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Journal of the Acoustical Society of America

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Oct 1979

Volume 66, Issue 4, pp. 945-1239

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Transmission and reception of short ultrasonic pulses by circular and square transducers

A. J. Hayman and J. P. Weight

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 945-951 (1979); (7 pages) | Cited 1 time

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The transient fields of circular and square wide‐band (1–5 MHz) ultrasonic transducers have been studied in water. Transmission and reception of short pulses have been observed using a small (150 μm) wide‐band probe as both receiver and transmitter. Transmit‐receive mode results from a small target have also been considered. Detailed comparisons with the theoretical waveforms for an ideal transducer (pistonlike in transmission and pressure‐sensitive in reception) exhibit generally good agreement. The principle of reciprocity between transmission and reception has been verified. Discrepancies from pistonlike behavior, most marked at short ranges near the axis of each transducer, have been shown by schlieren observations to be caused by an extra (’’head’’) wave which originates from a plate wave propagating laterally across the face. It is concluded that nearfield pulse echo results must be interpreted with some circumspection.
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43.38.Ar Transducing principles, materials, and structures: general
43.35.Yb Ultrasonic instrumentation and measurement techniques
43.38.Fx Piezoelectric and ferroelectric transducers

Electroacoustic transducers using piezoelectric polyvinylidenefluoride films

Reinhard Lerch

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 952-954 (1979); (3 pages) | Cited 2 times

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We have theoretically and experimentally analyzed microphones with cylindrical and spherical polyvinylidenefluoride diaphragms. In particular, the response of such microphones to airborne sound and to vibrations as a function of diaphragm geometry, acoustic impedance of the surrounding medium, coupling volume, and excitation was calculated. Most importantly, a relationship between the output voltage at low frequencies and the position of resonant frequencies was established. There is good agreement between calculated and measured frequency responses.
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43.38.Ar Transducing principles, materials, and structures: general
43.38.Bs Electrostatic transducers
43.38.Kb Microphones and their calibration
43.38.Fx Piezoelectric and ferroelectric transducers

A nearfield, underwater measurement system

Robert D. Marciniak

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 955-964 (1979); (10 pages) | Cited 1 time

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A nearfield acoustic measurement technique for accurately computing the farfield radiation characteristics of underwater sound transducers was developed, implemented, and evaluated. The analysis was based on evaluation of a form of the Helmholtz integral which utilizes a Green’s function that vanished over the surface of integration, thereby requiring only knowledge of the nearfield acoustic pressure for computing the farfield radiation. An experimental program was conducted to evaluate the technique. Details of the nearfield measurement instrumentation are presented. Comparisons between conventionally measured farfield properties of four different types of test transducers and the results obtained by using the nearfield technique are given. The results showed that excellent agreement was achieved for the radiation properties compared. For the directional responses, the nearfield technique matched the conventionally measured results over the minor lobe structure as well as over the major lobe structure of the pattern. The results also showed that absolute sound‐pressure levels could be determined accurately and with relative ease.
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43.38.Ar Transducing principles, materials, and structures: general
43.30.Bp Normal mode propagation of sound in water
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance

Horizontal resonant frequencies of vibration pickup on soil surfaces

Sadao Omata and Sakae Morita

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 965-975 (1979); (11 pages)

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A vibration pickup set on a soil surface has a resonant frequency caused by the mass of the pickup and the contact compliance of a setting point. The resonant frequency produced in the measurement system causes the errors in measurement and places restrictions on the measurement frequency range. This paper gives the characteristics of the horizontal resonant frequency and also derives expressions for a coupled motion of the vibration pickup model set on an elastic half‐space. It is shown graphically, by an example, that the height of the center of gravity and the contact areas of the pickup have considerable effects upon the horizontal resonant frequency. The derived solutions, which are approximately represented as the function of resonant frequency and the frequency of an exciting force, provide adequate accuracy for engineering analysis to the footings of little bodies.
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43.38.Ar Transducing principles, materials, and structures: general
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance

