Search

The possibility of using lasers for non-contact vibration measurements has been known since the mid-60s. This work describes the development of some applied areas: the use of laser vibrometry in near-field acoustic holography, verification of numerical models of vibrations of complex structures, and vibration flaw detection.

The paper describes the results of an experiment on studying long-range surface reverberation in the deep-water part of the Black Sea. The experiment employed tone pulses with a filling frequency of 2 kHz and a duration sufficient for narrowband spectral analysis. The source and receiver of acoustic signals were spatially offset in the water area; therefore, directional reception and time strobing made it possible to study different situations: forward scattering, bistatic scattering, and monostatic (back) scattering. The paper analyzes the Doppler scattering spectra for different values of the bistatic scattering angle.

The paper presents the results of processing measurement data on the spatiotemporal structures of sound fields in Lake Ladoga. Measurements were taken with an extended vertical receiver array. The aim of processing was to isolate the field components that were stable with respect to small variations in the waveguide parameters. Since a model of the medium is inevitably inaccurate, such components can be predicted with greater accuracy than the total field. In terms of the ray approach, a stable component is generated by a beam of rays propagating over close trajectories. The discussed experiment analyzed sound fields excited by a point source that emitted wideband pulses, as well as the fields of wave beams excited by the emitting vertical array at fixed frequencies. In both cases, the processing results showed that the isolated stable components, as expected, coincide substantially better with the prediction of theoretical calculation (by the wide angle parabolic equation method) than with the total wave field.