The Journal of the Acoustical Society of Korea (한국음향학회지)

The Acoustical Society of Korea (한국음향학회)
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Lofargram fusion methods based on local anisotropy

국부 비등방성에 기반한 LOFAR그램 융합 방법

  • 김주호 (국방과학연구소 소나체계개발단) ;
  • 안재균 (국방과학연구소 소나체계개발단) ;
  • 조점군 (국방과학연구소 소나체계개발단) ;
  • 이철목 (국방과학연구소 소나체계개발단) ;
  • 황수복 (국방과학연구소 소나체계개발단)
  • Received : 2018.10.30
  • Accepted : 2019.01.23
  • Published : 2019.01.31
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Abstract

In this paper, we present fusion methods for two different lofargrams. Since the conventional method synthesizes the lofargrams using frequency spectrum, it has limited performance in fusion of tonal signals which have two-dimensional information of the time-frequency domain. Proposed algorithm uses a two-dimensional directional bilateral filter for preprocessing and fuses two lofargrams based on comparison of local anisotropy of the lofargrams. After noise is suppressed and tonals are sharpened, the local anisotropy can be used as a criterion to divide tonals and noise. The experiment results using simulated data and real data showed that the proposed algorithms result in similar or lower noise level of the fused lofargram than conventional algorithms and decrease tonal omission in fusion process.

본 논문은 서로 다른 두 개의 LOFAR (LOw Frequency Analysis and Recording)그램을 융합하는 방법을 다룬다. 기존의 방법은 주파수 스펙트럼을 이용하여 LOFAR 그램을 융합하기 때문에, 시간-주파수의 2차원 정보인 토널 신호를 융합하는데 제한적인 성능을 갖는다. 제안하는 방법은 전처리 과정에서 2차원 방향성 양방향 필터링을 이용하며, 전처리된 LOFAR 그램의 국부 비등방성 비교를 기반으로 두 LOFAR 그램을 융합한다. 전처리 과정에서 잡음을 억제하고 토널을 부각시키고 나면 국부 비등방성은 토널과 잡음을 구분하기 위한 척도로 사용될 수 있다. 모의 데이터와 해상 데이터를 이용해 LOFAR 그램 융합 실험을 수행한 결과, 제안한 방법은 기존 기법에 비해 융합된 LOFAR 그램의 잡음레벨을 대등하게 하거나 감소시키는 결과를 낳으며, 융합시 토널 누락 현상을 감소시키는 것을 확인하였다.

Keywords

GOHHBH_2019_v38n1_128_f0001.png 이미지

Fig. 1. Block diagram for proposed algorithm A.

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Fig. 2. Block diagram for proposed algorithm B.

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Fig. 3. Evaluation of fusion results according to two input parameters(σd and σr). (a) and (b) are the values of C1 and C2, respectively, that are computed by conventional algorithm. (c) and (d) represents C1 and C2 that are computed using proposed algorithm A.

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Fig. 4. Comparison of fusion results between the conventional method and the proposed methods according to window size for (a) C1 and (b) C2.

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Fig. 5. (a) Original lofargram (b) results of 1D BF (Bilateral Filter)[2] (c) result of conventional directional BF[5] (d) result of proposed preprocessing.

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Fig. 6. (a) and (b) are original lofargram A and B, respectively, (c) is a result of fusion using finding maximum method, (d) is a fusion image by conventional method, (e) and (f) are fusion images based on proposed method A and B, respectively.

GOHHBH_2019_v38n1_128_f0007.png 이미지

Fig. 7. (a) and (b) are original lofargram A and B, respectively, (c) is a result of fusion using finding maximum method, (d) is a fusion image by conventional method, (e) and (f) are fusion images based on proposed method A and B, respectively.

Table 1. Comparison of performance between conven-tional method and proposed methods.

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