• The Journal of the Acoustical Society of Korea
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• v.36 no.1
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• pp.1-11
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• 2017

In this study, novel approximate form of the square-root operator of three dimensional acoustic Parabolic Equation (3D PE) is proposed using a rational approximant for two variables. This form has two advantages in comparison with existing approximation studies of the square-root operator. One is the wide-angle capability. The proposed form has wider angle accuracy to the inclination angle of ${\pm}62^{\circ}$ from the range axis of 3D PE at the bearing angle of $45^{\circ}$, which is approximately three times the angle limit of the existing 3D PE algorithm. Another is that the denominator of our approximate form can be expressed into the product of one-dimensional operators for depth and cross-range. Such a splitting form is very preferable in the numerical analysis in that the 3D PE can be easily transformed into the tridiagonal matrix equation. To confirm the capability of the proposed approximate form, comparative study of other approximation methods is conducted based on the phase error analysis, and the proposed method shows best performance.

• The Journal of the Acoustical Society of Korea
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• v.27 no.3
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• pp.149-153
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• 2008

General underwater target detection methods adopt short-time FFT for estimate target doppler. This paper proposes the efficient target detection method, instead of conventional FFT, using approximate FFT for distributed sensor network target detection, which requires lighter computations. In the proposed method, we decrease computational rate of FFT by the quantization of received signal. For validation of the proposed method, experiment result which is applied to FFT based active sonar detector and real oceanic data is presented.

• The Journal of the Acoustical Society of Korea
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• v.21 no.5
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• pp.494-502
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• 2002

In this paper, the Low Rank Approximation (LRA) method to suppress the interference of signals from temporal fluctuations is applied. The reverberation signals and temporally fluctuating signals are separated from the measured data using the Ink. The Singular value decomposition (SVD) method is applied to extract the low rank and the temporally stable reverberation was extracted using the LRA. The reverberation suppression is performed on the LRA residual value obtained by removing the approximate reverberation signals. In overall, the method can be applied to the suppression of reververation in active sonar system as well as to the modeling of reverberation.

• The Journal of the Acoustical Society of Korea
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• v.39 no.4
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• pp.255-262
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• 2020

In modern passive sonar systems, a towed array sensor is used to minimize the effects of own ship noise and to get a higher SNR. The thin and long towed array sensor can be guided in a non-linear form according to the maneuvering of tow-ship. If this change of the array shape is not considered, the performance of beamformer may deteriorate. In order to properly beamform the elements in the array, an accurate estimate of the array shape is required. Various techniques exist for estimating the shape of the linear array. In the case of a method using a heading sensor, the estimation performance may be degraded due to the effect of heading sensor noise. As means of removing this potential error, weighted polynomial fitting technique for estimating array shape is developed here. In order to evaluate the performance of proposed method, we conducted computer simulation. From the experiments, it was confirmed that the proposed method is more robust to noise than the conventional method.

• The Journal of the Acoustical Society of Korea
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• v.33 no.4
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• pp.232-237
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• 2014

A passive sonar of warship is composed of several directional or omni-directional sensors. In order to model the acoustic signal received into a warship sonar, the wave propagation modeling is usually required from arbitrary noise source to all sensors equipped to the sonar. However, the full calculation for all sensors is time-consuming and the performance of sonar simulator deteriorates. In this study, we suggest an asymptotic method to estimate the sonar signal arrived to sensors adjacent to the reference sensor, where it is assumed that all information of eigenrays is known. This method is developed using Taylor series for the time delay of eigenray and similar to Fraunhofer and Fresnel approximation for sonar aperture. To validate the proposed method, some numerical experiments are performed for the passive sonar. The approximation when the second-order term is kept is vastly superior. In addition, the error criterion for each approximation is provided with a practical example.

• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.12-16
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• 2001

To analyze the performance of array shape estimation techniques using auxiliary sensors, the appropriate number and the positions of auxiliary sensors are investigated. Also, a post-processing technique based on spline interpolation is proposed to improve the performance of array shape estimation. The simulation results showed that when auxiliary sensors are arranged uniformly, the performance of shape estimation is better than other arrangements of auxiliary sensors. Also, the proposed post-processing technique improved the performance of the existing shape estimation method, such as Kalman filter method.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.125-128
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• 2001

본 연구에서는 음성신호의 왜곡에 대해 음성 부재 확률을 고려한 MMSE(Minimum Mean Square Error) STSA(Short-Time Spectral Amplitude Estimator)를 전처리기로 도입하여 HMM(Hidden Markov Model)에 기반 한 음성인식시스템의 인식성능을 평가하였다. 음성인식 시스템의 실시간 구현을 고려하여, MMSE STSA 기법을 음성개선을 위한 전처리기로 사용할 때 MMSE STSA의 이득계산 과정에서 많은 계산량이 요구되는 modified Bessel 함수를 근사 화하여 사용하였다.

• The Journal of the Acoustical Society of Korea
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• v.39 no.3
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• pp.216-225
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• 2020

In this paper, broadband underwater propagation channel modeling based on eigenray analysis is discussed. Underwater channels are often formulated in frequency domain time-harmonic signals, which are impractical for simulating broadband signals in time domain. In this regard, time domain modeling of the underwater propagation channel is required for the simulation of broadband signals, for which the eigenray analysis based on ray tracing, resulting in multipath propagation delays in time-domain, is used in this paper. For discrete time system application, the phase, frequency-dependent loss and non-integer sample delays for each eigenray, are approximated by the finite impulse response of the broadband propagation channel.

• The Journal of the Acoustical Society of Korea
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• v.42 no.2
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• pp.83-93
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• 2023

Trapezoidal corrugated plates are often treated as orthotropic plates to simplify the modelling of the corrugation. However, this simplification is not valid at high frequencies in which the localized vibration within the parts of corrugation takes place. In this study, the vibrational and acoustical characteristics of corrugated plates are investigated up to high frequencies by means of the wavenumber domain numerical approach. Based on the findings from this numerical analysis, an approximate method to predict vibro-acoustic characteristics of corrugated plates is proposed. This approximate model consists of four equivalent plates which can represent global and local behaviours of corrugated plates. The radiation efficiency of corrugated plates is predicted from the approximate model and validated through the comparison with those of the numerical method.

• The Journal of the Acoustical Society of Korea
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• v.27 no.5
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• pp.221-228
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• 2008

To estimate array shape with reference sources in SONAR systems, nearfield signal modeling is required for the reference sources near a towed array. Array shape estimation method based on the nearfield signal modeling generally exploits the spatial covariance matrix of the received reference sources. Among those method, nearfield eigenvector method uses the eigenvector corresponding to the maximum eigenvalue as a steering vector of the reference source. In this paper, we propose a simplified subspace fitting method based on the nearfield signal modeling with spherical wave modeling. Furthermore, we analyze performance of the array shape estimation methods based on the nearfield signal modeling for various environments. The results of the numerical experiments indicate that the simplified subspace fitting method and the nearfield eigenvector method with single reference source shows almost similar performance. Furthermore, the simplified subspace fitting method with 2 reference sources consistently estimates the shape of the array regardless of the incident angle of the reference sources, whereas the nearfield eigenvector method cannot apply for the case of 2 reference sources.