A study of defects on infrasound Wind-Noise-Reduction Systems (WNRS) using in-situ calibration

Infrasound stations, including those of the International Monitoring System (IMS) as part of the Comprehensive Nuclear Test-Ban Treaty Organization (CTBTO), are used to determine the location of infrasound sources (such as earthquakes, volcanoes, explosions etc.). The triangulation of these sources is done by considering the delay of the arrival times of the signal using several detectors at precisely known locations in an array with an aperture of typically a few kilometers. It is, therefore, of great importance that the amplitude and, especially, the phase of the signal at each sensor in the array is precisely known. Although the calibration of microbarometers can be performed in a laboratory setting, it is much more difficult to determine the transfer function of the wind noise reduction systems (WNRS), designed to reduce the wind associated noise. In-situ calibration of these WNRS’s can be performed using a co-located reference sensor, and comparing the response to that of the array sensor (considering only highly coherent signals) to determine the relative response of the WNRS. System defects, such as flooded pipes or blocked inlets, have significant impacts on the response of the WNRS, and are therefore of interest for the infrasound community. Comparisons between models of these defective WNRS’s and experimental results will allow for the characterization of these effects on the measurements and improvements of the models and WNRS designs. The results of these calibration and WNRS defect experiments will be presented, and compared with models.