Submarine radiated noise far-field beam patterns for discrete frequencies from near-field measurements

Abstract

A theoretical model was developed which can predict discrete frequency far-field radiation patterns of submerged submarines from near-field measurements. The model developed utilizes the Helmholtz integral equation and the assumptions of the DRL method of near-field measurements. The DRL working formula is further modified by using a plane surface of integration and restricting the far-field points of interest to a horizontal plane containing the source. These assumptions and restrictions lead to a mathematical solution of the Helmholtz equation which is in the form of a Fourier transform. Near-field measurements on a horn speaker in an anechoic chamber were taken and the far-field beam pattern predicted by the model developed, using a simple computer program containing a Fourier transform routine. Computed beam patterns were in satisfactory agreement with measured far-field beam patterns, errors being concentrated in the outer side lobes from the acoustic axis. Problems which would be encountered in applying this model to at sea acoustic measurement are discussed. Methods for utilizing this model on an instrumented acoustic range to make underway radiated noise measurements on submarines are presented.