On the mechanism of transduction in optical fiber hydrophones

H. L. Price

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 976-979 (1979); (4 pages) | Cited 1 time

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The receiving sensitivity of optical fiber hydrophones is determined in part by the rate of change in the optical path length of the sensing fiber with respect to changes in the external pressure on the fiber. These changes in the optical path length are a result of the induced changes in index of refraction of the fiber (photoelasticity) and changes in the physical length of the fiber (elasticity). These two properties are analyzed to determine their individual impacts on the hydrophone sensitivity. It is shown that both of these two effects act to increase the optical path length of the fiber as it is subjected to an increasing external pressure. Therefore, the two effects act in concert with one another, not against one another, in their effect on hydrophone sensitivity.
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43.38.Ar Transducing principles, materials, and structures: general
43.30.Yj Transducers and transducer arrays for underwater sound; transducer calibration
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

A unidirectional acoustic focusing device with a group of three electrodes

Kohji Toda

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 980-982 (1979); (3 pages)

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A unidirectional device for acoustic focusing has been devised. The transducer consists of a group of three electrodes deposited on two surfaces of a thin piezoelectric ceramic plate. One of them is used as a common earth electrode and is on the substrate surface in contact with water. The others are interdigital electrodes on the other surface. The design and basic focusing properties of the device are described.
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43.38.Ar Transducing principles, materials, and structures: general
43.38.Fx Piezoelectric and ferroelectric transducers

Distinctive characteristics of underwater calls of the harp seal, Phoca groenlandica, during the breeding season

William A. Watkins and William E. Schevill

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 983-988 (1979); (6 pages) | Cited 3 times

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Underwater calls of the harp seal, Phoca groenlandica, from the early March whelping and breeding season (1967, Gulf of St. Lawrence) were analyzed. Seventy‐five percent of the seal calls were characterized by increasing amplitude and/or increasing frequency (Hz) components. In addition, 94% of the calls were repetitive. These features contrasted sharply with the general features of ambient noise, and provided a distinctive quality to the harp seal calls that could be used to recognize the reproductive herd at a distance.
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43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing

Acoustic correlates of perceived sexual identity in preadolescent children’s voices

Suzanne Bennett and Bernd Weinberg

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 989-1000 (1979); (12 pages) | Cited 1 time

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This project was undertaken to provide information about the sexual characteristics of preadolescent children’s voices. In one series of experiments, perceptual judgments of sexual identity were obtained in response to 73 children’s productions of isolated whispered and normally phonated vowels, normally spoken sentences, and sentences spoken in a monotonous fashion (Bennett and Weinberg, 1978). The purpose of this portion of the project was to describe certain acoustic and temporal characteristics of these children’s speech samples, and to assess the relationship of these variables to perceptual judgments of sexual identity. Sexual differences in the frequency location of vocal tract resonances were significantly correlated with listener judgments of child sex in all four utterance conditions. The origin of the observed differences in vocal tract resonance characteristics is discussed with reference to possible sexual differences in vocal tract size as well as certain articulatory behaviors. Average fundamental frequency was significantly related to listeners’ sex identifications in two utterance conditions. However, the influence of this variable was considerably less pronounced when compared to vocal tract information. Although certain measures of fundamental frequency variability (mean duration of level inflections and the rate of frequency change associated with upward shifts) were significantly related to perceptual measures of sexual identity, these cues were also interpreted to play a secondary role in defining maleness and femaleness in these children’s voices.
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43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.70.Dn Disordered speech

Acoustic invariance in speech production: Evidence from measurements of the spectral characteristics of stop consonants

Sheila E. Blumstein and Kenneth N. Stevens

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1001-1017 (1979); (17 pages) | Cited 17 times

