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1 Vol. 29(4): Ocean and Polar Research December 2007 Note»» w q w d ½ * Á½ ûá y w w w y ( )» w 29y Measurement of Low-Frequency Ocean Noise by a Self-Recording Hydrophone Bong-Chae Kim *, Byoung-Nam Kim, and Hong Sang Cho Marine Environment Research Department, KORDI Ansan P.O. Box 29, Seoul , Korea Abstract : Ocean noise may be used for monitoring wind speed and rainfall rate on the sea surface, as well as for tracking whales migration routes. In particular, low-frequency ocean noise has recently been of concern with relation to the behavior of marine mammals. Low-frequency ocean noise has been increasing over the past few decades due to increase of ship traffic and offshore oil industry activities. Mechanical noise such as flow noise and cable strumming noise may be induced if low-frequency ocean noise is measured by cabled traditional hydrophone in high current areas. To successfully measure low-frequency ocean noise in a shallow water environment with strong current, we developed a self-recording hydrophone. This paper describes the main configurations of the self-recording hydrophone and presents some results on measured data. Key words : low-frequency ocean noise, self-recording hydrophone, current velocity, wind speed 1. w w w p ùkü x wù q y y w v w. š w ù w k dw ù š (Urick 1983). w w wt t w y d w x š w» w» y š (Lemon 1984; Nystuen 1986; Heimlich et al. 2005). w w 2 z Knudsen et al.(1948) Wenz(1962) w *Corresponding author. bckim@kordi.re.kr š, z w y (Kerman 1988; Kerman 1993; Buckingham and Potter 1995). Andrew et al.(2002) McDonald et al. (2006) q w mw, w m œ ƒ w ƒw š šw. p x š w s yw w š w w (National Research Council 2003).» q w» y w w» d. w w» w f»», e s», f f f l. p w» w ƒyw š šw š. ù

2 312 Kim, B.-C. et al. f» ¼ f rw. (2004) d w tx w y d w š, NOAA ks w y (Pacific Marine Environmental Laboratory) w w w y l w» w x»(moored Autonomous Hydrophones) w. ù l ³ ƒ j» q š. f» w w w w q w d w p w ƒ v w. w Á w w (flow noise) f p (cable strumming noise) k» (Urick 1983). w w w q w d w w» w {»» w.»»» w w. š»» w q w d w š w. 2. w d q w d w w» w Ÿ»»(Kim 2006) šw q»» w.»» Fig. 1 ùkü. Fig. 1 ùkü»»», vl s», y»» e(cpu),,. p» q p š w q ƒ Rqiquˆu s ˆ x gsq q u uˆu r tq qxr qi pu s t p t q f (Bruel and Kjaer) 8103 w.»»» w y w» y y k z, vl s» q 16 Hz y w w s k. š ù y CPU 16 p, 4096 Hz v w» k.»» q p Fig. 2 ùkü.» t»» (½ 2006) w»» w. ü k q w. w»»»z ƒ w d w ü d w y w. Fig. 2 ùkü»» db re 1V/µPa š, q 16~1000 Hz 3dB ü skw. 52 m ûw w w d w. 6x iw pugs gy r tq qxr qi pu s t p t Sitqyg ui ˆuq g g sqyq r yqg u s u yq

3 Measurement of Low-Frequency Ocean Noise by a Self-Recording Hydrophone 313 Fig. 3 ew. w Õ yö l 1 œ»» w ew w d w. š w» w w d z w» w l f» ƒƒ 40 m 20 m e g w d w. w w d w y t, ww w. t (Weather Wizard III 7425) w t d w š, ADCP(Acoustic Doppler Current Profiler; RD Instruments 300) w 5 d w, (C80 48 nm) w 5 ww w. 3 ü www ww 5 30 s³w 1Hz 10~1000 Hz q w w rp w. š Fig. 2 ù kü»» w. 3. š y w d w t Fig. 4 ùkü. z ew w y w. w d w w w 0~0.8 m/s ü w w. p w x 40 m 52 m ƒƒ w d w 20 m w d x w. w d w t 0~4 m/s ü w, w # 5ˆq gsqp iqg u q qi y xqˆqx yw. w e»»( 52 m) d w w rp s³e Fig. 5 ùk ü. š 40 m 20 m e k f» d w w s³e ùkü. d w d (Andrew et al. 2002) w ùkû. š q 64~1000 Hz»» d w w rp f» d w w w. ù q 10~63 Hz»» d w w rp f» d w w 3~25 db û ùkû. p w w q 10~25 Hz x w.»» d w w rp s³e t r Fig. 6 " Vg ug u r i q ˆqx iu g p u p qqp u t g p g pg ppqˆug u r iqg u q qi y xqˆqx

