New Systems for Wind Noise Reduction for Infrasonic Measurements

Abstract

Wind noise is a significant problem for infrasound detection and localization systems. Pipe arrays are commonly used for suppressing wind noise by area averaging the relatively incoherent wind noise. The area averaging and physical construction of the pipe arrays limit the ability of the array to measure infrasound pulses with waveform fidelity. The need for waveform fidelity is motivated by the recent increase in the ability to predict waveforms theoretically from the meteorology data. This chapter investigates large cylindrical and hemispherical porous windscreens, which employ single-point sensors with little or no waveform distortion. The theory of wind noise generation is briefly outlined to provide a basis for understanding the windscreen research. Next, four recent experiments measuring the wind noise reduction of porous cylindrical screens with respect to bare sensors mounted flush with the ground, the wind noise reduction of porous fabric domes with respect to a sensor sitting on the ground surface, the wind noise reduction of porous metal domes with respect to other sensors, and the wind noise reduction of porous cylinders and fabric domes with respect to flush-mounted sensors and each other. The second and third experiments also demonstrate the ability of the windscreens to record impulses with waveform fidelity. The largest screens provide up to 20 dB of wind noise reduction down to wavenumbers on the order of the inverse of the height of the windscreen. A theory of wind noise reduction is developed and leads to a better understanding of the relative contribution of wind noise generated at the surface of the screen and wind noise generated by flow through the screen. It is concluded that construction of domes large enough to provide signal enhancement down to 0.1 Hz is feasible and would provide high fidelity time waveforms for comparison with theoretical predictions.