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이대재,Lee, Dae-Jae 한국수산과학회 2017 한국수산과학회지 Vol.50 No.5
A multi-resonant broadband acoustic transducer with six Tonpilz elements operating at different resonant frequencies in a transducer assembly was fabricated, tested, and analyzed. A compensated transducer, modified by adding series inductance to the developed multi-resonant broadband transducer, was shown to provide improved bandwidth performance with a relatively more uniform frequency response compared with the uncompensated transducer. By controlling the series inductance, flat frequency response characteristics at two frequency bands were obtained over the range 38-52 kHz with 1.1 mH inductance and 50-60 kHz with 0.4 mH inductance. These results suggest that the operating frequency of the developed multi-resonant broadband transducer in a chirp echo sounder can be shifted to a different frequency band that is optimized according to the environment for more effective echo surveys of fishing grounds.
부산 용호만에서 선박용 X-band 레이더에 의한 쇄파의 원격 모니터링
이대재 ( Dae Jae Lee ) 한국어업기술학회 2012 수산해양기술연구 Vol.48 No.3
This paper describes the remote monitoring of breaking ocean waves generated by Typhoon Nabi, whose name means butterfly in Korean, using a marine X-band radar in the Yongho Man, Busan, Korea. The basic purpose of this study is to investigate the dynamic behavior and to estimate the periods of breaking waves across the surf zone from radar image sequences. In these experiments, the land-based radar system imaged the inshore zone of three miles from the coastline to a isobath of 30 meters. The wave period and the dominant wave direction for breaking ocean waves extracted directly from radar image sequences were 157.4 meters and 298 degrees, respectively. However, the result calculated quantitatively by the continuous wavelet transform (CWT) showed that the period of breaking waves was 154.3 meters. The average difference in breaking wave periods between the value extracted by using EBRL (electronic bearing and range line) of radar and the calculated value by CWT was 3.1 meters, showing that the CWT method is also accurate. These results suggest that a marine X-band radar system is a viable method of monitoring the breaking ocean waves.
70 및 120kHz에서 쥐노래미와 감성돔에 대한 음향 반사 강도의 체장 의존성
이대재 ( Dae Jae Lee ) 한국어업기술학회 2012 수산해양기술연구 Vol.48 No.2
Black porgy and fat greenling are commercially important fish species due to the continuously increasing demand in Korea. When estimating acoustically the fish length by a fish sizing echo sounder, it is of crucial importance to know the target strength (TS) to length dependence. In relation to these needs, the target strength experiments for live fishes were conducted in an acrylic salt water tank using two split-beam echo sounders operating at 70 and 120kHz. The target strength under well-controlled laboratory conditions was simultaneously measured with the swimming movement by digital video recording (DVR) system and analyzed as a function of fish length (L) and frequency (or wavelength l). Equations of the form TS-alog (L)+blog (l)+c were derived for their TS-length dependence. The best fit regression of TS on fork length for black porgy was TS〓20.62 log (L, m)-0.62 log (l, m)-30.68 (r 2〓0.77). The best fit regression of TS on fork length for fat greenling was TS〓12.06 log (L, m)-5.85 log (l, m)-22.15 (r 2〓0.44).