It is demonstrated that seismic interface waves on the surface of a natural beach can be used to identify the position of a buried object. For this experiment, the waves were created with a sediment-coupling transducer and received on a three-element horizontal line array of triaxial geophones. The source and its coupling to the medium provided a high degree of signal repeatability, which was useful in improving signal-to-noise ratio. Reception of all three directions of particle velocity made it possible to augment conventional beamforming techniques with polarization filters to enhance interface-wave components. Reverberation in the beach was found to be large, though, and coherent background subtraction was required to isolate the component of the sound field reflected by the target. Propagation loss measurements provided comparisons of reflected signal power with predictions made previously, and the two were found to agree closely.
Acoustic measurements of insertion loss and echo reduction at normal incidence were made for thin plates of eight materials for evaluation of their use in underwater sound transducers in the frequency range 50–500 kHz. Materials tested included Lucite; silicone rubber RTV– 560; the commercial polyurethane products PRC–1527, CPC–19, Scotchcast 8, and Scotchcast 221; and two of these materials with talc added during curing to vary the properties. Values of longitudinal sound velocity, attenuation constant, and characteristic impedance are derived from comparison of theoretical and measured characteristics. Subject Classification: [43]30.30; [43]40.55; [43]55.75; [43]85.40.
The combustive sound source (CSS) can be used to generate high-intensity, low-frequency acoustic energy in a variety of mediums by using deployment configurations suitable to each medium. The basic principle of operation remains configuration independent. A gaseous fuel/oxidizer mixture is introduced into a combustion chamber and ignited with a spark. The ensuing combustion produces a bubble of expanding gas which, in turn produces high-intensity, low-frequency acoustic pulses. Three different deployment configuration experiments will be discussed, including water column, ocean-bottom seismic, and earth-surface seismic. In-situ measured energy levels and spectra produced by CSS are compared to other sources typical to each medium, including explosive and inertial. It is shown that CSS is capable of producing bulk waves in both water and earth mediums, as well as seismic interface waves for both air/earth and water/sea floor cases. It is demonstrated that CSS is a truly versatile acoustic energy source with a low cost deployment configuration which can be tailored easily to different environments. [Work supported by the U.S. Navy Office of Naval Research.]
Acoustic measurements of insertion loss and echo reduction at normal incidence were made for several materials for evaluation of their use as underwater sound transducer windows in the frequency range of 50–500 kHz. Materials tested included the commercial polyurethane products such as PR-1527, CPC-19, Scotchcast 221, Scotchcast 8, and some of these materials with talc added during curing to vary the density. Values of sound velocity are derived from the echo reduction data and allow determination of ρc values for each material. A computer model of the echo variation with frequency accurately matches the measured echo reduction plots.
KIM, J. Y. and BEHRENS, J. 1986, Experimental Evidence of S*-Wave, Geophysical Prospecting 34, 10C108.During development of theoretical methods to compute synthetic seismograms, a new type of wave called S*-wave was discovered by Hron and Mikhailenko. This wave propagates with the shear-wave velocity and can be interpreted as a non-geometrical wave arrival with large amplitudes strongly depending on the depth of a pure P-point source.In this first experimental verification of the existence of S*-waves by means of twodimensional model-seismics it is demonstrated that:1. the S*-wave exists and depends on the source distance from the free surface; 2. the S*-wave is generated as an ordinary shear wave on the free surface at the point located directly above the P-source, as illustrated in the synthetic seismograms. The measured seismograms agree remarkably well with the computed ones.
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