The sensitivity of noise directionality to geoacoustic parameters of bottom in shallow sea

The vertical directionality of ambient noise in shallow water is a relatively stable feature of noise, so it is possible to use it to do geoacoustic inversion. In order to determine the inversion strategy and improve the inversion accuracy, the sensitivity of the vertical directionality to the acoustic parameters of the seabed need to be analyzed before the inversion is performed. Considering the directivity of noise source, the attenuation in the water and the influence of the interface reflection loss, a model of wind-generated noise over a layered bottom is established. Using different parameters of seabed to calculate vertical directionality of ambient noise, it is shown that the directionality is sensitive to sound speed at all angle and is sensitive to density at steeper angle, and is sensitive to attenuation below the critical angle. Compared with the parameters in the sediment, the vertical directionality of ambient noise is less sensitive to the parameters in the seabed. The sound speed in the seabed mainly affects the position of the peak of the directionality curve, and the attenuation coefficient influences the part of the directionality curve which near the bottom. The simulation which is based on a virtual hydrophone array is also performed and the result is in good agreement with the theoretical result.