Acoustical properties of porous hose wind noise filters

Abstract

Observation of infrasound signals in the atmosphere is often masked by wind noise. A common means of filtering out the wind noise is to connect a commercial porous (or soaker) hose to the manifold of a micro barometer. The filtering effect is attributed to the ability of the porous hose to average the pressure variations over its length. The pressure variations due to the turbulent wind field are incoherent on a scale equal to the hose length and, therefore, are reduced in the averaging process. Infrasound signals, with wavelengths much longer than the hose, are reduced little in the averaging process. There remains the question, ‘‘How does the porous hose respond to infrasound signals that have wavelengths comparable to the hose length?’’ To answer this question, measurements have been made of infrasound signals radiated from a jet engine during takeoff using an infrasound sensor with a porous hose connected to its port, and an array of infrasound sensors distributed along the length of the porous hose. Measurements are reported for the hose oriented both in the direction and perpendicular to the direction of the sound source. [Work supported by the Space and Missile Defense Command is gratefully acknowledged.]