• 수산해양기술연구
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• 제46권3호
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• pp.239-247
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• 2010

Species of fish such as striped beakperch, bluefin searobin and konoshiro gizzard shad are commercially very important due to their high demand in the Korean market. When estimating acoustically the abundance of stocks for these species, it is of crucial importance to know the target strength (TS) to the length dependence. In relation to these needs, the TS experiments were conducted on three different species in an acrylic salt water tank using two split-beam echo sounders of 70 and 120 kHz. The TS for these three species under the controlled condition was simultaneously measured with the swimming movement by a DVR system and analyzed as a function of fish length (L) and frequency (or wavelength $\lambda$). The equation of the form TS=a log (L)+b log ($\lambda$)+c was derived for their TS-length dependence. The best fit regression of TS on fork length for striped beakperch was estimated as TS=35.67 log (L, m) -15.67 log ($\lambda$, m) -46.69 ($r^2$=0.78). Furthermore, the best fit regression of TS on fork length for konoshiro gizzard shad was shown to be TS=25.85 log (L, m) -5.85 log ($\lambda$, m) -32.22 ($r^2$=0.51). The averaged TS for 12 bluefin searobins with a mean length of 24.36cm at 70 kHz was analyzed to be -41.55dB. In addition, the averaged tilt angle obtained simultaneously by a DVR system with TS measurements for 27 konoshiro gizzard shads swimming within an acrylic salt water tank was estimated at $-2.7^{\circ}$.

• Fisheries and Aquatic Sciences
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• 제12권2호
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• pp.152-161
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• 2009

The largehead hairtail (Trichiurus lepturus) is one of the most common fisheries stocks in the East China Sea and the Yellow Sea. The species is caught using a variety of fishing tools, such as a stow net or a long line, as well as jigging and trawling. Scientific investigations have been conducted throughout the world to enable evidence-based estimations for the management and protection of the main fisheries biomass. For example, inshore and offshore hydro acoustic surveys are performed annually using bottom- and mid-water trawls around the Korean Peninsula. However, to date, no acoustic survey has been conducted to estimate fish size distribution, which is necessary to construct a data bank of target strength (TS) relative to fish species, length (L), and frequency. This study describes the frequency and length dependence of TS among fishes in Korean waters for the purpose of constructing such a TS data bank. TS measurements of the largehead hairtail were carried out in a water tank (L 5 m$\times$width 6 m$\times$ height 5 m) at frequencies of 50, 75, 120, and 200 kHz, using a tethering method. The average TS patterns were measured as a function of tilt angle, ranging from $-45^{\circ}$ (head down) to $+45^{\circ}$ (head up) every $0.2^{\circ}$. The length conversion constant ($b_{20}$) was estimated under the assumption that TS is proportional to the square of the length. In addition, in situ TS measurements on live largehead hairtails were performed using a split beam echo sounder.

• 한국정보통신학회논문지
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• 제21권1호
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• pp.157-164
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• 2017

본 연구는 균일한 조명을 얻기 위해 중첩 조명 모델(overlapped illumination model)을 사용하여 자유 형상 렌즈(freeform lens)를 제작하였으며, 제작한 LED 렌즈들의 특성을 비교 분석하였다. 제작한 렌즈는 LED 광원의 위치변화, 두께 및 기울임을 이용해 성능을 평가하였다. 아울러 조명영역은 평균 조도 (average illuminance)와 조도 균일도 (illuminance uniformity) 변화 값으로 측정하였다. 광도 분포의 Z축 방향변화에 대해서는 중첩 모델과 발산 모델이 대체로 비슷한 공차 특성을 보였으나, 렌즈두께 변화에 대해서는 중첩모델이 발산모델에 비해 조도 균일도 공차 특성은 현저히 개선됨을 확인하였다. 또한, 발산 조명 모델로 설계된 렌즈가 전반적으로 좋은 성능을 나타냈으나, LED 방출에 대한 성능은 중첩 모델에서 그 편차의 폭이 상대적으로 적게 나타났다.

• Fisheries and Aquatic Sciences
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• 제17권3호
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• pp.361-367
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• 2014

Cuttlefish Sepia esculenta are commercially important in Korea. Assessments of their biomass currently depend on fishery-landings data, which may be biased. Towards fishery-independent acoustic surveys of cuttlefish, target strength (TS) measurements at 70 and 120 kHz were made of 23 live cuttlefish, in early May 2010. The fish were caught by traps in the inshore waters around Geojedo, Korea. The TS were measured using split-beam echosounders (Simrad ES60 and EY500, respectively). The cuttlefish mantle lengths (L) ranged from 15.6 to 23.5 cm (mean L=17.8 cm) and their masses (W) ranged from 335 to 1020 g (mean W=556.1 g). Their mean TS values at 70 and 120 kHz were -33.01 dB (std=1.39 dB) and -31.76 dB (std=2.15 dB), respectively. The mean TS at 70 kHz was 0.17 dB higher than the TS-length relationship resulting from a least-squares fit to the data ($TS=24.67{\log}_{10}L(cm)-64.03$, $r^2$ = 0.52, N=23). The mean TS at 120 kHz was 0.45 dB higher than the fitted TS-length relationship ($TS=40.59{\log}_{10}L(cm)-82.96$, $r^2$ = 0.58, N=23). The differences between the mean TS values and an equation regressed from all of the TS measurements at both frequencies ($TS=24.92{\log}_{10}L(cm)-4.92{\log}_{10}{\lambda}(m)-22.82$, $r^2$ = 0.86, N=46) was 0.22 dB at 70 kHz and 0.31 dB at 120 kHz, respectively.

