The Journal of the Acoustical Society of Korea (한국음향학회지)

The Acoustical Society of Korea (한국음향학회)
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Ocean bottom reverberation and its statistical characteristics in the East Sea

동해 해역에서 해저면 잔향음 및 통계적 특징

  • 정영철 (서울대학교 조선해양공학과) ;
  • 이근화 (세종대학교 국방시스템공학과) ;
  • 성우제 (서울대학교 조선해양공학과) ;
  • 김성일 (국방과학연구소 제 6기술연구본부)
  • Received : 2018.10.22
  • Accepted : 2019.01.23
  • Published : 2019.01.31
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Abstract

In this study, we analyzed the beam time series of ocean reverberation which was conducted in the eastsouthern region of East Sea, Korea during the August, 2015. The reverberation data was gathered by moving research vessel towing LFM (Linear Frequency Modulation) source and triplet receiver array. After signal processing, we analyzed the variation of ocean reverberation level according to the seafloor bathymetry, source/receiver depth and sound speed profile. In addition, we used the normalized data by using cell averaging algorithm and identified the statistical characteristics of seafloor scatterer by using moment estimation method and estimated shape parameter. Also, we analyzed the coincidence of data with Rayleigh and K-distribution probability by Kolmogorov-Smirnov test. The results show that there is range dependency of reverberation according to the bathymetry and also that the time delay and the intensity level change depend on the depths of source and receiver. In addition, we observed that statistical characteristics of similar Rayleigh probability distribution in the ocean reverberation.

본 연구에서는 2015년 8월, 동해 동남방 해역에서 수행된 해양 잔향음 빔 데이터를 분석하였다. 잔향음 데이터는 이동하는 연구선에 의해 예인된 LFM (Linear Frequency Modulation) 음원과 삼중선 배열을 통해 수집되었으며, 신호처리 과정을 거친 이후 해저지형, 음원/수신기 수심, 음속구조에 따른 잔향음 준위의 변화를 분석하였다. 추가로 해저 잔향음의 확률적 특성을 해석하기 위해 셀 평균화 알고리즘이 적용된 정규화 데이터가 활용되었고, 모멘트 추정기법을 통해 형상 모수를 추정하여 해저 산란체의 확률적 특징을 확인하였다. 또한, 콜모고로프 스미르노프 검정 기법을 이용하여 데이터가 레일레이 분포와 K 분포 확률에 일치하는지를 분석하였다. 결과적으로 해저 지형에 따른 잔향음의 거리종속 특성과 음원/수신기 수심에 따른 시간 지연 및 세기 변화를 확인하였고, 잔향음에서 레일레이 확률분포와 유사한 특성을 관찰할 수 있었다.

Keywords

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Fig. 1. The geometry of sonar resolution cell. The scatterer number is related with beamwidth, bandwidth, grazing angle, slant range, scatterer density.[11]

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Fig. 2. Sea experiment site showing bathymetry and track of the ship towing array in the East Sea. Red circles are positions for LFM signal 2.8 kHz ~ 3.2 kHz, pulse length 0.3 s and blue diamonds are positions for LFM signal 2.5 kHz ~ 3.5 kHz, pulse length 1 s.

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Fig. 3. Sound speed profiles of sea experiment.

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Fig. 4. The analyzed process of ocean reverberation beam time series for the polar plot.

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Fig. 5. The analysis process for statistical characteristics of ocean reverberation.

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Fig. 6. Reverberation intensity level of 30th beam (84◦ clockwise from forward endfire) for the 2.8 kHz ~ 3.2 kHz LFMs and 1st ping.

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Fig. 7. Reverberation intensity level of 30th beam (84◦ clockwise from forward endfire) for the 2.5 kHz ~ 3.5 kHz LFMs and 84th ping.

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Fig. 8. Received beam intensity from the output of the matched filter for the 2.8 kHz ~ 3.2 kHz LFMs and 1st ping.

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Fig. 9. Ocean reverberation results for the beam 30th (84◦ clockwise from forward endfire) on the ship track. All pulses are 2.8 kHz ~ 3.2 kHz LFMs.

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Fig. 10. Ocean reverberation results for the beam 30th (84◦ clockwise from forward endfire) on the ship track. All pulses are 2.5 kHz ~ 3.5 kHz LFMs.

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Fig. 11. Ray diagrams using sound speed profile of sea experiment. The bottom is flat and depth is 1250 m. The sound speed of bottom 1452 m/s, bottom density 1480 kg/m3, bottom attenuation 0.1 dB/λ (a) source depth : 140 m, (b) source depth : 120 m.

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Fig. 12. K–S test statistic p values for the Rayleigh and K-distributions for beam 30th data (84◦ clockwise from forward endfire) and the inverse of the corresponding estimates of the K-distribution shape parameter. (a) 2.8 kHz ~ 3.2 kHz LFMs and 1st ping and (b) 2.5 kHz ~ 3.5 kHz LFMs and 84th ping.

Table 1. A list of well-organized multi-institutional and multinational reverberation experiments.[3]

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Table 2. Overall results of statistical analysis and K-S test at the 0.05 level for the 2.8 kHz ~ 3.2 kHz LFMs and 2.5 kHz ~ 3.5 kHz LFMs.

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Table 3. The results of statistical analysis and K-S test at the 0.05 level for the ping number 1 ~ 83, 2.8 ~ 3.2 kHz LFMs, pulse length 0.3 s.

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Table 4. The results of statistical analysis and K-S test at the 0.05 level for the ping number 84 ~ 171, 2.5 ~ 3.5 kHz LFMs, pulse length 1 s.

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