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Underwater plate vibration and its associated noise are of interest for the analysis of ship structures, propeller blades, and other areas of underwater acoustics. In order to analyze the relationship between a plate vibrating underwater and the acoustic pressure in the near-field, optical interferometric holography, using a blue-green laser beam, was used to determine surface displacement for the vibrating plate, which was excited through a fluid-coupled system. Acoustic measurements of the same source were made in a water tower concurrently with the holography and later at a precision acoustic testing facility. This method permits prediction of underwater plate modal frequencies and shapes with high accuracy.

Multiple Removal Procedures based upon tapped delay line models for the reverberation are derived and applied to data taken during the NSF-IDOE-East Atlantic Continental Margin Program. The effectiveness of these models are analyzed by, i) determining the amount of reverberation energy removed, ii) evaluating the distortion of underlying horizons, and iii) comparing record quality before and after processing. Programs based upon these models have been implemented as operational production programs and are currently being used aboard the R/V Atlantic II during the EACM studies.

The relations among the holographic parameters of focal length, aperture, and wavelength and the system parameters of resolution and stability in the horizontal and vertical are developed for the application of acoustic holography to mapping and searching the sea floor. The relative advantages of pulsed and continuous acoustic sources are discussed, the concept of the sanitized signals from a pulsed source is introduced, and the implications in terms of forbidden zones and statistical uncertainty in the amplitude of the mean scattered signal are developed. The information content of the acoustic holographic surface and the required sampling spatial density are presented. The area scan rate of the holographic system is related to the system parameters. A conceptual design of an acoustic deep-water holographic system, Sea Fan, is described as an example of the application of the constraints previously developed. The scan rate of Sea Fan is compared with some present methods of searching the sea floor. An optical reconstruction process involving the superposition of a cohologram and a quadrature hologram is described.

A theory is presented which enables the computation to be made of 200‐ to 3000‐cps bottom reverberation returning from very great ranges in shallow water. Typical computed curves are presented for reverberation level vs range/water depth. Computed curves are presented for scattering strength vs range/water depth. These later curves are presented for both the isospeed and negative sound‐speed gradient cases.

The transducer array theory developed in the field of underwater acoustics has been used for the design and construction of ultrasonic arrays in the frequency range 600–800 kHz. With these transducers it is possible to scan the acoustic beam electronically and to make the scanning process much faster and less expensive than with a mechanical system. The results show that even higher working frequencies and wider scanning angles can be obtained by developing the technology further.

The purposes, problems, and progress of radiated noise, self‐noise, and ambient noise research are reviewed. Purposes are related primarily to national defense, but applications to fishery and to the utilization of other natural resources are also noted. Basic problems, most of which were recognized 20 years or more ago, involve ascertainment of properties of the noise, identification of noise sources and mechanisms of noise generation, and the discovery and definition of noise dependencies on environmental factors. Many radiated and self‐noise sources and mechanisms have been identified. Major problems are those of noise measurement, noise reduction, and prevention. In the field of ambient noise, most measurements have been of sound‐pressure level. Some of the noise sources and environmental factors have been identified, and a capability for qualitative and gross prediction has been achieved. Recommended are further investigations of the variation of ambient noise with receiver depth, directionality of t...

Sources of information for electrical and electronics engineers have been studied by looking at 1965 IEEE publications to see what periodicals, books, conferences, etc., were cited. Cited journals have been ranked as information sources by the number of times they were cited as references. The data for 1965 have been compared with corresponding data for 1949 and 1934 to examine trends in volume and characteristics of reference information, country of publication, and age of reference.

An underwater acoustics laboratory course has been instituted at the University of Miami using a natural body of water as the experimental medium. The experiments are conducted in Bear Cut, which connects Biscayne Bay to the Straits of Florida. The 600‐ft acoustic range from the Institute of Marine Sciences pier to an instrument tower in Bear Cut is an almost flat channel with an average depth of about 13 ft. The majority of the equipment employed by the students consisted of piezoelectric projectors and hydrophones, and standard electronic laboratory apparatus such as oscillators, oscilloscopes, power amplifiers, filters, etc. The sequence of the experiments were planned for equipment familiarization and results needed for future tests. During the initial offering of this course in the Spring 1970 semester, experiments were conducted on the measurement of a piezoelectric transducer equivalent circuit, ambient‐noise spectrum, spreading loss for several distances, reciprocity calibration, and waveguide eff...