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On the basis of theoretical considerations and the results of experiments with synthetic consonant‐vowel syllables, it has been hypothesized that the short‐time spectrum sampled at the onset of a stop consonant should exhibit gross properties that uniquely specify the consonantal place of articulation independent of the following vowel. The aim of this paper is to test this hypothesis by measuring the spectrum sampled at the onsets and offsets of a large number of consonant–vowel (CV) and vowel–consonant (VC) syllables containing both voiced and voiceless stops produced by several speakers. Templates were devised in an attempt to capture three classes of spectral shapes: diffuse‐rising, diffuse‐falling, and compact, corresponding to alveolar, labial, and velar consonants, respectively. Spectra were derived from the utterances by sampling at the consonantal release of CV syllables and at the implosion and burst release of VC syllables, and these spectra (smoothed by a linear prediction algorithm) were matched against the templates. It was found that about 85% of the spectra at initial consonant release and at final burst release were correctly classified by the templates, although there was some variability across vowel contexts. The spectra sampled at the implosion were not consistently classified. A preliminary examination of spectra sampled at the release of nasal consonants in CV syllables showed a somewhat lower accuracy of classification by the same templates. Overall, the results support an hypothesis that, in natural speech, the acoustic characteristics of stop consonants, specified in terms of the gross spectral shape sampled at the discontinuity in the acoustic signal, show invariant properties independent of the adjacent vowel or of the voicing characteristics of the consonant. The implication is that the auditory system is endowed with detectors that are sensitive to these kinds of gross spectral shapes, and that the existence of these detectors helps the infant to organize the sounds of speech into their natural classes.
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43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.70.Dn Disordered speech
43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation

Bimodal cues for speech loudness

R. D. Glave and A. C. M. Rietveld

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1018-1022 (1979); (5 pages)

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This paper presents a bimodal (audio–visual) study of speech loudness. The same acoustic stimuli (three sustained vowels of the articulatory qualities ’’effort’’ and ’’noneffort’’) are first presented in isolation, and then simultaneously together with an appropriate optical stimulus (the speaker’s face on a video screen, synchronously producing the vowels). By the method of paired comparisons (law of comparative judgment) subjective loudness differences could be represented by different intervals between scale values. By this method previous results of effort‐dependent speech loudness could be verified. In the bimodal study the optical cues have a measurable effect, but the acoustic cues are still dominant. Visual cues act most effectively if they are presented naturally, i.e., if acoustic and optical effort cues vary in the same direction. The experiments provide some evidence that speech loudness can be influenced by other than acoustic variables.
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43.70.Dn Disordered speech
43.66.Cb Loudness, absolute threshold

Effects of selected vocal disguises upon speaker identification by listening

Alan R. Reich and James E. Duke

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1023-1028 (1979); (6 pages)

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This research was designed to investigate the effects of selected vocal disguises upon speaker identification by listening. The experiment consisted of 360 pair discriminations presented in a fixed‐sequence mode. The listeners were asked to decide whether two sentences were uttered by the same or different speakers and to rate their degree of confidence in each decision. The speakers produced two sentence sets utilizing their normal speaking mode and five selected disguises. One member of each stimulus pair in the listening task was always an undisguised speech sample; the other member was either disguised or undisguised. Two listener groups were trained for the task: a naive group of 24 undergraduate students, and a sophisticated group of three doctoral students and three professors of Speech and Hearing Sciences. Both groups of listeners were able to discriminate speakers with a moderately high degree of accuracy (92% correct) when both members of the stimulus pair were undisguised. The inclusion of a disguised speech sample in the stimulus pair significantly interfered with listener performance (59%–81% correct depending upon the particular disguise). These results present a similar pattern to this authors’ previous results utilizing spectrographic speaker‐identification tasks (Reich et al., 1976).
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43.72.Fx Talker identification and adaptation algorithms
43.70.Dn Disordered speech

Encoding voice fundamental frequency into vibrotactile frequency

Martin Rothenberg and Richard D. Molitor

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1029-1038 (1979); (10 pages) | Cited 1 time

