• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.6
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• pp.228-236
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• 2014

Towed array SONAR is deformed because it operates in fluid such as an ocean. It especially undergoes significant change in shape as a towing vessel takes a turn. In this case, beam pattern synthesis of the line array is limited, resulting in degradation in quality such as signal-to-noise ratio. This paper presents a modified two-step least squares algorithm based on the two-step least squares method. The shape of the sea-operated line array formation with the towing vessel changing course(angle) was modeled and the algorithm was subsequently applied. While changing course and location of the main lobe in beam pattern was altered, signal-to-noise ratio of steering beam pattern synthesis was analyzed by algorithm (proposed and others). As a result, the proposed algorithm presented improvement in performance by 2dB compared to other algorithms while forming relatively constant beam pattern.

• The Journal of the Acoustical Society of Korea
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• v.38 no.2
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• pp.177-183
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• 2019

In this paper, we proposed an application method of ICA (Independent Component Analysis) to passive line array sonar to separate interferences from target signals in low frequency band and compared performance of three conventional ICA algorithms. Since the low frequency signals are received through larger bearing angles than other frequency bands, neighboring beam signals can be used to perform ICA as measurement signals of the ICA. We use three ICA algorithms such as Fast ICA, NNMF (Non-negative Matrix Factorization) and JADE (Joint Approximation Diagonalization of Eigen-matrices). Through experiments on real data obtained from passive line array sonar, it is verified that the interference can be separable from target signals by the suggested method and the JADE algorithm shows the best separation performance among the three algorithms.

• The Journal of the Acoustical Society of Korea
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• v.38 no.2
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• pp.145-153
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• 2019

Adaptive beamforming methods are known to suppress sidelobes and improve detection performance of weak signal by constructing weight vectors depending on the received signal itself. A standard adaptive beamforming like the MVDR (Minimum Variance Distortionless Response) is very sensitive to mismatches between weight vectors and actual signal steering vectors. Also, a large computational complexity for estimating a stable covariance matrix is required when wideband beamforming for a large-scale array is used. In this paper, we exploit the WBRCB (Wideband Robust Capon Beamforming) method for stable and robust wideband adaptive beamforming of a passive large uniform line array sonar. To improve robustness of adaptive beamforming performance in the presence of mismatches, we extract a optimum mismatch parameter. WBRCB with extracted mismatch parameter shows performance improvement in beamforming using synthetic and experimental passive sonar signals.

• The Journal of the Acoustical Society of Korea
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• v.23 no.2
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• pp.109-116
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• 2004

This paper deals with data association using 3 sets of passive linear array sonars (PUS) geometrically positioned in a Y-shaped configuration, but fixed in an underwater environment. The data association problem is directly transformed into a 3-D assignment problem, which is known to be NP-hard. For generic passive sensors, it can be sotted using conventional algorithms, while it in PLAS becomes a formidable task due to the presence of bearing ambiguity. In particular, we proposed data association method robust to bearing measurements errors by incorporating frequency information and analyze a region of ghost problem by geometrical relation PUS and target. We analyzed the effectiveness of the proposed method by representative simulation in multi-target.

• The Journal of the Acoustical Society of Korea
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• v.20 no.8
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• pp.74-80
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• 2001

Because of ocean waves, swell, steering corrections, etc, the hydrophones of a towed array will not live along a straight line. However the degradation of bearing estimation performance occurs when beamforming is carried out on the hydrophone outputs of an acoustic towed array which is not straight. So it is required to estimate the shape of the array for the improved beamformer output. In this paper, an iterative array shape estimation technique is presented, which is based on the use of the least squares polynomial fitting to the data from heading sensors. The estimation error and the influence of deformations on the performance of the conventional beamformer output are investigated. Finally, the suggested method is applied to the real system in order to investigate the applicability.

