• The Journal of the Acoustical Society of Korea
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• v.12 no.6
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• pp.5-12
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• 1993

고주파 음원을 사용하여 측정한 천해 해역에서의 잔향음 특성 변화와 해양 환경요소와의 연관성을 고찰하고자 하였다. 여름철에 실시한 현장실험에서 획득한 잔향음신호를 분석하여 다음과 같은 결과를 얻었다. 1) 수직 음속이 음의 기울기를 갖고 있어서 해저면 잔향음이 우세하다. 2) 음파발사 방위각에 따라 19dB 이상의 해저면 잔향음준위 차이를 보인다. 3) 계산된 해저면 후방산란 강도는 기존의 측정자료에 비해 약간 높게 나타난다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.124-129
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• 1996

잔향실의 내부 음장을 해석한 결과 다음과 같은 결론을 얻을 수 있었다. 1) 벽면의 흡음률이 동일한 경우는 음향 임피던스의 실수항과 허수항의 변화, 즉 위상의 변화에 따른 음장의 변화가 없다. 2) 5각 형태의 잔향실은 벽면의 흡음률 변화에 따른 음장의 변화가 없다. 3) 4각 형태의 잔향실은 5각 형태의 잔향실보다는 음장이 불균일하며 벽면의 흡음률이 증가함에 따라 음압레벨이 표준편차가 커진다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06e
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• pp.3.2-6
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• 1998

본 논문에서는 실측된 실내 충격 응답을 모델링하여 실내 잔향 필터 설계를 시도하였다. 급강하법(steepest descent method)을 이용하여 측정된 실내 충격 응답을 4개의 콤 필터(comb filter)와 2개의 올패스 필터(allpass filter)로 이루어진 잔향 필터로 모델링하여, 잔향 필터의 계수를 결정하였다.

• The Journal of the Acoustical Society of Korea
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• v.21 no.8
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• pp.671-678
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• 2002

High-frequency monostatic reverberation model (HYREV: HanYang Univ. REVerberation model) suitable for shallow-water environment is presented. It is difficult to predict reverberation signals in shallow water due to scattering from sea surface and seafloor. The arrival times and transmission losses from the source to scatterers are obtained from the eigenrays. The composite roughness theory is used to predict the boundary scattering. The signals generated by the HYREV and the GSM were compared with the observed signals and it is showed that the HYREV model provided a closer fit to the observed signals than those obtained using the GSM.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.5
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• pp.839-848
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• 2000

This paper presents the results of an electromagnetic field analysis for a reverberation chamber that is an alternative method of a shielded anechoic chamber, which is widely used for the analysis and measurement of electromagnetic interference and immunity test. Inside the defined test volume of the rectangular and triangular type, the Schroeder Quadratic Residue Diffuser was employed. FDTD(Finite-Difference Time-Domain) simulation method was applied to produce the field characteristics inside those reverberation chambers. According to the results, field uniformities on the aforementioned two types of reverberation chambers were correlated within $\pm$3dB, and $\pm$4.4dB tolerances, and rectangular type reverberation chamber shows an independent polarization result.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.12
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• pp.152-158
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• 2008

In shallow water environment, the detection performance of an active sonar using matched filter with LFM(linear frequency modulation) pulse can be seriously degraded by reverberation which is considered as non-white noise. To reduce the effect of reverberation, a whitening filter preceding the matched fitter, is usually adopted. In the conventional pre-whitening filter, it is assumed that local stationarity is preserved between detection block and its right ahead block. And then by using the characteristics of the reverberation of preceding block, the reverberation of detection block is estimated and whitened. According to the environment of shallow water, the stationarity of reverberation may be preserved for more blocks. In this case, the reverberation of the detection block can be estimated more accurately if more blocks are used. In this paper, the real reverberation signal which is obtained from shallow sea is analyzed and its proper region of estimation block is examined. And the performance of pre-whitening matched filter is compared and analyzed according to the region of estimation block.

• The Journal of the Acoustical Society of Korea
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• v.28 no.8
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• pp.740-754
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• 2009

Sound in the ocean is scattered by inhomogeneities of many different kinds, such as the sea surface, the sea bottom, or the randomly distributed bubble layer and school of fish. The total sum of the scattered signals from these scatterers is called reverberation. In order to simulate the reverberation signal precisely, combination of a propagation model with proper scattering models, corresponding to each scattering mechanism, is required. In this article, we develop a reverberation model based on the ray theory easily combined with the existing scattering models. Developed reverberation model uses (1) Chapman-Harris empirical formula and APL-UW model/SSA model for the sea surface scattering. For the sea bottom scattering, it uses (2) Lambert's law and APL-UW model/SSA model. To verify our developed reverberation model, we compare our results with those in Ellis' article and 2006 reverberation workshop. This verified reverberation model SNURM is used to simulate reverberation signal for the neighboring seas of South Korea at mid frequency and the results from model are compared with experimental data in time domain. Through comparison between experiment data and model results, the features of reverberation signal dependent on environment of each sea is investigated and this analysis leads us to select an appropriate scattering function for each area of interest.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.241-244
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• 2000

잔향음 세한 환경에서 능동소오나를 운용시 잔향음은 표적탐지를 저해하는 중요한 요인으로 작용한다. 그러한 환경에서 잔향음을 효과적으로 제거하고 표적신호를 보존하기 위한 기법으로 priori estimation error를 사용하는 deterministic LSL(least squares lattice) 알고리즘을 적용하였으며, LSL 필터의 입력신호는 천해에서 고주파 센서를 이용하여 실측한 CW 및 FM 잔향음신호와 모의된 표적신호를 합성한 신호를 이용하였다. 모의 실험 결과 잔향음신호는 상당히 감소되었을 뿐 만 아니라 도플러 변화가 없는 표적신호에 대해서도 LSL필터는 양호한 응답을 보였다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06e
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• pp.19-22
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• 1998

인공 잔향은 콘서튼홀에서와 같이 수백.수천개의 극점과 영점들을 갖는 커다란 시스템을 모델링하기 위한 신호처리 분야 중에서 매우 매력적인 응용 분야중 하나이다. 이러한 인공잔향을 구현하기 위하여, 기존에는 순환적인 디지털 필터인 Comb 필터와 Allpass 필터를 조합시킨 인공 잔향기가 제안되어 왔다. 그러나, 이와 같은 방법은 시스템이 커질수록 실시간 처리와 안정도의 문제가 제기되고, 인공 잔향의 특성이 저하되는 문제점이 있다. 따라서, 최근에는 이와 같은 문제점을 효과적으로 감소시킬 수 있는 귀환 지연 회로망(Feedback Delay Networks : FDN's)과 디지털 도파관 회로망(Digital Waveguide Networks : DWN's)를 이용한 방법이 제안되어지고 있다. 그러므로, 본 연구에서는 귀환 행렬이 Circulant 행렬로 이루어진 귀환 지연 회로망(CFDN's)를 이용한 인공 잔향기 구현에 관하여 논의하고자 한다.

• The Journal of the Acoustical Society of Korea
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• v.18 no.4
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• pp.65-70
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• 1999

To examine the space variances of the sound pressure level for five different types (normal frequency spacing) of reverberation rooms, simulations were conducted using the Finite Element Method. In case of infinite surface impedance, nonrectangular reverberation rooms showed small Standard Deviations across the band of frequency, and in case of finite surface impedance, ideal rectangular reverberation rooms showed the similar results as those in irregular shaped reverberation rooms.