In the field of acoustic intensity measurement, the two microphone measurement technique by using the FFT method is widely used for obtaining time averaged sound intensity. However this method can not be applied for measuring time-dependent process of energy transfer in an acoustic field of flow noise due to its nonstationary characteristics. In this article, we propose the instantaneous intensity analysis method by using the harmonic wavelet transform. The analysis result of the data obtained by the measurement on ship reveals that the direction of flow induced sonar noise shows strong fluctuations but most of them are arrived from both directions of up and down quarters of the sonar array at high speeds.
