Infrasonic Noise Measurements in Ocean Using Screened Hydrophones

Effects of screening a hydrophone with open-cell foams are determined to reduce the level of infrasonic background noise, which is the self-noise probably induced by the presence of flow around the hydrophone, in shallow and deep seas. The result obtained in shallow sea with bottom-mounted geometry shows that the level of background noise could be reduced by more than 20 dB below 10 Hz if the hydrophone is screened. Also, the result of ship noise measurement conducted in deep sea with drifting geometry shows that a maximum background noise reduction of 15 dB could be achieved in the infrasonic band without affecting the true acoustic signals. (C) 2010 The Japan Society of Applied Physics