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Measured in this study was the ability of eight hearing and five deaf subjects to identify the stress pattern in a short sentence from the variation in voice fundamental frequency (F0), when presented aurally (for hearing subjects) and when transformed into vibrotactile pulse frequency. Various transformations from F0 to pulse frequency were tested in an attempt to determine an optimum transformation, the amount of F0 information that could be transmitted, and what the limitations in the tactile channel might be. The results indicated that a one‐ or two‐octave reduction of F0 vibrotactile frequency (transmitting every second or third glottal pulse) might result in a significant ability to discriminate the intonation patterns associated with moderate‐to‐strong patterns of sentence stress in English. However, accurate reception of the details of the intonation pattern may require a slower than normal pronounciation because of an apparent temporal indeterminacy of about 200 ms in the perception of variations in vibrotactile frequency. A performance deficit noted for the two prelingually, profoundly deaf subjects with marginally discriminable encodings offers some support for our previous hypothesis that there is a natural association between auditory pitch and perceived vibrotactile frequency.
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43.70.Jt Instrumentation and methodology for speech production research
43.70.Dn Disordered speech
43.66.Wv Vibration and tactile senses

Acoustic study of medial /t,d/ in American English

Victor W. Zue and Martha Laferriere

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1039-1050 (1979); (12 pages) | Cited 4 times

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This paper describes the acoustic characteristics of medial /t,d/ in American English as a function of phonetic environment. The data consisted of some 3000 word tokens, each embedded in a carrier phrase, recorded on two separate occasions by six subjects, three male and three female. Quantitative results were obtained on the acoustic characteristics of each stop for all phonetic environments, as well as the difference between /t/ and /d/ for a given phonetic environment. The interaction between certain phonological rules such as flapping and glottalization and low‐level phonetic recoding rules such as vowel nasalization and nasal deletion was investigated. Based on the statistics derived from our corpus, probabilities of occurrence were derived for all phonetic realizations. In addition, interspeaker variability was examined and a significant difference was found in the application of phonetic rules between male and female speakers.
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43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.70.Bk Models and theories of speech production
43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation

Intensity discrimination with gated and continuous sinusoids

David M. Green, Jacob Nachmias, Joseph K. Kearney, and Lloyd A. Jeffress

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1051-1056 (1979); (6 pages) | Cited 9 times

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Detectability of sinusoidal signals at several durations was measured in the presence of sinusoidal maskers of the same frequency. Maskers were either continuous or gated on and off with the signal. For all signal durations and both types of maskers, ΔI/I varied with I raised to the −0.1 power, approximately. Psychometric functions were two or three times steeper with continuous than with gated maskers. Signal duration had only a small effect that varied with the masking condition.
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43.66.Fe Discrimination: intensity and frequency
43.66.Dc Masking
43.66.Ba Models and theories of auditory processes

Auditory lateralization in monkeys: An examination of two cues serving directional hearing

Dirk Houben and George Gourevitch

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1057-1063 (1979); (7 pages) | Cited 1 time

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In assigning binaural ongoing time differences (phase) as the cue for localization of low frequencies, and binaural intensity differences as the cue for localization of high frequencies, the duplex theory has successfully accounted for human directional hearing of tones. Sensitivity of monkeys to these cues was examined in two experiments. The dependencies on frequency of interaural intensity difference thresholds (lateralization experiment I) and time difference thresholds (lateralization experiment II) were determined behaviorally on three monkeys (M. nemestrina). The range of frequencies was from 125 Hz to 8 kHz in experiment I and from 250 Hz to 2 kHz in experiment II. The results indicate that the duplex theory is applicable to monkeys. However, monkeys are less sensitive than man to both binaural cues. The shortest time disparity monkeys discriminate is 42 μs at 1.5 kHz and the smallest intensity difference is 3.5 dB at 500 Hz. Good agreement between the present findings and localization measurements [C. H. Brown et al., J. Acoust. Soc. Am. 63, 1484–1492 (1978)] suggests: (a) that monkeys utilize time disparity cues through higher frequencies than man; and (b) that inaccurate localization by monkeys at high frequencies reflects decreasing sensitivity to interaural intensity cues.
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43.66.Gf Detection and discrimination of sound by animals
43.66.Qp Localization of sound sources
43.66.Pn Binaural hearing
43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing

