Use of pitch-azimuth plots in determining the direction of a noise source in water with a vector sound-intensity probe

Abstract

A vector sound-intensity probe is used to determine the direction of a sound source in water. The probe consists of four pressure sensors in the tetrahedral arrangement, with each component of sound intensity measured simultaneously using the cross-spectral method. The probe dimensions are at least ten times less than the measured wavelengths. The probe has omnidirectional sensitivity with no 180 deg ambiguity. For plane waves, it is shown that direction finding with the vector probe is based on phase differences. Tests were conducted in a water tank to test the accuracy of direction finding of a sound source, with different types of noise interference. Results are expressed in the form of pitch-azimuth plots where the data points correspond to different frequencies in the frequency range of the measurements. These plots provide an all around three-dimensional view of the ambient sound field. Without interference the accuracy of direction finding is within ±2 deg. It is shown that, for an equivalent direction-finding capability, a vector intensity probe is two orders of magnitude smaller than a beamforming line array. It is suggested that vector sound intensity can be used to model directional hearing in animals.