Infrasound uncertainty propagation: Ensuring traceability from the laboratory to the field

Confidence in the quality of infrasound measurements is a necessity for the Comprehensive Nuclear-Test-Ban-Treaty Organization, which continuously acquires and analyzes measurements from numerous infrasound arrays as part of its international monitoring network. The entire measurement process, from laboratory calibration to the field, must be considered to estimate the confidence of the measurement through the associated uncertainty. This paper presents a methodology to obtain traceable measurements of the azimuth, trace velocity, and amplitude of a signal, taking into account the traceability chain and the other uncertainty sources arising from a thorough analysis of the measurement process. An in situ calibration method of infrasound sensors to be used in conjunction with the Gabrielson [J. Acoust. Soc. Am. 130, 1154-1163 (2011)] on-site calibration and to provide field traceability of measurements under varying environmental conditions at IS26 (Freyung, Gernmany) is presented. In the context of this application, the resulting standard uncertainties in the azimuth, between 0.05° and 7°, and trace velocity, between 0.2 and 60 m/s (from high to low frequency), were predominantly due to the Gabrielson phase uncertainty, and the amplitude uncertainty of 0.2 dB also had significant contributions from the temperature and pressure susceptibilities. This better understanding of the uncertainties will allow for more accurate source yield and location estimates.