• Fisheries and Aquatic Sciences
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• 제19권2호
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• pp.8.1-8.11
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• 2016

To quantitatively estimate the influence of cuttlebone on the target strength (TS) of golden cuttlefish, the cuttlebone was carefully extracted from 19 live cuttlefish caught using traps in the inshore waters around Geojedo, Korea, in early May 2010 and the TS was measured using split-beam echosounders (Simrad ES60 and EY500). The TS-length relationships for the cuttlefish (before the extraction of cuttlebone, Fish Aquat Sci. 17:361-7, 2014) and the corresponding cuttlebone were compared. The cuttlebone length ($L_b$) ranged from 151 to 195 mm (mean $L_b$ = 168.3 mm) and the mass ($W_b$) ranged from 29.3 to 53.2 g (mean $W_b$ = 38.8 g). The mean TS values at 70 and 120 kHz were -33.60 dB (std = 1.12 dB) and -32.24 dB (std = 1.87 dB), respectively. The mean TS values of cuttlebone were 0.19 dB and 0.04 dB lower than those of cuttlefish at 70 and 120 kHz, respectively. For 70 and 120 kHz combined, the mean TS value of cuttlebone was -32.87 dB, 0.11 dB lower than that of cuttlefish (-32.76 dB). On the other hand, the mean TS value of cuttlebone predicted by the regression ($TS_b$ = 24.86 $log_{10}$ $L_b$ - 4.86 $log_{10}$ ${\lambda}$ - 22.58, $r^2$ = 0.85, N = 38, P < 0.01) was -33.10 dB, 0.04 dB lower than that of cuttlefish predicted by the regression ($TS_c$ = 24.62 $log_{10}$ $L_c$ - 4.62 $log_{10}$ ${\lambda}$ - 22.64, $r^2$ = 0.85, N = 38, P < 0.01). That is, the contribution of cuttlebone to the cuttlefish TS determined by the measured results was slightly greater than that by the predicted results. These results suggest that cuttlebone is responsible for the TS of cuttlefish, and the contribution is estimated to be at least 99 % of the total echo strength.

• 대한전자공학회논문지TC
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• 제41권7호
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• pp.81-88
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• 2004

안테나의 기계적 다운 틸팅의 경우에 있어서, 틸팅각이 커지게 되면 수평 패턴의 왜곡 및 수평 빔폭의 증가 현상이 발생한다. 이는 핸드 오프 영역의 증가 및 기지국의 부하 증대를 유발한다. 이에 반해 전기적인 다운 틸팅은 틸팅 시에도 수평 빔폭이 일정하게 유지된다는 장점을 갖는다. 본 논문에서는 위상 배열 안테나 기술을 적용하여, 전기적인 다운 틸팅 기능을 갖는 800㎒ 대역의 이중 편파 기지국 안테나를 개발하였다. 이 안테나는 15㏈i의 이득과 0°∼14°의 다운 틸팅 범위를 갖는다. 복사 소자로는 적층형 마이크로스트립 패치 안테나를 사용하였으며, 단자간 분리도 및 교차 편파 특성 개선을 위하여 balanced feed technique을 적용하였다. 개발된 안테나에 대한 필드 테스트를 수행하였으며, 이를 통해 전기적 다운 틸팅 안테나의 효과를 확인하였다.

• 한국광학회지
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• 제8권3호
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• pp.230-235
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• 1997

광섬유의 단면을 적절한 곡률의 곡면으로 가공함으로써 종래 구조에 비해 우수한 특성의 광섬유 Fabry-Peror(FP)간섭 필터를 제작할 수 있음을 이론적으로 분석하였다. 광섬유 단면의 가공된 오목거울의 곡률은 계단형 단일모드 광섬유의 도파모드를 Gaussian빔으로 가정했을 때 광섬유에서 나와 일정거리의 자유공간을 진행한 빔의 파면의 곡률과 일치하여야 하며, 이때 거울의 기울기 0.2.deg., 곡률오차 70.mu.m, 공극거리 오차 8.mu.m, 광축의 횡편차 0.5.mu.m이내의 범위에서 이상적인 배치를 벗어난 경우에도 광섬유간의 거리가 15.mu.m일 때 0.5%이하의 결합손실을 가져 종래에 비해 훨씬 간단한 새로운 구조의 광섬유 FP필터가 제작될 수 있음을 확인하였다. 마지막으로 곡면가공된 광섬유 단면의 간섭파형을 통하여 광섬유 단면을 의도된 구조로 가공할 수 있음을 보였다.