Infrasound signal coherence across arrays: Observations from the international monitoring system

Abstract

Arrays of microbarometers are designed to exploit the coherence of infrasound signals between sensors in order to detect and characterize the impinging wavefield. However, signal coherence decreases with increasing distance between measurement locations due to effects that include, but are not limited to, signal multi-pathing, dispersion, and wavefront distortion. Therefore, the design of an array is a balance between ensuring the sensor separations are small enough to guarantee acceptable signal coherence, yet large enough to provide the required resolution when estimating signal azimuth and velocity. Here, we report coherence measurements from more than 30 events that have been recorded on the International Monitoring System microbarometer arrays that are being constructed as one of the verification measures for the Comprehensive Nuclear-Test-Ban Treaty. The results confirm those of Mack and Flinn (1971) that signal coherence is greater in directions parallel, and is less in directions perpendicular, to the direction of propagation. In contrast to earlier studies, we report larger inter-event variation in coherence structure and provide an assessment of how these findings may influence future microbarometer array design.