PARAMETERS OF INFRASONIC SIGNALS GENERATED IN THE ATMOSPHERE BY MULTIPLE EXPLOSIONS AT AN AMMUNITION DEPOT

Abstract

Purpose: The study lies in investigating the waveforms and the spectral content of the infrasonic signals generated by multiple explosions at an ammunition depot versus energy and distance. The aim of this study is investigating the features of the waveforms, amplitudes, and spectral content of the infrasonic signals which propagated over long distances (~ 150 to 180 km) from the ammunition depot near Vinnytsia (Ukraine) on September 26–27, 2017 during the man-caused catastrophe. Design/methodology/approach: The Ukrainian network of infrasonic stations was used to study the basic parameters (spectral content, amplitudes, predominant oscillation periods, duration of the oscillation trains, celerity) of the infrasonic waves which propagated over long distances (~ 150 to 180 km). The signal processing technique in this study added up to the following. First, the time dependences of atmospheric pressure fluctuation acquired in relative units were converted into absolute units. Then, they were filtered within the period range of 0.2 to 10 s. Next, the filtered variations were subjected to the system spectral analysis that includes the short-time Fourier transform, the Fourier transform in a sliding window with a width adjusted to be equal to a fixed number of harmonic periods, and the wavelet transform. In the latter transform, the Morlet wavelet was used as the basis function. Findings: It was shown that an upward trend in the amplitude and period of the predominant oscillation were observed when the energy release increased from 3 to 53 tons of TNT, while the duration of the oscillation trains increased from ≈1.5 to 2 min. The infrasonic signal parameters were determined to change insignificantly when the distance between the explosion epicenter and an infrasonic station location changed a little (by 15 to 18 %). The differences in the wave forms are related to orientation of the propagation path. The analysis has revealed that the harmonics in the 3 to 5-6 s period range were predominant when the energy release was equal to 53 tons of TNT. The duration of the trains of oscillations with such periods amounted to 40 s. The average celerity was calculated to change within 300 to 309 m/s for different propagation paths with stratospheric wave reflections, that provides evidence for the influence of the wind in the upper atmosphere on the infrasound propagation. The thermospheric reflection resulted in the signal amplitude smaller by a factor of a few times and the celerity equal from 245 to 250 m/s. Conclusions: The basic parameters of infrasonic signals generated during the recurrent explosions at the ammunition depot near Vinnytsia and propagating in the atmosphere have been studied.

Keywords

• infrasonic signals
• multiple explosions
• energy release
• waveform
• signal parameters
• spectral content
• celerity