Topographic effects on infrasound propagation

Abstract

Infrasound data were collected using portable arrays in a region of variable terrain elevation to quantify the effects of topography on observed signal amplitude and waveform features at distances less than 25 km from partially contained explosive sources during the Frozen Rock Experiment (FRE) in 2006. Observed infrasound signals varied in amplitude and waveform complexity, indicating propagation effects that are due in part to repeated local maxima and minima in the topography on the scale of the dominant wavelengths of the observed data. Numerical simulations using an empirically derived pressure source function combining published FRE accelerometer data and historical data from Project ESSEX, a time-domain parabolic equation model that accounted for local terrain elevation through terrain-masking, and local meteorological atmospheric profiles were able to explain some but not all of the observed signal features. Specifically, the simulations matched the timing of the observed infrasound signals but underestimated the waveform amplitude observed behind terrain features, suggesting complex scattering and absorption of energy associated with variable topography influences infrasonic energy more than previously observed.

CTBT infrasound network performance to detect the 2013 Russian fireball event

“…Most infrasonic signals can generally propagate over horizontal distances of ~100 km to a few 1000 km in such a stratospheric duct. Otherwise, they are dissipated over short distances near the Earth's surface [e.g., McKenna et al ., ] or attenuated at higher‐atmospheric altitudes as in the thermosphere at 100 km and higher. For the Chelyabinsk meteorite event, the infrasound signal was exceptionally strong and had a component of very low frequencies at about 0.025 Hz and lower [ Garcés , ] that are not as rapidly attenuated in the thermosphere [ Sutherland and Bass , ].…”

Remote Bridge Monitoring Using Infrasound

“…The close proximity of the arrays to Br 18-0009 is considered local propagation, roughly defined as less than 50 km (McKenna et al 2012); therefore, atmospheric effects are limited to the troposphere (<10 km). Analysis of the radiosonde data showed no significant winds, thereby reducing the sound speed [Eq.…”

“…Following the identification of the time of interest (March 1, 2014, 0900-1000 UTC) for FRC through InfraTool and analysis of meteorological data, infrasound data were manually processed with Geotool, a software package for visualization and characterization of seismic and acoustic data (Coyne and Henson 1995). This processing involved filtering the data, handpicking coherent signals, completing a Fourier analysis to identify modes and confirm that the modes are in the infrasound passband, and an F-K analysis to confirm the back azimuth from which the signal originated (McKenna et al 2009c(McKenna et al , 2012McComas et al 2016).…”

Realization of State-Space Models for Wave Propagation Simulations

“…These interactions have been observed and quantified by experimental data and models. 10 Our model, which we created for FDTD analyses of Equations (1), is summarized by Figure 2. It spans nearly 15 km to simulate propagation between an impulsive justabove-ground source at the U.S. Army Engineer Research and Development Center (ERDC) Big Black Test Site (BBTS) and an infrasound-sensing array at the ERDC Waterways Experiment Station (WES).…”

“…At this level the effect of terrain relief on the propagation is evident, as indicated by the topography-imaging character of Figure 3 and subsequent overlay results. Figure 3, we created a 512-state superstable model by populating the C Matrix of Equation (10). As expected, the fidel-* http://www.erdc.hpc.mil/hardware/index.html ity of the superstable model to the FDTD simulation is high when excited using the calibration source, which was down sampled to the FDTD-output sampling interval (i.e., the discrete signal outlined by the asterisks in Figure 2 (d)).…”