Anatoliy N. Ivakin
N. N. Andreev Acoustics Inst., Shvernika 4, Moscow 117036, Russia
There are two different types of irregularities giving the main contributions to bottom scattering: volume inhomogeneities of the sediment and roughness of its surface and interfaces. The problem of distinguishing and/or separating these contributions is considered using differences in frequency-angular dependencies of the scattering coefficient and analysis of the spatial autocorrelation function of the scattered field. The volume inhomogeneities of the sediment in turn can be considered as one of two types: spatial fluctuations of density and fluctuations of sound velocity. For water-saturated sediments (without gas), density fluctuations are usually stronger and their contribution to the total volume scattering is much more than that due to sound velocity fluctuations. But even low concentrations of gas bubbles can alter acoustic properties of sediments considerably, reducing the effective (average) sound velocity and enhancing fluctuations of sound velocity, with virtually no effect on the density. As a result, some specific features appear in sound scattering, and these can be used for remote acoustic characterization of sediments and determination of the type of bottom irregularities. [Work partially supported by ONR.]
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 Electroacoustics, 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 (H. E. von Gierke), and IEC/TC 29 (V. Nedzelnitsky), will report on current activities of these 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.
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, electroacoustics, 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 Electroacoustics, will also be discussed. The chairs of the respective U. S. Technical Advisory Groups for ISO/TC 43 (H. E. von Gierke), and IEC/TC 29 (V. Nedzelnitsky), will report on current activities of these Technical Committees. Scope of S1: Standards, specifications, methods of measurement and test and terminology in the field of physical acoustics including architectural acoustics, electroacoustics, sonics and ultrasonics, and underwater sound, but excluding those aspects which pertain to biological safety, tolerance and comfort.