摘要:

The decade of the 1950s marks the beginning of acoustic signal processing as a subfield of underwater acoustics. The forerunner, signal recognition, gradually evolved into a unified class of spatial and temporal processing techniques and theory which came to stand on its own. The doctrines that emerged in that decade, such as spectrum analysis, correlation, and multiple beamforming, have continued to grow in sophistication, until we now find methods such as the fast Fourier transform, sequential detection, and adaptive beamforming handed down to us from the 1960s. The milestones of signal processing over the past 20 years present a striking record of progress in that field.

ISSN:0001-4966    

DOI:10.1121/1.1912925

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

A mathematical description of ambient sea noise is presented that takes into account the two dominant sources—surface agitation and distant shipping. The contribution from surface agitation is shown to be linearly dependent upon the logarithm of wind speed for depths between 400 and 2500 fathoms at several sites near Bermuda. When this is taken into account, the ambient‐noise data that include both sources can be analyzed to determine the individual levels of the sources. Also, the standard deviations of the two sources can be determined from the standard deviations of the measured levels.

ISSN:0001-4966    

DOI:10.1121/1.1912926

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

A side‐looking sonar was used to study bottom features in Lake Mendota, Wisconsin. Interferences between direct and surface‐reflected signals gave a tiger‐striped pattern in the data. This pattern could be approximately interpreted as being the tracings of isoangle contours. However, this simple analysis was precluded by the strong gradients of sound‐velocity profile. Ray traces were used to construct a profile of the interference field. The profile was used to interpret the data. Features having lateral dimensions of 10 m and a few meters depth were contoured. The data was taken when the sonar was about 100 m from the features.

ISSN:0001-4966    

DOI:10.1121/1.1912927

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The history of the study of radiation characteristics from certain simple apertures, which extends at least from Lommel (1884) to the recent work of Zemanek (1971), is summarized. Theoretical and experimental data concerning resolution, minor lobe behavior, and axial pressure level as a function of range in the near‐ to farfield transition region are presented and compared for a circular disk and a strip line transducer. The use of near‐ to farfield information in transducer calibration, range determination, and sonar design, is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1912928

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The dependence of sound transmission on the statistics of a randomly rough interface between two dissimilar fluids is studied by use of the Kirchhoff‐Helmholtz integral. Both plane waves and waves from a point source are considered. The analysis is very similar to that of scatter from a randomly rough surface; for example, for low roughness, the transmitted mean‐square pressure is coherent ande−Rtimes the smooth surface value, whereas for large roughness the transmitted sound is incoherent and depends also on the surface correlation length. The critical roughness parameter for transmission isR = k22σ2[(c2/c1) cosθ1 − cosθ2]2wherek, c, and θ are the propagation constant, speed of propagation, and angle with the normal, respectively; subscript 1 refers to the incident medium; σ is the rms height of the surface.

ISSN:0001-4966    

DOI:10.1121/1.1912929

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

By admitting complex‐valued solutions to the equations of ray acoustics (complex rays), ray theory is extended to yield nontrivial sound‐pressure levels in the shadow zone adjoining a caustic. For a steady‐state source, the sound field in the shadow is found to decay exponentially with frequency and with distance from the caustic. In the transient case, the theory appears to be in general qualitative agreement with results from experiments involving explosive sources.

ISSN:0001-4966    

DOI:10.1121/1.1912930

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The frequency dependence of acoustic volume backscattering strength has been measured at depths of 100, 200, 300, and 400 ft in Saanich Inlet, British Columbia, Canada, over a 24‐h period. The measurements were made for comparison with open‐ocean (Pacific) results, since the biology of the inlet has been extensively studied, and it serves to some extent as a reference water volume. In the course of carrying out the above measurements, the backscattering spectral characteristics and strength of a school of young hake, of apparent mean size of 11 in., was obtained. The time series measurements revealed unchanging scattering characteristics at the 300‐ and 400‐ft depths, with broad peaks near 1.2 and 4.8 kHz superimposed on otherwise flat spectra. Greater variability was observed at the 200‐ft depth, while the greatest variability was observed near the surface, i.e., at the 100‐ft observation depth. The fish school, which was observed to be closely packed (less than a fish length spacing near the surface) and randomly oriented, was shown to have a flat backscattering spectrum between 1 and 9 kHz and an estimated backscattering strength of −47±3 dB.

ISSN:0001-4966    

DOI:10.1121/1.1912931

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Prolate spheroidal coordinates and associated prolate spheroidal wave functions have been used to study the sound radiation from arbitrarily vibrating prolate spheroids. A local radiation impedance is defined and discussed. This impedance shows the effect of the strong locally variable nearfield and indicates that the spheroid generatesL/2R(L/2R= fineness ratio) more acoustic power per unit area at the equator than at the poles. The high‐frequency asymptotic limit of the impedance is determined and from it a radiation criterion of higher modes determined.

ISSN:0001-4966    

DOI:10.1121/1.1912932

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

An experiment has been performed and the average monostatic scattering strength curve obtained. It is observed that the scattering strength curve for 39.0 kHz is essentially the same as that for 19.5 kHz for this experiment.

ISSN:0001-4966    

DOI:10.1121/1.1912933

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

In a channel in which the sound speed varies linearly with depth, the general determination of the initial ray angle for which a ray will intercept a fixed receiving point is inherently implicit, and an explicit expression is feasible only for certain source‐receiver configurations. However, an explicit general solution has been obtained in other studies.

ISSN:0001-4966    

DOI:10.1121/1.1912934

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP