• The Journal of the Acoustical Society of Korea
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• v.15 no.4
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• pp.65-69
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• 1996

In this paper, the techniques for target state analysis based on a single ping in the ocean environment are proposed and discussed. The first method utilizes the relationship between range and bearing in order to determine the aspect angle of target. The second method uses the Range-Doppler Map. The former method requires the multi-channel data, while the latter uses single channel data. It is concluded, from the simulation, that the target state analysis is quite possible and the techniques mentioned should be used simultaneously to get the improved results.

• The Journal of the Acoustical Society of Korea
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• v.28 no.8
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• pp.755-760
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• 2009

In this paper, we apply a reverberation suppression method using difference of singular values to improve the short-distance underwater obstacle detection probability in reverberation environment induced by a linear frequency modulation signal. The reverberation suppression method using difference of singular values suppresses LFM reverberation based on subtracting the singular values for a reference beam, assumed to contain only the reverberation, from those for the current beam of interest, assumed to contain the reverberation and target echo. For the validation, the reverberation suppression method using difference of singular values is applied to real oceanic data, which are acquired using the cross type array.

• The Journal of the Acoustical Society of Korea
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• v.26 no.3
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• pp.129-135
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• 2007

In this paper. we propose a prewhitening method for the km reverberation to enhance the target signal. The proposed algorithm uses the dechirping method which inversely compensates the frequency chirp rate of LFM and transforms the LFM reverberation to have stationary frequency property in each data block. Also, using the left and right adjacent beam signals as reference signals. we model frequency response of each data block by AR coefficients. From these coefficients, we implement inverse filter and prewhiten the LFM reverberation of the center beam efficiently.

• The Journal of the Acoustical Society of Korea
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• v.36 no.5
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• pp.353-360
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• 2017

The single sensor based acoustic reflection control system separates the incident and reflected signals from the single sensor output, and reduces the reflected signal by generating an out-of-phase signal from the incident signal component. In this paper, we propose an optimal filter design method for a single sensor based reflection control system. In the proposed method, it is shown that the optimum control filter design is possible by using the measured impulse responses of the reflection and control paths. The reflection control algorithm based on the proposed optimal filter achieves better performance than the conventional adaptive filter-based algorithm and effectively controls the reflection without the initial convergence time. We performed computer simulations using the signals obtained in a 1-dimensional acoustic duct environment, and from the simulation results, it was confirmed that the proposed optimal filter has robust performance even in noisy environment.

• Journal of Ocean Engineering and Technology
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• v.19 no.1 s.62
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• pp.64-70
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• 2005

Target Strength(TS) is an important factor for the detection of the target in an active sonar system: thus the numerical model for the prediction of TS is widely being developed. For the frequency range of several kHz, the most important scattering mechanism is known to be specular reflection, which is largely affected by the geometrical shape of the target. In this paper, a numerical algorithm to predict TS is developed based on the Kirchhoff approximation which is computationally efficient. The developed algorithm is applied to the canonical targets of simple shapes, for which the analytical solutions exist. The numerical results show good agreement with the analytical solutions. Also, the algorithm is applied to more complex scatterers, and is compared with the experimental data obtained in the water tank experiment for the purpose of verifying the developed numerical model. Discussions on the effect of spatial sampling and other aspects of numerical m odeling are presented.

• The Journal of the Acoustical Society of Korea
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• v.26 no.2
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• pp.87-94
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• 2007

In active sonar system, aspect angle and length of a target can be estimated by calculating the cross-correlation between left and right split-beams of a LFM(Linear Frequency Modulated) signal. However, high-resolution performances in bearing and range are required to estimate the information of a remote target. Because a certain higher sampling frequency than the Nyquist sampling frequency is required in this performance, an over-sampling process through interpolation method should be required. However, real-time implementation of split-beam processing with over-sampled split-beam outputs on a COTS(commercial off-the-shelf) DSP platform limits its performance because of given throughput and memory capacity. This paper proposes a cumulative processing algorithm for split-beam processing to solve the problems. The performance of the proposed method was verified through some simulation tests. Also, the proposed method was implemented as a real-time system using an ADSP-TS101.

• The Journal of the Acoustical Society of Korea
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• v.20 no.6
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• pp.17-25
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• 2001

Traditional adaptive noise cancelling methods rely their performance on various interfering parameters, such as convergence speed, tracking ability, numerical stability, relative frequency characteristics between target and reverberation signals, and activity of the target. In this paper, an adaptive noise cancelling method is suggested, which Provides a successful tradeoff mon these factors. It is designed to work on the transform domain, adopts the Gram-Schmidt orthogonalization process, and is implemented by the escalator algorithm. The transform domain approach supports a tradeoff between the convergence speed and numerical cost. The proposed method is verified by applying a real-data collected in the shallow waters off the east coasts of korea. It is shown that it has a good reverberation-rejection capability even for the target signal with adjacent frequency components to those of the reverberation, and its performance is invariant for the activity of the target.

• The Journal of the Acoustical Society of Korea
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• v.33 no.3
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• pp.174-183
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• 2014

When a active sonar signal is transmitted and returned back from a target, it has been distorted by various properties of acoustic channel such as multipath arrivals. And signals have been appeared to be different form by target position and attitude. Therefore, we simulated the target echo signal using 3 dimensional target model include reflects target features. In this paper, we develop components form of a simulated target model is made up equally spaced highlight points, and each part of the target consists of shape function. We can simulate a target echo signal and Target strength (TS) according to wave incident angle. To verify, we made small scale target in kit form and we had got underwater target signal for comparing simulation result in water tank.

• 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.

• Journal of Korea Society of Industrial Information Systems
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• v.24 no.5
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• pp.95-104
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• 2019

In this paper, we propose a method to design a generalized sinusoidal frequency modulated(GSFM) pulse that is robust to reverberation environment. GSFM pulses are a generalized form of SFM(Sinusoidal frequency modulated) pulses, which have the advantage of having a thumbtack ambiguity function with excellent range and Doppler resolution. However, the periodicity disappears during the generalization process, therefore, the detection performance is reduced in reverberation environment compared to SFM pulse with comb spectrum. In this paper, the trade-off relationship between the reverberation suppression performance of the SFM pulse and the range resolution performance of the GSFM pulse is analyzed by appropriately changing the parameter ${\rho}$ of the GSFM pulse. In order to verify the performance of the proposed GSFM pulse, the simulation was performed and it was confirmed that the proposed GSFM pulse has excellent distance resolution while detecting the slow Doppler target.