Perception of the simple difference tone (f2−f1)

Larry E. Humes

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1064-1074 (1979); (11 pages) | Cited 3 times

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The present study examined the dependence of difference tone level [L (f2−f1)] on the following parameters of the two‐tone input: f1, f2/f1 (f2≳f1), L1, L2, and L1=L2. Difference tone levels were estimated in four normal hearers using a 2AFC adaptive temporal gap‐masking paradigm. The key finding in this study is the apparent interaction of each factor with the other. For example, primary level (L1=L2) was found to affect the dependence of L (f2−f1) on f1 and on f2/f1. In addition, the frequency separation of the primaries (f2/f1) was also seen to exert an influence on the dependence of difference tone level on L1, L2, and L1=L2.
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43.66.Ki Subjective tones
43.66.Dc Masking

Relationship between psychophysical tuning curves and ’’suppression’’

Honor O’Malley and Lawrence L. Feth

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1075-1087 (1979); (13 pages) | Cited 1 time

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This study examined two‐tone unmasking and auditory frequency selectivity about 3 kHz for the purpose of demonstrating a qualitative relationship between the two. An adaptive 2IFC forward‐masking procedure was used to collect psychophysical tuning curves (PTC’s) and two‐tone masking data under a quiet and noise condition for the same normal‐hearing listeners. In the noise condition, a narrowband noise masker, centered one decade down from the probe, was gated on with the tonal masker(s). Kiang and Moxon [J. Acoust. Soc. Am. 55, 620–630 (1974)] have found that low‐frequency narrowband noise serves to decrease the sharpness of electrophysiological tuning curves by affecting only the tip segments. The data for four highly practiced listeners indicate that the gated‐noise masker was effective in broadening the PTC’s and in lessening the magnitude of two‐tone unmasking. The mutually reflected changes in tuning curves and in two‐tone unmasking indicate a close relationship between frequency selectivity and unmasking: the greater the magnitude of unmasking above the center frequency of the PTC, the sharper the tuning of the PTC.
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43.66.Dc Masking
43.66.Hg Pitch
43.64.Kc Cochlear mechanics
43.66.Fe Discrimination: intensity and frequency

Effects of wind and ground plane attenuation on sound propagation near the ground

Rene N. Foss

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1088-1092 (1979); (5 pages) | Cited 1 time

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A series of measurements of outdoor sound transmission near the ground was conducted to determine the effects of wind shear and ground plane attenuation. At the lower frequencies (250–500 Hz), where surface and ground waves predominate, the results obtained in still air were in good agreement with current theoretical predictions of ground plane attenuation. The direction and velocity of the wind had little effect on the transmissions at these frequencies. At higher frequencies, however, the data showed considerably more attenuation than the theory predicts, and the effect of wind shear was pronounced.
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43.50.Vt Topographical and meteorological factors in noise propagation
43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors
43.50.Sr Community noise, noise zoning, by-laws, and legislation

Vp/Vs and Poisson’s ratios in marine sediments and rocks

Edwin L. Hamilton

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1093-1101 (1979); (9 pages) | Cited 17 times

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The ratio of compressional wave velocity Vp to shear wave velocity Vs, and Poisson’s ratio in marine sediments and rocks are important in modeling the sea floor for underwater acoustics, geophysics, and foundation engineering. Vp and Vs versus depth information was linked at common depths in terrigenous sediments (to 1000 m) and in sands (to 20 m) to yield data on Vp vs Vs, and Vp/Vs and Poisson’s ratios versus depth. Soft, terrigenous sediments usually grade with depth into mudstones and shales; Vp/Vs ratios vary from about 13 or more at the sea floor to about 2.6 at 1000 m. Poisson’s ratios vary from above 0.49 at the sea floor to about 0.41 at 1000 m. In sands, Vp, Vs, and Vp/Vs have very high gradients in the first few meters; below about 5 m, Vp/Vs ratios decrease from about 9 to about 6 at 20 m; Poisson’s ratios vary from above 0.49 at the surface to above 0.48 at 20 m. The mean value of Vp/Vs in 30 laboratory samples of chalk and limestone is 1.90 (standard error: 0.03); mean Poisson’s ratio is 0.31. Literature data on basalts from the sea floor are reviewed. Equations relating Vp to Vs are given for terrigenous sediments, sands, and basalts.
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43.40.Ph Seismology and geophysical prospecting; seismographs
43.30.Dr Hybrid and asymptotic propagation theories, related experiments
92.10.Vz Underwater sound
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants

The influence of a submerged duct on sound propagation in a surface duct

Marshall Hall

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1102-1107 (1979); (6 pages)

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Acoustic intensities at receivers in a surface duct and in a deep submerged duct are calculated using a normal‐mode theory. The sound source is in the surface duct, which is 60 m thick, and the calculations are repeated for thicknesses of the submerged duct ranging from 0 to 150 m, at frequencies from 160 to 400 Hz. Intensities in the surface duct at 400 Hz and above are not significantly affected by the submerged duct. As the frequency is lowered, the intensity decreases at a rate that varies inversely with the thickness of the submerged duct. The intensity in the submerged duct (in the shadow zone) is almost independent of frequency in the band between the cutoff frequencies of the two ducts; but decreases as the frequency is lowered past the smaller of the two cutoff frequencies.
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43.30.Bp Normal mode propagation of sound in water
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance

Effects of tidally varying sound speed on acoustic propagation over a sloping ocean bottom

K. G. Hamilton, W. L. Siegmann, and M. J. Jacobson

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1108-1119 (1979); (12 pages)

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The influence of sound‐speed fluctuations on propagation of a CW signal in an ocean with a uniformly sloping bottom and a horizontal surface is analyzed using ray theory. The mean sound‐speed structure is modeled as bilinear, with bottomed source and receiver above and below the SOFAR axis, respectively. The horizontally independent fluctuations oscillate with a 12‐h period in the upper ocean. An examination is made of possible types of rays for down‐slope propagation that might exist, depending on bottom‐slope angle and source–receiver separation. The total acoustic field is investigated for its dependence on these parameters and time. For certain conditions when up to three rays comprise the mean total field, three patterns of time evolution are described, each of which may have significant amplitude variations. Numerically computed examples of each type are presented. The linear relationships between phase variations of individual rays and the sound‐speed fluctuations are derived. Then, formulas are developed to explain the most frequent behavior of the relative amplitude and phase of the multipath total field. Predictions from the formulas show very good agreement with the numerical calculations.
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43.30.Bp Normal mode propagation of sound in water
92.10.Vz Underwater sound
43.30.Cq Ray propagation of sound in water

Analysis of acoustical effects of receiver and source motions at short ranges in a deep ocean

J. L. Kays, M. J. Jacobson, and W. L. Siegmann

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1120-1130 (1979); (11 pages)

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An analytical approach is used to determine general results on a CW signal transmitted through a deep ocean channel at short ranges. A bilinear sound‐speed profile is used. The receiver and source are restricted to the surface, and only SRBR rays are relevant. Time‐dependent expressions for the total‐field amplitude and phase are developed for appropriately limited time intervals, and numerical results are presented. General analytical expressions for the total field are derived and demonstrated to approximate closely numerical results. These expressions provide the basis for a study of the acoustical effects of varying motion parameters and initial range. It is demonstrated that effects of differences in range on total‐field phase rate and the time interval between amplitude maxima are significant at short ranges and diminish as range increases. Effects on total field due to receiver motion are shown to be both significant and widely varying, depending on receiver and source directions and speeds.
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43.30.Bp Normal mode propagation of sound in water
43.30.Sf Acoustical detection of marine life; passive and active
43.20.Dk Ray acoustics

