• 제어로봇시스템학회:학술대회논문집
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• 1997.10a
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• pp.1750-1753
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• 1997

This paper describes how the directivity pattern of the back-scattered sound pressure is distributed when a plane acoustic wave is incident on a righid spherical shell underwater. A coupled Finite Element-Boundary Element mehtod is developed as numerical technique. The result of the coupled FE-BE method is agreed with theoretical solution for algorithmic confirmation.

• 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.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06c
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• pp.495-498
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• 1998

수중폭발성음원인 SUS(signal underwater sound)는 수중에서의 폭발과 동시에 충격파와 기포파들이 연속적으로 발생한다. 이러한 신호는 광범위한 주파수대역을 가지고 전파거리가 길어지면서 굴절과 반사등의 다중경로 전파효과에 의한 신호의 변형까지 생긴다. (1,2,3). 본 연구에서는 deconvolution 방법을 이용하여 수신신호중에서 기포파효과를 최소화시켜 충격파의 수신기 도달시간을 파악하고, 각 충격파들의 전파경로를 추정하여 이 중 직접경로와 해저면 반사경로의 신호를 이용하여 해저면 반사계수를 계산하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.5
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• pp.1061-1066
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• 2014

Transmission characteristics of the sound propagation is very complicate and sparse in shallow water. To increase the performance of underwater acoustic communication system, lots of channel estimation technique has been proposed. In this paper, we proposed the channel estimation based on LMS(Least Mean Square) algorithm which has faster convergence speed than conventional sparse-aware LMS algorithms. The proposed method combines $L_p$-norm LMS with soft decision process. Simulation was performed by using the sound velocity profile which acquired in real sea trial. As a result, we confirmed that the proposed method shows the improved performance and faster convergence speed than conventional methods.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.33 no.6
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• pp.581-584
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• 2000

In order to obtain the fundamental data about method of luring fish schools by underwater audible sound, the auditory threshold of black rockfish Sebastes inermis on the coast of Cheju Island was investigated by heartbeat conditioning technique using pure tones coupled with a delayed electric shock, The audible range of black rockfish extended from 80 Hz to 800 Hz with a peak sensitivity at 300 Hz. The mean auditory thresholds of black rockfish at the frequencies of 80 Hz, 100 Hz, 200 Hz, 300 Hz, 500 Hz and 800 Hz were 102 dB, 103 dB, 99 dB, 96 dB, 116 dB and 122 dB, respectively, As the frequency became higher than 300 Hz, the auditory threshold increased rapidly.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.16 no.1
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• pp.1-15
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• 1980

An underwater recording system was designed to measure the sound spectra of the underwater noises produced by fishing gears in operation. Recorded were noi~es from three types of fishing gears: an anchovy set net, three anchovy boat seine net and a stern trawlnet. Acoustic analysis were made using a heterodyne analyzer, a digital frequency analyzer and a level recorder. The no;'e produced by the anchovy set net was found in the high frequency region of the onset of ambient noise spectrum with a slope of - 6 dB/octave. Here the ambient noise spectrum is higher, though similar in shape, than Knudsen spectrum, and is attributed to the breaking action of the coastal wave. Measured noise spectra during the fishing operations of the anchovy boat seine nets are attributed to the background noise of the sea in the presence of the fishing vessels. The frequency distribution of the noise was 20~5, 000 Hz in the case of two steel anchovy boat seiners, and 20-3,000 Hz in the case of the wooden anchovy boat seiner. The predominant frequency range was 250~350 Hz and maximum sound pressure level was 122 dB (re $1\muPa$) in the case of the steel boat and ] 17 dB in the case of the wooden boat. The noises produced by the trawl fishing gears are remarkably higher than the background noi~e in the presence of the fishing vessel. The frequency distribution of the noi~e was 20-6,300 Hz. The predominant frequency range was 100~200 Hz and maximum sound pressure level was 137 dB ( re $1\muPa$) . The noise spectra were not so much different from that caused by vibrations of the towing cable and the structure of the ground rope of the trawl net towed in an experimental tank.

• 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.

• The Korean Journal of Petroleum Geology
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• v.12 no.1
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• pp.14-19
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• 2006

The electromagnetic (light) waves have a limitation to penetrate media, ie, water and sea-bottom layers, due to high energy attenuation, but acoustic (sound) waves play as the good messenger to gather the underwater target information. Therefore, the acoustic methods are applied to almost all of ocean equipments and technology in terms of in-water and sub-bottom surveys. Generally the sound character is controlled by its frequency. In case that the sound source is low frequency, the penetration is high and the resolution is low. On the other hand, its character is reversed at the high frequency. The common character at the both of light and sound is the energy damping according to the travel distance increase.

• 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.

• Journal of the Korea Society for Simulation
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• v.31 no.4
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• pp.11-22
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• 2022

Unlike a short-range, a long-range underwater acoustic communication(UWAC) uses low frequency signal and deep sound channel to minimize propagation loss. In this case, even though communication signals are modulated using a covert transmission technique such as spread spectrum, it is hard to conceal the existence of the signals. The unconcealed communication signal can be utilized as active sonar signal by enemy and presence of underwater vehicles may be exposed to the interceptor. Since it is very important to maintain stealthiness for underwater vehicles, the detection probability of friendly underwater vehicles should be considered when interceptor utilizes our long-range UWAC signal. In this paper, we modeled a long-range UWAC environment for analyzing the detection performance of underwater vehicles and proposed the region of interest(ROI) setup method and the measurement of detection performance. By computer simulations, we yielded parameters, analyzed the detection probability and the detection performance in ROI. The analysis results showed that the proposed detection performance analysis method for underwater vehicles could play an important role in the operation of long-range UWAC equipment.