摘要:

Reverberation was measured from smooth young ice and from heavily rafted winter ice in the Canadian East Coast waters. “Point” charges were used as sound sources and an omnidirectional hydrophone as the receiver. Backscattering strengths were measured in octave bands from 0.4 to 25.6 kc/sec over a range of grazing angles from 15° to 60°. The scattering strengths for the rough ice are approximately equal to the smallest that have been reported for Arctic ice and are substantially greater than those measured for the smooth ice. Values previously reported for young broken and refrozen ice in the Gulf of St Lawrence generally fall between those measured for the rough and smooth ice. There is little variation of scattering strength with frequency for either rough or smooth ice.

ISSN:0001-4966    

DOI:10.1121/1.1910016

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

A previous paper has shown an interesting structure for the optimum array‐processing system using long observation time to detect weak stationary Gaussian signal in stationary Gaussian noise fields. For dominant amplifier and system noise (Case I discussed by Middleton and Groginsky), this structure is “factored.” The previous result is generalized to linear nonidentical hydrophones. A valid procedure for finding causal optimum filters is presented. The results are extended to the case or known signal; the optimum filters are not matched to the signal, but to a waveform dependent on signal, noise, and array structure.

ISSN:0001-4966    

DOI:10.1121/1.1910017

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

A ring‐shaped directivity pattern has been observed when an acoustical signal is transmitted from an orifice in the wall of a buried pipe when the gaseous medium in the pipe is under high pressure. This effect appears to result from a combination of conditions that are similar to those that produce jet noise patterns and acoustical streaming around an orifice. The experimental work in which these effects were measured was sponsored by the American Gas Association as part of a sonic leak‐pinpointing project.

ISSN:0001-4966    

DOI:10.1121/1.1910018

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1910020

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1910021

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1910022

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1910024

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

In ray‐theory solutions of propagation problems, one often determines a geometric boundary between an ensonified region and a shadow zone. It is desirable to be able to investigate the diffraction of sound into the shadow zone by a method of comparative simplicity. It is shown that the pressure discontinuity and the discontinuity of the normal derivative of the pressure determine the densities of a distribution of dipoles and of simple sources, respectively, such that there is a mutual annihilation of the geometric wave discontinuities and the distribution singularities. The radiation from the distributions (into both the ensonified region and the shadow zone) can be obtained by ray theory or by approximate wave‐theoretic techniques. In the case of a classical problem (for a homogeneous medium), there was agreement between the results of the above method and the classical results.

ISSN:0001-4966    

DOI:10.1121/1.1942670

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

A short sound pulse, transmitted horizontally between two points in deep ocean water, arrives at the receiver as a continuous superposition of time‐separated wavepackets. This fact has been demonstrated by a detailed analysis of the crosscovariance between such pulses carrying a phase reversal and atruncatedreplica. In all, about 280 pulses were selected from over 3000 that were previously studied [N. W. Lord, J. Acoust. Soc. Am.36, 1043(A) (1964)] for the transmission time fluctuation. For these 1200‐cps pulses, the phase spreading becomes tangible at a range of 7 km, where it is approximately π/3, or about 0.2 msec. As an estimate ofinstantaneous phase spread, this value is reasonable as compared to the transmission‐time fluctuation, for this range, of 0.7 msec between pulses spaced every 0.6 sec. The use of a truncated replica on a long pulse depresses most of the side‐lobe crosscovariance peaks. The magnitude of the central peak is related to both the phase spreading and the chosen length of the truncated replica, although this latter dependence is lost by a slow phase reversal. Hence, for these measurements, if Δ is the phase spread, the magnitude of the crosscovariance peak is (sinΔ)/Δ. At ranges under 7 km, Δ is small and the peak is close to unity with small fluctuation. At ranges over 7 km, the peak declines and fluctuates more among the successive pulses. [Hudson Laboratories of Columbia University Informal Documentation No. 108. Work supported by the U. S. Office of Naval Research.]

ISSN:0001-4966    

DOI:10.1121/1.1942672

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The data resulting from a 23‐month ambient‐noise measurement program are reviewed. 2‐min‐long broad‐band magnetic tape recordings were made every 2 h, from omnidirectional hydrophones at fixed locations. Ten noise‐level readings were made in each of ten logit frequency bands between 100 and 1000 cps from each recording. The mean value obtained from each set of ten readings was taken as the representative level of that 2‐min sample in subsequent data processing. The data clearly show the dependence of ambient‐noise level upon wind‐speed and a lesser dependence upon wave height. The spectrum is seen to change markedly with wind speed and to suggest the presence of both wind‐dependent and non wind‐dependent mechanisms. Level‐distribution histograms show dependence upon both frequency and season. The standard deviation is shown to be a function of both frequency and wind speed. Power‐spectrum analyses indicate the occurrence of cyclical noise variations with periods up to 55 h.

ISSN:0001-4966    

DOI:10.1121/1.1942678

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP