摘要:

Satisfactory agreement between theory and experiment has been secured for the propagation of very low frequency sound (10 and 20 cps) emitted by a point source in a thick sedimentary layer (607m) overlying a solid elastic basement. In the theory the sediment is treated as a fluid of sound velocity varying with the depthzlike(pz+a)−12, and the basement is represented by a solid elastic half space of Poisson's ratio14. The wave equation has been integrated numerically on an electronic computer. The physical theory, and, in particular, the interesting coupling effects between sound waves and Stoneley or interface waves are discussed. The experimental procedure was the same as the one used in a previously published account of experiments in a different frequency range. Theoretical predictions of the behavior of the sound field in the range of 1 to 5 km are in substantial agreement with the measurements.

ISSN:0001-4966    

DOI:10.1121/1.1907880

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

To study acoustic propagation in shallow water without the idealization of conventional theory or the many unknowns in field trials, a model with known realistic parameters is used. A water layer 0.5 to 2 cm deep overlies a 2‐in. slab of Hycar rubber with greater density and sound speed. With frequencies from 55 to 600 kc, a small probe in the water allows measurements of phase and group velocities, vertical pressure distributions, mode interferences, and attenuation coefficients. Theoretical predictions about the effects of compressional absorption and shear waves in the bottom, and of sloping bottoms, are supported. An analysis of the additional attenuation caused by rough surfaces is made by spreading small metal spheres on the bottom. This attenuation is proportional to area density of the spheres, the free‐field scattering cross section of a sphere, and the acoustic intensity at the depth of the spheres. An additional factor is the fractiongof scattered power actually lost;gcorrelates empirically with the ratioswater depth to sphere radiusandsphere radius to acoustic wavelength. A phenomenological theory ties these results together.

ISSN:0001-4966    

DOI:10.1121/1.1907881

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Equations are presented for the computation of sound speed that are designed to agree with Kuwahara's tables. These are in general use for the mass reduction of oceanographic data. The equations give the temperature, salinity, depth, and latitude dependence and the interaction effects due to the simultaneous variation of temperature, salinity, and depth. Somein situmeasurements utilizing the bathyscaph are presented.

ISSN:0001-4966    

DOI:10.1121/1.1907859

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Measurements of the backscattering of 60‐kc sound from the surface of the sea have been made in Puget Sound in an effort to relate the strength of the scattered sound to the character of the surface. In addition to providing a means of predicting reverberation levels, an attempt has been made to obtain a better understanding of the fundamental mechanism of scattering at the air‐water boundary.The reverberation measurements are presented, along with observations of several oceanographic and meteorological parameters. An examination of the data allows the following conclusions: (1) reverberation pulses from an area of several square yards follow a Rayleigh distribution; (2) reverberation cannot be directly related to the wave height, but is closely correlated with wind speed; (3) reverberation increases with wind speed to a speed of 14 knots, and remains constant for higher wind speeds; and (4) reverberation is independent of the angle with the surface for angles from 20 to 60 degrees, but drops off rapidly as the angle is decreased below 20 degrees.

ISSN:0001-4966    

DOI:10.1121/1.1907860

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The range dependence of variation coefficients has been investigated foreachof eight selected experiments performed in New Zealand waters during midsummer for a variety of meteorological conditions. These experiments have employed 1.3‐msec pulses of 14.5 kc sound from a projector of variable depth (40 to 100 ft). The pulses have been simultaneously received by a vertical string of six equidistant hydrophones (extreme depths 40 and 165 ft) and the square of theaveragevariation coefficientVfor the six hydrophones has been plotted against the rangeRto test for the eight individual experiments the applicability of the Mintzer fluctuation formula. This predicts for a medium exhibiting temperature microstructure thatV2 ∝ R ⋅ f2α2a, wherefis the frequency and α andaare, respectively, the rms values of the refractive index and the correlation length of fluctuation in the refractive index. An area was selected where the sea is fed by no rivers of any size, the depth varying with experiment from 40 to 200 fathoms. Drought conditions prevailed over the whole period of the work, and, as far as is known, no confluence of local ocean currents here produces microstructure. The latter if present should presumably be confined to surface layers and be due to diurnal insolation. One has hence selected for analysis those experiments performed during small swell and sea state in. (a) the early morning, (b) hot sunshine during the mid and late afternoons, (c) the mid afternoon during cool days with a completely covered sky, and (d) early evening after hot cloudless days. Close correlation exists between insolation and intensity fluctuations which follow the Mintzer dependence on range and the values of α2aobtained [(5.0–11.0)×10−7] are near the mean value reported by Sheehy (5.0×10−7.The fact that the Mintzer formula is obeyed by case (b) only and the small values ofVand independence ofVuponRfor the aforementioned conditions (a), (c) and (d) are interpreted to mean a diurnal cycle of growth and decay of insolation‐produced microstructure in the surface layers of the sea in summer.

ISSN:0001-4966    

DOI:10.1121/1.1907861

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Measurements of the detectability of a noise signal in noise are reported in this paper. Parameters of the noise signal such as the band width, duration, and center frequency are investigated. The results are compared with an optimum‐detection model. For some constant detectability the equation generated by the model and one constant, an attenuation factor, closely fit the experimental data over the major range of the experimental parameters. The major area of discrepancy between model and data is the shape of the psycho‐physical function. Implications of the data for the critical‐band mechanism are also discussed.

ISSN:0001-4966    

DOI:10.1121/1.1907862

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Thresholds for interaural difference between the intensities of dichotic tone pulses were measured on five subjects by the method of constant stimuli, at frequencies between 250 and 10 000 cps and at a sensation level of 50 db. The just noticeable dichotic difference in intensity is about 1 db at 1000 cps, a little smaller at lower frequencies, and still smaller (0.5 db) at higher frequencies. This function is compared with the interaural difference in intensity produced by the just noticeable deviation from the median plane of an actual source of tone pulses. At low frequencies, where phase or time differences are generally considered more important than intensity differences for auditory localization, these two functions differ greatly. At frequencies between 1500 and 6000 cps, the threshold for a dichotic difference in intensity matches the interaural difference in intensity that is produced by the just noticeable deviation from the median plane of an actual source. The relation between the discrimination of dichotic differences in phase and intensity and the discrimination of actual direction is shown in a graphical summary.

ISSN:0001-4966    

DOI:10.1121/1.1907864

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Three experiments designed to examine latent effects of low noise‐level stimulation gave completely negative results. It is concluded that noises that do not themselves produce TTS (temporary threshold shift) have no effect on the growth or decay of TTS produced by higher level exposures.

ISSN:0001-4966    

DOI:10.1121/1.1907865

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The fading of the color of the congo red dyestuff at concentrations 0.016. 0.01, and 0.005 g per liter under the influence of ultrasonic radiation from a Mullard generator with barium titanate crystal having a frequency of 1 Mc/sec and power output 225 w has been studied and the reaction is found to be unimolecular, the average velocity constants being respectively, 0.129, 0.209, and 0.193. The fading of congo red is not due to the production of hydrogen peroxide, and it is neither an oxidation nor a reduction process in the ordinary sense. The high cavitation energy appears to be responsible for the breaking down of the molecule of congo red resulting in the color fading.

ISSN:0001-4966    

DOI:10.1121/1.1907867

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

It is shown that the acoustic radiation force on a uniformly moving smooth body is given correctly to the third order by simple first‐order theory, in agreement with a calculation by Nabarro [Phil. Mag.41, 1276 (1950)].

ISSN:0001-4966    

DOI:10.1121/1.1907868

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP