• 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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• spring
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• pp.240-243
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• 1999

본 논문에서는 칼만 필터 방법을 이용하여 견인 어레이의 3차원 형상을 추정하고, 어레이 합성 기법인 ETAM방법이 추정된 3차원 형상에서도 적용 가능함을 입증한다. 기존의 합성 기법들은 모두 견인 어레이가 직선 형태를 유지하고 있다는 가정을 필요로 하지만, ETAM 방법은 3차원 형상추정이 가능한 경우에 그러한 가정이 필요 없게 된다. 단, 3차원 어레이 형상에서 어레이를 확장하기 위해서는 절대 좌표를 추정할 수 있으며, 어레이가 동일한 견인 경로를 따라간다는 가정이 필요하다. 컴퓨터 모의 실험 결과 신호원의 입사각을 추정하였을 때, 주엽폭과 부엽레벨이 감소하는 등 합성이 가능함을 확인하였다.

• The Journal of the Acoustical Society of Korea
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• v.23 no.2
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• pp.125-133
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• 2004

Most of the way shape estimation method using reference sources assume that the reference sources are in the farfield. That is, the reference sources are assumed to be far from the array. However, in applications of the array with reference sources, the reference sources are not far from the way, so that in practical ocean environments, the conventional method using farfield source model fail to estimate the positions of the hydrophones. In this paper, based on the nearfield source model, a subspace-based array shape estimation method was proposed. In the proposed method, nearfield reference source is modeled using the differential time delay at each hydrophone, and nearfield parameters are derived. Using these parameters, a subspace-based array shape estimation method that generalizes the existing farfield subspace fitting method which can work regardless of the range of the source is proposed. The Cramer-Rao lower bound for the proposed method is investigated. The results of the numerical experiments indicate that the proposed method performs well in estimating the shape of a perturbed way regardless of the ranges of the reference sources.

• The Journal of the Acoustical Society of Korea
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• v.23 no.4
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• pp.282-287
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• 2004

This paper proposes the nearfield eigenvector method for array shape estimation using reference signals basted on the nearfield signal modeling. Generally. direction finding methods assume the reference signals to be plainwave. However, in case of the reference signals in nearfield, this assumption is inadequate for array shape estimation. In this paper. the nearfield reference signals are modeled. and we propose the nearfield eigenvector method. The numerical experiments indicated that the proposed method shows good performance for array shape estimation regardless of the ranges of the reference signals.

• The Journal of the Acoustical Society of Korea
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• v.21 no.5
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• pp.478-484
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• 2002

Linear towed arrays (LTA) have a nonlinear shape due to tow vessel motion, ocean swells and currents. By reasons of nominally linear shape, various towed array shape estimation techniques have been developed since the perturbed shape cause the error in target detection. In this paper,, we propose the beamforming method for the perturbed LTA with simple structure. The proposed method linearizes a nonlinear phase of steering vector with position information measured by two reference sensors. It can be proved using some properties of Markov transition matrix, and iteration number of linearization process is decided by variance of cross phase difference. As a result of computer simulation in the ocean environment, beampattern of the proposed method is almost same with the ideal case in my type of array shape. In the signal-to-noise ratio (SNR) performance simlation, the DOA estimation performance of the proposed beamforming method is evaluated, and the comparison with Bartlett beamformer of the LTA shows that the proposed method can estimate. the spatial characteristic of sources more accuracy.

• 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.

• The Journal of the Acoustical Society of Korea
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• v.23 no.6
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• pp.428-436
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• 2004

Synthetic Aperture Sonar is a technique of extending Physically limited length of an array by signal processing to enhance bearing resolution of a system. The previous techniques estimate most or away shapes as linear. so when towed array shapes are distorted. this can create a deviation from actual situation. In this paper. we estimated perturbed away shapes. and compensated distortion by using estimated array shapes and synthesized arrays in aperture domain. As experimental data, we used the one obtained from towed array in neighboring waters of the Korean peninsula. We extended array by compensating differences in time and spatial position between overlapped subarrays by using SAS techniques. In simulation results. we confirmed that the bearing resolution was enhanced.

• The Journal of the Acoustical Society of Korea
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• v.19 no.3
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• pp.72-76
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• 2000

A calibration technique is proposed to improve the performance of 2-D towed array shape estimation using the Kalman filter. In the case of using displacement sensors, 2-D hydrophone positions estimated by the Kalman filter are calculated by assuming that the adjacent hydrophones are horizontally equi-spaced so that maximum distance is equal to the array length. The assumption causes errors in estimating hydrophone positions. The proposed technique using linear model approximation or spline interpolation can reduce the errors by exploiting the fact that the whole length of array is preserved whatever the array shape is. The numerical experiments show that the proposed method is very effective.

• The Journal of the Acoustical Society of Korea
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• v.25 no.4
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• pp.172-177
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• 2006

Various research and development on Synthetic Aperture Sonar technique is under way to enhance bearing resolution of a SONAR system. In this paper, we estimated perturbed array shapes, and compensated distortion by using estimated away shapes and synthesized arrays in aperture domain such as an ETAM technique. As experimental data, we used the one obtained from towed array in neighboring waters of the Korean peninsula. Through simulation on data where tow-ship speed is maintained at a constant level, we confirmed that synthesis effect of increasing SNR and narrowed beam width of main lobe was consistently demonstrated for about 1 minute when coherence of target signal was maintained. Also, we showed that the synthesis effect with respect to time was constantly maintained.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.455-458
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• 2004

소나 시스템의 표적 탐지 성능을 향상시키기 위해 물리적으로 제한된 길이의 어레이를 확장하는 합성 어퍼쳐 소나에 대한 연구와 실험이 이루어지고 있다. 본 논문에서는 왜곡된 어레이의 형상을 추정하여 왜곡을 보상한 후에 빔 영역에서 어레이를 합성하는 FFTSA(Fast Fourier Transform Synthetic Aperture) 기법의 성능을 분석하였다. 실험 데이터로는 한국 근해에서 견인 어레이로부터 획득한 데이터를 이용하였으며 실측된 데이터로 부어레이 간의 시-공간적인 위상 차이를 보상함으로써 어레이 길이를 확장하였다.