• The Journal of the Acoustical Society of Korea
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• v.25 no.4
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• pp.178-183
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• 2006

A hydrophone away is used to measure spatial distribution in underwater sound field and to detect incoming direction of sound waves in the ocean. It is not usually convenient to handle the hydrophone away because of its extensive scale. And it is not easy to purchase the hydrophone away because of expensive price. A hydrophone logger combined with a hydrophone and data logger was developed to consist conveniently of a hydrophone away for use to receive underwater sound waves. And a hydrophone array system with the hydrophone loggers was developed. Main configurations of the hydrophone 1o99er and the hydrophone array system are introduced in this paper. Also we present some measurement results by the hydrophone logger in a water tank and measurement examples on ambient noise in the sea by the hydrophone away system. And we discuss some advantages in use of the hydrophone array system.

• Ocean and Polar Research
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• v.28 no.2
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• pp.145-151
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• 2006

A broadband self-recording hydrophone was developed to conveniently assemble a hydrophone array for use in receiving underwater sound waves. A trigger device with an electromagnetic induction coupler was also developed to control the hydrophone's operation. Main configurations and specifications of the self-recording hydrophone are introduced in this paper. We present experiment results conducted in a water tank to examine the operating behavior of the hydrophone. Some advantages are discussed when the self-recording hydrophones are used to make up a hydrophone array.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.14 no.4
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• pp.265-268
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• 1981

The direction and spectra of underwater sound wave were a remarkable contrast to the sound wave in the air because of the difference of transmissive medium. The linear hydrophone array of passive system has so far been applied to find out the direction and spectra of underwater sound wave from the sources for many purposes. The conventional methods are generally classified into two systems such as, the system which varying frequency responses, other parameters and pattern of signal like an adaptive array controlled by internal feedback, and another system which obtaining maximum of S/N ratio by giving a appropriate delay and a weighting coefficient in the output of each hydrophone. The array device of passive system can easily change the amplitude and the phase of signal by separately controlled hydrophone. And here we introduce a method that the spectral analyzing and the direction finding can be simultaneously carried out using a linear array of hydrophones. By making a circular convolution of output of signal from each hydrophone with appropriate rectangular weighting coefficient on the array, a sharp response of single lobe directivity and the spectral analyzing by time averaging were simultaneously obtained. In tile computer simulation of the array system with the length of 250cm and the interhydrophone distance of l0cm the power levels of sound signals received from given array direction were 16dB higher than those from the other directions when processing with rectangular weightings, and 8dB higher when processing with rectangular sound signals and rectangular weightings.

• The Journal of the Acoustical Society of Korea
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• v.20 no.7
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• pp.89-93
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• 2001

In recent years Fiber optic hydrophone systems have been the focus of much attention in the sonar world. For sonar arrays, a fiber optic approach offers the major benefit of passive multiplexing of large numbers of hydrophones without underwater electronics. This paper describes recent development work covering array construction, opto-electronics development, hydrohpone design and sea trials. And the development of an interferometric mult-channel fiber optic hydrophone system which uses time division multiplexing capable of driving in excess of 32 channel is described. For this, a 12 channel time division multiplexing array has been constructed, and the performance of this system is demonstrated by sea trial.

• Economic and Environmental Geology
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• v.29 no.6
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• pp.739-744
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• 1996

'Kite' is a newly developed single-channel seismic imaging system capable of producing high resolution three dimensional images of subbottom geology in one traverse of a survey region. The system consists of a horizontally towed hydrophone array and active source. The hydrophone array is towed axis perpendicular to ship direction and the airgun source at the end of the hydrophone array is excited at timed intervals during the progression. The construction of the three dimensional subbottom image was made simply by using conventional multichannel seismic reflection data processing techniques. Common source shot (CSS) gathers of the hydrophone traces are evaluated using Dix's equation for average interval velocity of each subbottom layer. From the interval velocity profile and the normal consolidation stress condition, values of shear modulus, porosity, and shear velocity are deduced from the chosen values of physical constants. The system has been successfully tested at several locations on the North Atlantic continental shelf.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.12
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• pp.287-291
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• 2013

The low- frequency hydrophone sensor, using the recently developed FBG has an excellent merits which the existing fiber-optic sensor has and also it has an excellent signal sensing effect in the environment of low-frequency(30Hz-300Hz), not to be detected by the PZT sensor. we have the detection of frequency 19KHz right signals when was using more Hopper lenz WDM than $1{\times}3$ optical coupler. furthermore, we can expect the uitilization of low-frequency signal detection to be used for the military purpose and also it can be developed as the high-sensibility multiplexing through the sensor array system.

• Journal of Sensor Science and Technology
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• v.9 no.4
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• pp.307-315
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• 2000

To set up the arrays system of FBG(Fiber Bragg Grating) Hydrophone sensor and realize the multi-point signal detection for the wide scope underwater, using WDM(Wavelength Division Multiplexing) method and Passive band-pass filter system, underwater acoustic signal detection of the newly designed two FBG Transducers is successfully experimented. As a result of the experiment, it was possible each signal with different frequent signals is detected for the multi-point up to 1.3KHz in underwater. We can, therefore, prove the possibility on the system design of Hydrophone sensor arrays, using the newly made FBG Transducers.

• The Journal of the Acoustical Society of Korea
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• v.34 no.3
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• pp.200-209
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• 2015

An underwater sound surveillance system detects and tracks enemy ships in real-time using hydrophone arrays, in which seabed-mounted sensor arrays play a pivotal role. In this paper the conceptual design of seabed-mounted, cylindrical hydrophone arrays for use in shallow coastal waters is performed via finite element calculations. To stabilize the receiving characteristics under the ocean ambient noise, a technique for whitening the ambient noise spectrum using a metal baffle is proposed. Optimization of the array configuration is performed to achieve the directivity in the vertical and azimuthal directions. And the effects of the sonar dome shape and material on the structural vibration and sound scattering properties are studied. It is demonstrated that a robust hydrophone array, having a sensitivity deviation less than 4 dB over the frequency range of interest, can be obtained through the whitening of the ambient noise, the optimization of the array configuration, and the design of acoustically transparent sonar domes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.749-754
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• 2003

In this paper, we introduce the measurement of the underwater noise with 32channel hydrophone array of Samsung CAvitation Tunnel (SCAT) and the detection technique of noise sources by using the beam-forming method. Measurement and way signal Processing under fluid flow are essential works for the underwater acoustics, especially for the detection of noise sources. As the acoustic impedance of the water is relatively high and the tunnel is an enclosed system, we have to consider the interaction between tunnel and water together with the reflection of noise in the beam-forming technique. Also, for a hydrophone array system that is fixed on one side of tunnel wall as done in SCAT is liable to suffer from some limitations in the detection of the noise sources with the array, we discuss these limitations particularly on the frequency range and spacing of noise sources.

• The Journal of the Acoustical Society of Korea
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• v.21 no.7
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• pp.606-613
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• 2002

In this paper we applied a transmit beamforming technique to the underwater acoustic communication system for high rate data transmission. A prototype transmit system was designed and implemented with the general purpose DSP processor and multiple digital-to-analog converters. The performances of the implemented system were evaluated by the experiment in water tank. In order to simplify the procedure the channel coding and equalizer were omitted. And the simplest OOK (On-Off Keying) technique in digital communication methods was applied. The experimental result shows that the transmission data rate is higher about 3 times in the case of 5 hydrophone transmitting may than 1 hydrophone transmitter at bit error rate 10/sup -2/. We verified that the maximum data rate was 400 bps for speech signal transmission in water tank.