On array gain modification in ship radiated noise measurement using vertical linear array

In the measurement of ship radiated noise using vertical linear array (VLA), the array gain is often calculated without considering the effects of the ocean environment, especially in shallow water environment, resulting in a large difference between the measured and the source noise levels and unavoidable signature distortion. In this paper, a method is proposed to modify the ship radiated noise measurement results based on the array gain calculation taking the environmental conditions into account. In this method, the transfer functions between the source (the noise-radiating ship) and the measuring hydrophones are calculated by the SCOOTER model based on wavenumber integration techniques. Then, the array gain formula based on the acoustic field environment is re-derived using the calculated transfer functions. Finally, the ship radiated noise (spectrum) level is modified accordingly. Numerical simulations in a typical shallow water environment are used to demonstrate the effectiveness of the proposed method. Compared to the conventional array gain calculation method, the proposed method achieved a superior performance. The average difference between the original ship radiated noise (spectrum) level and the measurements modified by the proposed method is about 1dB.