• Journal of the Korean Institute of Intelligent Systems
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• v.23 no.4
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• pp.304-309
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• 2013

This paper proposes a intelligent approach on range decision of figure of merit. Unknown range of the underwater target and the non-fixed signal excess make the uncertainty for the tracking process. Using the input data of signal excess related to the range, we establish the rule of the fuzzy set and the original data acquired by sonar can be transformed to the fuzzified data set. To reduce the error arisen from the unexpected data, we use the new data transformed in fuzzy set. The piecewise relations of the min value, max one, and the mean one are calculated. The three values are used for the expected range of the underwater target. By analysing the fluctuation of the data, we can expect the target's position and the characteristics of the maneuvering. The examples are presented to show the performance and the effectiveness of the proposed method.

• Journal of the Korea Institute of Military Science and Technology
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• v.11 no.3
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• pp.129-137
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• 2008

Hull-Mounted Sonar(HMS) has been the main equipment to detect and track underwater threats like torpedoes and enemy submarines. The HMS has short warming-up time and is employable independently with sea-state and weather condition. But these bad environmental condition and ship maneuvering make ship's roll and pitch. Ship's roll and pitch make unstability of sensor position, then cause degradation of the HMS performance. In this paper, we will show how the unstability influences the HMS performance, propose the 'Beam Stabilization Beamforming Technique' to overcome these phenomenon. And present the effectiveness of proposed technique by comparing with conventional beamforming result.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.3
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• pp.37-46
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• 2012

In RADAR and SONAR detection systems, noise environment can be classified into homogeneous and heterogeneous environment. Especially heterogeneous environments are modelled as target masking and clutter edge. Since the variability-index (VI) CFAR, a composed CFAR algorithm, dynamically selects one of the mean-level algorithms based on the VI and the MR (mean ratio) test, it is robust to various environments. However, the VI CFAR still suffers from lowered detection probabilities in heterogeneous environments. To overcome these problems, we propose an improved VI CFAR processor where TM (trimmed mean) CFAR and a sub-windowing technique are introduced to minimize the degradation of the detection probabilities appeared in heterogeneous environments. Computer simulation results show that the proposed method has the better performance in terms of detection probability and false alarm probability compared to the VI CFAR and single CFAR algorithms.

• The Journal of the Acoustical Society of Korea
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• v.15 no.5
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• pp.118-124
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• 1996

Signal frequency lines generated from the acoustic targets are of particular importance for target detection and classification in passive sonar systems. The underwater noise consists of a mixture of ambient noise and radiated noise of targets. Detction of exact signal frequency lines depends on signal detection threshold and variation of ambient noise. In this paper, a detection method of signal frequency lines for acoustic targets using autoassociative memory (ASM) neural network, which is not sensitive to variation of signal detection threshold and ambient noise, is proposed. It is confirmed by simulation and application of real acoustic targets that the proposed method shows good performance for detection of signal frequency lines.

• The Journal of the Acoustical Society of Korea
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• v.35 no.2
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• pp.158-165
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• 2016

Many researches for improving detection performance in the reverberation environment have been conducted in active sonar systems. Especially the type of active pulse makes an impact on the detection performance in the reverberation environment. Thus, this paper describes the detection performance of PTFM (Pulse Trains of Frequency Modulated waveform), Costas, and Geometric Comb pulses which are known for their outstanding performance against the reverberation. Sea trial data of those pulses was analyzed and it was figured out that the range resolution of PTFM pulse was deteriorated by its sub-pulses. Costas pulse showed performance degradations of the doppler resolution by multipath signals. Geometric Comb pulse showed the best doppler resolution.

• The Journal of the Acoustical Society of Korea
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• v.40 no.6
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• pp.546-554
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• 2021

In the signal processing of synthetic aperture sonar, it is subject that the platform in which the sensor array is installed moves along the straight line path. In practical operation in underwater, however, the sensor platform will have trajectory disturbances, diverting from the line path. It causes phase errors in measured signals and then produces deteriorated SAS images. In this study, in order to develop towed SAS, as tools to remove the phase errors associated with the trajectory disturbances of the towfish, motion compensation technique using Redundant Phase Center (RPC) and also Phase Gradient Autofocus (PGA) method is investigated. The performances of these two approaches are examined by means of a simulation for SAS system having a sway disturbance.

• 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.

• Journal of Advanced Navigation Technology
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• v.21 no.6
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• pp.593-600
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• 2017

This paper analyzes the performances of direction finding, interference cancellation, and beamforming performance by array antenna pattern measurement distance between the center of array antenna and reference emitter. Array antenna is widely adopted for example as wireless communications, radar, and sonar. In order to use array antenna, array antenna pattern must be known and it can be measured in anechoic chamber. However, the size of anechoic chamber is generally limited. So measurement error of array antenna can be occurred and this could effect performance decrease of direction finding, interference cancellation, and beamforming. It is verified by computer simulation that the performances of direction finding, interference cancellation, and beamforming by array antenna pattern measurement distance.

• The Journal of the Acoustical Society of Korea
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• v.36 no.3
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• pp.179-185
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• 2017

The problem that occurred in the design/fabrication/testing of the wideband transmitting power amplifier for an embedded active SONAR (Sound Navigation and Ranging) system operating underwater was analyzed and the solution of the problem was proposed in this paper. Wideband acoustic SONAR systems had been developed in order to improve the underwater detection performance. The underwater acoustic transmission system had been also developed to achieve the wideband SONAR system. In this paper, the wideband acoustic transmission signal was generated using a 2 Level sawtooth type Class D PWM (Pulse Width Modulation) which was not complicated to implement. When the sonar signals having two or more frequencies were simultaneously generated, parasitic frequencies were added to the original signals by integer multiples of the frequency difference of the original signal. To cope with this problem, we proposed a way to remove the parasitic frequency from the source signal through modeling and simulation of the implemented power amplifier and PWM control hardware using MATLAB and Simulink.

• The Journal of the Acoustical Society of Korea
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• v.42 no.4
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• pp.370-376
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• 2023

In the underwater image, it is not clear to distinguish the shape of the target due to underwater noise and low resolution. In addition, as an input of deep learning, underwater images require pre-processing and segmentation must be preceded. Even after pre-processing, the target is not clear, and the performance of detection and identification by deep learning may not be high. Therefore, it is necessary to distinguish and clarify the target. In this study, the importance of target shadows is confirmed in underwater images, object detection and target area acquisition by shadows, and data containing only the shape of targets and shadows without underwater background are generated. We present the process of converting the shadow image into a 3-mode image in which the target is white, the shadow is black, and the background is gray. Through this, it is possible to provide an image that is clearly pre-processed and easily discriminated as an input of deep learning. In addition, if the image processing code using Open Source Computer Vision (OpenCV)Library was used for processing, the processing speed was also suitable for real-time processing.