2019_programme: ACOUSTIC NOISE MEASUREMENT OF VESSELS WITH ADAPTIVE CHANNEL EQUALIZATION

• Session: 02. Underwater acoustic calibration, testing, facilities and standards
  Organiser(s): Robinson Stephen, Humphrey Victor, Linné Markus, Évora Victor
• Lecture: ACOUSTIC NOISE MEASUREMENT OF VESSELS WITH ADAPTIVE CHANNEL EQUALIZATION
  Paper ID: 768
  Author(s): Hovem Jens M, Dong Hefeng
  Presenter: Hovem Jens M
  Presentation type: oral
  Abstract: This contribution reports on recent measurements and analysis of acoustic noise of fishing vessels. The measurements were conducted according to internationally accepted standards with a hydrophone close to the bottom and with the vessel following straight tracks of 1-2 km and passing the hydrophone at a distance of about 100- 200 m distance. The motivation for the study was partly to confirm that the noise is lower than acceptable level and partly to investigate the propagation of low frequency 100-300 Hz the frequency band of species, as codfish are most sensitive to anthropogenic noise. \nThe measurements confirms that with a shallow source, as a surface vessel, the Lloyd mirror effect is very important for the propagation of self-noise and therefore important for fishing. The effect is caused by interference between a direct arrival and a surface reflected arrival. At short ranges this interference results in rapidly varying noise level, but at longer ranges the noise level decays with range (r) at a rate of 40 log(r). \nNormally the noise measurements are corrected for the propagation loss from the vessel to the hydrophones by assuming spherical spreading of 20 log(r) or in some cases 18 log(r). This method for distance correction has serious weaknesses since it does not take into account the varying oceanographic conditions and frequency dependency. A novel technique is presented for adaptive calibration for the Lloyd mirror effects in noise measurement of noise from surface vessels. This technique uses a probe signal and signal processing combined with advanced propagation modeling to estimate the actual underwater acoustic channel thereby reducing the distortion effects on the measured noise spectrum. The paper presents the concept and demonstrates the feasibility by a simulated example.\n
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• Corresponding author: Mr Hovem Jens M
  Affiliation: Norwegian University of Science and Technology, Trondheim Norway
  Country: Norway
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