Predominant phenomenon of the migration in source locations and arrival orientations for infrasound excitation was clearly identified by using a combination of two arrays deployed at the coast of the Lützow-Holm Bay (LHB), Antarctica during the period from January to April in 2017. A few tens of infrasound source locations were determined in several individual days during four months in 2017. These identified source locations appeared to be migrated from the north-east direction to the north-west direction from January to April in 2017, the evidence assumed to be caused by time-offset effects between katabatic winds from continental ice sheet and the microbaroms from the LHB, based on comparison with oceanic wave heights around Antarctica and Southern Indian Ocean calculated by the wave model (WAM). The latter source locations in the north-west direction were also considered to be related with the sea-ice dynamics involving collapse and/or discharge from the LHB to the Ocean by comparison with MODIS satellite image.
Long-term Infrasound data at Syowa Station (SYO; 39E, 69S), in the Lützow-Holm Bay (LHB), East Antarctica was analyzed during the period from 2008 to 2014. Seasonal variations in microbaroms and high-frequency harmonic tremors were especially investigated. Infrasound data were strongly involved in local dynamics of surface environments. The microbaroms have relatively low amplitudes in austral winters by extending area of sea-ice around LHB, with decreasing oceanic swell loading effects. The other reasons of seasonal variations in microbaroms amplitudes were caused by the affections of a number of storms during whole year and snow accumulation over the porous hoses on the infrasound station at SYO. In contrast, non-linear high-frequency harmonic tremors were considered to be caused by the katabatic winds from Antarctic continent flowing in northeast dominant orientation. The high-frequency tremors had characteristics of daily variations in particular in austral summer. It is required to continue more than a few years of observation in order to identify relationships with climate change and global warming effects in the Antarctic. Continuous measurement of infrasound in the coastal margin of Antarctica is a proxy for monitoring multi-sphere interaction between the continent and surrounding Southern Ocean.
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.
InfraMatics is an international peer-reviewed journal dedicated to presenting observational and theoretical stud- ies of atmospheric infrasound generation, propagation, and reception that address outstanding problems in basic and applied research.
A standardized, self-similar, multiresolution algorithm is developed for scaling infrasonic signal time, frequency, and power within the framework of fractional octave bands. This work extends accepted fractional octave band schemas to 0.001 Hz (1000 s periods) to facilitate the analysis of broadband signals as well as the deep acoustic-gravity and Lamb waves captured by the global infrasound network. The Infrasonic Energy, Nth Octave (INFERNO) multiresolutionEnergy Estimator is applied to computing the total acoustic energy of the Russian meteor signature recorded in the 45mHz-9 Hz frequency band by IMS array 131KZ, Kazakhstan.
Volcanic eruptions are valuable calibrating sources of infrasonic waves worldwide detected by the International Monitoring System (IMS) of the Comprehensive Nuclear Test-Ban-Treaty Organization (CTBTO) and other experimental stations. In this study, we assess the detection capability of the European infrasound network to remotely detect the eruptive activity of Mount Etna. This well-instrumented volcano offers a unique opportunity to validate attenuation models using multi-year near-and far-field recordings. The seasonal trend in the number of detections of Etna at the IS48 IMS station (Tunisia) is correlated to fine temporal fluctuations of the stratospheric waveguide structure. This observed trend correlates well with the variation of the effective sound speed ratio which is a proxy for the combined effects of refraction due to sound speed gradients and advection due to along-path wind on infrasound propagation. Modeling results are consistent with the observed detection capability of the existing regional network. In summer, during the downwind season, a minimum detectable amplitude of ~10 Pa at a reference distance of 1 km from the source is predicted. In winter, when upwind propagation prevails, detection thresholds increase up to ~100 Pa. However, when adding four experimental arrays to the IMS network, the corresponding thresholds decrease down to ~20 Pa in winter. The simulation results provide here a realistic description of long- to mid-range infrasound propagation and allow predicting fine temporal fluctuations in the European infrasound network performance with potential application for civil aviation safety.
Acoustic/infrasonic measurements contain physical information enabling an estimate of the yield of a single-point explosion that is on or above ground. A variety of semi-empirical and numerical models have been developed for estimating the yield based on the amplitude of a recorded acoustic signal. This paper utilizes existing semi-empirical models-suitable for timely yield estimation—and develops the mathematical framework to properly account for uncertainties in these models, in addition to measurement uncertainties. The inclusion of calibration parameters into our mathematical model allows for the correction of constant path specific effects that are not captured in existing semi-empirical models. The calibrated model provides a yield estimate and associated error bounds that correctly partitions total error into model error and background noise. Yield estimation with the models is demonstrated with single-point, above ground chemical explosions at Los Alamos National Laboratory (LANL) experimental testing facilities.