Underwater sound has provided means for measuring distances for nearly half a century. The first successful means echo sounding is still the one most widely used. It is likely that continued research can make it a valuable oil industry tool in offshore exploration and operations. Introduction As the mineral industries exploit deeper and deeper areas of the ocean, they will almost certainly rely more and more heavily on underwater acoustical instruments. One can only guess at the instruments that will prove useful, but it may be helpful to describe some past experiences in naval research and development and indicate the paths of research and development that seem to be needed for producing a suitable array of acoustical tools for industry. Military Use of Underwater Acoustics Underwater acoustics has been employed in undersea warfare since World War I. It is used for detecting, tracking and localizing enemy targets, either submarines or surface ships; and some weapons are fired by means of acoustic sensors. The use of sound rather than optical or radar devices is dictated by the rapid attenuation of electromagnetic waves in sea water compared with that of air. The variability of the ocean both in place and time puts constraints on sonar systems that the navies of the world must know about in some detail that least where they expect to operate. As a result, an elaborate program of environmental research, focused on the needs of sonar, has paralleled and paced the development of military systems. Military sonar systems themselves. are not generally useful to industry because of their specialized design. Although some elements of these systems may be of interest because their development has advanced the state of the art, the most generally useful part of naval research and development probably will be the methods that have been developed for measuring the environment. In fact, in the continuing interaction with the oil industry particularly, several of the navy's methods and apparatus have already been adopted. Deep Water Exploration and Drilling The offshore oil development in the Gulf of Mexico, off Southern California, and in the Persian Gulf long ago heralded the exploitation of the mineral wealth of the ocean. Most of the resulting production has been in less than 100 ft of water. In the past 5 years, however, there has developed a powerful thrust into deeper water that has already carried the oil industry to the edge of the continental shelf and beyond, both in geophysical exploration and in drilling. Even very conservative prognostications indicate that oil wig be produced in several thousand feet of water in 10 to produced in several thousand feet of water in 10 to 20 years. The corresponding development of solid minerals from the sea floor is now estimated to be far slower. Nevertheless, the geology of the sea floor is imperfectly understood, to say the least, and there may well be some surprises awaiting us in hard minerals. Whether for oilfield development, which is upon us, or mining, which will develop more slowly, it is clear that much of the work must be done underwater. JPT P. 1277

The acoustic systems corresponding to closed oscillatory electric circuits, to radiating electric systems, and to coupled circuits, are described. The design of submarine signaling transmitters and receivers on an engineering basis is described, and actual installations are discussed. The resemblance of submarine signaling engineering and radio engineering, and the relation between these fields are considered.

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.

Recent experimental results in the field of non-linear underwater acoustics are reviewed and two proposed applications to sonar systems where the exploitation of acoustic non-linearities may be viable are discussed and evaluated.

This paper presents a numerical evaluation of the rigorous solution to the wave equation for the internal field of an underwater, spherical, liquid lens that is being irradiated by plane waves. The numerical computations, which were performed for three refracting liquids with indices of refraction 1.8, 2.25, 2.82, and for the range 1⩽d/λ0⩽15 (d, the diameter of the lens; λ0 the wavelength in water), are presented graphically. The relative pressure and the relative intensity were computed along the axis of the lens. It was found that the intensity is not proportional to the square of the pressure and, furthermore, that the focal point for the intensity field did not always coincide with the focal point for the pressure field. Since hydrophones commonly used for measurements in underwater acoustics are pressure‐sensitive, only the focal point for the pressure field was considered. Pressure polar patterns were then calculated at the focal point for the pressure field. Also, the beamwidth and gain were determined as a function of d/λ0. In general, the theoretical results were found to be in good agreement with the experimental observations of W. J. Toulis [J. Acoust. Soc. Am. 35, 286–292 (1963)].

The problems involved in designing an underwater sound transducer for the audio-frequency range are discussed, and a new transducer for the range from about 40 cps to about 20 kc is described.

A corrugated, acoustic waveguide has been constructed to operate in a water medium over the frequency range 17.5–20 kHz. The waveguide is made of stainless‐steel disks 0.0135 in. (0.343 mm) in thickness and 1.5 in. (3.81 cm) in radius separated by stainless‐steel spacers 0.10 in. (2.54 mm) in thickness and 0.5 in. (1.27 cm) in radius. The phase velocity of the guide was measured experimentally and computed theoretically. After a small (5%) empirical increase was made in the value of the bulk modulus of the disks and the entrapped water, excellent agreement between theory and experiment was obtained. The waveguide was next used as the slow velocity element in an end‐fire radiator. As the length of the guide increased from 10 in. (25.4 cm) to 28 in. (71.1 cm) the half‐power beamwidth at 18.0 kHz of the major lobe decreased monotonically from 29° to 16°, and the height of the first minor lobe remained nearly constant at −10 dB. The shape of the radiation pattern can be predicted accurately from probe measurements near the guide plus an empirical adjustment for the contribution of the source.

Pulse position modulation (PPM) is a simple and effective technique for transmitting information via the underwater acoustic channel. In this paper engineering design considerations for an underwater acoustic PPM system, including the location of threshold and the effects of multipath, attenuation, and time dispersion, are discussed. Techniques for calculating the required transmitter power, pulse repetition rate, and pulse width to communicate over some specified geometry are given.