Instrumentation for Measuring Underwater Acoustic Intensity

Abstract

Instrumentation has been developed to measure one component of underwater acoustic intensity. Acoustical intensity is defined as the rate of flow of acoustical power per unit area in a direction normal to that area. It is equal to the product of the sound pressure and particle velocity at a point averaged over a period long relative to that of the lowest frequency component present. Transducers have been developed to measure both the sound pressure and particle acceleration. The outputs of the two transducers are amplified and filtered. The voltage proportional to the particle acceleration also is integrated. Thus, two voltages proportional to the sound pressure and particle velocity whose relative phase is the same as existed between the pressure and particle velocity are multiplied and averaged to provide a measure of the intensity. This instrumentation measures the acoustical intensity in octave bands from 50 to 2000 cps. A method of calibrating the pickups in the near field of a sound projector also is described.