• 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.

• The Journal of the Acoustical Society of Korea
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• v.36 no.3
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• pp.218-227
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• 2017

In this paper, an algorithm to calculate both bearing and distance error for target detection and localization is proposed using the Cramer Rao lower bound to estimate the minium variance of their error in DOA (Direction Of Arrival) estimation. The performance of arrays in detection and localization depends on the accuracy of DOA, which is affected by a variation of SNR (Signal to Noise Ratio). The SNR is determined by sonar parameters such as a SL (Source Level), TL (Transmission Loss), NL (Noise Level), array shape and beam steering angle. For verification of the suggested method, a Monte Carlo simulation was performed to probabilistically calculate the bearing and distance error according to the SNR which varies with the relative position of the target in space and noise level.

• Journal of the Korea Society of Computer and Information
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• v.25 no.2
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• pp.59-66
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• 2020

In this paper, we propose a pipe leak detection system through data collection using low-power wireless acoustic sensor modules and data analysis using deep auto-encoder. Based on the Fourier transform, we propose a low-power wireless acoustic sensor module that reduces data traffic by reducing the amount of acoustic sensor data to about 1/800, and we design the system that is robust to noise generated in the audible frequency band using only 20kHz~100kHz frequency signals. In addition, the proposed system is designed using a deep auto-encoder to accurately detect pipe leaks even with a reduced amount of data. Numerical experiments show that the proposed pipe leak detection system has a high accuracy of 99.94% and Type-II error of 0% even in the environment where high frequency band noise is mixed.

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.601-609
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• 2022

In August 2007, coastal upwelling occurred off the east coast of Korea, and vertical water temperature and salinity data were obtained from a real-time surface ocean buoy. Based on the time series observation data, a vertical sound velocity structure was calculated before, during, and after the occurrence of the coastal upwelling, and how the coastal upwelling affects the sound propagation and detection environment through acoustic modeling considering the horizontal scale and actual seabed topography. As a result of comparing and analyzing the low-frequency (500 Hz) sound transmission loss and the target detection range by depth using the parabolic equation model, it was analyzed that if coastal upwelling occurs, a detection gain of up to about 10 dB can be expected. In addition, through this study, it was confirmed that the characteristics of sound propagation can be greatly changed even in a short period of about 2 to 3 days before and after coastal upwelling.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.199-209
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• 2022

Typical anomaly detection algorithms are trained by using prior data. Thus the batch learning based algorithms cause inevitable performance degradation when characteristics of newly incoming normal data change over time. We propose an online anomaly detection algorithm which can consider the gradual characteristic changes of incoming normal data. The proposed algorithm based on one-class classification model includes both offline and online learning procedures. In offline learning procedure, the algorithm learns the prior data to be close to centroid of the latent space and then updates the centroid of the latent space incrementally by new incoming data. In the online learning, the algorithm continues learning by using the updated centroid. Through experiments using public underwater acoustic data, the proposed online anomaly detection algorithm takes only approximately 2 % additional learning time for the incremental centroid update and learning. Nevertheless, the proposed algorithm shows 19.10 % improvement in Area Under the receiver operating characteristic Curve (AUC) performance compared to the offline learning model when new incoming normal data comes.

• Geophysics and Geophysical Exploration
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• v.27 no.1
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• pp.57-68
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• 2024

Offshore wind power is increasingly regarded as a viable solution for reducing greenhous emissions due to the construction of wind farms and their superior power generation efficiency. Submarine power cables play a crucial role in transmitting the electricity generated offshore to land. To monitor cables and identify points of failure, analyzing the location or depth of burial of submarine cables is necessary. This study reviewed the technology and research for detecting submarine power cables, which were categorized into seismic/acoustic, electromagnetic, and magnetic exploration. Seismic/acoustic waves are primarily used for detecting submarine power cables by installing equipment on ships. Electromagnetic and magnetic exploration detects cables by installing equipment on unmanned underwater vehicles, including autonomous underwater vehicles (AUV) and remotely operated vihicles (ROV). This study serves as a foundational resource in the field of submarine power cable detection.

• Defense and Technology
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• no.2 s.156
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• pp.30-35
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• 1992

현대의 어뢰는 함정의 회피운동만으로는 대처하기 곤란하며, 차폐, 방해, 기만등으로 어뢰에 대항하는 방법과 저소음화, 피채율 감소 등으로 상대방이 탐지하지 못하게 하는 방법이 있다. 어뢰공격으로부터 함정을 보호하기 위해 영국, 프랑스, 이스라엘 등은 음향대항전 체계를 개발해사용하고 있으나, 이에 관련된 기술은 매우 신중히 보호하고 있으며 노출시키지않고 있다. 이 음향대항전 체계는 주문구매가 가능하나 극비에 속하는 자국함정의 음향징표를 제작국에 제시해야 하므로, 상호 기밀을 유지할수 없는 현실을 감안할때, 이 분야는 독자개발이 바람직하다 하겠다

• The Journal of the Acoustical Society of Korea
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• v.5 no.1
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• pp.41-48
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• 1986

본 논문에서는 그레이디드 인덱스 다중모드 광섬유에 압력을 가함으로써 발생되는 마이크로벤딩 을 모드결합 이론으로 서술하였다. 그 이론에 의하여 모드결합이 최적으로 일어나는 정적벤딩을 통한 주기성을 얻어 시제품 광섬유 음향 트랜스듀서를 설계 및 제작하였다. 제작된 트랜스듀서의탐지 가능한 최소검출압력을 정적벤딩 실험을 통하여 계산하였으며, 아울러 제작된 광섬유 음향 트랜스듀서의 특성 을 실험하였다.

• Proceedings of the Korean Society of Disaster Information Conference
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• 2023.11a
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• pp.325-326
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• 2023

해상 사고 시 일반 전파를 이용한 통신 시스템으로 찾기 어려운 수중 위치 추적에 사용하기 위해 몸에 부착할 수 있는 크기의 소형화된 수중 음향 모듈을 제작하고 이를 서해 상에서 거리에 따른 음향 신호를 측정했다.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.149-152
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• 2004

본 연구에서는 Split-beam 변환기에 적용 가능한 방향 탐지 알고리듬으로써 4분 샘플링에 의한 시간 영역에서의 음원 도래 방향 탐지법을 검토하고자 한다. 외부 잡음을 고려한 환경하에서도 완전 샘플링 및 4분 샘플링 후 주파수 영역에서의 시간 지연 계산법보다 4분 샘플링에 의한 시간 영역에서의 상호상관 기법이 경제적인 측면과 분해능의 측면에서 적절하다는 것을 확인하였다.