Application of Propagation Modeling to Verify and Discriminate Ground-Truth Infrasound Signals at Regional Distances

Abstract

An infrasound field campaign was performed in 2011/2012 utilizing single infrasound sensors along the great circle path between a known ground-truth source (Ariane 5 engine test facility, Lampoldshausen, Germany) and a regional receiver (German infrasound array IS26, Bavarian Forest) covering a distance of rough 320 km in total. The gathered recordings provide new insights in the infrasonic wave propagation at regional and near-source distances by comparing measured signals with modeling results within this study. Ray-tracing and parabolic equation approaches are utilized to model infrasound propagation from the ground-truth source to the line profile sensors and explain the obtained detections and non-detections. Modeling and observation results are compared by estimating their amplitude, quantifying amplitude deviations and also considering observed and calculated travel times and celerities. Modeling results show a significant influence of small-scale atmospheric variations in effective sound speed profiles on the propagation pattern, which results in varying tropospheric and stratospheric ducting behavior. A large number of gravity wave profiles are tested to investigate the influences of atmospheric dynamics on the infrasound wave field and improve the modeling results. The modeling is furthermore applied to a case of two potential, contemporaneous and closely spaced infrasound sources. Propagation modeling is used here to resolve the source ambiguity between a ground-based and a higher altitude source giving a strong preference to the latter with respect to the observed infrasonic signatures. The good agreement between modeling and observation results within this study successfully shows the benefit of applying infrasound propagation modeling to the validation of infrasound measurements, verification of ducting behavior and discrimination of infrasound sources.

Isolating the Source Region of Infrasound Travel Time Variability Using Acoustic Sensors on High-Altitude Balloons

“…The acoustic wave underwent upward refraction before reaching the receiver, thereby spending enough time in the stratosphere where gravity wave amplitudes are non-negligible. Our findings are consistent with previous studies that also mention gravity wave perturbations as an important factor behind signal detections in an acoustic shadow zone (e.g., [65,67,78]).…”

“…The atmosphere is a dynamic and complex medium that undergoes changes on small and large scales, oftentimes hindering efforts to adequately characterize infrasound signal detections not only from far-field sources but also those at regional distances (e.g., [36,65]). Atmospheric specifications currently available from models and observations are expected to provide a reasonable estimate of various parameters, including the presence of propagation waveguides.…”

The European Infrasound Bulletin

“…For this study, the time duration is more than doubled and the number of stations is more than tripled, which results in an increase in the number of detected infrasound events by approximately a factor of ten. Furthermore, this study improves the following: (1) the source localization of the previous study by using ray-tracing methods, climatologies and analysis data from numerical weather prediction models for realistic atmospheric background conditions and infrasound propagation modeling is obtained (Garcés et al 1998;Drob et al 2003;Pilger et al 2013); (2) the seasonal and diurnal variations of the sources and detected infrasonic activity are highlighted in greater detail;…”

1001 Rocket Launches for Space Missions and Their Infrasonic Signature

“…(i) Effective sound speed ratios are derived from 1D atmospheric profiles (spaceport and receiver). (ii) Acoustic signals are generated solely by the engine boost (e.g., see Koch, 2010; Pilger et al., 2013) and not also the possible supersonic boom. The thrust energy is considered in direct relation to the acoustic signals, without considering efficiency.…”