoustic tranceivers has been constructed for velocity measurement in coastal seas. This is a moored-type tomography system, which can be used for measuring vortex-included current fields. In this system, all clock signals are synchronized by the GPS clock pulse signals through PLL (phase locked loop). When the GPS signals are unavailable, it is replaced by the high-accuracy time base module (Seascan Inc.) which the long-term stability of which is 5*10＾-8. The maximum station number of sixteen can be processed for this system. The CDMA (code-division multiple-access) method is applied to identify signals from individual stations with the aid of a set of 10th-order Gold sequence. Every station is designed to be equipped with at least one hydrophone and one DSP (digit signal processor). The major role of DSP is to calculate instantly the correlation function of received signals. The number of hydrophone and DSP can be increased up to four, depending on the number of the station.
A full tomography experiment to measure tidal vortices generated in the Seto Inland Sea, Japan will be carried out during Feb. 16-18, 1999.
