• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.44 no.1
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• pp.37-45
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• 2008

Assessment and management of fisheries abundance in fresh water like a river or a lake is very important to maintain fisheries itself as well as tourist industry even if their scale is not much large. The species for catch in fresh water are mainly a mandarin fish, a carp, an eel, and others. Because oriental river prawn is a main prey of these species and the change in its abundance is directly related to their abundance change in fresh water, information on the abundance and distribution of the species are necessary. Hydroacoustic survey is known to one of the efficient method among several methodology. Information on acoustic target strength is key parameter to estimate abundance for acoustic survey. In this study, measurements on oriental river prawn, Macrobrachium koreana, were conducted for two high frequencies(200kHz and 420kHz) with tilt angle using automatic rotating system. The results of acoustic target strength obtained from the experiment were compared with those of acoustic scattering model, Distorted Wave Born Approximation(DWBA) model. For 200kHz, the result of acoustic target strength experiments was expressed in terms of the averaged target strength dependence on the body langth(BL, cm) as a following relationship; < $TS_{200kHz}$ > = 45.9log(BL) - 107.4. These results provide basic information for studying acoustic target strength and conducting acoustic survey of oriental river prawn.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.38 no.4
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• pp.265-275
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• 2005

A prerequisite for deriving the abundance estimates from acoustic surveys for commercially important fish species is the identification of target strength measurements for selected fish species. In relation to these needs, the goal of this study was to construct a data bank for converting the acoustic measurements of target strength to biological estimates of fish length and to simultaneously obtain the target strength-fish length relationship. Laboratory measurements of target strength on 15 commercially important fish species were carried out at five frequencies of 50, 70, 75, 120 and 200 kHz by single and split beam methods under the controlled conditions of the fresh and the sea water tanks with the 389 samples of dead and live fishes. The target strength pattern on individual fish of each species was measured as a function of tilt angle, ranging from $-45^{\circ}$ (head down aspect) to $+45^{\circ}$ (head up aspect) in $0.2^{\circ}$ intervals, and the averaged target strength was estimated by assuming the tilt angle distribution as N $(-5.0^{\circ},\;15.0^{\circ})$. The TS to fish length relationship for each species was independently derived by a least-squares fitting procedure. Also, a linear regression analysis for all species was performed to reduce the data to a set of empirical equations showing the variation of target strength to a fish length, wavelength and fish species. For four of the frequencies (50, 75, 120 and 200 kHz), an empirical model for fish target strength (TS, dB) averaged over the dorsal sapect of 602 fishes of 10 species and which spans the fish length (L, m) to wavelength (\Lambda,\;m)$ ratio between 5 and 73 was derived: $TS=19.44\;Log(L)+0.56\;Log(\Lambda)-30.9,\;(r^2=0.53)$.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.812-819
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• 2007

Acoustic Target Strength (TS) is a major parameter of the active sonar equation, which indicates the ratio of the radiated intensity from the source to the re-radiated intensity by a target. This research provides the time pattern of TS in time domain, which is applicable to pulse modulated acoustic pressure field. If the time pattern of TS is predicted by using TS equation in frequency domain, it takes long time and difficult since time function pulsed acoustic wave may be decomposed into their frequency domain components. But TS equation in time domain has a convenience. If the expression for pulsed acoustic field has been obtained, the problem can be solved. Furthermore this paper introduces about mathematical equivalence quantities between EM wave and Acoustic Wave.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.39 no.3
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• pp.239-248
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• 2003

This paper was conducted as an attempt in order to construct the data bank of target strength for acoustic estimation of fish length in the coastal waters of Korea. The fish length dependence of acoustic target strength for 13 large yellow croakers (Pseudosciaena crocea) at 75 kHz was investigated and the prediction of the target strength by using the Kirchhoff-Ray Mode model (KRM model) was compared with target strength measurements. The results obtained are summarized as follows; 1. In the averaged target strength pattern for 13 large yellow croakers the maximum target strength was -35.13 dB at $-13.35^{\circ}$ on a tilted angle. 2. The relationship between fork length(L, cm) and averaged target strength(TS, dB) was expressed as follows; TS=23. 76log (L) -73.45 (r=0.47) TS=20log(L) -67.35 From this result, the conversion coefficient was -73.45 dB and 6.1 dB lower than the coefficient -67.35 dB where the value of the slope of the regression equation is forced to be 20. 3. Averaged target strength and a length conversion coefficient derived from a target strength histogram for 13 large yellow croakers of mean length 25.59 cm were -41.23 dB, -69.72 dB, respectively. 4. In the range of $$2;{\ll} L (fish length /{\lambda}(wave length);{\ll}40$$, the prediction of the averaged target strength by the KRM model increased gradually with the increasing of $L/{\lambda}$ and was lower than the measured target strength.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.5 s.143
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• pp.528-533
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• 2005

