One-year analysis of systematic detection and location of infrasounds in a protoype CTBT station

Abstract

Within the framework of the Comprehensive Test Ban Treaty, the Department of Analysis and Monitoring of the Environment (DASE) of the French Atomic Commission has developed an automatic processing software providing detection of coherent infrasound signals. The infrasound’s parameters are calculated by using the progressive multichannel correlation method as a real-time detector. Each week, an automatic bulletin summarizes all detections by giving the wave parameters (velocity and azimuth), the amplitude, the frequency range, and the correlation coefficient. The one-year bulletins enable the identification of most of the infrasounds (sonic boom of supersonic aircraft, mining explosions of known quarries, storms, ocean swell). Most of the man-made infrasounds are produced by quarry blasts and the Concorde. Other infrasounds are produced by severe weather (storms, hail). Excluding false detections, an average number of 40 detections is obtained each day. For some infrasounds, statistics show several phases related to the different reflections in the stratosphere and thermosphere with seasonal characteristics. In order to detect coherent signals with poor signal-to-noise ratio (detection in windy period, fine detection of phases with low amplitudes), the thresholds of detections are set at a low level. In the future, this study will help to determine operational thresholds.