The scattered acoustic boundary wave generated by grazing incidence at a slightly rough rigid surface

H. Medwin, J. Bailie, J. Bremhorst, B. J. Savage, and I. Tolstoy

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1131-1134 (1979); (4 pages) | Cited 2 times

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A new theory describing sound scatter from a low roughness rigid surface [I. Tolstoy, ’’The scattering of spherical pulses by slightly rough surfaces,’’ J. Acoust. Soc. Am. 66, 1135–1144 (1979)] has predicted that at near‐grazing incidence a boundary wave will be formed in the fluid above the surface, and that at sufficient ranges the amplitude of this scattered boundary wave will exceed that of the direct wave. A model experiment has been conducted using a point source and receiver embedded in a rough plane surface constructed of close‐packed rigid hemispherical bosses and the prediction of the amplitude of the boundary wave has been fully confirmed. In addition, the experiment has revealed that the coherent scattered boundary wave, which at lowest frequencies or ranges leads the incident wave by 90°, becomes more nearly in phase with the incident spherical wave as frequency or range are increased, thereby further strengthening the signal at the rough surface relative to smooth surface propagation.
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43.30.Bp Normal mode propagation of sound in water
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries

The scattering of spherical pulses by slightly rough surfaces

I. Tolstoy

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1135-1144 (1979); (10 pages) | Cited 5 times

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Using a ’’small roughness’’ boundary condition due to Biot, which incorporates the effects of multiple scatter, one can obtain simple, closed‐form solutions for the coherent scattering of transient spherical waves. Combining this boundary condition with the normal coordinate technique leads to explicit solutions for impulsive or other point sources above or on a rough, rigid plane, i.e., for both finite and grazing angles of incidence. This approach distinguishes naturally between two types of arrival: body (or volume) waves and boundary waves; the latter incorporate the backscatter. The boundary wave dies off rapidly with distance from the surface. But, parallel to the boundary, in the absence of attenuation, its amplitude decreases only as r−1/2 so that for sufficiently large r, and for source and receiver at or near the surface, the boundary‐wave will dominate the direct acoustic pulse arrivals. The methods and results of this paper can be extended to problems of scatter and diffraction of spherical pulses by rigid (or free) plane rough surfaces bounding stratified media or by rough objects of other shapes, e.g., spheres, cylinders, ellipsoids, etc. This theory, valid for wavelengths or pulsewidths long compared to the characteristic roughness dimensions, leads to results that are different from those of the usual perturbation techniques and have been verified experimentally by Medwin et al. in a companion paper.
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43.30.Bp Normal mode propagation of sound in water
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.20.Bi Mathematical theory of wave propagation

An examination of the influence of the range dependence of the ocean bottom on the adiabatic approximation

Steven R. Rutherford and Kenneth E. Hawker

J. Acoust. Soc. Am. Volume 66, Issue 4, pp. 1145-1151 (1979); (7 pages) | Cited 2 times

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The effects of radial sediment sound‐speed derivative and sloping water–sediment interface on the adiabatic approximation to the set of coupled radial equations of coupled‐mode theory are examined. The investigation was carried out using the adiabatic criterion of Milder. This criterion requires that the coupling coefficient between adjacent modes be small compared to the mode‐cycle distance. It is determined that sediments having large characteristic acoustic impedances can have larger radial sediment sound‐speed gradients within the adiabatic approximation than can sediments with smaller characteristic impedances. It is also determined that this trend is reversed for the case of sloping water–sediment interface with sediments of small characteristic impedance being able to have more bottom slope within the adiabatic approximation than sediments of higher impedance.
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43.30.Bp Normal mode propagation of sound in water
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance
92.10.Vz Underwater sound
43.30.Dr Hybrid and asymptotic propagation theories, related experiments
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