This paper refers to an experiment where acoustic intensity meters, in which two microphones closely spaced together were used, were applied to underwater acoustic measurements.
First, errors due to the finite difference approximation in these underwater acoustic measurements were calculated. In addition, the errors associated with an equipment phase mismatching were also calculated. Using these results, for a hydrophone separation of 20 mm and an initial phase shift of 0.5 degrees, measurement errors were shown to be less than 3 dB from 300 Hz to 20 kHz. Finally, underwater acoustic intensity meters in which two hydrophones were used were tested in an anechoic water chamber.
The results of the experiments indicate that this intensity meter obtained reliable data and can be applied to under water noise measurements.

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