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Estimation on Audibility of Large Cetaceans for Improvement of the Under Water Speaker

100%

Yamada H. , Kagami L. , Yonehara Y. , Matsunaga H. , Kato H. , Terada M. , Takahashi R. , Okanoya K. , Kawamoto T.

tom Vol. 6, no. 4

589--593

In order to avoid collisions between the hydrofoil (HF) and cetaceans, the Under Water Speaker (UWS) has been installed on the HF. Because of its potential in utility, we tried to improve the UWS to minimize the risk of the collisions. Under our project, we examined three subprojects; 1) Analyzing the characteristics of the HF underwater noise; 2) Assessing audibility of major large cetaceans by measuring their vocalizations and 3) An anatomical prediction of the audible range by examining the cochlear basal membrane. Through the analyses, it was identified that the noise produced by the HF was a broad-band noise with approximately 150dB re 1μPa-m.That noise level was lower than those of larger boats suggesting difficulties for cetaceans in sensing approach of the vessels. In addition, analysis of their vocalizations and anatomical obervation indicated that dominant frequency of their audible range was lower than signals produced by the existing UWS.

Ship's underwater noise measurements using sound intensity method

100%

Gloza I.

tom Vol. 12

53-60

Ship noise is a most important part of the field of underwater acoustics. Its reduction and monitoring is an important aspect in the performance of underwater acoustic systems and in the habitability of the vessel for the crew and passengers. In naval operations the noise radiated by a ship is also dominant source of information for underwater sonar systems. Sound intensity is the vector quantity which informs us about the sound power flux, the position and the direction of the sound source. The probe tracks the position of source and at the same time, measures the component of sound-intensity vector. Generally only one component of vector sound intensity was measured, perpendicular to a given measurement surface. The sound intensity of a moving source includes effects such as flow noise that are not present when the source is stationary. The accuracy of measuring acoustic intensity using two closely spaced hydrophones by correcting the phase mismatch error by measuring the transfer function between the two detector systems was examined. The two measuring hydrophone instrumentation systems were earlier calibrated. Our results have been obtained using digital methods, where was used PULSE measuring system.

Impact of salinity on the underwater noise generated by small scale air entrainment events

100%

Szuszkiewicz J. , Klusek Z. , Gorska N.

tom Vol. 20

167--172

Some part of the energy released in the wave breaking process is transformed into the energy of the noise. This sound depends on the water properties, however, there is a lack of reliable data concerning the underwater noise generated by less energetic events. The aim of this study was to understand the impact of salinity on the underwater noise produced during small scale air entrainment events, typical for low wind speed conditions. The tipping trough experiment was performed in a small tank to generate the small scale air injections. Four, linearly placed hydrophones HTI-96-MIN were used to record the acoustic noise accompanying this phenomenon. The bubble plume development, and underwater noise spectra, were compared for salty and fresh water. The potential energy of the modeled events resulted in different spectra, and salinity played an essential role in the emitted underwater noise.

Observations on relations between marine aerosol fluxes and surface-generated noise in the Southern Baltic Sea

63%

Markuszewski P. , Klusek Z. , Nilsson E. D. , Petelski T.

tom 62

nr 4PA