Kazuhiko Ohta
5th Res. Ctr., Technical Res. and Development Ctr., Japan Defense Agency, Yokosuka, 239 Japan
Itaru Morishita
Shunji Ozaki
Tsuneo Ishiwata
Oki Electric Industry Co., Ltd., Tokyo, 108 Japan
A stochastic inversion method is applied to the problem of determining sound-speed profile in bottom sediment from modal eigenvalues, which can be observed from the FFT beamformed output of a horizontal array in a range-independent shallow-water waveguide. Under a noisy field, each observed eigenvalue has different variance depending on the signal-to-noise ratio (SNR) of modal peaks in the output wave-number spectrum; this difference in SNR originates from the relation between mode shape and source/receiver depths. Thus by using those variances in a covariance matrix involved in stochastic inversion method, it is numerically demonstrated that we can improve the estimation for the solution as compared to that obtained by using a uniform covariance matrix. It is also shown that combination of the same modal eigenvalues observed at the different source or receiver depth can reduce the variance of estimated solution. Application of the stochastic inversion method to real data is also discussed together with comparison with a regularization method. [Work support by JDA.]
Standards Committee S1 on Acoustics. Working group chairs will report on their preparation of standards on methods of measurement and testing, and terminology, in physical acoustics, electro-acoustics, sonics, ultrasonics, and underwater sound. Work in progress includes measurement of noise sources, noise dosimeters, integrating sound-level meters, and revision and extension of sound level meter specifications. Open discussion of committee reports is encouraged. The international activities in ISO/TC 43 Acoustics, and IEC/TC 29 Electro-acoustics, will also be discussed. The chairs of the respective U.S. Technical Advisory Groups for ISO/TC 43 (P. D. Schomer), and IEC/TC 29 (V. Nedzelnitsky), will report on current activities of these international Technical Committees. Scope of S1: Standards, specifications, methods of measurement and test and terminology in the field of physical acoustics including architectural acoustics, electro-acoustics, sonics and ultrasonics, and underwater sound, but excluding those aspects which pertain to biological safety, tolerance and comfort.
Standards Committee S3 on Bioacoustics. The current status of standards under preparation will be discussed. In addition to those topics of interest, including hearing conservation, noise, dosimeters, hearing aids, etc., consideration will be given to new standards which might be needed over the next few years. Open discussion of committee reports is encouraged. The international activities in ISO/TC 43 Acoustics, and IEC/TC 29 Electro-acoustics, and ISO/TC 108/SC4 Human Exposure to Mechanical Vibration and Shock, will also be discussed. The Chairs of the U.S. Technical Advisory Groups for ISO/TC 43 (P. D. Schomer), IEC/TC 29 (V. Nedzelnitsky), and ISO/TC 108/SC4 (H. E. von Gierke) will report on current activities of these international Technical Committees and Subcommittees. Scope of S3: Standards, specifications, methods of measurement and test, and terminology in the fields of mechanical shock and physiological acoustics, including aspects of general acoustics, shock, and vibration which pertain to biological safety, tolerance and comfort.