Recently, an acoustic intensity measuring method has been developed which can be applied to measure underwater noise radiated from a ship. This paper reports how first, the accuracy of intensity measuring method using a 3-dimensional intensity probe with four hydrophones was experimentally verified, and second, how this method using this instrument was then applied to measure underwater noise radiated from a ship.
In this report, the directional characteristics of the 3-dimentional intensity probe were tested in an anechoic room, and the vibration isolation effect of the hydrophone stand was also tested in an anechoic water chamber. Based on the results of these tests, errors associated with this instrument were estimated. Finally, this intensity measuring method using this instrument was applied to measure underwater noise radiated from a ship.
It has been confirmed that this method can satisfactorily measure the transmission paths of thruster noise and radiation patterns of underwater radiated noise from a machine even at a dock side test.

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The cone ring piezoceramic is applied to the underwater transducer, and its underwater acoustic characteristics is studied. The vibration mode of this transducer differs remarkably from the conventional type which uses piezoceramic cylinder, and shows distinctive features at frequencies higher than fundamental resonant frequency (f0). Measurements of the underwater characteristics show virtually flat response in the frequencies f/f0 = 1.1-1.2 and vertical directivity that is high by about 10 dB in the slant direction with little frequency dependence. It has also been found that the transducer is almost omnidirectional in the horizontal plan in the frequency range. The transducer shows characteristics which are not available in the conventional cylindrical type, and can be used effectively transducer in oceanography.

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