A mono-static high frequency acoustic target strength analysis scheme was developed for underwater targets, based on the far-field Kirchhoff approximation. Au adaptive triangular beam method and a concept of virtual surface were adopted for considering the effect of hidden surfaces and multiple reflections of an underwater target, respectively. A test of a simple target showed that the suggested hidden surface removal scheme is valid. Then some numerical analyses, for several underwater targets, were carried out; (1) for several simple underwater targets, like sphere, square plate, cylinder, trihedral corner reflector, and (2) for a generic submarine model, The former was exactly coincident with the theoretical results including beam patterns versus azimuth angles, and the latter suggested that multiple reflections have to be considered to estimate more accurate target strength of underwater targets.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.2
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• pp.196-209
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• 2010

For the analysis of Acoustic Target Strength(TS) that indicates the scattered acoustic intensity from the underwater vehicles, an analysis program that is applicable to scatterers insonified by spherical wave source in near field is developed. In this program, the Physical Optics(PO) method is embedded as a base component. To increase the accuracy of the program, multiple bounce effects based on Geometrical Optics(GO) method are applied. To implement multiple bounce effects, GO method is used together with PO method. In detail, GO method has a concern in the evaluation of the effective area, and PO method is involved in the calculation of Acoustic Target Strength for the final effective area that is evaluated by GO method. For the embodiment of near field spherical wave source originated multiple bounce effects, image source concept is implemented additively to the existing multiple bounce algorithm which assumes plane wave insonification. Various types of models are tested to evaluate the reliability of the developed program and finally, a submarine is analyzed as an arbitrary scatterer.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.46 no.3
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• pp.248-256
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• 2010

Acoustic side-aspect target strength (TS) of living Japanese anchovy (Engraulis japonicus) was measured at 120kHz during in situ experiments. The data were collected by lowering and horizontally projecting the splitbeam transducer into the anchovy school. For analysis and interpretation of the side-aspect TS data, acoustic theoretical model, based on the fish morphology, and dorsal-aspect TS data were used. Total length of the anchovy ranged from 6.6 to 12.8cm (mean length 9.3cm). The side-aspect TS distributed between -40 and -55dB, has an obvious length dependency. The mean side-aspect TS of the anchovy was -47.8dB, and the TS was about 2dB higher than mean TS generated from dorsal-aspect measurements. With reference to maximum TS, the results of the side-aspect TS were distributed within the range of the theoretical and dorsal-aspect TS. Apparently these tendency indicates that side-aspect TS measured from the study is useful data. These in situ measurements of side-aspect TS can be applied to improve acoustic detection and estimates of the anchovy, and is necessary to measure with a various frequency and length for making enhance data.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.51 no.5
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• pp.566-570
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• 2018

This study determined the acoustic target strength (TS; dB) of black seabream Acanthopagrus schlegeli off the southern coast of Korea. For the ex-situ measurements, 200 kHz split beam transducers were used, and a Kirchhoff-ray mode (KRM) model acoustic model was used for the calculation. The fork length and total weight of the black seabream ranged from 6.4 to 30.8 cm and 6.4 to 683.8 g. respectively 200 kHz, the TS could beexpressed as a function of fork length as: $TS_{max}=20log_{10}(FL)-60.35(R=0.92)$ and $TS_{avg.}=20log_{10}(FL)-66.89(R=0.88)$. These TS results for black seabream can be used for estimating the biomass of fish in acoustic surveys in coastal areas.

• International Journal of Ocean System Engineering
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• v.3 no.3
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• pp.158-163
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• 2013

The acoustic target strength (TS) is one of the most important parameters for a submarine's stealth design. Because modem submarines are larger than their predecessors, TS must be managed at each design stage in order to reduce it. To predict the TS of a submarine, TASTRAN R1 was developed based on a Kirchhoff approximation in a high-frequency range. This program can present TS values that include multi-bounce effect in the exterior and interior of the structure by combining geometric optics (GO) and physical optics (PO) methods, anechoic coating effect by using the reflection coefficient, and response time pattern for a detected target. In this paper, TS calculations for a submarine model with the above effects are simulated by using this developed program, and the TS results are discussed.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.41 no.4
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• pp.296-305
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• 2005

Acoustic target strength (TS) of 12 commercially important fish species caught in the Korean waters had been investigated and their results were presented. Laboratory measurements of target strength on 12 dominant fish species were carried out at a frequencies of 75 kHz by single beam method under the controlled condition of the water tank with the 241 samples of dead and live fishes. The target strength pattern on individual fish of each species was measured as a function of tilt angle, ranging from $-45^{\circ}$ (head down aspect) to $45^{\circ}$ (head up aspect) in $0.2^{\circ}$ intervals, and the averaged target strength was estimated by assuming the tilt angle distribution as N ($-5.0^{\circ}$, $^15.0{\circ}$). The 75 to fish length relationship for each species was independently derived by a least - squares fitting procedure. Also, a linear regression analysis for all species was performed to reduce the data to a set of empirical equations showing the variation of target strength to fish length and fish species. An empirical model for fish target strength(TS, dB) averaged over the dorsal aspect of 158 fishes of 7 species and which spans the fish length(L, m) to wavelength(${\lambda}$, m) ratio between 6.2 and 21.3 was derived: TS: 27.03 Log(L)-7.7Log(${\kanbda}$)-17.21, ($r^2$=0.59).