Abstract
Noise is one of the important problems for hydroacoustic surveys of fisheries resources, because it may cause a large error in estimated results and it may shorten detectable range. It is necessary to estimate and reduce the contribution of acoustic noise for precise and accurate surveys. Noise is classified into low-frequency noise (audible by fish) and high-frequency noise (affecting echo sounders). High-frequency noise usually results in an overestimate of acoustic return. The average power of the high-frequency noise was measured by the echo-integrator. The echo-integrator output was converted into the equivalent noise spectrum level which can be compared with noises received by other quantitative echo-sounding systems or environmental noises. The noise measurements of several fisheries research vessels, ranging from 29.5-m length (RV ‘‘Taka Maru’’) to 93-m length (RV ‘‘Kaiyo Maru’’), were conducted to know their characteristics of noise. The dependence of noise upon the ship speed and the screw propeller’s setting was investigated for each vessel. The vessel’s performance for hydroacoustic survey is discussed from a viewpoint of noise level.
Published Version
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