Underwater measurement of narrowband sound power and directivity using Supersonic Intensity in Reverberant Environments

A laboratory underwater acoustic measurement technique, Supersonic Intensity in Reverberant Environments (SIRE), is developed analytically and validated experimentally and numerically. Unlike standard free or diffuse field techniques, SIZE enables the measurement of narrowband sound power and directivity in an environment with inexact field conditions. The technique takes advantage of underwater vector sensors, measuring only acoustic pressure and the normal components of particle velocity/acceleration, and supersonic wavenumber filtering in the near field of a source. he result is outward-propagating acoustic waves separated from interfering incoming and/or evanescent waves. The SIRE technique was experimentally applied to monopole and dipole sources and the results are compared with theory and standard methods. SIRE is shown to accurately measure radiated sound power to within the limits of ANSI S12.51 and to accurately measure the directivity indices of simple sources to within +/- 3 dB. A coupled finite element/boundary element model of a point driven, thin-walled cylinder is also developed to establish the limitations of the S(sic)E technique. The model results show that the measurement standoff distance should b(sic)less than the reciprocal of the largest wavenumber in the frequency band of interest. Furthermore, the maximum measurement grid spacing must be less than twice the star doff distance. (C) 2012 Elsevier Ltd. All rights reserved.