• Title/Summary/Keyword: Range-frequency domain spectrogram

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Influence of the Shear Property of Seabed Appearing in the Striation Pattern of the Spectrogram of Ship-radiated Noise Measured in a Shallow Sea (천해에서 측정한 선박 방사소음 스펙트로그램의 줄무늬 패턴에 나타나는 해저면 전단성 영향)

  • Lee, Seong-Wook;Hahn, Joo-Young;Baek, Woon;Na, Jung-Yul
    • The Journal of the Acoustical Society of Korea
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    • v.23 no.3
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    • pp.197-205
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    • 2004
  • This paper represents the results of interpretation on the cause of sign changing of the striation slopes appearing in the range-frequency domain spectrogram of ship-radiated noise measured in a shallow sea. Striation patterns and dispersion characteristics simulated from a numerical model based on mode theory at various seabed conditions show that the sign changing of the striation slopes appearing in measured signal is caused by the shear property of seabed. more specifically by the shear property of the basement lying below the sediment which is estimated about 3±1m thick.

Influence of the Geoacoustic Parameters of Seabed Appearing in the Broadband Interference Pattern by Moving Targets (이동 표적에 의한 광대역 간섭패턴의 지음향 인자 영향)

  • Hahn, Joo-Young;Lee, Hyeong-Uk;Lee, Bong-Ki
    • Journal of the Korea Institute of Military Science and Technology
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    • v.10 no.3
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    • pp.43-50
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    • 2007
  • A range-frequency interference pattern is analyzed in the course of the propagation of ship noise in shallow water. It has been shown to exhibit striated bands of intensity maxima and minima in the spectrogram. The slope of the striations is an invariant of the modal interference and is described by a waveguide invariant parameter $\beta$. It turns out that this interference pattern is useful for identifying the physical properties of the waveguide such as seabed properties. In this article, the interference pattern is analyzed using image processing techniques to produce the distribution of the beta and the effects of sediment types and geoacoustic parameters on beta distribution are examined and characterized by moments of the distributions.

A study on the target detection method of the continuous-wave active sonar in reverberation based on beamspace-domain multichannel nonnegative matrix factorization (빔공간 다채널 비음수 행렬 분해에 기초한 잔향에서의 지속파 능동 소나 표적 탐지 기법에 대한 연구)

  • Lee, Seokjin
    • The Journal of the Acoustical Society of Korea
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    • v.37 no.6
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    • pp.489-498
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    • 2018
  • In this paper, a target detection method based on beamspace-domain multichannel nonnegative matrix factorization is studied when an echo of continuous-wave ping is received from a low-Doppler target in reverberant environment. If the receiver of the continuous-wave active sonar moves, the frequency range of the reverberation is broadened due to the Doppler effect, so the low-Doppler target echo is interfered by the reverberation in this case. The developed algorithm analyzes the multichannel spectrogram of the received signal into frequency bases, time bases, and beamformer gains using the beamspace-domain multichannel nonnnegative matrix factorization, then the algorithm estimates the frequency, time, and bearing of target echo by choosing a proper basis. To analyze the performance of the developed algorithm, simulations were performed in various signal-to-reverberation conditions. The results show that the proposed algorithm can estimate the frequency, time, and bearing, but the performance was degraded in the low signal-to-reverberation condition. It is expected that modifying the selection algorithm of the target echo basis can enhance the performance according to the simulation results.

Sound Enhancement of low Sample rate Audio Using LMS in DWT Domain (DWT영역에서 LMS를 이용한 저 샘플링 비율 오디오 신호의 음질 향상)

  • 백수진;윤원중;박규식
    • The Journal of the Acoustical Society of Korea
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    • v.23 no.1
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    • pp.54-60
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    • 2004
  • In order to mitigate the problems in storage space and network bandwidth for the full CD quality audio, current digital audio is always restricted by sampling rate and bandwidth. This restriction normally results in low sample rate audio or calls for the data compression scheme such as MP3. However, they can only reproduce a lower frequency range than a regular CD quality because of the Nyquist sampling theory. Consequently they lose rich spatial information embedded in high frequency. The propose of this paper is to propose efficient high frequency enhancement of low sample rate audio using n adaptive filtering and DWT analysis and synthesis. The proposed algorithm uses the LMS adaptive algorithm to estimate the missing high frequency contents in DWT domain and it then reconstructs the spectrally enhanced audio by using the DWT synthesis procedure. Several experiments with real speech and audio are performed and compared with other algorithm. From the experimental results of spectrogram and sonic test, we confirm that the proposed algorithm outperforms the other algorithm and reasonably works well for the most of audio cases.