Coherent ambient infrasound recorded by the International Monitoring System

Abstract

Ambient noise recorded by the International Monitoring System (IMS) infrasound network includes incoherent wind noise and coherent infrasonic signals; both affect detection of signals of interest. We present summary statistics of coherent infrasound recorded by the IMS network. We have performed systematic broadband (0.01-5 Hz) array processing of the IMS historical dataset (39 stations from 2005 to 2010) using an implementation of the Progressive Multi-Channel Correlation (PMCC) algorithm in log-frequency space. From these results, we estimate multi-year 10th, 50th, and 90th percentiles of the rms pressure of coherent signals in 15 frequency bands for each station. We compare the resulting coherent noise models in the 15 frequency bands with raw power spectral density noise models, which inherently include both incoherent and coherent noise. We show that IMS arrays consistently record coherent ambient infrasound across the broad frequency range from 0.01 to 5 Hz when wind-noise levels permit. Multi-year averaging of PMCC detection bulletins emphasizes continuous signals such as oceanic microbaroms, as well as persistent transient signals such as repetitive volcanic, surf, or anthropogenic activity (e.g., mining or industrial activity).