• The Journal of the Acoustical Society of Korea
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• v.40 no.4
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• pp.297-303
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• 2021

When sound waves propagate over long distances in shallow water, measured transmission loss is greater than predicted one using underwater acoustic model with the Rayleigh reflection model due to inhomogeneity of the bottom. Accordingly, the US Navy predicts sound wave propagation by applying the empirical formula-based High Frequency Bottom Loss (HFBL) model. In this study, the measurement and analysis of transmission loss was conducted using mid-frequency (2.3 kHz, 3 kHz) in the shallow water of the East Sea in summer. BELLHOP eigenray tracing output shows that only sound waves with lower grazing angle than the critical angle propagate long distances for several kilometers or more, and the difference between the predicted transmission loss based on the Rayleigh reflection model and the measured transmission loss tend to increase along the propagation range. By comparing the Rayleigh reflection model and the HFBL model at the high grazing angle region, the bottom province, the input value of the HFBL model, is estimated and BELLHOP transmission loss with HFBL model is compared to measured transmission loss. As a result, it agrees well with the measurements of transmission loss.

• The Journal of the Acoustical Society of Korea
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• v.14 no.1E
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• pp.5-13
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• 1995

In order to estimate the variability of the wave propagation loss (PL) du e to hourly variations of the sound speed profiles (SSPs), we conducted oceanographic measurements every hour for 39 hours in October 1993 in the Korea Strait. Currents and meteorological data were measured simultaneously to examine the causes of the temporal variations of temperatures. During the experiment, the temporal variations of temperatures in the surface layer highly depend on the water mass transport from adjacent seas. The PL for low frequency (75-300 Hz) is calculated using the parabolic equation scheme and averaged over the whole water depth. The hourly variation of the SSP may cause a PL difference of up to 10 dB over a 30-50 km range. The variability of PL, represented by standard deviation for the 39 SSPs, is as large as 3 dB over a 50 km range.

• The Journal of the Acoustical Society of Korea
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• v.32 no.4
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• pp.301-307
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• 2013

SONAR detection performance is one of the key survivability factors in underwater weapon systems. In order to catch the acoustic ability of SONAR, multilayer SONAR structures are analyzed using the elastic theory. The applied results for the simple models are compared with those from commercial program, ANSYS, and the reliable results are obtained. The analysis of sound pressure level (SPL) and echo reduction (ER) by the thickness change of multilayer SONAR structures are performed using the verified elastic theory. As the thickness of anechoic layer is increased, SPL is distributed evenly and ER is increased slightly with the frequency. In decoupling layers and steel layers, SPL are hardly changed and ER is slightly decreased with the thickness increase of those layers. SPL and ER are not affected by the thickness change of the carbon reinforced plastic (CRP) layer. Therefore, to improve the acoustic ability of multilayer SONAR structures, the thickness increase of the anechoic layer and minimization of the decoupling layer, steel layer and CRP layer are desirable.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.43 no.3
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• pp.206-211
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• 2007

The sciaenid species, which has swimbladder, generates sounds by vibrating in its length wards when spawning or getting stimulus from something else. This research analyzed on sound frequency characteristics relatives to their swimbladder length of three sciaenid species, yellow croaker(Larimichthys polyactis), brown croaker(Miichthys miiuy), and white flower croaker(Nibea albiflora). As results, the dominant frequency for yellow croaker ranged over 38.08 to 141.60Hz in wide frequency band, and the averaged pulse duration expressed in $280.3{\pm}156.0ms$. For brown croaker, the dominant frequency ranged in 49.80 to 59.57Hz, and the averaged pulse duration was $129.1{\pm}36.9ms$. Moreover, the dominant frequency of white flower croaker ranged in 73.24 to 86.91Hz, and the averaged pulse duration was $88.0{\pm}15.9ms$, it has shorter pulse duration than any two species. Therefore, the dominant frequency relatives to swimbladder length of sciaenidae showed that it had widely resonant characteristics and long pulse duration as in shorter swimbladder length. Additionally, for white flower croaker, we could confirm their behavior and sounds in response to production of recorded sounds using underwater speaker.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.58 no.2
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• pp.141-152
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• 2022

As a method to understand the ecological habits around the artificial reef, various reports such as fishing gear survey, diving, sound survey, underwater CCTV and camera, etc. are reported. Among them, the sound survey method is carried out by installing an acoustic system on the ship and can be investigated regardless of the marine environment such as time constraints and turbidity. Such method, however, takes a lot of manpower and time as the ship travels at a constant speed. Investigations around artificial reefs are being conducted in an artificial way, and a lot of time and labor are consumed as such. Maritime buoys have been operated for various purposes such as route signs, weather observation, marine environment monitoring and defense monitoring for navigation safety in the past, but studies on monitoring systems for ecological habits and distribution of fish using marine buoys are remarkably insufficient. Therefore, this study aims to develop a system that allows users to directly monitor fish group detector data by estimating the distribution of fish groups around artificial reefs and using wireless communication at sea. In order to confirm the suitability of the maritime buoy used in this study, it was operated to compare data using LTE-equipped buoys capable of wireless communication and a data logger-type system buoy. Data transmission of buoys capable of LTE communication was carried out in a 10-minute ON, 10-minute OFF method due to the limitation of the power supply capacity, and data of the data logger-type buoy received full data. We compared and analyzed the data received from the two fish detectors. It is expected that real-time monitoring of the wireless buoy detection device using LTE will be possible through future research.

