It is better to use a simple configuration to enhance the applicability of sound speed profile inversion in shallow water. A matched-field inversion method based on a horizontal line array is used by researchers from the Institute of Acoustics of the Chinese Academy of Sciences to retrieve the variation of water column.

Empirical orthogonal functions are used to represent the sound speed profiles and reduce the unknown parameters, and the Matched-Field Inversion method is used to invert for sound speed profiles.

The performance of the horizontal line array acoustic inversion is verified using the experiment data from South China Sea in June 2010. The mean sound speed profiles at different times within a range of 40 km are inverted from the measured linear frequency module acoustic signals.

Nearly 9-hour long inversion results show the validity of the inversion scheme. It is the first special sound speed profile inversion experiment using a horizontal line array in shallow water conducted in China.

In China, the vertical line array had been used in sound speed profile inversion successfully. And the horizontal line array should be used in a shore-based sonar system. When a shore-based sonar system works, concurrent sound speed profile is needed. It might be an alternative method to get the mean sound speed profile from the acoustic signal for a shore-based sonar application.

Using the pulse signals, researchers has previously demonstrated the feasibility of sound speed profile inversion from the horizontal line array in the Yellow Sea. However, the experimental configuration was not for sound speed profile inversion. Only several sound speed profiles and signals were measured during the experiment.

It is worthy to design a special experiment for sound speed profile inversion tests using a horizontal line array and repeated acoustic signals from a transducer.

After this research, nevertheless, some issues remain to be investigated. For example, different groups of normal modes can be well excited if the source is located at different depths.

In addition, the group velocities of some modes at special frequencies are more sensitive to the thermocline depth variations. Therefore, additional research is needed to optimize the frequency band of the signal and the source depth according to the water depth.

This research was supported by the National Natural Science Foundation of China (Grant Nos. 11434012, 11404366, 11125420 and 11074269).

References:

LI Zhenglin, HE Li, ZHANG Renhe, LI Fenghua1, YU YanXin, LIN Peng. Sound Speed Profile Inversion Using a Horizontal Line Array in Shallow Water. SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY (Vol. 58, No. 1: 014301, pp. 1-7, January 2015). DOI: 10.1007/s11433-014-5526-x

Contact:

LI Zhenglin

State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, 100190 Beijing, China

Email: lzhl@mail.ioa.ac.cn