What does infrasound signal duration tell us about signal propagation distance and waveguide structure?

Abstract

A global network of microbarograph arrays is currently being constructed to support verification of the Comprehensive Nuclear-Test-Ban Treaty. The identification of explosively generated infrasound signals that have propagated thousands of kilometers to the arrays, and the subsequent association of signals across the sparse network, remains a challenge. One signal parameter that has not been extensively studied, but may assist in source identification procedures, is the signal duration. The durations of 42 high signal-to-noise ratio signals from 35 near-surface explosions, recorded at distances of between 25 and 6300 km, exhibit a weak relationship with source-to-receiver range; longer propagation paths result in longer signal durations. The variation in signal duration at a given source-to-receiver range depends upon the atmospheric waveguide structure. At propagation distances greater than 2000 km, long duration signals are generated within weak waveguides characterized by a small excess in stratospheric effective sound speed compared to that at the ground surface. These waveguides permit signal propagation with high celerity (up to 335 m/s). Shorter duration signals at these distances occur in stronger waveguides that exhibit greater along-path variability; these signals do not exhibit celerities greater than 315 m/s. The utility of signal duration within the context of explosion monitoring is explored.