• The Journal of the Acoustical Society of Korea
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• v.20 no.2
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• pp.44-51
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• 2001

This Paper the practical echo signal synthesis model to predict the target strength and signal shape of a submarine for a valuable tool to active sonar engineer. It is based on UTAHID (Underwater TArget by Highlight Distribution) model which is relocated highlight points along to external hull for aspect angle, and synthesized echo signal by modified grouping highlights to internal scatter cloud. Proposed model is analyzed target strength characteristics on various incident pulse length, and synthesis signal signature, target time spreading loss, echo elongation effect and so on. Thus it can be efficiently used in various real systems related to underwater target echo signal synthesis, that is, active sonar, acoustic countermeasure and surveillance system.

• Journal of the Korea Institute of Military Science and Technology
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• v.4 no.1
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• pp.93-103
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• 2001

A reflection signal in an active sonar using a high frequency is mainly formed of a specular reflection from the surface of an object along with several equivalent scatters inside, which are characterized by the spatial distribution of the highlight on the object. This study analyze the existing echo signal synthesis models eq, random distribution model, equivalent interval distribution model & MUTAHID(Modified Underwater TArget by HIlight Distribution) model for simulated target, and compare the characteristics of the reflected signal synthesis results for each model in various conditions. These highlight distribution models can be efficiently applied to the simulated target signals synthesis of various real systems requiring the echo signal synthesis on the underwater target.

• The Journal of the Acoustical Society of Korea
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• v.19 no.7
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• pp.15-22
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• 2000

This paper proposes a distributed highlight algorithm to generate efficiently echo signal for underwater target. In this algorithm, echo signal is synthesized by discontinuity highlights that are varied to incident angle, by equivalent and specified position highlights according to the spatial target structure. Completed UTAHID(Underwater TArget by Highlight Distribution) model is confrimed that PTS, ETS, echo elongation effect, target time spreading loss and envelope fluctuation are satisfied to expected values by various simulations. Thus it can be efficiently used in all sorts of real systems related to underwater target echo signal synthesis in active sonar.

• The Journal of the Acoustical Society of Korea
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• v.13 no.2E
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• pp.5-13
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• 1994

Simulation of the target-scattered echo requires the understanding of scattering mechanism at the highlight points. In this paper, the basic assumption of Highlight Model is reviewed through the analyzed data obtained in the acoustic water tank experiment. The analysis shows that the scattering mechanism involves pulse elongation and frequency shift as elements of target-scattered echo, and that the internal structures affect the temporal response of the target-scattered echo significantly. The band-limited impulse response or Green's function due to the diffraction from highlight points of internal structures is not mere delta function, but acts like a filter, which causes frequency shift and is elongated in time.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.7 s.337
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• pp.49-56
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• 2005

In this paper, we describe a solution to improve the effects of the transmitter leakage signals on the frequency modulated continuous wave (FMCW) radar with a single antenna configuration. We analyze characteristics of the IF noise caused by insufficient isolation between transmitter and receiver. The magnitude of the intermediate frequency (IF) noise from a front-end can be reduced by matching the LO signal delay time with that of the largest leakage source. Because the IF noise has periodic singularities at nT$_{m}$/2, t=0,1,2$\cdots$, we find that spectrum of the IF noise due to the leakage signals is very similar to that of the VCO moduation signal except low frequency elements in the vicinity of DC. Based on the studies, we fabricated a W-band homodyne FMCW radar sensor and verified the proposed solution. The results are applicable to design of the homodyne FMCW radar with a single antenna configuration.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.7
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• pp.486-492
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• 2001

We propose a novel optical channel-selective filter whose center wavelength and bandwidth can be fully controlled. The Proposed filter consists of three identical chirped fiber Bragg gratings (CFBG’s) with fiber stretchers which is to control the reflection spectra of the CFBG’s. We experimentally demonstrate that the proposed tunable filter can select arbitrary channels from a WDM signal.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.27 no.1
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• pp.1-12
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• 1991

An experiment has been carefully designed and performed to verify the theory for the echointergration technique of estimating the density of fish school by the use of steel spheres in a laboratory tank. The spheres used to simulate a fish school were randomly distributed throughout the insonified volume to produce the acoustic echoes similar to those scattered from real fish schools. The backscattered echoes were measured as a function of target density at tow frequencies of 50kHz and 200kHz. Data acquisition, processing and analysis were performed by means of the microcomputer-based sonar-echo processor including a FFT analyzer. Acoustic scattering characteristics of a 36cm mackerel was investigated by measuring fish echoes with frequencies ranging from 47.8kHz to 52.0kHz. The fluctuation of bottom echoes caused by the effects of fish-school attenuation and multiple scattering which occurred in dense aggregations of fishes was also examined by analyzing the echograms of sardine schools obtained by a 50kHz telesounder in the set-net's bagnet, and the echograms obtained by a scientific echo sounder of 50kHz in the East China Sea, respectively. The results obtained can be summarized as follows: 1. The measured and the calculated echo shapes on the steel sphere used to simulate a fish school were in close agreement. 2. The waveform and amplitude of echo signals by a mackerel without swimbladder fluctuated irregularly with the measuring frequency. 3. When a collection of 30 targets/m super(3) lied the shadow region behind another collection of 5 targets/m super(3), the mean losses in echo energy for the 30 targets/m super(3) were about -0.4dB at 50kHz and about -0.2dB at 200kHz, respectively. 4. In the echograms obtained in the East China Sea, the bottom echoes fluctuated remarkably when the dense aggregations of fish appeared between transducer and seabed. Especially, in the case of the echograms of sardine school obtained in a set-net's bagnet, the disappearance of bottom echoes and the lengthening of the echo trace by fish aggregations were observed. Then the mean density of the sardine school was estimated as 36 fish/m super(3). It suggests that when the distribution density of fishes in oceans is greater than this density, the effects of fish-school attenuation and multiple scattering must be taken into account as a possible source of error in fish abundance estimates. 5. The relationship between mean backscattering strength (, dB) and target density ($\rho$, No./m super(3)) were expressed by the equations: =-46.2+13.7 Log($\rho$) at 50kHz and =-43.9+13.4 Log($\rho$) at 200kHz. 6. The difference between the experimentally derived number and the actual number of targets gradually decreased with an increase in the target density and was within 20% when the density was 30 targets/m super(3). From these results, we concluded that when the number of targets in the insonified volume is large, the validity of the echo-integration technique of estimating the density of fish schools could be expected.