• The Journal of the Acoustical Society of Korea
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• v.37 no.1
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• pp.66-72
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• 2018

In this paper, we propose an adaptive beamforming algorithm of triplet arrays for active sonar systems. The proposed algorithm consists of three steps: matched filters, cardioid beamforming, and line array beamforming. First, we apply a matched filter of a transmitted pulse to received individual sensor signals and obtain filterd signals. Then, we perform the fast Fourier transform to the matched filter results, and make a cardioid beam for each triplet data, respectively. Finally, we apply an adaptive beamforming by assuming that the cardioid beams are input signals of a line array. Experimental results demonstrate that the proposed algorithm provides better performances than conventional algorithms.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.299-304
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• 1999

시, 공간적으로 변하는 해양환경에서 선배열 소나의 성능예측 정보를 추출하기 위해서는 정밀 해양 DB (Data Base)와 함께 현장에서 실시간으로 측정한 해양자료의 연동이 필수적이다. 이러한 실시간 정보와 DB 정보를 융합하여 얻을 수 있는 정보들로는 전술적 운용상황, 근거리 환경소음 분포, 전파손실/탐지확률 분포, 그리고 음파의 전파 경로 등이 있다. 소나 운용자는 이들 정보로부터 최종적으로 전술상황을 판단함과 동시에 소나의 최적 운용 수심 및 방향을 권고할 수 있다. 국과연에서는 이러한 정보를 획득하기 위하여 음탐환경분석 S/W를 개발하였으며, 수차례의 해상시험을 통하여 그 성능을 검증하였다. 본 논문에서는 실시간 해양정보와 DB정보의 융합을 통하여 선배열 소나의 핵심 성능예측 기법인 전파손실/탐지확률 계산과 근거리 환경소음 계산을 수행하는 알고리즘을 제시한다. 아울러 S/W로 구현된 이들 기법들의 해상시험 결과도 제시하고자 한다.

• Journal of the Korea Institute of Military Science and Technology
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• v.8 no.1 s.20
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• pp.25-31
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• 2005

PLA(Passive Linear Array) system has been primarily utilized to detect and track underwater targets, such as submarines. This system has difficulty in distinguishing between underwater targets and surface ships in a dense target environment. And a single-PLA system does not provide target state observability. At least two PLAs are necessary to observe a track uniquely. To classify and localize the underwater targets effectively, first of all, it is very of importance to discriminate the surface ships in the multi-target environment. These problems can be overcome by the association of distributed PLAs and radars. In this paper, we present an algorithm to solve the track-to-track association of the heterogeneous data from three PLAs and one radar are noncollocated with known sensor positions. Also, this paper shows the simulation results to verify the proposed algorithm.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.2 s.17
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• pp.32-40
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• 2004

In this paper, a simulation model for FLAS(Fixed Linear Arrays System) is presented and methods for effectiveness analysis are studied to analyze the valid target detection effectiveness of this system. The simulation model is constructed taking the FLAS operational specification into account, and thus the change in system specification is effectively reflected on the simulation results. The computational burden is reduced by using the pre-processed simulation parameters which are calculated from the real environmental database. Also, the cell effectiveness and TMOE(Total Measurement of Effectiveness) are computed. The target detection effectiveness of FLAS can be simulated under the multiple target interference simulation. It is shown that the presented algorithm is suitable for the underwater system which needs the simulation model for the optimum system design.

• Journal of the Korea Institute of Military Science and Technology
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• v.27 no.2
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• pp.156-166
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• 2024

This paper conducts a study on methods for associating multipath tracks received by a horizontal line array sonar. The horizontal line array sonar introduces conical bearing ambiguities due to its array-shaped characteristics. Target signals are often subject to multipath propagation in the ocean, resulting in errors in target bearing estimation due to these bearing ambiguities. Recent research efforts have been directed toward using multipath tracks to estimate the positions of targets. However, there has been a lack of research dedicated to identifying multipath tracks from the measurements of a horizontal line array sonar. Therefore, this study identifies the conical bearing characteristics of multipath signals based on the result of experiment and establishes criteria for associating multipath tracks. Additionally, Simulations are performed to determine the ability to associate multipath tracks.