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    Wyświetlanie 1-3 z 3
    Tytuł:
    Effect of Emergence Angle on Acoustic Transmission in a Shallow Sea
    Autorzy:
    Lu, Yanyang
    Yang, Kunde
    Liu, Hong
    Huang, Chunlong
    Powiązania:
    https://bibliotekanauki.pl/articles/177665.pdf
    Data publikacji:
    2020
    Wydawca:
    Polska Akademia Nauk. Czasopisma i Monografie PAN
    Tematy:
    underwater acoustic
    emergence angle
    transmission loss
    active sonar detection
    Opis:
    In this study, the effect of the emergence angle of a source array on acoustic transmission in a typical shallow sea is simulated and analyzed. The formula we derived for the received signal based on the Normal Mode indicates that the signal is determined by the beamform on the modes of all sources and the samplings of all modes at the receiving depth. Two characteristics of the optimal emergence angle (OEA) are obtained and explained utilizing the aforementioned derived formula. The observed distributions of transmission loss (TL) for different sources and receivers are consistent with the obtained characteristics. The results of this study are valuable for the development and design of active sonar detection.
    Źródło:
    Archives of Acoustics; 2020, 45, 1; 3-9
    0137-5075
    Pojawia się w:
    Archives of Acoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    A Dedispersion Transform Method for Extracting the Normal Modes of a Shallow Water Acoustic Signal in the Pekeris Waveguide
    Autorzy:
    Yang, G.- B.
    Lü, L.- G.
    Gao, D.- Z.
    Jiang, Y.
    Liu, H.- N.
    Powiązania:
    https://bibliotekanauki.pl/articles/177234.pdf
    Data publikacji:
    2015
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    normal mode extraction
    dedispersion transform
    Pekeris waveguide
    source ranging
    Opis:
    The normal modes cannot be extracted even in the Pekeris waveguide when the source-receiver distance is very close. This paper introduces a normal mode extraction method based on a dedispersion transform (DDT) to solve this problem. The method presented here takes advantage of DDT, which is based on the waveguide invariant such that the dispersion associated with all of the normal modes is removed at the same time. After performing DDT on a signal received in the Pekeris waveguide, the waveform of resulting normal modes is very close to the source signal, each with different position and amplitude. Each normal mode can be extracted by determining its position and amplitude parameters by applying particle swarm optimization (PSO). The waveform of the extracted normal mode is simply the waveform of the source signal; the real waveform of the received normal mode can then be recovered by applying dispersion compensation to the source signal. The method presented needs only one receiver and is verified with experimental data.
    Źródło:
    Archives of Acoustics; 2015, 40, 1; 11-18
    0137-5075
    Pojawia się w:
    Archives of Acoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Comparison of Moving Average and Differential Operation for Wheeze Detection in Spectrograms
    Autorzy:
    Hsueh, Meng-Lun
    Chen, Jin-Peng
    Lu, Bing-Yuh
    Wu, Huey-Dong
    Liu, Pei-Yi
    Powiązania:
    https://bibliotekanauki.pl/articles/31340111.pdf
    Data publikacji:
    2022
    Wydawca:
    Polska Akademia Nauk. Czasopisma i Monografie PAN
    Tematy:
    differential operation
    moving average
    signal
    lung sound
    wheeze
    Opis:
    A moving average (MA) is a commonly used noise reduction method in signal processing. Several studies on wheeze auscultation have used MA analysis for preprocessing. The present study compared the performance of MA analysis with that of differential operation (DO) by observing the produced spectrograms. These signal preprocessing methods are not only applicable to wheeze signals but also to signals produced by systems such as machines, cars, and flows. Accordingly, this comparison is relevant in various fields. The results revealed that DO increased the signal power intensity of episodes in the spectrograms by more than 10 dB in terms of the signal-to-noise ratio (SNR). A mathematical analysis of relevant equations demonstrated that DO could identify high-frequency episodes in an input signal. Compared with a two-dimensional Laplacian operation, the DO method is easier to implement and could be used in other studies on acoustic signal processing. DO achieved high performance not only in denoising but also in enhancing wheeze signal features. The spectrograms revealed episodes at the fourth or even fifth harmonics; thus, DO can identify high-frequency episodes. In conclusion, MA reduces noise and DO enhances episodes in the high-frequency range; combining these methods enables efficient signal preprocessing for spectrograms.
    Źródło:
    Archives of Acoustics; 2022, 47, 3; 383-388
    0137-5075
    Pojawia się w:
    Archives of Acoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-3 z 3

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