• The Journal of the Acoustical Society of Korea
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• v.27 no.1
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• pp.47-56
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• 2008

In the detection of an underwater target, there exists an optimal search depth for the sonar systems, at which the Probability of Detection is maximized. The optimal search depth is dependent on the depths of the target and sonar, the sound speed profile, and the bathymetry. In this paper, we address this question in range-dependent environments, particularly for the bathymetry with slope and with warm eddy. For range-dependent bathymetry, the typical sound profile in the East Sea of Korea was used. The detection range was greater when the sonar was located in deep water than in shallow water. As for the case of eddy, mesoscale warm eddy was used, and the detection range was greater when looking out of the warm eddy than when looking into the eddy.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.472-482
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• 2019

This paper describes the stabilization of underwater TAS winch system Deploy/Recover operation performance. TAS winch installed on the stern of submarine performs to deploy/recover sensor, towing cable and rope tail which is deployed from the stern and separated from submarine itself. Also TAS winch provides transmission path of power to the sensor and data transmitting/receiving path which data are acquired from underwater environment like sound, depth and temperature. At the step of TAS winch evaluation test, sporadic standstill and rotating speed oscillation phenomenon were occurred. Winch motor provides the available torque to deploy/recover TAS and root cause analysis to the winch motor was done to find exact reason to sporadic malfunction. When winch motor was disassembled, eccentricity of rotor, slip-ring and the other composition part for winch motor were found. These might cause magnetic field distortion. To make TAS winch system more stable and block magnetic field distortion, this paper suggests methods to enhance fixing status installed in winch motor. For reliable data acquisition for TAS winch operation, the deploy/recover function of the improved type of TAS winch was verified in LBTS making similar condition with sea status. At the end of stage, improved type of TAS winch was tested on some functions not only deploy/recover function, but sustainability of TAS operation on specific velocity, steering angle of submarine in the sea trial. Improved type of TAS winch was verified in accordance with design requirement. Also, validity of suggested methods were verified by the sea trial.

• The Journal of the Acoustical Society of Korea
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• v.43 no.2
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• pp.225-233
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• 2024

Active sonar transmits sound waves to detect covertly maneuvering underwater objects and detects the signals reflected back from the target. However, in addition to the target's echo, the active sonar's received signal is mixed with seafloor, sea surface reverberation, biological noise, and other noise, making target recognition difficult. Conventional techniques for detecting signals above a threshold not only cause false detections or miss targets depending on the set threshold, but also have the problem of having to set an appropriate threshold for various underwater environments. To overcome this, research has been conducted on automatic calculation of threshold values through techniques such as Constant False Alarm Rate (CFAR) and application of advanced tracking filters and association techniques, but there are limitations in environments where a significant number of detections occur. As deep learning technology has recently developed, efforts have been made to apply it in the field of underwater target detection, but it is very difficult to acquire active sonar data for discriminator learning, so not only is the data rare, but there are only a very small number of targets and a relatively large number of non-targets. There are difficulties due to the imbalance of data. In this paper, the image of the energy distribution of the detection signal is used, and a classifier is learned in a way that takes into account the imbalance of the data to distinguish between targets and non-targets and added to the existing technique. Through the proposed technique, target misclassification was minimized and non-targets were eliminated, making target recognition easier for active sonar operators. And the effectiveness of the proposed technique was verified through sea experiment data obtained in the East Sea.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.407-410
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• 2000

In the using of FBG developed in home land, We designed and manufactured three types of FBG sound transducers the first in Korea. Analysizing special character's on FBG transducers manufactured, we made an experiment on respective frequency peculiarities in the water and we made an experiment on multi-point signal detection and direction about optional acoustic underwater. As the experimental result, we made it possible acoustic detection on frequency peculiarities to maximum 18k0z and made certain the system arrary possibilities, from now on we prepared the practical use study possibilities.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.22 no.3
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• pp.36-41
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• 1986

Uederwater ambient noise was measured at the set net in the Neung-Po Eay. The environment characteristics depend upon oceanographic conditions of sound propagation and its implication on the source of ambient noise. The results of measurement and analysis were as follows: 1. The frequency of the maximum noise level of two passenger. vessels was around 300 Hz. The spectrum level of the fast vessel (the Air-Ferry) was lower than the little slow vessel (the Olympic) between 50-150 Hz in frequences. 2. The spectrum level of the surface in the playground of the set net was lower than the deeper water till 500 Hz, but over that frequency the level was getting lower as the depth was deep. 3. The spectrum level outside the bag of the set net was greater than the inside between 50 and 700 Hz, but over 1,500 Hz the level inside the bag was higher than the outside. 4. The spectrum level of the outside of the breeding tank was higher than the inside in the daytime. However at night opposite phenomenon occurs.