4 314 Kim, B.-C. et al. ƒƒ q w w s³e t r 2 w ùküš. š 40 m 20 m e k f» d w w rp s³e t r ùkü. q 60~ 1000 Hz»» d w w rp t r f» d w w t r w. ù q 10~60 Hz»» d w w rp t r f» d w w t r û ùkû. š»» w rp t r q 10~20 Hz 50~1000 Hz w q 20~50 Hz d. ù f» w rp t r q 40~1000 Hz w q 10~40 Hz ùkû. Fig. 4 Fig. 5 ùkü w d w, p w x q 10~63 Hz»» d w w f» d w w w û ùkû. w w» w p q w t w.» p q»»» d w ƒ w 20 Hz ƒ 100 Hz ƒƒ w. w q 20 Hz 100 Hz ƒƒ w Fig. 7 ùkü. š w w xz w (r) t w. w, q 100 Hz w ùkû. ù q 20 Hz»» d w, f» d w ùkû.»» w d w, f» w w f p y w d w ƒ. t w q 20 Hz 100 Hz ƒƒ w Fig. 8 ùkü. š w t w xz w (r) t w. Fig. 8 w, t 4m/s w w t w % Iiqg u q xqˆqx g qxqi qp r qƒ q iuq ˆq i q ˆqx iu d ƒ w, q 20 Hz 100 Hz ƒ ƒ w t ùkû. w q 500 Hz~50 khz w j š š (Urick 1983), Fig. 8 w ew ƒ. Fig. 4 Fig. 5 ùkü q 10~ 63 Hz f» d w w»» d w w w ùkû, f» w w w w» q. w w w q w d

5 Measurement of Low-Frequency Ocean Noise by a Self-Recording Hydrophone 315 d w.»» w d w yw w, yw q w d e œw. p»» q 10~63 Hz w yw d w w f» w w f p w w yw d w.»» w w w q w y d w. mw š w w Ì ¾. š & Iiqg u q xqˆqx g qxqi qp r qƒ q iuq ˆq u p qqp w f» w f p w p w ƒ v w. š»»ƒ w ƒ. 4. q w d w w» w»» w. ûw w»» w q w d w. š z w» w f» w q w ½ {» l. w wwz, 25, vy, x x tx w y d. 5z w» ù. w, Andrew, R.K., B.M. Howe, J.A. Mercer, and M.A. Dzieciuch Ocean ambient sound: Comparing the 1960s with the 1990s for a receiver off the California coast. Acoust. Res. Lett. Online, 3, Buckingham, M.J. and J.R. Potter Sea Surface Sound '94 - Proceedings of the III International Meeting on Natural Physical Processes Related to Sea Surface Sound. World Scientific, Singapore. Heimlich, S.L., D.K. Mellinger, S.L. Nieukirk, and C.G. Fox Types, distribution, and seasonal occurrence of sounds attributed to Bryde's whales(balaenoptera edeni) recorded in the eastern tropical Pacific, J. Acoust. Soc. Am., 118, Kerman, B.R Sea Surface Sound - Natural Mechanism of Surface Generated Noise in the Ocean. Kluwer, Dordrecht. Kerman, B.R Natural Physical Sources of Underwater Sound - Sea Surface Sound(2). Kluwer, Dordrecht. Kim, B.-C.G Development of a broadband selfrecording hydrophone. Ocean & Polar Res., 28, Knudsen, V.O., R.S. Alford, and J.W. Emling Underwater ambient noise. J. Mar. Res., 7, Lemon, D.D., D.M. Farmer, and D.R. Watts Acoustic measurements of wind speed and precipitation over a

6 316 Kim, B.-C. et al. continental shelf. J. Geophys. Res., 89, MacDonald, M.A., J.A. Hildebrand, and S.M. Wiggins Increases in deepg ocean ambient noise in the Northeast west of San Nicolas Island, California. J. Acoust. Soc. Am., 120, Moored Autonomous Hydrophones. < gov/vents/acoustics/haru_system.html>. National Research Council Ocean Noise and Marine Mammals. National Academy Press, Washington, DC. Nystuen, J.A Rainfall measurements using underwater ambient noise. J. Acoust.G Soc. Am., 79, Urick, R.J Principles of Underwater Sound. Peninsula Publishing, Los Altos. Wenz, G.M Acoustic ambient noise in the ocean: Spectra and sources. J. Acoust. Soc. Am., 34, Received Nov. 7, 2007 Accepted Dec. 11, 2007